Gradient magnetic field sensor and magnetic object detection device

Abstract

To provide a gradient magnetic field sensor capable of suppressing variation of sensitivity due to a passing position of a magnetized foreign material while preventing occurrence of a dead zone.SOLUTION: A gradient magnetic field sensor includes: a first magnetic core including a linear shaped part; a second magnetic core including a linear shaped part; an N pieces of first coils sequentially arranged on the linear shaped part included in the first magnetic core; an N pieces of second coils sequentially arranged on the linear shaped part included in the second magnetic core; and a body part provided with the first magnetic core and the second magnetic core. Among the N pieces of first coils, a first coil being n-th from the tip end of the first magnetic core is differentially connected with a second coil being n-th from the tip end of the second magnetic core among the N pieces of second coils. N is an integer being two or more, and n is an integer in a range of one or more and N or smaller.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Research and development have been carried out on a gradient magnetic field sensor that detects the gradient of the magnetic field strength at two different points. Here, the gradient is the difference in the magnetic field strength at each of the two different points.

[0003] The gradient magnetic field sensor includes two sensor heads in order to detect the magnetic field strength at two different points. In the gradient magnetic field sensor, one of these two sensor heads detects the magnetic field strength at one of these two different points. Also, in the gradient magnetic field sensor, the other of these two sensor heads detects the magnetic field strength at the other of these two different points. And the gradient magnetic field sensor detects the gradient of the magnetic field strength at these two different points according to the signals output from these two sensor heads. The gradient of the magnetic field strength at these two different points changes depending on the presence or absence of an object (for example, a magnetic body, etc.) that can change the magnetic field. Utilizing this, the gradient magnetic field sensor can use such an object as a detection target and detect the detection target.

[0004] However, there is a dead zone in each of the two sensor heads included in the gradient magnetic field sensor, and there has been a case where the detection target cannot be detected.

[0005] Regarding this, a first sensor head is formed of a magnetic body including a linear shape, and a first detection coil magnetically coupled to a part of the linear shape in the magnetic body is disposed on a first magnetic core through which an alternating current and a direct current for excitation are passed. A second sensor head is formed of a magnetic body including a linear shape, and a common current is passed through the magnetic body together with the alternating current and the direct current for excitation passed through the first magnetic core. A second detection coil is disposed on a second magnetic core disposed in parallel facing the first magnetic core, and the second detection coil is magnetically coupled by differential coupling to a part of the linear shape in the magnetic body at a rotationally symmetric position with respect to the first detection coil. A gradient magnetic field sensor including a sensor circuit that outputs a gradient magnetic field based on the detection voltages output from the first and second sensor heads is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, in the gradient magnetic field sensor described in Patent Document 1, since the second detection coil is differentially coupled to the first detection coil at a rotationally symmetric position, when the detection object passes near the center in the longitudinal direction of the magnetic core, the waveform of the detection signal has a bimodal waveform having two similar peak-shaped peaks. However, in this gradient magnetic field sensor, