Gradient magnetic field sensor and magnetic material detection device

Abstract

To provide a gradient magnetic field sensor capable of improving sensitivity for detecting a detection object.SOLUTION: A gradient magnetic field sensor includes: a first magnetic core; a second magnetic core; a first coil arranged in the first magnetic core; a second coil arranged in the second magnetic core; and magnetism collection mechanisms. The second coil is differentially connected to the first coil. The magnetism collection mechanism includes a high magnetic-permeability material and a low magnetic-permeability material. The high magnetic-permeability material has a magnetic permeability being equal to or more than a predetermined first threshold. The low magnetic-permeability material has permeability lower than a predetermined second threshold. The second threshold is equal to or less than the first threshold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a gradient magnetic field sensor and a magnetic material detection device. [Background technology]

[0002] Research and development are underway on gradient magnetic field sensors that detect the gradient of magnetic field strength at two different locations. Here, the gradient refers to the difference in magnetic field strength at each of the two different locations.

[0003] A gradient magnetic field sensor has two sensor heads to detect the strength of the magnetic field at two different locations. In a gradient magnetic field sensor, one of the two sensor heads detects the strength of the magnetic field at one of the two different locations. The other sensor head detects the strength of the magnetic field at the other location. The gradient magnetic field sensor then detects the gradient of the magnetic field strength at these two different locations according to the signals output from these two sensor heads. The gradient of the magnetic field strength at these two different locations changes depending on the presence or absence of an object that can change the magnetic field. By utilizing this, a gradient magnetic field sensor can detect such an object as a target object.

[0004] In this regard, a gradient magnetic field sensor is known that includes: an AC power supply connection terminal to which a first power supply terminal of an AC power supply is connected; a first magnetic core connected between the AC power supply connection terminal and ground; a second magnetic core connected in parallel with the first magnetic core between the AC power supply connection terminal and the ground; an AC current control unit connected between the AC power supply connection terminal and at least one of the first magnetic core and the second magnetic core, and configured to control an AC current flowing through at least one of the first magnetic core and the second magnetic core; a first detection coil wound around the first magnetic core; a second detection coil wound around the second magnetic core and differentially connected to the first detection coil; and a detection circuit configured to detect a voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The gradient magnetic field sensor as described in Patent Document 1 can reduce noise and improve the detection sensitivity for the detection target by making the detection sensitivity for the detection target by the first magnetic core and the detection sensitivity for the detection target by the second magnetic core substantially equal or equal. However, in the gradient magnetic field sensor, the smaller the detection target is, or the weaker the magnetic force of the magnetized detection target is, the less sufficient the detection sensitivity for the detection target becomes, and as a result, the detection of the detection target may fail in some cases.

[0007] The present invention has been made in consideration of such circumstances, and an object thereof is to provide a gradient magnetic field sensor and a magnetic object detection device that can further improve the detection sensitivity for a detection target.

Means for Solving the Problems

[0008] One aspect of the present invention is a gradient magnetic field sensor comprising a first magnetic core, a second magnetic core, a first coil disposed in the first magnetic core, a second coil disposed in the second magnetic core, and a magnetic field collection mechanism, wherein the second coil is differentially connected to the first coil, and the magnetic field collection mechanism includes a high-permeability material and a low-permeability material, wherein the high-permeability material has a permeability of a predetermined first threshold or higher, and the low-permeability material has a permeability of a predetermined second threshold or lower, and the second threshold is less than or equal to the first threshold.

[0009] Furthermore, one aspect of the present invention is a magnetic material detection device comprising a gradient magnetic field sensor, the gradient magnetic field sensor comprising a first magnetic core, a second magnetic core, a first coil disposed in the first magnetic core, a second coil disposed in the second magnetic core, and a magnetic collection mechanism, wherein the second coil is differentially connected to the first coil, and the magnetic collection mechanism includes a high-permeability material and a low-permeability material, the high-permeability material having a permeability of a predetermined first threshold or higher, and the low-permeability material having a permeability of a predetermined second threshold or lower. [Effects of the Invention]

[0010] According to the present invention, the detection sensitivity of the object to be detected can be further improved. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example of the configuration of the magnetic material detection device 1. [Figure 2] Figure 1 is a perspective view of the gradient magnetic field sensor 12. [Figure 3] This figure shows an example of how the first magnetic collection mechanism CM1 increases the amount of magnetic flux that links with the first magnetic core CR1 from the magnetic flux generated from the object DM being detected. [Figure 4] This figure shows an example of how a portion of the magnetic flux generated from the object to be detected DM links with the first magnetic core CR1 when the gradient magnetic field sensor 12 does not have a first magnetic collection mechanism CM1. [Figure 5]This figure is used to compare the amount of magnetic flux linked with the first magnetic core CR1 shown in Figure 3 and the first magnetic core CR1 shown in Figure 4. [Figure 6] This figure shows an example of how the noise-generating magnetic flux flows through the first magnetic core CR1 and the second magnetic core CR2 without linking with them, respectively, by passing through the first magnetic collector CM1 and the second magnetic collector CM2. [Figure 7] This figure shows an example of how the magnetic flux that causes noise, as shown in Figure 6, links with the first magnetic core CR1 and the second magnetic core CR2 when the gradient magnetic field sensor 12 does not have a first magnetic collection mechanism CM1 and a second magnetic collection mechanism CM2. [Figure 8] This diagram illustrates how to determine the number N of the first high-permeability materials in the first magnetic collection mechanism CM1, the length t of the first high-permeability materials in the central axis direction of the first magnetic collection mechanism CM1, and the length t' of the first low-permeability material in the central axis direction of the first magnetic collection mechanism CM1. [Figure 9] This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the value of the first relative permeability ratio mag is changed in the gradient magnetic field sensor 12 in the target state. [Figure 10] This diagram illustrates how to determine the ratio of the length Ltotal of the first magnetic collecting mechanism CM1 in the central axis direction to the length Lcore of the first magnetic core CR1 in the central axis direction. [Figure 11] This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of length Ltotal to length Lcore is changed in the gradient magnetic field sensor 12 in the target state. [Figure 12] This diagram illustrates how to determine the ratio of the width w1 of the first magnetic collection mechanism to the diameter φcore1 of the first magnetic core. [Figure 13] This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of the width w1 of the first magnetic collection mechanism to the diameter φcore1 of the first magnetic core is changed in the gradient magnetic field sensor 12 in the target state. [Figure 14]This diagram illustrates how to determine the ratio of the height h1 of the first magnetic collection mechanism to the diameter φcore1 of the first magnetic core. [Figure 15] This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of the height h1 of the first magnetic collection mechanism to the diameter φcore1 of the first magnetic core of the gradient magnetic field sensor 12 in the target state is changed. [Figure 16] This diagram illustrates how to determine the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism. [Figure 17] This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism is changed in the gradient magnetic field sensor 12 in the target state. [Figure 18] This figure shows an example of the detection sensitivity of the gradient magnetic field sensor 12. [Figure 19] This figure shows an example of noise detected by the gradient magnetic field sensor 12. [Figure 20] This figure shows an example of the noise floor for noise detected by the gradient magnetic field sensor 12. [Figure 21] This is a perspective view showing an example of a gradient magnetic field sensor 12 equipped with two magnetic shields. [Figure 22] This figure shows an example of the circuit configuration of the gradient magnetic field sensor 12. [Figure 23] This figure shows an example of the configuration of the first magnetic core CR1, which includes multiple magnetic materials. [Figure 24] This figure shows a modified configuration of the first sensor head S1 and the second sensor head S2. [Figure 25] This figure shows an example of the circuit configuration of the gradient magnetic field sensor 12A. [Modes for carrying out the invention]

[0012] <Embodiment> Embodiments of the present invention will be described below with reference to the drawings.

[0013] <Overview of Magnetic Material Detection Device> First, an overview of the magnetic material detection device according to this embodiment will be described.

[0014] The magnetic material detection device according to this embodiment includes a gradient magnetic field sensor according to this embodiment, the gradient magnetic field sensor comprises a first magnetic core, a second magnetic core, a first coil disposed in the first magnetic core, a second coil disposed in the second magnetic core, and a magnetic collection mechanism. Here, the second coil is differentially connected to the first coil. The magnetic collection mechanism includes a high-permeability material and a low-permeability material. The high-permeability material has a permeability of a predetermined first threshold or higher. The low-permeability material has a permeability of a predetermined second threshold or lower. The second threshold is less than or equal to the first threshold.

[0015] As a result, the gradient magnetic field sensor and the magnetic object detection device according to the embodiment can further improve the detection sensitivity of the object to be detected.

[0016] The configurations of the magnetic object detection device and the gradient magnetic field sensor according to the embodiment will be described in detail below.

[0017] <Configuration of a magnetic material detection device> The configuration of a magnetic object detection device according to an embodiment will be described below, with magnetic object detection device 1 as an example of a magnetic object detection device according to an embodiment. Here, in this embodiment, a conductor that transmits an electrical signal corresponding to DC power or an electrical signal corresponding to AC power will be referred to as a transmission line. The transmission line may be, for example, a conductor printed on a substrate, a wire formed in the shape of a line, or any other conductor. Also, in this embodiment, when referred to as voltage, it means the potential difference from a predetermined reference potential, and the illustration and explanation of the reference potential will be omitted. Here, the reference potential may be any potential. In this embodiment, as an example, the case where the reference potential is the ground potential will be described. Also, in this embodiment, when referred to as ground, it refers to the same ground.

[0018] Figure 1 shows an example of the configuration of the magnetic object detection device 1. Here, the three-dimensional coordinate system TC is a three-dimensional Cartesian coordinate system that indicates the direction in the figure in which the three-dimensional coordinate system TC is drawn. For the sake of explanation, the X-axis in the three-dimensional coordinate system TC will be simply referred to as the X-axis. For the sake of explanation, the Y-axis in the three-dimensional coordinate system TC will be simply referred to as the Y-axis. For the sake of explanation, the Z-axis in the three-dimensional coordinate system TC will be simply referred to as the Z-axis. For the sake of explanation, the positive direction of the Z-axis will be referred to as up or upward, and the negative direction of the Z-axis will be referred to as down or downward.

[0019] Magnetic object detection device 1 is a device that detects objects using a magnetic field. The objects to be detected are objects that can change the magnetic field, such as magnetized magnetic materials.

[0020] The magnetic object detection device 1 comprises, for example, a frame CS, a first roller RL1, a second roller RL2, a magnetization device 11, a gradient magnetic field sensor 12, and an information processing device 20. The gradient magnetic field sensor 12 comprises two sensor heads, a first sensor head S1 and a second sensor head S2. Note that in Figure 1, to avoid making the diagram complicated, cables connecting the information processing device 20 to other components in the magnetic object detection device 1 are omitted. Furthermore, the magnetic object detection device 1 may be configured without some or all of the frame CS, the first roller RL1, the second roller RL2, the magnetization device 11, and the information processing device 20. Also, the magnetic object detection device 1 may be configured with other components, other devices, etc., along with the gradient magnetic field sensor 12, instead of some or all of the frame CS, the first roller RL1, the second roller RL2, the magnetization device 11, and the information processing device 20. Furthermore, the magnetic material detection device 1 may be configured to include, in addition to the frame CS, the first roller RL1, the second roller RL2, the magnetization device 11, and the information processing device 20, other components, other devices, etc., together with the gradient magnetic field sensor 12.

[0021] The components of the magnetic object detection device 1 are attached to the frame CS. The frame CS mainly consists of a top plate (not shown), a bottom plate (not shown), and multiple support columns connecting the top plate and the bottom plate. In the example shown in Figure 1, the external shape of the frame CS is approximately a rectangular parallelepiped. However, the external shape of the frame CS may be any shape.

[0022] Inside the frame CS, there are a first roller RL1 and a second roller RL2.

[0023] The first roller RL1 is a roller on which a sheet member ST, which is to be inspected for the presence or absence of an object to be detected, is wound in a roll shape. The second roller RL2 is a roller that winds up the sheet member ST that has been pulled out from the first roller RL1 while transporting it along a predetermined path. The second roller RL2 is rotated by a servo motor (not shown) or the like. This allows the second roller RL2 to wind up the sheet member ST that has been pulled out from the first roller RL1. In other words, the second roller RL2 is a driven roller. The first roller RL1 is a passive roller that rotates in accordance with the rotation of the second roller RL2 while the sheet member ST is wound up. The servo motor is controlled, for example, by an information processing device 20.

[0024] The sheet member ST is transported through a magnetic field generated by the magnetization device 11 from the time it is pulled out from the first roller RL1 until it is wound up by the second roller RL2. As a result, any magnetic material attached to the sheet member ST becomes magnetized. In other words, in the example shown in Figure 1, the magnetic material detection device 1 detects the magnetic material magnetized by the magnetization device 11 as the object to be detected. After being transported through the magnetic field, the sheet member ST is transported through a predetermined detection area where the gradient magnetic field sensor 12 can detect the presence or absence of the object to be detected. Then, the sheet member ST is wound up onto the second roller RL2.

[0025] Here, the magnetization device 11 is a device that generates a magnetic field of a predetermined strength in a predetermined magnetization region and magnetizes a magnetic material that enters the magnetization region. Since the magnetization device 11 is a known device, further detailed explanation will be omitted.

[0026] The gradient magnetic field sensor 12 detects the gradient of the magnetic field strength at two different points in the aforementioned detection area using sensor heads, namely the first sensor head S1 and the second sensor head S2, which are positioned at each of these two different points. Based on this, the information processing device 20, which acquires the detection signal output from the gradient magnetic field sensor 12, can determine whether or not an object to be detected was attached to the sheet member ST that was transported through the detection area. For the sake of explanation, in the following, the gradient of the magnetic field strength at the two points, the point where the first sensor head S1 is positioned and the point where the second sensor head S2 is positioned, will be simply referred to as the gradient.

[0027] Here, Figure 2 is a perspective view of the gradient magnetic field sensor 12 shown in Figure 1. Arrow A1 in Figure 2 indicates the direction in which the sheet member ST moves relative to the gradient magnetic field sensor 12. The object to be detected DM shown in Figure 2 is an example of an object to be detected by the gradient magnetic field sensor 12. The object to be detected DM is actually attached to the sheet member ST. However, in Figure 2, the sheet member ST is omitted to avoid making the diagram cluttered, and only the object to be detected DM is shown. Therefore, in Figure 2, arrow A1 indicates the direction in which the object to be detected DM moves.

[0028] The gradient magnetic field sensor 12 comprises a first sensor head S1, a second sensor head S2, a main body to which the first sensor head S1 and the second sensor head S2 are connected, and a magnetic field collecting mechanism CM. The main body of the gradient magnetic field sensor 12 is mounted on a circuit board containing various circuits for controlling the gradient magnetic field sensor 12. Each of the first sensor head S1 and the second sensor head S2 is electrically connected to at least some of these various circuits. Each of the first sensor head S1 and the second sensor head S2 is supported by the main body of the gradient magnetic field sensor 12. Note that in Figure 2, the main body of the gradient magnetic field sensor 12 is omitted for simplification of the diagram.

[0029] The first sensor head S1 detects the strength of the magnetic field at a predetermined first position. The second sensor head S2 detects the strength of the magnetic field at a second position different from the first position. Both the first sensor head S1 and the second sensor head S2 have a linear portion. Below, as an example, we will describe the case in which both the first sensor head S1 and the second sensor head S2 are substantially linear in shape as a whole, as shown in Figure 2. For this reason, in the example shown in Figure 2, the first sensor head S1 and the second sensor head S2 are depicted as linear objects extending in a direction parallel to the X-axis. In this example, the first sensor head S1 and the second sensor head S2 are arranged such that the plane containing the first sensor head S1 and the second sensor head S2 is parallel to the XY plane. The XY plane is a virtual plane drawn by the X-axis and the Y-axis. In this example, the first sensor head S1 and the second sensor head S2 are arranged facing each other and parallel to each other. As a result, the gradient magnetic field sensor 12 can detect magnetic fields in the same direction, and consequently, the detection sensitivity to magnetic fields that are noise, such as the Earth's magnetic field and far-field uniform time, can be made approximately the same for both the first sensor head S1 and the second sensor head S2. The first sensor head S1 and the second sensor head S2 may be arranged so that their planes are not parallel to the XY plane. The first sensor head S1 and the second sensor head S2 may also be arranged side by side, not parallel to each other. Furthermore, the first sensor head S1 and the second sensor head S2 may be arranged coaxially. Either or both of the first sensor head S1 and the second sensor head S2 may be sensor heads of other shapes that have a linear shape instead of being approximately linear, or sensor heads of other shapes that do not have a linear shape. Furthermore, in this embodiment, the description of various components that are substantially linear in shape overall (for example, the first sensor head S1 and the second sensor head S2, etc.) applies to the linear portion of each of these components if they are partially linear in shape.

[0030] Furthermore, as shown in Figure 2, the first sensor head S1 includes a first magnetic core CR1 and a first coil CL1.

[0031] The first magnetic core CR1 has a linear portion. In this example, the first sensor head S1 is a sensor head that is substantially linear in shape overall. In this case, the first magnetic core CR1 is also a magnetic core that is substantially linear in shape overall, as shown in Figure 2. Furthermore, as an example, we will describe the case where the cross-sectional shape of the first magnetic core CR1, when cut by a hypothetical plane perpendicular to the direction in which the substantially linear first magnetic core CR1 extends, is circular. That is, in this case, the first magnetic core CR1 is a cylindrical magnetic core. In the example shown in Figure 2, the direction in which the first magnetic core CR1 extends is parallel to the X-axis. For the sake of explanation, we will refer to this cross-section as the cross-section of the first magnetic core CR1 below. Furthermore, for the sake of explanation, we will refer to the axis passing through the center of this cross-section (i.e., the centroid, center of gravity, etc.) in the direction in which the first magnetic core CR1 extends as the central axis of the first magnetic core CR1 below. For the sake of explanation, the direction in which the first magnetic core CR1 extends will be referred to as the direction of the central axis of the first magnetic core CR1. The cross-sectional shape of the first magnetic core CR1 may be elliptical, rectangular, or any other shape, instead of circular.

[0032] The first coil CL1 is positioned on the first magnetic core CR1. More specifically, the first coil CL1 is a conductor positioned (wound) around the first magnetic core CR1 as a solenoid coil. Therefore, when magnetic flux is linked with the first magnetic core CR1, a current flows through the first coil CL1 in proportion to the change in linked magnetic flux. The value of the current flowing through the first coil CL1 increases as the amount of magnetic flux linked with the first magnetic core CR1 increases, and decreases as the amount of magnetic flux linked with the first magnetic core CR1 decreases.

[0033] The second magnetic core CR2 has a linear portion. In this example, the second sensor head S2 is a sensor head that is substantially linear overall. In this case, the second magnetic core CR2 is also a magnetic core that is substantially linear overall, as shown in Figure 2. Furthermore, as an example, we will describe the case where the shape of the cross-section obtained by cutting the second magnetic core CR2 with a hypothetical plane perpendicular to the direction in which the substantially linear second magnetic core CR2 extends is substantially the same as the shape of the cross-section of the first magnetic core CR1, i.e., circular, excluding deviations due to manufacturing errors, etc. In this case, the second magnetic core CR2 is a cylindrical magnetic core. In the example shown in Figure 2, the direction in which the second magnetic core CR2 extends is parallel to the X-axis. For the sake of explanation, in the following description, this cross-section will be referred to as the cross-section of the second magnetic core CR2. Furthermore, for the sake of explanation, the axis passing through the center of the cross-section (i.e., the centroid, center of gravity, etc.) in the direction in which the second magnetic core CR2 extends will be referred to as the central axis of the second magnetic core CR2. Similarly, for the sake of explanation, the direction in which the second magnetic core CR2 extends will be referred to as the direction of the central axis of the second magnetic core CR2. Note that the cross-sectional shape of the second magnetic core CR2 may be elliptical, rectangular, or any other shape, instead of circular.

[0034] The second coil CL2 is positioned on the second magnetic core CR2. More specifically, the second coil CL2 is a conductor positioned (wound) around the second magnetic core CR2 as a solenoid coil. Therefore, when magnetic flux is linked with the second magnetic core CR2, a current flows through the second coil CL2 in proportion to the change in linked magnetic flux. The value of the current flowing through the second coil CL2 increases as the amount of magnetic flux linked with the second magnetic core CR2 increases, and decreases as the amount of magnetic flux linked with the second magnetic core CR2 decreases.

[0035] Here, the second coil CL2 is differentially connected to the first coil CL1. The circuit configuration of the gradient magnetic field sensor 12, including the first coil CL1 and the second coil CL2, will be described later.

[0036] The gradient magnetic field sensor 12 detects an object passing directly beneath the sensor head region. The sensor head region is a virtual rectangular area having the first sensor head S1 and the second sensor head S2, each configured in this way, as opposing sides. If a part of the first sensor head S1 is non-linear and a part of the second sensor head S2 is non-linear, the sensor head region is a virtual rectangular area having the linear portion of the first sensor head S1 and the linear portion of the second sensor head S2 as opposing sides.

[0037] The magnetic collection mechanism CM is a component that increases the amount of magnetic flux linked with the first magnetic core CR1 from the magnetic flux generated from the object to be detected, and also increases the amount of magnetic flux linked with the second magnetic core CR2 from the magnetic flux generated from the object to be detected. Below, as an example, we will describe a case in which the magnetic collection mechanism CM includes a first magnetic collection mechanism CM1 and a second magnetic collection mechanism CM2, as shown in Figure 2. Note that the magnetic collection mechanism CM may also be configured to include one or more other magnetic collection mechanisms in addition to the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2. Furthermore, the magnetic collection mechanism CM may be configured to include one of the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2, but not the other of the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2.

[0038] The first magnetic collection mechanism CM1 is a component that increases the amount of magnetic flux that links with the first magnetic core CR1 from the magnetic flux generated from the object to be detected. The first magnetic collection mechanism CM1 has a linear shape. Below, as an example, we will describe the case in which the first magnetic collection mechanism CM1 is a component that is substantially linear as a whole, as shown in Figure 2. Also below, as an example, we will describe the case in which the cross-sectional shape of the first magnetic collection mechanism CM1 when it is cut by a hypothetical plane perpendicular to the direction in which it extends is square, as shown in Figure 2. That is, in this case, the shape of the first magnetic collection mechanism CM1 is a rectangular prism with a square cross-section. Here, in the example shown in Figure 2, the direction in which the first magnetic collection mechanism CM1 extends is parallel to the X-axis. Below, for the sake of convenience of explanation, this cross-section will be referred to as the cross-section of the first magnetic collection mechanism CM1. Furthermore, for the sake of explanation, the axis passing through the center of the cross-section (i.e., the centroid, center of gravity, etc.) in the direction in which the first magnetic collecting mechanism CM1 extends will be referred to as the central axis of the first magnetic collecting mechanism CM1. Also, for the sake of explanation, the direction in which the first magnetic collecting mechanism CM1 extends will be referred to as the direction of the central axis of the first magnetic collecting mechanism CM1. Note that the cross-sectional shape of the first magnetic collecting mechanism CM1 may be circular, elliptical, rectangular, or any other shape, instead of a square.

[0039] The first magnetic collector mechanism CM1 is positioned in a predetermined first position relative to the first magnetic core CR1. In this case, the first magnetic collector mechanism CM1 is positioned in the first position such that the magnetic resistance of the first magnetic collector mechanism CM1 is lowest in the direction from the first magnetic collector mechanism CM1 toward the first magnetic core CR1. For example, if the cross-section of the first magnetic collector mechanism CM1 is square, as in this example, the first magnetic collector mechanism CM1 is positioned in the first position such that two sides of the square cross-section of the first magnetic collector mechanism CM1 are approximately parallel to a virtual plane containing the first magnetic core CR1 and the second magnetic core CR2, excluding deviations due to assembly errors, etc. This is because, when the cross-sectional shape of the first magnetic collecting mechanism CM1 is square, the magnetic resistance of the first magnetic collecting mechanism CM1 in the direction parallel to each side of the square is approximately equal, except for deviations due to manufacturing errors, and the magnetic resistance of the first magnetic collecting mechanism CM1 in the direction not parallel to each side of the square is higher than the magnetic resistance of the first magnetic collecting mechanism CM1 in the direction parallel to each side of the square. Also, for example, when the cross-sectional shape of the first magnetic collecting mechanism CM1 is rectangular, the first magnetic collecting mechanism CM1 is positioned in a first arrangement position such that the two short sides of the rectangle, which is the cross-sectional shape of the first magnetic collecting mechanism CM1, are approximately parallel to a virtual plane containing the first magnetic core CR1 and the second magnetic core CR2, except for deviations due to assembly errors, etc. This is because, when the cross-sectional shape of the first magnetic collecting mechanism CM1 is rectangular, the magnetic resistance of the first magnetic collecting mechanism CM1 in the direction parallel to the longer side of the rectangle is lower than the magnetic resistance of the first magnetic collecting mechanism CM1 in other directions.

[0040] In the example shown in Figure 2, the first arrangement position is such that the substantially linear first magnetic core CR1 and the substantially linear first magnetic collection mechanism CM1 are substantially parallel, excluding any misalignment due to assembly errors, and are aligned from top to bottom in the order of first magnetic core CR1, then first magnetic collection mechanism CM1. In this example, the first arrangement position is such that, when viewing the gradient magnetic field sensor 12 from top to bottom, the center of the first magnetic core CR1 in the direction of its central axis and the center of the first magnetic collection mechanism CM1 in the direction of its central axis are substantially coincide, excluding any misalignment due to assembly errors. In this case, in the vertical direction, the central axis of the first magnetic collection mechanism CM1 substantially overlaps with the central axis of the first magnetic core CR1, excluding any misalignment due to assembly errors. Note that the first arrangement position may be any other position between the region through which the object to be detected passes and the first magnetic core CR1. Therefore, the first magnetic collecting mechanism CM1 may be non-parallel to the first magnetic core CR1. Also, for this reason, part or all of the central axis of the first magnetic collecting mechanism CM1 does not have to coincide with the central axis of the first magnetic core CR1 in the vertical direction. Furthermore, the first magnetic collecting mechanism CM1 may be in contact with the first coil CL1 arranged on the first magnetic core CR1, or it may be separated from it. However, when the first magnetic collecting mechanism CM1 and the first coil CL1 are in contact, the first magnetic collecting mechanism CM1 is electrically insulated from the first coil CL1 by an insulating coating on the surface of the conductor wound as the first coil CL1. In the following explanation, for convenience, the distance between the first coil CL1 and the first magnetic collecting mechanism CM1 in the vertical direction will be referred to as the first separation distance g1.

[0041] Here, the first magnetic collecting mechanism CM1 includes N first high-permeability materials and M first low-permeability materials, with HM being the first high-permeability material and LM being the first low-permeability material. N can be any integer greater than or equal to 1. M can also be any integer greater than or equal to 1. In the example shown in Figure 2, N is 15. In this example, M is N-1, i.e., 14. Also in Figure 2, to avoid making the diagram too complex, only two of the 15 first high-permeability materials are shown as HM. Also in Figure 2, to avoid making the diagram too complex, only two of the 14 first low-permeability materials are shown as LM.

[0042] High-permeability material HM is a component having a permeability of a predetermined first threshold or higher, and is, for example, a component made of a magnetic material such as ferrite.

[0043] The low-permeability material LM is a component having a permeability below a predetermined second threshold, and is, for example, a non-magnetic material such as a fine ceramic. Here, the second threshold can be any value as long as it is less than or equal to the first threshold. In addition, the low-permeability material LM may be a magnetic material having a permeability below the second threshold, or it may be air, instead of a non-magnetic material.

[0044] In the first magnetic collection mechanism CM1, the first high-permeability material and the first low-permeability material are arranged alternately, as shown in Figure 2. Therefore, as shown in Figure 3, the first magnetic collection mechanism CM1 can increase the amount of magnetic flux that links with the first magnetic core CR1 from the magnetic flux generated from the object DM. Figure 3 is an example of how the first magnetic collection mechanism CM1 increases the amount of magnetic flux that links with the first magnetic core CR1 from the magnetic flux generated from the object DM. Figure 3 also shows an example of a side view of the first magnetic collection mechanism CM1 and the first sensor head S1, viewed from a direction parallel to the sensor head region, which is perpendicular to the central axis of the first magnetic collection mechanism CM1 and the central axis of the first magnetic core CR1. In the example shown in Figure 3, the object DM shown in Figure 2 is located directly below the first magnetic collection mechanism CM1. The arrows in Figure 3 show an example of a part of the path taken by the magnetic flux generated from the object DM. As shown in Figure 3, the magnetic flux generated from the object to be detected DM passes through the first high-permeability material, which has lower magnetic resistance than the first low-permeability material, and links with the first magnetic core CR1. Here, since the first high-permeability material and the first low-permeability material are arranged alternately in the first magnetic collection mechanism CM1, the spread of the magnetic flux passing through the first high-permeability material in the direction of the central axis of the first magnetic collection mechanism CM1 is suppressed. For this reason, most of the magnetic flux passing through the first high-permeability material links with the first magnetic core CR1, as shown in Figure 3. For this reason, the first magnetic collection mechanism CM1 can increase the amount of magnetic flux generated from the object to be detected DM that links with the first magnetic core CR1. Note that in Figure 3, to avoid making the diagram too complex, the flow of the magnetic flux after linking with the first magnetic core CR1 is omitted.

[0045] On the other hand, Figure 4 shows an example of how a portion of the magnetic flux generated from the object to be detected DM links with the first magnetic core CR1 when the gradient magnetic field sensor 12 does not have the first magnetic collection mechanism CM1. In this case, as shown in Figure 4, most of the magnetic flux generated from the object to be detected DM forms a magnetic circuit that returns to the object to be detected DM without linking with the first magnetic core CR1. Therefore, in this case, the amount of magnetic flux generated from the object to be detected DM that links with the first magnetic core CR1 is less than when the gradient magnetic field sensor 12 has the first magnetic collection mechanism CM1. In other words, this indicates that when the gradient magnetic field sensor 12 has the first magnetic collection mechanism CM1, the amount of magnetic flux generated from the object to be detected DM that links with the first magnetic core CR1 is greater than when the gradient magnetic field sensor 12 does not have the first magnetic collection mechanism CM1.

[0046] Figure 5 is a diagram for comparing the amount of magnetic flux linked with the first magnetic core CR1 shown in Figure 3 and the first magnetic core CR1 shown in Figure 4. Here, the first magnetic core CR1 shown in Figure 3 is the first magnetic core CR1 of the first sensor head S1 equipped with the first magnetic collection mechanism CM1. The first magnetic core CR1 shown in Figure 4 is the first magnetic core CR1 of the first sensor head S1 that is not equipped with the first magnetic collection mechanism CM1. The horizontal axis of the graph in Figure 5 shows the position of the object to be detected DM when the object to be detected is moved directly below the first magnetic core CR1 in a direction parallel to the central axis of the first magnetic core CR1. Therefore, the origin of the horizontal axis shows the position of the center of the first magnetic core CR1 in the direction of the central axis of the first magnetic core CR1. The vertical axis of the graph shows the amount of magnetic flux linked with the first magnetic core CR1. Furthermore, the curve F1 plotted on the graph shows an example of the change in the amount of magnetic flux linked with the first magnetic core CR1 from the magnetic flux generated from the object DM when the object DM moves in the direction directly beneath the first magnetic core CR1 shown in Figure 3. Similarly, the curve F2 plotted on the graph shows an example of the change in the amount of magnetic flux linked with the first magnetic core CR1 from the magnetic flux generated from the object DM when the object DM moves in the direction directly beneath the first magnetic core CR1 shown in Figure 4. As shown in Figure 5, in this graph, the peak height of curve F1 is higher than the peak height of curve F2. Thus, when the gradient magnetic field sensor 12 is equipped with the first magnetic collection mechanism CM1, the gradient magnetic field sensor 12 can increase the amount of magnetic flux linked with the first magnetic core CR1.

[0047] The second magnetic collecting mechanism CM2 increases the amount of magnetic flux that links with the second magnetic core CR2 from the magnetic flux generated from the object to be detected. The configuration of the second magnetic collecting mechanism CM2 is the same as that of the first magnetic collecting mechanism CM1. For this reason, a detailed explanation of the configuration of the second magnetic collecting mechanism CM2 is omitted in this embodiment. The shape of the second magnetic collecting mechanism CM2 may differ from that of the first magnetic collecting mechanism CM1. Also, for the sake of explanation, the direction in which the substantially linear second magnetic collecting mechanism CM2 extends will be referred to as the direction of the central axis of the second magnetic collecting mechanism CM2. In the example shown in Figure 2, the direction of the central axis of the second magnetic collecting mechanism CM2 is parallel to the X-axis. Also, for the sake of explanation, the cross-section obtained when the second magnetic collecting mechanism CM2 is cut by a hypothetical plane perpendicular to the direction of the central axis of the second magnetic collecting mechanism CM2 will be referred to as the cross-section of the second magnetic collecting mechanism CM2. Furthermore, for the sake of explanation, the axis passing through the center of the cross-section (i.e., the centroid, center of gravity, etc.) in the direction of the central axis of the second magnetic collecting mechanism CM2 will be referred to as the central axis of the second magnetic collecting mechanism CM2. Furthermore, for the sake of explanation, each of the N high-permeability materials HM included in the second magnetic collecting mechanism CM2 will be referred to as the second high-permeability material. Furthermore, for the sake of explanation, each of the M high-permeability materials HM included in the second magnetic collecting mechanism CM2 will be referred to as the second low-permeability material. In this way, the second magnetic collecting mechanism CM2, which has the same configuration as the first magnetic collecting mechanism CM1, can increase the amount of magnetic flux that links with the second magnetic core CR2 from the magnetic flux generated from the object to be detected.

[0048] The second magnetic collector mechanism CM2 is positioned in a predetermined second position relative to the second magnetic core CR2. In this case, the second magnetic collector mechanism CM2 is positioned in the second position such that the magnetic resistance of the second magnetic collector mechanism CM2 is lowest in the direction from the second magnetic collector mechanism CM2 toward the second magnetic core CR2. For example, if the cross-section of the second magnetic collector mechanism CM2 is square, as in this example, the second magnetic collector mechanism CM2 is positioned in the second position such that two sides of the square cross-section of the second magnetic collector mechanism CM2 are approximately parallel to a virtual plane containing the first magnetic core CR1 and the second magnetic core CR2, excluding deviations due to assembly errors, etc. Furthermore, for example, if the cross-section of the second magnetic collecting mechanism CM2 is rectangular, the second magnetic collecting mechanism CM2 is positioned at a second placement location such that the two short sides of the rectangular cross-section of the second magnetic collecting mechanism CM2 are substantially parallel to a virtual plane containing the first magnetic core CR1 and the second magnetic core CR2, excluding deviations due to assembly errors, etc. Here, if the cross-sectional shape of the second magnetic collecting mechanism CM2 is substantially the same as the cross-sectional shape of the first magnetic collecting mechanism CM1, excluding deviations due to manufacturing errors, etc., the gradient magnetic field sensor 12 can make the amount of magnetic flux flowing into the first magnetic core CR1 and the amount of magnetic flux flowing into the second magnetic core CR2 substantially the same for magnetic flux generated from an object to be detected that is equidistant from both the first magnetic core CR1 and the second magnetic core CR2. As a result, the gradient magnetic field sensor 12 can accurately cancel out the noise detected by the first sensor head S1 and the noise detected by the second sensor head S2 through the differential connection of the first coil CL1 and the second coil CL2. Furthermore, if the cross-sectional shape of the first magnetic collecting mechanism CM1 and the cross-sectional shape of the second magnetic collecting mechanism CM2 are rectangular (i.e., square, rectangular, etc.), the magnetic flux generated from the object to be detected can be efficiently channeled to the first magnetic core CR1 and the second magnetic core CR2 compared to the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2 having other cross-sectional shapes.

[0049] In the example shown in Figure 2, the second arrangement position is such that the substantially linear second magnetic core CR2 and the substantially linear second magnetic collection mechanism CM2 are substantially parallel, excluding any misalignment due to assembly errors, and are arranged from top to bottom in the order of second magnetic core CR2 followed by second magnetic collection mechanism CM2. Furthermore, in this example, when viewing the gradient magnetic field sensor 12 from top to bottom, the second arrangement position is such that the center of the second magnetic core CR2 in the direction of its central axis and the center of the second magnetic collection mechanism CM2 in the direction of its central axis are substantially coincide, excluding any misalignment due to assembly errors. In this case, in the vertical direction, the central axis of the second magnetic collection mechanism CM2 substantially overlaps with the central axis of the second magnetic core CR2, excluding any misalignment due to assembly errors. Here, if such center alignment and central axis alignment are achieved in the first sensor head S1 and the second sensor head S2, the gradient magnetic field sensor 12 can improve the detection sensitivity of the magnetic field by the first magnetic core CR1 and the second magnetic core CR2 as a whole. The second placement position may be any other position as long as it is between the region through which the object to be detected passes and the second magnetic core CR2. For this reason, the second magnetic collection mechanism CM2 may be non-parallel to the second magnetic core CR2. Also for this reason, part or all of the central axis of the second magnetic collection mechanism CM2 does not have to overlap with the central axis of the second magnetic core CR2 in the vertical direction. Furthermore, the second magnetic collection mechanism CM2 may be in contact with the second coil CL2 placed on the second magnetic core CR2, or it may be separated from it. However, if the second magnetic collection mechanism CM2 and the second coil CL2 are in contact, the second magnetic collection mechanism CM2 is electrically insulated from the second coil CL2 by an insulating coating on the surface of the conductor wound as the second coil CL2. For the sake of explanation, the distance between the second coil CL2 and the second magnetic collection mechanism CM2 in the vertical direction will be referred to as the second separation distance g2.

[0050] In the following, as an example, we will describe the case where the virtual plane containing the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2 is approximately parallel to the sensor head region (or the virtual plane containing the first magnetic core CR1 and the second magnetic core CR2), excluding deviations due to assembly errors, etc. In this case, since the sensor head region is approximately parallel to the XY plane, the virtual plane containing the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2 is also approximately parallel to the XY plane. In the gradient magnetic field sensor 12, these two planes may be non-parallel.

[0051] Here, the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2, configured as described above, can increase the amount of magnetic flux linked with the first magnetic core CR1 and the second magnetic core CR2, respectively, and can also suppress the linking of noise magnetic flux with the first magnetic core CR1 and the second magnetic core CR2, respectively. Figure 6 shows an example of how noise magnetic flux flows through the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2 without linking with the first magnetic core CR1 and the second magnetic core CR2, respectively. Figure 6 is also a front view showing the first sensor head S1, the second sensor head S2, the first magnetic collecting mechanism CM1, and the second magnetic collecting mechanism CM2, respectively, when the gradient magnetic field sensor 12 is viewed from directions parallel to the central axis direction of the first magnetic core CR1 and the central axis direction of the second magnetic core CR2, respectively. The arrows shown in Figure 6 show an example of the flow of noise magnetic flux. That is, in the example shown in Figure 6, the noise magnetic flux flows from the negative side of the Y-axis to the positive side of the Y-axis. Such noisy magnetic flux will try to flow towards a component with relatively lower magnetic resistance than the first sensor head S1 if such a component exists around the first sensor head S1. The first high-permeability material included in the first magnetic collection mechanism CM1 is an example of a component with relatively lower magnetic resistance than the first sensor head S1.

[0052] In this example, the central axis direction of the first magnetic collector CM1 and the central axis direction of the first magnetic core CR1 are approximately parallel, and the first magnetic collector CM1 is located directly below the first magnetic core CR1. Therefore, as shown in Figure 6, most of the magnetic flux that becomes noise tends to flow from the first magnetic collector CM1 towards the second magnetic collector CM2 into the first high-permeability material of the first magnetic collector CM1. Also, in this example, the cross-section of the first high-permeability material is square. For this reason, in the example shown in Figure 6, the magnetic flux flowing through the first high-permeability material flows towards the second magnetic collector CM2 because it loses less energy if it travels in a straight line rather than changing direction along the way. For the same reason, as shown in Figure 6, the magnetic flux that flows from the first magnetic collector CM1 into the second magnetic collector CM2 does not flow towards the second magnetic core CR2, but rather flows in the opposite direction to the direction from the second magnetic collector CM2 towards the first magnetic collector CM1.

[0053] These circumstances are the same even when the noise-generating magnetic flux flows from the positive Y-axis side to the negative Y-axis side. In other words, in this case, if there is a material around the second sensor head S2 that has a relatively lower magnetic resistance than the second sensor head S2, the noise-generating magnetic flux will try to flow towards that material, avoiding the second sensor head S2. The second high-permeability material included in the second magnetic collection mechanism CM2 is an example of a material that has a relatively lower magnetic resistance than the second sensor head S2. And, since the magnetic flux flowing through the second high-permeability material loses less energy if it travels in a straight line than if it changes direction along the way, it flows towards the first magnetic collection mechanism CM1. For the same reason, the magnetic flux flowing from the second magnetic collection mechanism CM2 to the first magnetic collection mechanism CM1 does not flow towards the first magnetic core CR1, but flows in the opposite direction to the direction from the first magnetic collection mechanism CM1 to the second magnetic collection mechanism CM2.

[0054] As shown in Figure 6, at least a portion of the noise magnetic flux passes through the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2 without linking with the first magnetic core CR1 and the second magnetic core CR2, respectively. Therefore, by including the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2, the gradient magnetic field sensor 12 can suppress the linking of noise magnetic flux with the first magnetic core CR1 and the second magnetic core CR2, respectively. This means that when the gradient magnetic field sensor 12 is equipped with the first magnetic collecting mechanism CM1 and the second magnetic collecting mechanism CM2, the amount of magnetic flux that links with the first magnetic core CR1 and the second magnetic core CR2 from the magnetic flux generated from the object to be detected can be increased, and the gradient magnetic field sensor 12 can suppress the detection of noise magnetic fields. As a result, the gradient magnetic field sensor 12 can improve the S(Signal) / N(Noise) ratio for detection of magnetic fields generated from the object to be detected by the first sensor head S1 and the second sensor head S2, respectively, and as a result, the detection sensitivity of the object to be detected can be improved.

[0055] Furthermore, if there are no components around the first sensor head S1 with relatively lower magnetic resistance than the first sensor head S1, the magnetic flux that generates noise will link with the first magnetic core CR1 of the first sensor head S1, as shown in Figure 7. Figure 7 is a diagram showing an example of how the magnetic flux that generates noise, as shown in Figure 6, links with the first magnetic core CR1 and the second magnetic core CR2 when the gradient magnetic field sensor 12 does not have a first magnetic collection mechanism CM1 and a second magnetic collection mechanism CM2. The arrows shown in Figure 7 indicate an example of the flow of the magnetic flux that generates noise.

[0056] Furthermore, if the magnetic field collection mechanism CM includes only one of the first magnetic field collection mechanism CM1 or the second magnetic field collection mechanism CM2, the magnetic field collection mechanism CM (i.e., either the first magnetic field collection mechanism CM1 or the second magnetic field collection mechanism CM2) is perpendicular or oblique to the substantially linear first sensor head S1 and the substantially linear second sensor head S2 when the gradient magnetic field sensor 12 is viewed from top to bottom. Even in this case, by including the magnetic field collection mechanism CM, the gradient magnetic field sensor 12 can improve the signal-to-noise ratio for detection of the magnetic field generated from the object to be detected by the first sensor head S1 and the second sensor head S2, respectively, and as a result, the detection sensitivity of the object to be detected can be improved.

[0057] Furthermore, a more detailed description of the configuration methods of the first magnetic collection mechanism CM1 and the second magnetic collection mechanism CM2 described above will be given later. Note that some or all of the N first high-permeability materials described above may be of different types. Also, some or all of the N second high-permeability materials described above may be of different types. Also, some or all of the M first low-permeability materials described above may be of different types. Also, some or all of the M second low-permeability materials described above may be of different types.

[0058] Returning to Figure 1, the information processing device 20 is connected to the gradient magnetic field sensor 12 in a communicative manner. As described above, the information processing device 20 determines whether or not an object to be detected was attached to the sheet member ST that was transported through the detection area, based on the detection signal output from the gradient magnetic field sensor 12.

[0059] For example, if the information processing device 20 determines that a target object is attached to the sheet member ST being transported through the detection area, it controls the servo motor to stop the winding of the sheet member ST by the second roller RL2 and performs a notification process to notify that a target object was attached to the sheet member ST. The notification process is, for example, a process that displays information on the display of the information processing device 20 indicating that a target object was attached to the sheet member ST. This allows the user of the magnetic object detection device 1 to remove the target object from the sheet member ST, identify the sheet member ST as a defective product, etc. Alternatively, the notification process may output sound, vibration, light, etc., indicating the information.

[0060] The information processing device 20 may be, for example, a notebook PC (Personal Computer), a tablet PC, a desktop PC, a workstation, a multifunction mobile phone terminal (smartphone), a mobile phone terminal, or a PDA (Personal Digital Assistant). The information processing device 20 may also be other information processing devices such as a microcontroller.

[0061] In addition, in the magnetic material detection device 1, some or all of the magnetization device 11, gradient magnetic field sensor 12, and information processing device 20 may be configured as a single unit.

[0062] Furthermore, the object that the magnetic material detection device 1 inspects for the presence or absence of the object to be detected may be other objects capable of being inspected for the presence or absence of the object to be detected, instead of the sheet member ST. For example, a magnetic material detector equipped with a gradient magnetic field sensor 12 detects the presence or absence of magnetic materials in the ground. In this case, the magnetic material detector is an example of the magnetic material detection device 1. Also, magnetic materials in the ground are an example of the object to be detected in this case.

[0063] <More detailed configuration methods for the first and second magnetic collection mechanisms> The following describes the configuration methods of the first and second magnetic field collecting mechanisms in more detail. For the sake of clarity, the gradient magnetic field sensor 12 with the first and second magnetic field collecting mechanisms CM1 and CM2 removed will be referred to as the gradient magnetic field sensor 12X to distinguish it from the gradient magnetic field sensor 12 with the first and second magnetic field collecting mechanisms CM1 and CM2 still attached. The gradient magnetic field sensor 12X corresponds to a conventional gradient magnetic field sensor.

[0064] First, we will explain how to determine the number N of the first high-permeability materials in the first magnetic collection mechanism CM1, the length t of the first high-permeability materials in the central axis direction of the first magnetic collection mechanism CM1, and the length t' of the first low-permeability material in the central axis direction of the first magnetic collection mechanism CM1. Figure 8 is a diagram illustrating how to determine the number N of the first high-permeability materials in the first magnetic collection mechanism CM1, the length t of the first high-permeability materials in the central axis direction of the first magnetic collection mechanism CM1, and the length t' of the first low-permeability material in the central axis direction of the first magnetic collection mechanism CM1. Figure 8 is also a side view of the first sensor head S1 and the first magnetic collection mechanism CM1 when viewed from a direction parallel to the sensor head region, which is perpendicular to the central axis of the first magnetic core CR1. In Figure 8, the lengths t and t' are shown visually. The number N, length t, and length t' are each given by equations (1) and (2) below, which represent the proportion of the first high-permeability material in the first magnetic collecting mechanism CM1 and the relative permeability μ of the first high-permeability material. r It is related to the first relative permeability ratio mag obtained by multiplying by .

[0065]

number

[0066]

number

[0067] Here, in equations (1) and (2) above, d represents the ratio of length t to the sum of length t and length t'.

[0068] On the other hand, when the object to be detected DM is placed at a predetermined position X1 relative to the first magnetic core CR1 of the gradient magnetic field sensor 12, the amount of magnetic flux linked to the first magnetic core CR1 changes according to the value of the first relative permeability ratio mag. For the sake of explanation, in the following, among the states of the gradient magnetic field sensor 12, the state in which the object to be detected DM is placed at position X1 will be referred to as the target state. Here, the amount of magnetic flux can be obtained by simulation, experiment, etc. for each value of the first relative permeability ratio mag. Figure 9 is a diagram showing an example of the change in the amount of magnetic flux linked to the first magnetic core CR1 when the value of the first relative permeability ratio mag is changed in the gradient magnetic field sensor 12 in the target state. Note that the graph shown in Figure 9 is a graph obtained by simulation. The horizontal axis of the graph shown in Figure 9 shows the value of the first relative permeability ratio mag. The vertical axis of the graph shows the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. Furthermore, the straight line SH1 drawn on the graph represents a predetermined third threshold for the total amount of magnetic flux linkage within the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state). The third threshold is, for example, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state, but it may also be any other predetermined value for the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. In the example shown in Figure 9, looking at the nine points plotted as black circles on the graph, it can be seen that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 exceeds the third threshold if the value of the first relative permeability ratio mag is within the range of 0.1 to 0.9. In other words, a manufacturer of the gradient magnetic field sensor 12 can select a value for the first relative permeability ratio mag within the range of 0.1 to 0.9, and based on the selected value and the above equations (1) and (2), determine the number N, length t, and length t' such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state.In other words, the number N, length t, and length t' are determined based on the value of the first relative permeability ratio mag, which is selected in this way, and the above equations (1) and (2), such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. Note that the peak in the graph of the amount of magnetic flux linked to the first magnetic core CR1 is the peak that appears when length t and length t' are the same length. This is thought to be because when length t is shorter than length t', it becomes difficult for the magnetic flux to pass through the first high-permeability material toward the first magnetic core CR1, and when length t is longer than length t', the magnetic flux spreads in the direction of the central axis of the first magnetic collection mechanism CM1 within the first high-permeability material, causing the peak to appear. In other words, in the gradient magnetic field sensor 12, by making lengths t and t' approximately the same, excluding deviations due to manufacturing errors, it is possible to more reliably increase the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state compared to the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state.

[0069] Here, the method for determining the number N of the second high-permeability materials in the second magnetic collecting mechanism CM2, the length t of the second high-permeability materials in the central axis direction of the second magnetic collecting mechanism CM2, and the length t' of the second low-permeability material in the central axis direction of the second magnetic collecting mechanism CM2 is the same as the method for determining the number N of the first high-permeability materials in the first magnetic collecting mechanism CM1, the length t of the first high-permeability materials in the central axis direction of the first magnetic collecting mechanism CM1, and the length t' of the first low-permeability material in the central axis direction of the first magnetic collecting mechanism CM1, so the explanation is omitted. However, in determining the number N of the second high-permeability material in the second magnetic field collecting mechanism CM2, the length t of the second high-permeability material in the central axis direction of the second magnetic field collecting mechanism CM2, and the length t' of the second low-permeability material in the central axis direction of the second magnetic field collecting mechanism CM2, a predetermined fourth threshold is used instead of the third threshold described above, based on the total amount of linked magnetic flux within the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state). The fourth threshold may be different from the third threshold, or it may be the same as the third threshold. The fourth threshold is, for example, the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12X in the target state, but it may also be any other value predetermined for the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state.

[0070] Next, the length L of the first magnetic core CR1 in the central axis direction of the first magnetic core CR1. core The length L of the first magnetic collecting mechanism CM1 in the central axis direction relative to the given value. total The method for determining the ratio will be explained. Figure 10 shows the length L of the first magnetic core CR1 in the central axis direction of the first magnetic core CR1. core The length L of the first magnetic collecting mechanism CM1 in the central axis direction relative to the given value. total This is a diagram to explain how the ratio is determined. Figure 10 is also a side view of the first sensor head S1 and the first magnetic collection mechanism CM1, respectively, when viewed from a direction parallel to the sensor head region, which is perpendicular to the central axis of the first magnetic core CR1. In Figure 10, length L core And, length L totaland each of them are shown so as to be visually distinguishable.

[0071] The amount of magnetic flux interlinking the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state varies according to the value of the ratio of the length L to the length L core total . Here, the amount of the magnetic flux can be obtained for each value of the ratio through simulation, experiment, or the like. FIG. 11 is a diagram showing an example of a change in the amount of magnetic flux interlinking the first magnetic core CR1 when the value of the ratio of the length L to the length L is varied in the gradient magnetic field sensor 12 in the target state. Note that the graph shown in FIG. 11 is a graph obtained by simulation. The horizontal axis of the graph shown in FIG. 11 indicates the value of the ratio of the length L to the length L core total core total . The vertical axis of the graph indicates the amount of magnetic flux that has interlinked the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. In addition, the straight line SH2 drawn on the graph indicates a predetermined fifth threshold value for the total interlinkage magnetic flux amount in the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state (that is, the amount of magnetic flux interlinking the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state). The fifth threshold value is, for example, the same value as the third threshold value, but may be a value different from the third threshold value. Further, the curve F3 plotted on the graph shows an example of a change in the amount of magnetic flux interlinking the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state when the value of the ratio d shown in the above formula (2) is 0.1 and the value of the ratio of the length L to the length L is varied core total . Further, the curve F4 plotted on the graph shows an example of a change in the amount of magnetic flux interlinking the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state when the value of the ratio d is 0.9 and the value of the ratio of the length L to the length L is varied core total . Further, the curve F5 plotted on the graph shows an example of a change in the amount of magnetic flux interlinking the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state when the value of the ratio d is 0.25 and the value of the ratio of the length L to the length L is varied core total ​​​​​​​This shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 changes when the value of the ratio is changed. Furthermore, the curve F6 plotted on the graph is when the value of the ratio d is 0.75 and the length L core Length L total This shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 changes when the value of the ratio is changed. Furthermore, the curve F7 plotted on the graph is the case when the value of the ratio d is 0.5 and the length L core Length L total This shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state changes when the value of the ratio is changed. In the example shown in Figure 11, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is given by the length L as shown in equation (3) below. total Length L core If it is 0.9 times or more, it can be seen that the value of ratio d exceeds the fifth threshold within the range of 0.1 to 0.9.

[0072]

number

[0073] In other words, the manufacturer of the gradient magnetic field sensor 12 has a length L core Based on the fifth threshold, the length L is set such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. total Length L core It can be determined to be a value of 0.9 or greater. In other words, the length L core Length L total The value of the ratio is determined to be 0.9 or greater, based on the fifth threshold, such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. After determining the value of the ratio, the manufacturer then combines the determined value with a predetermined length L coreBased on this, length L total It is possible to make a decision.

[0074] Here, L is the length of the second magnetic core CR2 in the direction of the central axis of the second magnetic core CR2. core The length L of the second magnetic collecting mechanism CM2 in the central axis direction relative to the second magnetic collecting mechanism CM2. total The method for determining the ratio is the length L of the first magnetic core CR1 in the central axis direction of the first magnetic core CR1. core The length L of the first magnetic collecting mechanism CM1 in the central axis direction relative to the given value. total The method for determining the ratio is the same as above, so the explanation will be omitted. However, the length L of the second magnetic core CR2 in the central axis direction of the second magnetic core CR2 core The length L of the second magnetic collecting mechanism CM2 in the central axis direction relative to the second magnetic collecting mechanism CM2. total In determining the ratio, instead of the fifth threshold mentioned above, a sixth threshold predetermined for the total amount of linked magnetic flux within the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state) is used. The sixth threshold may be different from the fifth threshold, or it may be the same as the fifth threshold. The sixth threshold is, for example, the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12X in the target state, but it may also be any other value predetermined for the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state.

[0075] Next, the diameter of the first magnetic core φ core The method for determining the ratio of the width w1 of the first magnetic collection mechanism to 1 will be explained. Here, the diameter φ of the first magnetic core is... core φ is the diameter of the circumscribed circle that circumscribes the cross-sectional shape of the first magnetic core CR1. In this example, the cross-sectional shape of the first magnetic core CR1 is circular. Therefore, the diameter of the first magnetic core φ core1 is the diameter of the cross-section of the first magnetic core CR1. The width w1 of the first magnetic collector mechanism is the length of the first magnetic collector mechanism CM1 in a direction parallel to a hypothetical plane containing the first magnetic collector mechanism CM1 and the second magnetic collector mechanism CM2, and perpendicular to the central axis direction of the first magnetic collector mechanism CM1. In this example, the cross-sectional shape of the first magnetic collector mechanism CM1 is square. Therefore, the width w1 of the first magnetic collector mechanism is the length of each of the two sides of this square that are parallel to the central axis direction of the first magnetic collector mechanism CM1. Figure 12 shows the diameter φ of the first magnetic core. core This figure illustrates how to determine the ratio of the width w1 of the first magnetic collection mechanism to 1. Figure 12 is a front view of the first sensor head S1 and the first magnetic collection mechanism CM1, respectively, viewed from the central axis direction of the first magnetic core CR1. Figure 12 shows the diameter φ of the first magnetic core. core The dimensions of 1 and the width w1 of the first magnetic collection mechanism are shown in a way that is easily understood visually.

[0076] The amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is the diameter of the first magnetic core φ core It changes according to the ratio of the width w1 of the first magnetic collection mechanism to 1. Here, the amount of magnetic flux can be obtained for each value of the ratio by simulation, experiment, etc. Figure 13 shows the diameter of the first magnetic core φ in the gradient magnetic field sensor 12 in the target state. core This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of the width w1 of the first magnetic collection mechanism to 1 is varied. Note that the graph shown in Figure 13 is a graph obtained through simulation. The horizontal axis of the graph in Figure 13 represents the diameter φ of the first magnetic core. coreThis shows the ratio of the width w1 of the first magnetic collection mechanism to 1. The vertical axis of the graph shows the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. The straight line SH3 drawn on the graph shows a predetermined seventh threshold for the total amount of linked magnetic flux within the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state). The seventh threshold is, for example, the same value as the third threshold, but it may also be a different value from the third threshold. The curve F8 plotted on the graph represents the diameter φ of the first magnetic core. core This shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state changes when the ratio of the width w1 of the first magnetic collection mechanism to 1 is changed. In the example shown in Figure 13, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is the diameter of the first magnetic core φ core If the ratio of the width w1 of the first magnetic collection mechanism to 1 is within the range of 0.5 to 60, it can be seen that the seventh threshold is exceeded. In other words, the manufacturer of the gradient magnetic field sensor 12 should design the first magnetic core diameter φ such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. core The ratio of the width w1 of the first magnetic collection mechanism to 1 can be determined to a value within the range of 0.5 to 60 shown in the following equation (4). In other words, the first magnetic core diameter φ core The ratio of the width w1 of the first magnetic collection mechanism to 1 is determined based on the seventh threshold value to be within the range of 0.5 to 60 such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. After determining the value of the ratio, the manufacturer then compares the determined value with the diameter φ of the first magnetic core. core Based on 1, the width w1 of the first magnetic collection mechanism can be determined.

[0077]

number

[0078] Note that the variable w shown in equation (4) above is the variable to which the width w1 of the first magnetic collection mechanism is substituted.

[0079] Here, the diameter of the second magnetic core is φ core The method for determining the ratio of the width w2 of the second magnetic collection mechanism to 2 is as follows: core The method for determining the ratio of the width w1 of the first magnetic collection mechanism to 1 is the same, so the explanation is omitted. However, the diameter of the second magnetic core φ core 2 is the diameter of the circumscribed circle that circumscribes the cross-sectional shape of the second magnetic core CR2. In this example, the cross-sectional shape of the second magnetic core CR2 is circular. Therefore, the diameter of the second magnetic core φ core 2 is the diameter of the cross-section of the second magnetic core CR2. The width w2 of the second magnetic collector mechanism is the length of the second magnetic collector mechanism CM2 in a direction parallel to the imaginary plane containing the first magnetic collector mechanism CM1 and the second magnetic collector mechanism CM2, and perpendicular to the central axis direction of the second magnetic collector mechanism CM2. In this example, the cross-sectional shape of the second magnetic collector mechanism CM2 is a square. Therefore, the width w2 of the second magnetic collector mechanism is the length of each of the two sides of this square that are parallel to the central axis direction of the second magnetic collector mechanism CM2. Also, the diameter φ of the second magnetic core. core In determining the ratio of the second magnetic core width w2 to 2, w in equation (4) above is treated as a variable to which the second magnetic core width w2 is substituted. Also, the second magnetic core diameter φ core In determining the ratio of the width w2 of the second magnetic collection mechanism to 2, instead of the seventh threshold mentioned above, an eighth threshold predetermined for the total amount of linked magnetic flux within the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state) is used. The eighth threshold may be different from the seventh threshold, or it may be the same as the seventh threshold. The eighth threshold is, for example, the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12X in the target state, but it may also be any other value predetermined for the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state.

[0080] Next, the diameter of the first magnetic core φ core The method for determining the ratio of the height h1 of the first magnetic collector to 1 will be explained. Here, the height h1 of the first magnetic collector is the length of the first magnetic collector CM1 in a direction perpendicular to a hypothetical plane containing the first magnetic collector CM1 and the second magnetic collector CM2. In this example, the cross-sectional shape of the first magnetic collector CM1 is a square. Therefore, the height h1 of the first magnetic collector is the length of each of the two sides of this square that are perpendicular to the plane. Figure 14 shows the diameter φ of the first magnetic core. core This figure illustrates how to determine the ratio of the height h1 of the first magnetic collection mechanism to 1. Figure 14 is also a front view of the first sensor head S1 and the first magnetic collection mechanism CM1, viewed from the central axis direction of the first magnetic core CR1. Figure 14 shows the diameter φ of the first magnetic core. core The values ​​of 1 and the height h1 of the first magnetic collection mechanism are shown in a way that is easily understood visually.

[0081] Here, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is the diameter of the first magnetic core φ core It changes according to the ratio of the height h1 of the first magnetic collection mechanism to 1. Here, the amount of magnetic flux can be obtained for each value of the ratio by simulation, experiment, etc. Figure 15 shows the diameter φ of the first magnetic core of the gradient magnetic field sensor 12 in the target state. core This figure shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 changes when the ratio of the height h1 of the first magnetic collection mechanism to 1 is varied. Note that the graph shown in Figure 15 is a graph obtained through simulation. The horizontal axis of the graph in Figure 15 represents the diameter φ of the first magnetic core. coreThis shows the ratio of the height h1 of the first magnetic collection mechanism to 1. The vertical axis of the graph shows the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. The straight line SH4 drawn on the graph shows a predetermined ninth threshold for the total amount of linked magnetic flux within the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state). The ninth threshold is, for example, the same value as the third threshold, but may also be a different value from the third threshold. The curve F9 plotted on the graph represents the diameter φ of the first magnetic core. core This shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state changes when the ratio of the height h1 of the first magnetic collection mechanism to 1 is changed. In the example shown in Figure 15, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is the diameter of the first magnetic core φ core If the ratio of the height h1 of the first magnetic collection mechanism to 1 is within the range of 0.5 to 50, it can be seen that the ninth threshold is exceeded. In other words, the manufacturer of the gradient magnetic field sensor 12 should design the first magnetic core diameter φ such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. core The ratio of the height h1 of the first magnetic collection mechanism to 1 can be determined to a value within the range of 0.5 to 50 shown in the following equation (5). In other words, the first magnetic core diameter φ core The ratio of the height h1 of the first magnetic collection mechanism to 1 is determined based on the ninth threshold, to a value within the range of 0.5 to 50 such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. After determining the value of this ratio, the manufacturer then compares the determined value with the diameter of the first magnetic core φ core Based on 1, the height h1 of the first magnetic collection mechanism can be determined.

[0082]

number

[0083] Note that the variable h shown in equation (5) above is the variable to which the height h1 of the first magnetic collection mechanism is substituted.

[0084] Here, the diameter of the second magnetic core is φ core The method for determining the ratio of the height h2 of the second magnetic collection mechanism to 2 is as follows: core The method for determining the ratio of the height h1 of the first magnetic collector to 1 is the same, so the explanation is omitted. However, the height h2 of the second magnetic collector is the length of the second magnetic collector CM2 in a direction perpendicular to the imaginary plane containing the first magnetic collector CM1 and the second magnetic collector CM2. In this example, the cross-sectional shape of the second magnetic collector CM2 is a square. Therefore, the height h2 of the second magnetic collector is the length of each of the two sides of this square that are perpendicular to the plane. Also, the diameter φ of the second magnetic core core In determining the ratio of the width w2 of the second magnetic collecting mechanism to 2, h in equation (5) above is treated as a variable to which the height h2 of the second magnetic collecting mechanism is substituted. Also, the diameter φ of the second magnetic core core In determining the ratio of the height h2 of the second magnetic collection mechanism to 2, instead of the ninth threshold mentioned above, a tenth threshold predetermined for the total amount of magnetic flux linkage within the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state) is used. The tenth threshold may be different from the ninth threshold, or it may be the same as the ninth threshold. The ninth threshold is, for example, the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12X in the target state, but it may also be any other value predetermined for the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state.

[0085] Next, we will explain how to determine the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism. Figure 16 is a diagram illustrating how to determine the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism. Figure 16 is also a front view of the first sensor head S1 and the first magnetic collection mechanism CM1, respectively, when viewed from the central axis direction of the first magnetic core CR1. Figure 16 shows the height h1 of the first magnetic collection mechanism and the first separation distance g1 in a way that is visually clear.

[0086] Here, the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state changes according to the value of the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism. Here, the amount of magnetic flux can be obtained for each value of the ratio by simulation, experiment, etc. Figure 17 is a figure showing an example of the change in the amount of magnetic flux linked to the first magnetic core CR1 when the value of the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism is changed in the gradient magnetic field sensor 12 in the target state. Note that the graph shown in Figure 17 is a graph obtained by simulation. The horizontal axis of the graph shown in Figure 17 shows the value of the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism. The vertical axis of the graph shows the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state. Furthermore, the straight line SH5 drawn on the graph represents a predetermined 11th threshold for the total amount of magnetic flux linkage within the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state). The 11th threshold is, for example, the same value as the 3rd threshold, but may also be a different value from the 3rd threshold. The curve F10 plotted on the graph shows an example of how the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state changes when the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism is changed. In the example shown in Figure 17, it can be seen that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state exceeds the 11th threshold if the value of the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism is within the range of 0 to 4. In other words, a manufacturer of the gradient magnetic field sensor 12 can determine the value of the ratio of the first separation distance g1 to the height h1 of the first magnetic collection mechanism to a value within the range of 0 to 4 shown in the following equation (6), such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state.In other words, the ratio of the first separation distance g1 to the height h1 of the first magnetic collecting mechanism is determined based on the 11th threshold value to be within the range of 0 to 4 such that the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12 in the target state is greater than the amount of magnetic flux linked to the first magnetic core CR1 of the gradient magnetic field sensor 12X in the target state. After determining the value of this ratio, the manufacturer can then determine the first separation distance g1 based on the determined value and the height h1 of the first magnetic collecting mechanism. That is, this means that the first separation distance g1 is determined based on the 11th threshold value and the height h1 of the first magnetic collecting mechanism to be greater than or equal to 0 and within the range of 4 times or less the height h1 of the first magnetic collecting mechanism.

[0087]

number

[0088] In equation (6) above, h is a variable to which the height h1 of the first magnetic collection mechanism is substituted. Also, g is a variable to which the first separation distance g1 is substituted.

[0089] Here, the method for determining the ratio of the second separation distance g2 to the height h2 of the second magnetic collecting mechanism is the same as the method for determining the ratio of the first separation distance g1 to the height h1 of the first magnetic collecting mechanism, so the explanation is omitted. Also, in determining the ratio of the second separation distance g2 to the height h2 of the second magnetic collecting mechanism, h in equation (6) above is treated as a variable to which the height h2 of the second magnetic collecting mechanism is substituted. Also, in determining the ratio of the second separation distance g2 to the height h2 of the second magnetic collecting mechanism, g in equation (6) above is treated as a variable to which the second separation distance g2 is substituted. In determining the ratio of the second separation distance g2 to the height h2 of the second magnetic collecting mechanism, instead of the 11th threshold value above, a predetermined 12th threshold value is used for the total amount of magnetic flux linkage within the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state (i.e., the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state). The 12th threshold may be different from the 11th threshold, or it may be the same as the 11th threshold. The 12th threshold is, for example, the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12X in the target state, but it may be any other value predetermined for the amount of magnetic flux linked to the second magnetic core CR2 of the gradient magnetic field sensor 12 in the target state.

[0090] <Regarding the detection sensitivity of gradient magnetic field sensors> The detection sensitivity of the gradient magnetic field sensor 12 will be described below.

[0091] Figure 18 shows an example of the detection sensitivity of the gradient magnetic field sensor 12. The horizontal axis of the graph in Figure 18 shows the position of the object DM when it is moved directly below the sensor head area in a direction parallel to the central axis of the first magnetic core CR1, so that it is equidistant from both the first magnetic core CR1 and the second magnetic core CR2. Therefore, the origin of the horizontal axis is the position of the center of the first magnetic core CR1 in the direction of the central axis of the first magnetic core CR1 (or the position of the center of the second magnetic core CR2 in the direction of the central axis of the second magnetic core CR2). The vertical axis of the graph shows the detection sensitivity of the gradient magnetic field sensor 12. In the example shown in Figure 18, the detection sensitivity of the gradient magnetic field sensor 12 is shown by the value obtained by dividing the voltage of the differential signal output from the first coil CL1, which is differentially connected to the second coil CL2, by the magnetic moment of the object DM. The curve F11 plotted in the graph shows an example of the change in the sensitivity of the gradient magnetic field sensor 12 when the object DM moves in that direction directly below the sensor head area. Furthermore, the curve F12 plotted on the graph shows an example of the change in detection sensitivity of the gradient magnetic field sensor 12X when the object DM to be detected moves in that direction directly below the sensor head area. By comparing curve F11 and curve F12, it can be seen that the peak detection sensitivity of the gradient magnetic field sensor 12 is approximately 1.4 times higher than the peak detection sensitivity of the gradient magnetic field sensor 12X. In other words, the gradient magnetic field sensor 12 can further improve the detection sensitivity of the object to be detected by equipping it with a first magnetic collection mechanism CM1 and a second magnetic collection mechanism CM2.

[0092] Here, if the detection sensitivity of the gradient magnetic field sensor 12 is improved by providing the first magnetic field collection mechanism CM1 and the second magnetic field collection mechanism CM2, the S / N ratio for detection of the magnetic field generated from the object to be detected by the first sensor head S1 and the second sensor head S2, respectively, is expected to be improved. For this reason, it is expected that the detection of noise by the gradient magnetic field sensor 12 is suppressed. Figure 19 is a diagram showing an example of noise detected by the gradient magnetic field sensor 12. The graph shown in Figure 19 is a graph showing the frequency spectrum obtained when the noise detected by the gradient magnetic field sensor 12 is Fourier transformed. The horizontal axis of the graph shows the frequency of the noise. The vertical axis of the graph shows the strength of the noise for each frequency. Curve F13 plotted on the graph shows an example of the frequency spectrum of the noise detected by the gradient magnetic field sensor 12. Curve F14 plotted on the graph shows an example of the frequency spectrum of the noise detected by the gradient magnetic field sensor 12X. By comparing curves F13 and F14, it can be seen that the noise intensity detected by the gradient magnetic field sensor 12 is reduced overall compared to the noise intensity detected by the gradient magnetic field sensor 12X, as previously expected. This reduction in noise detected by the gradient magnetic field sensor 12 is also reflected in the noise floor shown in Figure 20. Figure 20 is a diagram showing an example of the noise floor for noise detected by the gradient magnetic field sensor 12. The upper noise floor in Figure 20 shows an example of the noise floor for noise detected by the gradient magnetic field sensor 12. The lower noise floor in Figure 20 shows an example of the noise floor for noise detected by the gradient magnetic field sensor 12X. By comparing these two noise floors, it can also be seen that the noise intensity detected by the gradient magnetic field sensor 12 is reduced overall compared to the noise intensity detected by the gradient magnetic field sensor 12X, as previously expected.

[0093] Furthermore, the noise detected by the gradient magnetic field sensor 12 can be further reduced by providing a magnetic shield to the gradient magnetic field sensor 12, as shown in Figure 21. Figure 21 is a perspective view showing an example of a gradient magnetic field sensor 12 with two magnetic shields. Note that in Figure 21, the main body of the gradient magnetic field sensor 12 is omitted to avoid making the diagram cluttered.

[0094] In the example shown in Figure 21, the gradient magnetic field sensor 12 further comprises a first magnetic shielding section SD1 and a second magnetic shielding section SD2.

[0095] The first magnetic shielding part SD1 is a component made of magnetic material. The first magnetic shielding part SD1 is a component that shields at least a portion of the magnetic field generated from components other than the object to be detected DM, which is applied to the first sensor head S1 and the second sensor head S2. In the example shown in Figure 21, the first magnetic shielding part SD1 is a rectangular flat plate-shaped component. The shape of the first magnetic shielding part SD1 may be other shapes such as circular or elliptical instead of rectangular. The shape of the first magnetic shielding part SD1 may also be other three-dimensional shapes such as cylindrical, hemispherical, or multi-layered instead of flat plate-shaped. Furthermore, the shape of the first magnetic shielding part SD1 may have an uneven surface or other shapes.

[0096] The first magnetic shielding unit SD1 is positioned directly above the sensor head region. Therefore, when viewing the first magnetic shielding unit SD1 downwards, the contour of the first magnetic shielding unit SD1 includes the sensor head region.

[0097] The surface of the first magnetic shield SD1 that faces the sensor head region is parallel or approximately parallel to the sensor head region. This prevents the magnetic field generated from the magnetized object DM from bypassing the first sensor head S1 and the second sensor head S2 and directly entering the first magnetic shield SD1. As a result, the first magnetic shield SD1 can prevent a decrease in the detection sensitivity of the object DM passing directly beneath the sensor head region by the first sensor head S1 and the second sensor head S2. In the example shown in Figure 21, the first magnetic shield SD1 has a rectangular flat plate shape. Therefore, in this example, the surface of the first magnetic shield SD1 that faces the sensor head region, i.e., the lower surface of the first magnetic shield SD1, is parallel or approximately parallel to the sensor head region. The gradient magnetic field sensor 12 includes a first magnetic shielding unit SD1 positioned directly above the sensor head region, thereby shielding the magnetic field applied to the first sensor head S1 and the second sensor head S2 from the region above the sensor head region. As a result, the gradient magnetic field sensor 12 can suppress the detection of the magnetic field as noise. Here, since the first magnetic shielding unit SD1 is made of a magnetic material, its magnetic resistance is lower than that of air. Therefore, the magnetic flux of the magnetic field has difficulty entering the space between the first magnetic shielding unit SD1 and the second magnetic shielding unit SD2. As a result, the first magnetic shielding unit SD1 can suppress the application of the magnetic field to the first sensor head S1 and the second sensor head S2 from the region above the sensor head region.

[0098] The second magnetic shielding part SD2 is a component made of magnetic material. The second magnetic shielding part SD2 is a component that shields at least a portion of the magnetic field generated from components other than the object to be detected DM, which is applied to the first sensor head S1 and the second sensor head S2. In the example shown in Figure 21, the second magnetic shielding part SD2 is a rectangular flat plate-shaped component. However, the shape of the second magnetic shielding part SD2 may be other shapes such as circular or elliptical instead of rectangular. Also, the shape of the second magnetic shielding part SD2 may be other three-dimensional shapes such as cylindrical, hemispherical, or multi-layered instead of flat plate-shaped. Furthermore, the shape of the second magnetic shielding part SD2 may be a shape with irregularities or other shapes. Also, in this example, the shape of the second magnetic shielding part SD2 is the same as the shape of the first magnetic shielding part SD1. However, the shape of the second magnetic shielding part SD2 may be different from the shape of the first magnetic shielding part SD1.

[0099] The second magnetic shielding unit SD2 is positioned directly below the sensor head region. Therefore, when viewing the second magnetic shielding unit SD2 upwards, the contour of the second magnetic shielding unit SD2 includes the sensor head region.

[0100] The surface of the second magnetic shielding unit SD2 that faces the sensor head region is parallel or approximately parallel to the sensor head region. This prevents the magnetic field generated from the magnetized object DM from bypassing the first and second sensor heads S1 and S2 and directly entering the second magnetic shielding unit SD2. As a result, the second magnetic shielding unit SD2 can prevent a decrease in the detection sensitivity of the object DM passing directly beneath the sensor head region by the first and second sensor heads S1 and S2. In the example shown in Figure 21, the second magnetic shielding unit SD2 has a rectangular flat plate shape. Therefore, in this example, the surface of the second magnetic shielding unit SD2 that faces the sensor head region, i.e., the upper surface of the second magnetic shielding unit SD2, is parallel or approximately parallel to the sensor head region. The gradient magnetic field sensor 12 includes a second magnetic shielding unit SD2 positioned directly below the sensor head region, thereby shielding the magnetic field applied to the first sensor head S1 and the second sensor head S2 from the region below the sensor head region. As a result, the gradient magnetic field sensor 12 can suppress the detection of the magnetic field as noise. Here, since the second magnetic shielding unit SD2 is made of a magnetic material, its magnetic resistance is lower than that of air. Therefore, the magnetic flux of the magnetic field has difficulty penetrating the space between the first magnetic shielding unit SD1 and the second magnetic shielding unit SD2. As a result, the second magnetic shielding unit SD2 can suppress the application of the magnetic field to the first sensor head S1 and the second sensor head S2 from the region below the sensor head region.

[0101] As described above, in the gradient magnetic field sensor 12, the first magnetic shielding section SD1 and the second magnetic shielding section SD2 are arranged such that the first sensor head S1 and the second sensor head S2 are located in the space between the first magnetic shielding section SD1 and the second magnetic shielding section SD2. As a result, the gradient magnetic field sensor 12 can more reliably increase the amount of magnetic flux that links with the first magnetic core CR1 and the second magnetic core CR2 from the magnetic flux generated from the object to be detected, and can more reliably suppress the detection of noisy magnetic fields. In other words, by including the first magnetic shielding section SD1 and the second magnetic shielding section SD2, the gradient magnetic field sensor 12 can more reliably improve the detection sensitivity of the object to be detected. Note that the first magnetic shielding section SD1 and the second magnetic shielding section SD2 may be supported, for example, by the main body of the gradient magnetic field sensor 12, or by at least one of the first sensor head S1 and the second sensor head S2.

[0102] In the example shown in Figure 21, the aforementioned sheet member ST moves in the space between the sensor head region and the second magnetic shield portion SD2. Alternatively, it may be configured to move in the space between the sensor head region and the first magnetic shield portion SD1. In this case, the gradient magnetic field sensor 12 detects the object DM passing directly above the sensor head region.

[0103] Furthermore, the gradient magnetic field sensor 12 may be configured to include either a first magnetic shielding section SD1 or a second magnetic shielding section SD2. However, the noise detected by the gradient magnetic field sensor 12 is reduced more when the gradient magnetic field sensor 12 includes the first magnetic shielding section SD1 but not the second magnetic shielding section SD2 compared to when the gradient magnetic field sensor 12 does not include the first magnetic shielding section SD1 but does include the second magnetic shielding section SD2.

[0104] <Circuit configuration of a gradient magnetic field sensor> The circuit configuration of the gradient magnetic field sensor 12 will be described below with reference to Figure 22. Figure 22 is a diagram showing an example of the circuit configuration of the gradient magnetic field sensor 12.

[0105] The gradient magnetic field sensor 12 includes an AC power supply connection terminal CT1, a first sensor head S1, a second sensor head S2, a zero phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT, a detection signal output terminal CT2, a DC power supply connection terminal CT3, and a DC current control unit CC2. The first sensor head S1 includes a first magnetic core CR1 and a first coil CL1. The second sensor head S2 includes a second magnetic core CR2 and a second coil CL2. The zero phase shift circuit PS0 has two terminals: an input terminal PS01 and an output terminal PS02. The AC current control unit CC1 has a first input terminal CC11, a second input terminal CC12, a first output terminal CC13, and a second output terminal CC14. Furthermore, the AC current control unit CC1 includes a first phase shift circuit PS1, a first variable resistor VR11, a first capacitor C1, a second phase shift circuit PS2, a second variable resistor VR12, and a second capacitor C2. Furthermore, the detection circuit DT has a first input terminal DTT1, a second input terminal DTT2, and an output terminal DTT3. Furthermore, the detection circuit DT includes a phase detection circuit PD, a low-pass filter LF, an error amplifier EA, a resistor R1, and a third capacitor C3. Furthermore, the phase detection circuit PD has a first input terminal PD1, a second input terminal PD2, and an output terminal PD3. Furthermore, the DC current control unit CC2 has an input terminal CC21, a first output terminal CC22, and a second output terminal CC23. Furthermore, the DC current control unit CC2 includes a first variable resistor VR21, a first inductor L1, a second variable resistor VR22, and a second inductor L2.

[0106] Furthermore, the gradient magnetic field sensor 12 is connected to both the AC power supply P1 and the DC power supply P2 via a transmission line. More specifically, the AC power supply connection terminal CT1 of the gradient magnetic field sensor 12 is connected via a transmission line to the first power supply terminal P11, which is one of the two power supply terminals of the AC power supply P1. The other power supply terminal of the AC power supply P1, the second power supply terminal P12, is grounded via a transmission line. The DC power supply connection terminal CT3 of the gradient magnetic field sensor 12 is connected via a transmission line to the positive power supply terminal of the DC power supply P2. The negative power supply terminal of the DC power supply P2 is grounded via a transmission line. Here, the AC power supply P1 may be any AC power supply, and the DC power supply P2 may be any DC power supply. Furthermore, other circuit elements, devices, etc. may be connected between the AC power connection terminal CT1 and the first power terminal P11, provided that this does not impair the function of the gradient magnetic field sensor 12. Similarly, other circuit elements, devices, etc. may be connected between the second power terminal P12 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12. Also, other circuit elements, devices, etc. may be connected between the DC power connection terminal CT3 and the positive power terminal, provided that this does not impair the function of the gradient magnetic field sensor 12. Finally, other circuit elements, devices, etc. may be connected between the negative power terminal and ground, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0107] Furthermore, the gradient magnetic field sensor 12 is connected to the information processing device 20 via a transmission line. More specifically, the detection signal output terminal CT2 of the gradient magnetic field sensor 12 is connected to the information processing device 20 via a transmission line. Note that other circuit elements, other devices, etc., may be connected between the detection signal output terminal CT2 and the information processing device 20, provided that this does not impair the functionality of the gradient magnetic field sensor 12.

[0108] Furthermore, the AC power supply connection terminal CT1 is connected via a transmission line to the input terminal PS01 of the 0th phase shift circuit PS0 and the first input terminal DTT1 of the detection circuit DT. The output terminal PS02 of the 0th phase shift circuit PS0 is connected via a transmission line to the first input terminal CC11 of the AC current control unit CC1 and the second input terminal CC12 of the AC current control unit CC1. Note that other circuit elements, other devices, etc. may be connected between the AC power supply connection terminal CT1 and the input terminal PS01, provided that this does not impair the function of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the AC power supply connection terminal CT1 and the first input terminal DTT1, provided that this does not impair the function of the gradient magnetic field sensor 12. Furthermore, the connection between the output terminal PS02 and the first input terminal CC11 may include other circuit elements, devices, etc., as long as it does not impair the function of the gradient magnetic field sensor 12. Similarly, the connection between the output terminal PS02 and the second input terminal CC12 may include other circuit elements, devices, etc., as long as it does not impair the function of the gradient magnetic field sensor 12.

[0109] Furthermore, the DC power supply connection terminal CT3 is connected via a transmission line to the input terminal CC21 of the DC current control unit CC2. Note that other circuit elements, devices, etc., may be connected between the DC power supply connection terminal CT3 and the input terminal CC21, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0110] Furthermore, in the AC current control unit CC1, the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1 are connected in series between the first input terminal CC11 and the first output terminal CC13 via a transmission line. Also, in the AC current control unit CC1, the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2 are connected in series between the second input terminal CC12 and the second output terminal CC14 via a transmission line. Note that, between the first input terminal CC11 and the first output terminal CC13, other circuit elements, other devices, etc., may be connected along with the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1, as long as the function of the gradient magnetic field sensor 12 is not impaired. Furthermore, between the first input terminal CC11 and the first output terminal CC13, the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1 may be connected in series in any order. Furthermore, between the second input terminal CC12 and the second output terminal CC14, other circuit elements, other devices, etc., may be connected along with the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2, as long as the functions of the gradient magnetic field sensor 12 are not impaired. Also, between the second input terminal CC12 and the second output terminal CC14, the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2 may be connected in series in any order.

[0111] Furthermore, the first magnetic core CR1 of the first sensor head S1 is connected to the ground via a transmission line between the first output terminal CC13 of the AC current control unit CC1 and the ground. Also, the second magnetic core CR2 of the second sensor head S2 is connected to the ground via a transmission line between the second output terminal CC14 of the AC current control unit CC1 and the ground. For the sake of explanation, the AC current flowing from the first output terminal CC13 to the first magnetic core CR1 will be referred to as the first AC excitation current AC1, as shown in Figure 22. Similarly, for the sake of explanation, the AC current flowing from the second output terminal CC14 to the second magnetic core CR2 will be referred to as the second AC excitation current AC2, as shown in Figure 22. Note that, within the limits that do not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc., may be connected to the ground along with the first magnetic core CR1 via a transmission line. Furthermore, other circuit elements, other devices, etc., may be connected between the second output terminal CC14 of the AC current control unit CC1 and ground, as long as this does not impair the function of the gradient magnetic field sensor 12, along with the second magnetic core CR2.

[0112] Furthermore, in the DC current control unit CC2, the first variable resistor VR21 and the first inductor L1 are connected in series between the input terminal CC21 and the first output terminal CC22 via a transmission line. Also, in the DC current control unit CC2, the second variable resistor VR22 and the second inductor L2 are connected in series between the input terminal CC21 and the second output terminal CC23 via a transmission line. Note that, within the limits that do not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal CC21 and the first output terminal CC22 along with the first variable resistor VR21 and the first inductor L1. Also, within the limits that do not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal CC21 and the second output terminal CC23 along with the second variable resistor VR22 and the second inductor L2. Furthermore, the first variable resistor VR21 and the first inductor L1 may be connected in series between the input terminal CC21 and the first output terminal CC22 in any order. Also, the second variable resistor VR22 and the second inductor L2 may be connected in series between the input terminal CC21 and the second output terminal CC23 in any order.

[0113] Furthermore, the first output terminal CC22 of the DC current control unit CC2 is connected via another transmission line to the transmission line connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1. Note that other circuit elements, devices, etc., may be connected between the first output terminal CC22 and the transmission line connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0114] Furthermore, the second output terminal CC23 of the DC current control unit CC2 is connected via another transmission line to the transmission line connecting the second output terminal CC14 of the AC current control unit CC1 and the second magnetic core CR2. Note that other circuit elements, devices, etc., may be connected between the second output terminal CC23 and the transmission line connecting the second output terminal CC14 of the AC current control unit CC1 and the second magnetic core CR2, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0115] Furthermore, in the detection circuit DT, the first input terminal DTT1 is connected via a transmission line to the first input terminal PD1 of the phase detection circuit PD. The output terminal PD3 of the phase detection circuit PD is connected via a transmission line to an input terminal (not shown) of the low-pass filter LF. The output terminal (not shown) of the low-pass filter LF is connected via a transmission line to the inverting input terminal of the error amplifier EA. The non-inverting input terminal of the error amplifier EA is grounded via a transmission line. The output terminal of the error amplifier EA is connected via a transmission line to the output terminal DTT3 of the detection circuit DT and to one of the two terminals of resistor R1. The other of the two terminals of resistor R1 is connected via a transmission line to the second input terminal DTT2 of the phase detection circuit PD and to one of the two terminals of the third capacitor C3. Furthermore, the other of the two terminals of the third capacitor C3 is connected via a transmission line to the second input terminal PD2 of the phase detection circuit PD. Thus, the detection circuit DT is a PSD (Phase Sensitive Detector) circuit. Note that other circuit elements, devices, etc. may be connected between the first input terminal DTT1 and the first input terminal PD1, provided that this does not impair the function of the detection circuit DT. Also, other circuit elements, devices, etc. may be connected between the output terminal PD3 and the input terminal of the low-pass filter LF, provided that this does not impair the function of the detection circuit DT. Also, other circuit elements, devices, etc. may be connected between the output terminal of the low-pass filter LF and the inverting input terminal of the error amplifier EA, provided that this does not impair the function of the detection circuit DT. Also, other circuit elements, devices, etc. may be connected between the non-inverting input terminal of the error amplifier EA and ground, provided that this does not impair the function of the detection circuit DT. Furthermore, other circuit elements, devices, etc., may be connected between the output terminal of the error amplifier EA and the output terminal DTT3, provided that this does not impair the function of the detection circuit DT.Furthermore, other circuit elements, devices, etc. may be connected between the output terminal of the error amplifier EA and resistor R1, provided that this does not impair the function of the detection circuit DT. Also, other circuit elements, devices, etc. may be connected between resistor R1 and third capacitor C3, provided that this does not impair the function of the detection circuit DT. Furthermore, other circuit elements, devices, etc. may be connected between the third capacitor C3 and second input terminal PD2, provided that this does not impair the function of the detection circuit DT. Also, other circuit elements, devices, etc. may be connected between the transmission line connecting resistor R1 and third capacitor C3 and second input terminal DTT2, provided that this does not impair the function of the detection circuit DT.

[0116] Furthermore, the second input terminal DTT2 of the detection circuit DT is connected via a transmission line to one of the two terminals of the first coil CL1. The other terminal of the first coil CL1 is connected via a transmission line to one of the two terminals of the second coil CL2. The other terminal of the second coil CL2 is grounded via a transmission line. However, the second coil CL2 is differentially connected to the first coil CL1. Note that other circuit elements, other devices, etc. may be connected between the second input terminal DTT2 and the first coil CL1, as long as it does not impair the function of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the first coil CL1 and the second coil CL2, as long as it does not impair the function of the gradient magnetic field sensor 12. Furthermore, other circuit elements, other devices, etc., may be connected between the second coil CL2 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0117] <Operation of the gradient magnetic field sensor according to this embodiment> Next, the operation of the gradient magnetic field sensor 12 will be explained.

[0118] In the gradient magnetic field sensor 12 with the circuit configuration described above, the AC power supply P1 inputs an AC current to the AC power supply connection terminal CT1. The AC current input to the AC power supply connection terminal CT1 is split into two. One of the two split AC currents is input to the 0th phase shift circuit PS0 as an AC excitation current. The other of the two split AC currents is input to the first input terminal DTT1 of the detection circuit DT as a reference signal.

[0119] The AC excitation current input to the zeroth phase shift circuit PS0 is shifted by the zeroth phase shift circuit PS0 and then split into two AC excitation currents: the first AC excitation current AC1 and the second AC excitation current AC2.

[0120] The first AC excitation current AC1 flows to the first magnetic core CR1 via the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1. Therefore, the first AC excitation current AC1 is phase-shifted by the first phase shift circuit PS1 and its amplitude is adjusted by the first variable resistor VR11. The first AC excitation current AC1 is then input to the first magnetic core CR1 from the first output terminal CC13. The first capacitor C1 is a capacitor for AC coupling. The presence of the first capacitor C1 prevents DC current from flowing from the first output terminal CC13 to the first input terminal CC11 in the gradient magnetic field sensor 12.

[0121] On the other hand, the second AC excitation current AC2 flows to the second magnetic core CR2 via the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2. Therefore, the second AC excitation current AC2 is phase-shifted by the second phase shift circuit PS2 and its amplitude is adjusted by the second variable resistor VR12. The second AC excitation current AC2 is then input to the second magnetic core CR2 from the second output terminal CC14. The second capacitor C2 is a capacitor for AC coupling. The presence of the second capacitor C2 prevents DC current from flowing from the second output terminal CC14 to the second input terminal CC12 in the gradient magnetic field sensor 12.

[0122] In the gradient magnetic field sensor 12 with the circuit configuration described above, the DC power supply P2 inputs a DC current to the DC power supply connection terminal CT3. The DC current input to the DC power supply connection terminal CT3 is input to the DC current control unit CC2 as a DC excitation current.

[0123] The DC excitation current input to the DC current control unit CC2 is split into two DC excitation currents: the first DC excitation current DC1 and the second DC excitation current DC2.

[0124] In the DC current control unit CC2, the magnitude of the first DC excitation current DC1 is adjusted by the first variable resistor VR21. The first DC excitation current DC1 is then input to the first magnetic core CR1 from the first output terminal CC22. As a result, a voltage is induced in the first coil CL1 that corresponds to the first AC excitation current AC1 flowing through the first magnetic core CR1, the first DC excitation current DC1 flowing through the first magnetic core CR1, and the strength of the magnetic field applied to the first coil CL1. In other words, in the gradient magnetic field sensor 12, this voltage also changes according to the strength of the magnetic field applied to the first coil CL1 from the outside. For the sake of explanation, this voltage will be referred to as the first induced voltage below. The first inductor L1 is an inductor for DC coupling. The presence of the first inductor L1 prevents the AC current from flowing from the first output terminal CC22 to the input terminal CC21 in the gradient magnetic field sensor 12.

[0125] Meanwhile, in the DC current control unit CC2, the magnitude of the second DC excitation current DC2 is adjusted by the second variable resistor VR22. The second DC excitation current DC2 is then input to the second magnetic core CR2 from the second output terminal CC23. As a result, a voltage is induced in the second coil CL2 that corresponds to the second AC excitation current AC2 flowing through the second magnetic core CR2, the second DC excitation current DC2 flowing through the second magnetic core CR2, and the strength of the magnetic field applied to the second coil CL2. In other words, in the gradient magnetic field sensor 12, this voltage also changes according to the strength of the magnetic field applied to the second coil CL2 from the outside. For the sake of explanation, this voltage will be referred to as the second induced voltage below. The second inductor L2 is an inductor for DC coupling. The presence of the second inductor L2 prevents the AC current from flowing from the second output terminal CC23 to the input terminal CC21 in the gradient magnetic field sensor 12.

[0126] In the gradient magnetic field sensor 12, signals corresponding to the first induced voltage and the second induced voltage induced in this manner are input as a differential signal Vout to the second input terminal DTT2 of the detection circuit DT. The phase detection circuit PD of the detection circuit DT inputs a signal corresponding to the difference between the differential signal Vout input in this manner and the reference signal input from the AC power supply P1 as a detection signal to the low-pass filter LF. The low-pass filter LF outputs an output signal, from which components above a predetermined frequency have been removed from the detection signal input from the phase detection circuit PD, to the inverting input terminal of the error amplifier EA. The error amplifier EA outputs a signal corresponding to the potential difference between the potential of the output signal input to the inverting input terminal of the error amplifier EA and the ground potential as a detection signal to the detection signal output terminal CT2 and resistor R1, respectively. The third capacitor C3 is a capacitor for AC coupling. A buffer circuit (e.g., a voltage follower) is connected to the terminal of the third capacitor C3 opposite to the terminal connected to the phase detection circuit PD. This buffer circuit is omitted from the diagram for simplicity.

[0127] The detection signal input to resistor R1 does not go to the third capacitor C3 due to the presence of a buffer circuit (not shown), but instead flows as a feedback current from the second input terminal DTT2 towards the first coil CL1.

[0128] The detection circuit DT, which performs this operation, can be adjusted so that when the signal level of the differential signal Vout is 0[V], a detection signal with a signal level of 0[V] is output from the detection signal output terminal CT2, and when the signal level of the differential signal Vout is not 0[V], a detection signal with a signal level of not 0[V] is output from the detection signal output terminal CT2. Since the adjustment of the detection circuit DT is already known, further detailed explanation will be omitted.

[0129] Through the operations described above, the gradient magnetic field sensor 12 detects the gradient.

[0130] The gradient magnetic field sensor 12 according to this embodiment may be configured without a 0th phase shift circuit PS0.

[0131] Furthermore, the gradient magnetic field sensor 12 according to this embodiment may be configured without either the first phase shift circuit PS1 or the second phase shift circuit PS2.

[0132] Furthermore, the gradient magnetic field sensor 12 according to this embodiment may be configured without either the first variable resistor VR11 or the second variable resistor VR12.

[0133] Furthermore, the gradient magnetic field sensor 12 according to the embodiment may be configured without at least one of the first capacitor C1 and the second capacitor C2. However, these are capacitors for AC coupling. For this reason, it is preferable for the gradient magnetic field sensor 12 to include both the first capacitor C1 and the second capacitor C2.

[0134] Furthermore, in the gradient magnetic field sensor 12 according to this embodiment, the AC current control unit CC1 may be configured to include a first amplification circuit that amplifies the amplitude of the first AC excitation current AC1, either in place of the first variable resistor VR11 or in addition to the first variable resistor VR11.

[0135] Furthermore, in the gradient magnetic field sensor 12 according to this embodiment, the AC current control unit CC1 may be configured to include a second amplification circuit that amplifies the amplitude of the second AC excitation current AC2, either in place of the second variable resistor VR12 or in addition to the second variable resistor VR12.

[0136] The gradient magnetic field sensor 12 has a circuit configuration that performs the operation described above. This allows the gradient magnetic field sensor 12 to detect the gradient of magnetic field strength at two different points using its two sensor heads, the first sensor head S1 and the second sensor head S2. Furthermore, as mentioned above, the gradient magnetic field sensor 12 is equipped with a first magnetic shielding unit SD1 and a second magnetic shielding unit SD2, thereby suppressing the detection of noisy magnetic fields.

[0137] Note that the gradient magnetic field sensor 12 having the circuit configuration shown in Figure 22 may be configured without either the first variable resistor VR21 or the second variable resistor VR22. Alternatively, the gradient magnetic field sensor 12 may be configured with a resistive element whose resistance value cannot be changed in place of either the first variable resistor VR21 or the second variable resistor VR22.

[0138] Furthermore, the gradient magnetic field sensor 12 having the circuit configuration shown in Figure 22 may, based on the results of prior tests, etc., be configured to include a resistor element whose resistance value cannot be changed in place of either the first variable resistor VR21 or the second variable resistor VR22, if it is possible to prepare a resistor element with the same resistance value as the first variable resistor VR21 and the second variable resistor VR22 described above.

[0139] Furthermore, the gradient magnetic field sensor 12 having the circuit configuration shown in Figure 22 may also be configured without at least one of the first inductor L1 and the second inductor L2. However, as mentioned above, these are capacitors for DC coupling. For this reason, it is preferable for the gradient magnetic field sensor 12 to have both the first inductor L1 and the second inductor L2.

[0140] The first magnetic core CR1 described above may also include two or more magnetic materials connected in series. In this case, the first magnetic core CR1 may be configured such that some or all of these two or more magnetic materials are connected in series by a non-magnetic conductor. Figure 23 shows an example of the configuration of the first magnetic core CR1 including multiple magnetic materials. In the example shown in Figure 23, the first magnetic core CR1 includes two magnetic materials. More specifically, in this example, the first magnetic core CR1 has a magnetic material CR1A, a magnetic material CR1B, a non-magnetic conductor CR1C, terminals CR1D and CR1E. Magnetic materials CR1A and CR1B are connected by the conductor CR1C. Terminal CR1D is provided at the end of magnetic material CR1A opposite to the end connected to the conductor CR1C. Terminal CR1D is, for example, the terminal connected to the first output terminal CC13 of the AC current control unit CC1 in Figure 22. Furthermore, a terminal CR1E is provided at the end of the magnetic material CR1B opposite to the end connected to the conductor CR1C. Terminal CR1E is, for example, the terminal grounded to ground in Figure 22.

[0141] Furthermore, the second magnetic core CR2 described above may include two or more magnetic materials connected in series. In this case, the second magnetic core CR2 may be configured such that some or all of these two or more magnetic materials are connected in series by a non-magnetic conductor. Note that the configuration of the second magnetic core CR2 including multiple magnetic materials is the same as the configuration of the first magnetic core CR1 including multiple magnetic materials, so a diagrammatic explanation is omitted.

[0142] Furthermore, as shown in Figure 24, the first sensor head S1 and the second sensor head S2 described above may each have a first coil CL1 and a second coil CL2 composed of multiple coils. Figure 24 shows a modified example of the configuration of the first sensor head S1 and the second sensor head S2. Figure 24 is also a cross-sectional view of the gradient magnetic field sensor 12 when the gradient magnetic field sensor 12 is cut in a plane that includes both the central axis AX1 of the first magnetic core CR1 and the central axis AX2 of the second magnetic core CR2.

[0143] In the example shown in Figure 24, the first coil CL1 is composed of four coils: the first coil CL11, the first coil CL12, the first coil CL13, and the first coil CL14. In this example, the second coil CL2 is composed of four coils: the second coil CL21, the second coil CL22, the second coil CL23, and the second coil CL24. In this case, the circuit configuration of the gradient magnetic field sensor 12 is, for example, as shown in Figure 25. Figure 25 is a diagram showing another example of the circuit configuration of the gradient magnetic field sensor 12. For the sake of explanation, the gradient magnetic field sensor 12 having the circuit configuration shown in Figure 25 will be referred to as the gradient magnetic field sensor 12A below.

[0144] In the example shown in Figure 25, the gradient magnetic field sensor 12A includes detection circuits DT1 to DT4 instead of detection circuit DT. Furthermore, the gradient magnetic field sensor 12A also includes a signal processing unit PR.

[0145] The detection circuit DT1 has three terminals: an input terminal DTT11 connected to the AC power supply connection terminal CT1, an input terminal DTT12, and an output terminal DTT13.

[0146] The detection circuit DT2 has three terminals: input terminal DTT21, input terminal DTT22, and output terminal DTT23, which are connected to the AC power supply connection terminal CT1.

[0147] The detection circuit DT3 has three terminals: input terminal DTT31, input terminal DTT32, and output terminal DTT33, which are connected to the AC power supply connection terminal CT1.

[0148] The detection circuit DT4 has three terminals: input terminal DTT41, input terminal DTT42, and output terminal DTT43, which are connected to the AC power supply connection terminal CT1.

[0149] The signal processing unit PR has five terminals: input terminal PR1, input terminal PR2, input terminal PR3, input terminal PR4, and output terminal PR5.

[0150] Furthermore, the input terminal DTT12 of the detection circuit DT1 is connected via a transmission line to the hot terminal of the two terminals of the first coil CL11. The cold terminal of the two terminals of the first coil CL11 is connected via a transmission line to the cold terminal of the two terminals of the second coil CL21. The hot terminal of the two terminals of the second coil CL21 is grounded via a transmission line. In other words, the first coil CL11 and the second coil CL21 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DTT12 and the first coil CL11, as long as it does not impair the function of the gradient magnetic field sensor 12A. Also, other circuit elements, other devices, etc. may be connected between the first coil CL11 and the second coil CL21, as long as it does not impair the function of the gradient magnetic field sensor 12A. Furthermore, other circuit elements, devices, etc., may be connected between the second coil CL21 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12A. Also, in Figure 25, the differential signal Vout output from the first coil CL11 is shown by the differential signal Vout1.

[0151] Furthermore, the input terminal DTT22 of the detection circuit DT2 is connected via a transmission line to the hot terminal of the two terminals of the first coil CL12. The cold terminal of the two terminals of the first coil CL12 is connected via a transmission line to the cold terminal of the two terminals of the second coil CL22. The hot terminal of the two terminals of the second coil CL22 is grounded via a transmission line. In other words, the first coil CL12 and the second coil CL22 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DTT22 and the first coil CL12, as long as it does not impair the function of the gradient magnetic field sensor 12A. Also, other circuit elements, other devices, etc. may be connected between the first coil CL12 and the second coil CL22, as long as it does not impair the function of the gradient magnetic field sensor 12A. Furthermore, other circuit elements, devices, etc., may be connected between the second coil CL22 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12A. Also, in Figure 25, the differential signal Vout output from the first coil CL12 is shown by the differential signal Vout2.

[0152] Furthermore, the input terminal DTT32 of the detection circuit DT3 is connected via a transmission line to the hot terminal of the two terminals of the first coil CL13. The cold terminal of the two terminals of the first coil CL13 is connected via a transmission line to the cold terminal of the two terminals of the second coil CL23. The hot terminal of the two terminals of the second coil CL23 is grounded via a transmission line. In other words, the first coil CL13 and the second coil CL23 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DTT32 and the first coil CL13, as long as it does not impair the function of the gradient magnetic field sensor 12A. Also, other circuit elements, other devices, etc. may be connected between the first coil CL13 and the second coil CL23, as long as it does not impair the function of the gradient magnetic field sensor 12A. Furthermore, other circuit elements, devices, etc., may be connected between the second coil CL23 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12A. Also, in Figure 25, the differential signal Vout output from the first coil CL13 is shown by the differential signal Vout3.

[0153] Furthermore, the input terminal DTT42 of the detection circuit DT4 is connected via a transmission line to the hot terminal of the two terminals of the first coil CL14. The cold terminal of the two terminals of the first coil CL14 is connected via a transmission line to the cold terminal of the two terminals of the second coil CL24. The hot terminal of the two terminals of the second coil CL24 is grounded via a transmission line. In other words, the first coil CL14 and the second coil CL24 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DTT42 and the first coil CL14, as long as it does not impair the function of the gradient magnetic field sensor 12A. Also, other circuit elements, other devices, etc. may be connected between the first coil CL14 and the second coil CL24, as long as it does not impair the function of the gradient magnetic field sensor 12A. Furthermore, other circuit elements, devices, etc., may be connected between the second coil CL24 and ground, provided that this does not impair the function of the gradient magnetic field sensor 12A. Also, in Figure 25, the differential signal Vout output from the first coil CL14 is shown by the differential signal Vout4.

[0154] Note that the circuit configurations of detection circuits DT11 to DT14 are similar to, for example, the circuit configuration of detection circuit DT. Therefore, a detailed explanation of the circuit configurations of detection circuits DT11 to DT14 will be omitted.

[0155] Furthermore, input terminal PR1 of the signal processing unit PR is connected to output terminal DTT13 of the detection circuit DT1 via a transmission line. Also, input terminal PR2 of the signal processing unit PR is connected to output terminal DTT23 of the detection circuit DT2 via a transmission line. Furthermore, input terminal PR3 of the signal processing unit PR is connected to output terminal DTT33 of the detection circuit DT3 via a transmission line. Also, input terminal PR4 of the signal processing unit PR is connected to output terminal DTT43 of the detection circuit DT4 via a transmission line. Furthermore, output terminal PR5 of the signal processing unit PR is connected to detection signal output terminal CT2 via a transmission line. Note that other circuit elements, devices, etc., may be connected between input terminal PR1 and output terminal DTT13, provided that this does not impair the function of the gradient magnetic field sensor 12. Furthermore, other circuit elements, devices, etc. may be connected between input terminal PR2 and output terminal DTT23, provided that this does not impair the function of the gradient magnetic field sensor 12. Similarly, other circuit elements, devices, etc. may be connected between input terminal PR3 and output terminal DTT33, provided that this does not impair the function of the gradient magnetic field sensor 12. Furthermore, other circuit elements, devices, etc. may be connected between input terminal PR4 and output terminal DTT43, provided that this does not impair the function of the gradient magnetic field sensor 12. Additionally, other circuit elements, devices, etc. may be connected between output terminal PR5 and detection signal output terminal CT2, provided that this does not impair the function of the gradient magnetic field sensor 12.

[0156] The signal processing unit PR performs various signal processing operations on the detection signals input from each of the detection circuits DT1 to DT4 to detect the gradient. The circuit configuration of the signal processing unit PR can be any configuration as long as it is capable of detecting the gradient based on the detection signals input from each of the detection circuits DT1 to DT4.

[0157] Even when the gradient magnetic field sensor 12A with the above configuration is equipped with a magnetic collection mechanism CM, the gradient magnetic field sensor 12A can improve the signal-to-noise ratio for detection of the magnetic field generated from the object to be detected by the first sensor head S1 and the second sensor head S2, respectively, and as a result can improve the detection sensitivity of the object to be detected.

[0158] Furthermore, the matters described above may be combined in any way.

[0159] As described above, the gradient magnetic field sensor according to the embodiment (in the example described above, the gradient magnetic field sensor 12) comprises a first magnetic core (in the example described above, the first magnetic core CR1), a second magnetic core (in the example described above, the second magnetic core CR2), a first coil (in the example described above, the first coil CL1) disposed in the first magnetic core, a second coil (in the example described above, the second coil CL2) disposed in the second magnetic core, and a magnetic collection mechanism (in the example described above, the magnetic collection mechanism CM), wherein the second coil is differentially connected to the first coil, and the magnetic collection mechanism includes a high-permeability material (in the example described above, the high-permeability material HM) and a low-permeability material (in the example described above, the low-permeability material LM), wherein the high-permeability material has a permeability of a predetermined first threshold or higher, and the low-permeability material has a permeability of a predetermined second threshold or lower, and the second threshold is less than or equal to the first threshold. This allows the gradient magnetic field sensor to further improve the detection sensitivity of the object being detected.

[0160] <Note> [1] The first magnetic core and The second magnetic core, A first coil disposed in the first magnetic core, The second coil is positioned in the second magnetic core, Magnetic collection mechanism, Equipped with, The second coil is differentially connected to the first coil, The magnetic collection mechanism includes a high-permeability material and a low-permeability material. The aforementioned high-permeability material has a permeability of a predetermined first threshold or higher. The low-permeability material has a permeability below a predetermined second threshold, The second threshold is less than or equal to the first threshold. Gradient magnetic field sensor. [2] The magnetic collection mechanism includes a first magnetic collection mechanism and a second magnetic collection mechanism. The first magnetic collection mechanism is positioned at a predetermined first position relative to the first magnetic core. The second magnetic collection mechanism is positioned at a predetermined second position relative to the second magnetic core. The gradient magnetic field sensor described in [1]. [3] The first magnetic collection mechanism has a linear portion, The second magnetic collection mechanism has a linear portion, The linear portion of the second magnetic collection mechanism is substantially parallel to the linear portion of the first magnetic collection mechanism. The gradient magnetic field sensor described in [2]. [4] The first magnetic core has a linear portion, The second magnetic core has a linear portion, The first coil is positioned in the linear portion of the first magnetic core. The second coil is positioned in the linear portion of the second magnetic core. The linear portion of the first magnetic collection mechanism is substantially parallel to the linear portion of the first magnetic core. The linear portion of the second magnetic collection mechanism is substantially parallel to the linear portion of the second magnetic core. The gradient magnetic field sensor described in [3]. [5] The linear portion of the second magnetic core faces the linear portion of the first magnetic core in a direction perpendicular to the linear portion of the second magnetic core. The linear portion of the second magnetic collection mechanism faces the linear portion of the first magnetic collection mechanism in a direction perpendicular to the linear portion of the second magnetic collection mechanism. The virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is substantially parallel to the virtual plane including the linear portion of the first magnetic core and the linear portion of the second magnetic core. The gradient magnetic field sensor described in [4]. [6] The first magnetic collection mechanism includes N of the first high-permeability materials, with the high-permeability material being designated as the first high-permeability material, and M of the first low-permeability materials, with the low-permeability material being designated as the first low-permeability material. The second magnetic collection mechanism includes N of the high-permeability material, with the high-permeability material being designated as the second high-permeability material, and M of the low-permeability material, with the low-permeability material being designated as the second low-permeability material. In the first magnetic collection mechanism, the first high-permeability material and the first low-permeability material are arranged alternately. In the second magnetic collection mechanism, the second high-permeability material and the second low-permeability material are arranged alternately. The arrangement of the high-permeability material and the low-permeability material in the second magnetic collection mechanism is the same as the arrangement of the high-permeability material and the low-permeability material in the first magnetic collection mechanism. N is an integer greater than or equal to 1. M is an integer greater than or equal to 1. The gradient magnetic field sensor described in [5]. [7] In a first direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, the central axis of the linear portion of the first magnetic collection mechanism and the central axis of the linear portion of the first magnetic core substantially overlap. In the first direction, the center of the first magnetic collection mechanism in the central axis direction of the linear portion of the first magnetic collection mechanism substantially coincides with the center of the first magnetic core in the central axis direction of the linear portion of the first magnetic core. In the first direction, the central axis of the linear portion of the second magnetic collection mechanism and the central axis of the linear portion of the second magnetic core substantially overlap. In the first direction, the center of the second magnetic collection mechanism in the central axis direction of the linear portion of the second magnetic collection mechanism substantially coincides with the center of the second magnetic core in the central axis direction of the linear portion of the second magnetic core. The gradient magnetic field sensor described in [6]. [8] The number of the first high-permeability materials, the length of the first high-permeability materials in the central axis direction of the linear portion of the first magnetic collection mechanism, and the length of the first low-permeability materials in the central axis direction of the linear portion of the first magnetic collection mechanism are each determined based on a predetermined third threshold for the total magnetic flux linkage within the first magnetic core and a first relative permeability ratio obtained by multiplying the ratio of the first high-permeability materials to the proportion of the first high-permeability materials in the linear portion of the first magnetic collection mechanism by the relative permeability of the first high-permeability materials. The number of the second high-permeability material, the length of the second high-permeability material in the central axis direction of the linear portion of the second magnetic collection mechanism, and the length of the second low-permeability material in the central axis direction of the linear portion of the second magnetic collection mechanism are each determined based on a predetermined fourth threshold for the total magnetic linkage within the second magnetic core and a second relative permeability ratio obtained by multiplying the ratio of the second high-permeability material to the proportion of the second high-permeability material in the linear portion of the second magnetic collection mechanism by the relative permeability of the second high-permeability material. The gradient magnetic field sensor described in [7]. [9] The first relative permeability ratio and the second relative permeability ratio are each within the range of 0.1 times or more the relative permeability of the high-permeability material and 0.9 times or less the relative permeability of the high-permeability material. The gradient magnetic field sensor described in [8].

[10] The length of the linear portion of the first magnetic collecting mechanism in the direction of the central axis of the linear portion of the first magnetic core is determined based on the length of the linear portion of the first magnetic core in the direction of the central axis of the linear portion of the first magnetic core and a predetermined fifth threshold value for the total magnetic flux linkage within the first magnetic core. The length of the linear portion of the second magnetic collecting mechanism in the direction of its central axis is determined based on the length of the linear portion of the second magnetic core in the direction of its central axis and a predetermined sixth threshold value for the total magnetic flux linkage within the second magnetic core. The gradient magnetic field sensor described in [9].

[11] The length of the linear portion of the first magnetic collecting mechanism in the direction of the central axis is 0.9 or more the length of the linear portion of the first magnetic core in the direction of the central axis of the linear portion of the first magnetic core. The length of the linear portion of the second magnetic collecting mechanism in the direction of its central axis is 0.9 or more the length of the linear portion of the second magnetic core in the direction of its central axis. The gradient magnetic field sensor described in

[10] .

[12] The ratio of the width of the first magnetic collection mechanism to the diameter of the first magnetic core is determined based on a predetermined seventh threshold value for the total magnetic flux linkage within the first magnetic core. The diameter of the first magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the first magnetic core. The width of the first magnetic collection mechanism is the length of the first magnetic collection mechanism in a direction parallel to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, and in a direction perpendicular to the central axis direction of the linear portion of the first magnetic collection mechanism. The ratio of the width of the second magnetic collection mechanism to the diameter of the second magnetic core is determined based on an eighth threshold value predetermined for the total magnetic flux linkage within the second magnetic core. The diameter of the second magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. The width of the second magnetic collection mechanism is the length of the second magnetic collection mechanism in a direction parallel to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, and in a direction perpendicular to the central axis direction of the linear portion of the second magnetic collection mechanism. A gradient magnetic field sensor as described in any one of items [7] to

[11] .

[13] The ratio of the width of the first magnetic collecting mechanism to the diameter of the first magnetic core, and the ratio of the width of the second magnetic collecting mechanism to the diameter of the second magnetic core, are each within the range of 0.5 to 60. The gradient magnetic field sensor described in

[12] .

[14] The ratio of the height of the first magnetic collection mechanism to the diameter of the first magnetic core is determined based on a predetermined ninth threshold for the total magnetic flux linkage within the first magnetic core. The diameter of the first magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the first magnetic core. The height of the first magnetic collection mechanism is the length of the first magnetic collection mechanism in a direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism. The ratio of the height of the second magnetic collection mechanism to the diameter of the second magnetic core is determined based on a predetermined 10th threshold value for the total magnetic flux linkage within the second magnetic core. The diameter of the second magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. The height of the second magnetic collection mechanism is the length of the second magnetic collection mechanism in a direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism. A gradient magnetic field sensor as described in any one of items [7] to

[13] .

[15] The ratio of the height of the first magnetic collection mechanism to the diameter of the first magnetic core, and the ratio of the height of the second magnetic collection mechanism to the diameter of the second magnetic core, are each within the range of 0.5 to 50. The gradient magnetic field sensor described in

[14] .

[16] The shortest distance between the outer circumference of the first coil and the first magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is determined based on the height of the first magnetic collection mechanism and an 11th threshold value predetermined for the total magnetic flux linkage within the first magnetic core. The outer circumference of the first coil is the circumference of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first coil is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic core. The shortest distance between the outer circumference of the second coil and the second magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is determined based on the height of the second magnetic collection mechanism and a predetermined 12th threshold value for the total magnetic flux linkage within the second magnetic core. The outer circumference of the second coil is the circumference of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second coil is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. A gradient magnetic field sensor as described in

[14] or

[15] .

[17] The shortest distance between the outer circumference of the first coil and the first magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is 0 or greater, and within a range of 4 times or less the height of the first magnetic collection mechanism. The shortest distance between the outer circumference of the second coil and the second magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is greater than or equal to 0 and within a range of 4 times or less the height of the second magnetic collection mechanism. The gradient magnetic field sensor described in

[16] .

[18] The first magnetic core has a linear portion, The second magnetic core has a linear portion, The first coil is positioned in the linear portion of the first magnetic core. The second coil is positioned in the linear portion of the second magnetic core. The linear portion of the first magnetic collection mechanism is non-parallel to the linear portion of the first magnetic core. The linear portion of the second magnetic collection mechanism is non-parallel to the linear portion of the second magnetic core. A gradient magnetic field sensor as described in any one of items [3] through

[17] .

[19] The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is substantially the same as the cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism. A gradient magnetic field sensor as described in any one of items [3] through

[18] .

[20] The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism is a rectangle. The cross-sectional shape of the second magnetic collection mechanism when it is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is a rectangle. The gradient magnetic field sensor described in

[19] . [twenty one] The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism is a square. The cross-sectional shape of the second magnetic collection mechanism when it is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is square. The gradient magnetic field sensor described in

[20] . [twenty two] The central axis of the linear portion of the second magnetic collection mechanism substantially coincides with the central axis of the linear portion of the first magnetic collection mechanism. The gradient magnetic field sensor described in [3]. [twenty three] Equipped with a gradient magnetic field sensor, The gradient magnetic field sensor is The first magnetic core and The second magnetic core, A first coil disposed in the first magnetic core, The second coil is positioned in the second magnetic core, Magnetic collection mechanism, Equipped with, The second coil is differentially connected to the first coil, The magnetic collection mechanism includes a high-permeability material and a low-permeability material. The aforementioned high-permeability material has a permeability of a predetermined first threshold or higher. The low-permeability material has a permeability below a predetermined second threshold, The second threshold is less than or equal to the first threshold. Magnetic material detection device.

[0161] Although embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may be modified, substituted, deleted, etc., as long as it does not depart from the spirit of this invention. [Explanation of Symbols]

[0162] 1…Magnetic material detection device, 11…Magnetic device, 12, 12X…Gradient magnetic field sensor, 20…Information processing device, C1…First capacitor, C2…Second capacitor, C3…Third capacitor, CC1…AC current control unit, CC2…DC current control unit, CC3…AC current control unit, CL1…First coil, CL2…Second coil, CM…Magnetic collection mechanism, CM1…First magnetic collection mechanism, CM2…Second magnetic collection mechanism, CR1…First magnetic core, CR1A…Magnetic material, CR1B…Magnetic material, CR1C…Conductor, CR1D…Terminal, CR1E…Terminal, CR2…Second magnetic core, CS…Frame, DC1…First DC excitation current, DC2…Second DC excitation current, DM…Detection target, DT…Detection circuit, EA…Error amplifier, HM…High permeability material L1...First inductor, L2...Second inductor, LF...Low-pass filter, LM...Low-permeability material, mag...First relative permeability ratio, P1...AC power supply, P2...DC power supply, PD...Phase detection circuit, PS0...0th phase shift circuit, PS1...1st phase shift circuit, PS2...2nd phase shift circuit, R1...Resistor, RL1...1st roller, RL2...2nd roller, RVC...Inverting circuit, S1...1st sensor head, S2...2nd sensor head, SD1...1st magnetic shield section, SD2...2nd magnetic shield section, ST...Sheet material, SWC1...1st switching circuit, SWC2...2nd switching circuit, TC...Three-dimensional coordinate system, VR11...1st variable resistor, VR12...2nd variable resistor, VR21...1st variable resistor, VR22...2nd variable resistor

Claims

1. A first magnetic core, which is positioned at a first location, includes a magnetic material, and has a linear portion, A second magnetic core is positioned at a second position different from the first position, and includes a magnetic material and has a linear portion. A first coil, which is a conductor wound around the first magnetic core as a solenoid coil, A second coil, which is a conductor wound around the second magnetic core as a solenoid coil, A magnetic collection mechanism including a first magnetic collection mechanism arranged in correspondence with the first magnetic core and a second magnetic collection mechanism arranged in correspondence with the second magnetic core, Detection circuit and Equipped with, The second coil is differentially connected to the first coil in order to obtain a signal based on the output difference with the first coil. The first magnetic collection mechanism is positioned between the region through which the object to be detected passes and the first magnetic core, and has a linear portion. The second magnetic collection mechanism is positioned between the region through which the object to be detected passes and the second magnetic core, and has a linear portion. The first magnetic collection mechanism and the second magnetic collection mechanism each include a high-permeability material and a low-permeability material, In the first magnetic collection mechanism and the second magnetic collection mechanism, the high-permeability material and the low-permeability material are arranged alternately. The aforementioned high-permeability material has a permeability of a predetermined first threshold or higher. The low-permeability material has a permeability below a predetermined second threshold, The second threshold is less than or equal to the first threshold. A first induced voltage is induced in the first coil, which changes according to the strength of the magnetic field at the first position. A second induced voltage is induced in the second coil, which changes according to the strength of the magnetic field at the second position. The input terminal of the detection circuit is connected to one of the two terminals of the first coil. The other of the two terminals of the first coil is connected to the one of the two terminals of the second coil. The other of the two terminals of the second coil is grounded. The first coil and the second coil are connected such that a differential signal corresponding to the difference between the first induced voltage and the second induced voltage is input to the input terminal of the detection circuit. The detection circuit outputs a detection signal indicating the difference between the magnetic field strength at the first position and the magnetic field strength at the second position, based on the differential signal. Gradient magnetic field sensor.

2. The magnetic collection mechanism includes a first magnetic collection mechanism and a second magnetic collection mechanism. The first magnetic collection mechanism is positioned at a predetermined first position relative to the first magnetic core. The second magnetic collection mechanism is positioned at a predetermined second position relative to the second magnetic core. The gradient magnetic field sensor according to claim 1.

3. The first magnetic collection mechanism has a linear portion, The second magnetic collection mechanism has a linear portion, The linear portion of the second magnetic collection mechanism is substantially parallel to the linear portion of the first magnetic collection mechanism. The gradient magnetic field sensor according to claim 2.

4. The first magnetic core has a linear portion, The second magnetic core has a linear portion, The first coil is positioned in the linear portion of the first magnetic core. The second coil is positioned in the linear portion of the second magnetic core. The linear portion of the first magnetic collection mechanism is substantially parallel to the linear portion of the first magnetic core. The linear portion of the second magnetic collection mechanism is substantially parallel to the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 3.

5. The linear portion of the second magnetic core faces the linear portion of the first magnetic core in a direction perpendicular to the linear portion of the second magnetic core. The linear portion of the second magnetic collection mechanism faces the linear portion of the first magnetic collection mechanism in a direction perpendicular to the linear portion of the second magnetic collection mechanism. The virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is substantially parallel to the virtual plane including the linear portion of the first magnetic core and the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 4.

6. The first magnetic collection mechanism includes N first high-permeability materials, with the high-permeability material being designated as the first high-permeability material, and M first low-permeability materials, with the low-permeability material being designated as the first low-permeability material. The second magnetic collection mechanism includes N of the high-permeability materials, with the high-permeability material being designated as the second high-permeability material, and M of the low-permeability materials, with the low-permeability material being designated as the second low-permeability material. In the first magnetic collection mechanism, the first high-permeability material and the first low-permeability material are arranged alternately. In the second magnetic collection mechanism, the second high-permeability material and the second low-permeability material are arranged alternately. The arrangement of the high-permeability material and the low-permeability material in the second magnetic collection mechanism is the same as the arrangement of the high-permeability material and the low-permeability material in the first magnetic collection mechanism. N is an integer greater than or equal to 1, M is an integer greater than or equal to 1. The gradient magnetic field sensor according to claim 5.

7. In a first direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, the central axis of the linear portion of the first magnetic collection mechanism and the central axis of the linear portion of the first magnetic core substantially overlap. In the first direction, the center of the first magnetic collection mechanism in the central axis direction of the linear portion of the first magnetic collection mechanism substantially coincides with the center of the first magnetic core in the central axis direction of the linear portion of the first magnetic core. In the first direction, the central axis of the linear portion of the second magnetic collection mechanism and the central axis of the linear portion of the second magnetic core substantially overlap. In the first direction, the center of the second magnetic collection mechanism in the central axis direction of the linear portion of the second magnetic collection mechanism substantially coincides with the center of the second magnetic core in the central axis direction of the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 6.

8. The number of the first high-permeability materials, the length of the first high-permeability materials in the central axis direction of the linear portion of the first magnetic collection mechanism, and the length of the first low-permeability materials in the central axis direction of the linear portion of the first magnetic collection mechanism are each determined based on a predetermined third threshold for the total magnetic flux linkage within the first magnetic core and a first relative permeability ratio obtained by multiplying the ratio of the first high-permeability materials to the proportion of the first high-permeability materials in the linear portion of the first magnetic collection mechanism by the relative permeability of the first high-permeability materials. The number of the second high-permeability material, the length of the second high-permeability material in the central axis direction of the linear portion of the second magnetic collection mechanism, and the length of the second low-permeability material in the central axis direction of the linear portion of the second magnetic collection mechanism are each determined based on a predetermined fourth threshold value for the total magnetic linkage within the second magnetic core and a second relative permeability ratio obtained by multiplying the ratio of the second high-permeability material to the proportion of the second high-permeability material in the linear portion of the second magnetic collection mechanism by the relative permeability of the second high-permeability material. The gradient magnetic field sensor according to claim 7.

9. The first relative permeability ratio and the second relative permeability ratio are each within the range of 0.1 times or more the relative permeability of the high-permeability material and 0.9 times or less the relative permeability of the high-permeability material. The gradient magnetic field sensor according to claim 8.

10. The length of the linear portion of the first magnetic collecting mechanism in the direction of the central axis is determined based on the length of the linear portion of the first magnetic core in the direction of the central axis of the linear portion of the first magnetic core and a predetermined fifth threshold value for the total magnetic flux linkage within the first magnetic core. The length of the linear portion of the second magnetic collecting mechanism in the direction of its central axis is determined based on the length of the linear portion of the second magnetic core in the direction of its central axis and a predetermined sixth threshold value for the total magnetic flux linkage within the second magnetic core. The gradient magnetic field sensor according to claim 9.

11. The length of the linear portion of the first magnetic collecting mechanism in the direction of the central axis is 0.9 or more of the length of the linear portion of the first magnetic core in the direction of the central axis of the linear portion of the first magnetic core. The length of the linear portion of the second magnetic collecting mechanism in the direction of the central axis is 0.9 or more the length of the linear portion of the second magnetic core in the direction of the central axis of the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 10.

12. The ratio of the width of the first magnetic collection mechanism to the diameter of the first magnetic core is determined based on a predetermined seventh threshold value for the total magnetic flux linkage within the first magnetic core. The diameter of the first magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the first magnetic core. The width of the first magnetic collection mechanism is the length of the first magnetic collection mechanism in a direction parallel to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, and in a direction perpendicular to the central axis direction of the linear portion of the first magnetic collection mechanism. The ratio of the width of the second magnetic collection mechanism to the diameter of the second magnetic core is determined based on an eighth threshold value predetermined for the total magnetic flux linkage within the second magnetic core. The diameter of the second magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. The width of the second magnetic collection mechanism is the length of the second magnetic collection mechanism in a direction parallel to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism, and in a direction perpendicular to the central axis direction of the linear portion of the second magnetic collection mechanism. The gradient magnetic field sensor according to claim 7.

13. The ratio of the width of the first magnetic collecting mechanism to the diameter of the first magnetic core, and the ratio of the width of the second magnetic collecting mechanism to the diameter of the second magnetic core, are both within the range of 0.5 to 60. The gradient magnetic field sensor according to claim 12.

14. The ratio of the height of the first magnetic collection mechanism to the diameter of the first magnetic core is determined based on a predetermined ninth threshold for the total magnetic flux linkage within the first magnetic core. The diameter of the first magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the first magnetic core. The height of the first magnetic collection mechanism is the length of the first magnetic collection mechanism in a direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism. The ratio of the height of the second magnetic collection mechanism to the diameter of the second magnetic core is determined based on a predetermined tenth threshold value for the total magnetic flux linkage within the second magnetic core. The diameter of the second magnetic core is the diameter of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second magnetic core is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. The height of the second magnetic collection mechanism is the length of the second magnetic collection mechanism in a direction perpendicular to a virtual plane that includes the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism. The gradient magnetic field sensor according to claim 7.

15. The ratio of the height of the first magnetic collection mechanism to the diameter of the first magnetic core, and the ratio of the height of the second magnetic collection mechanism to the diameter of the second magnetic core, are both within the range of 0.5 to 50. The gradient magnetic field sensor according to claim 14.

16. The shortest distance between the outer circumference of the first coil and the first magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is determined based on the height of the first magnetic collection mechanism and an eleventh threshold value predetermined for the total magnetic flux linkage within the first magnetic core. The outer circumference of the first coil is the circumference of the circumscribed circle that circumscribes the cross-sectional shape obtained when the first coil is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic core. The shortest distance between the outer circumference of the second coil and the second magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is determined based on the height of the second magnetic collection mechanism and a predetermined twelfth threshold value for the total magnetic flux linkage within the second magnetic core. The outer circumference of the second coil is the circumference of the circumscribed circle that circumscribes the cross-sectional shape obtained when the second coil is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 14.

17. The shortest distance between the outer circumference of the first coil and the first magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is 0 or greater, and within a range of 4 times or less the height of the first magnetic collection mechanism. The shortest distance between the outer circumference of the second coil and the second magnetic collection mechanism in a direction perpendicular to a virtual plane including the linear portion of the first magnetic collection mechanism and the linear portion of the second magnetic collection mechanism is 0 or greater, and within a range of 4 times or less the height of the second magnetic collection mechanism. The gradient magnetic field sensor according to claim 16.

18. The first magnetic core has a linear portion, The second magnetic core has a linear portion, The first coil is positioned in the linear portion of the first magnetic core. The second coil is positioned in the linear portion of the second magnetic core. The linear portion of the first magnetic collection mechanism is non-parallel to the linear portion of the first magnetic core. The linear portion of the second magnetic collection mechanism is non-parallel to the linear portion of the second magnetic core. The gradient magnetic field sensor according to claim 3.

19. The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is substantially the same as the cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism. The gradient magnetic field sensor according to claim 3.

20. The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism is a rectangle. The cross-sectional shape of the second magnetic collection mechanism when it is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is a rectangle. The gradient magnetic field sensor according to claim 19.

21. The cross-sectional shape obtained when the first magnetic collection mechanism is cut by a virtual plane perpendicular to the central axis of the linear portion of the first magnetic collection mechanism is a square. The cross-sectional shape of the second magnetic collection mechanism when it is cut by a hypothetical plane perpendicular to the central axis of the linear portion of the second magnetic collection mechanism is square. The gradient magnetic field sensor according to claim 20.

22. The central axis of the linear portion of the second magnetic collection mechanism substantially coincides with the central axis of the linear portion of the first magnetic collection mechanism. The gradient magnetic field sensor according to claim 3.

23. A gradient magnetic field sensor as described in Claim 1, Magnetic material detection device.

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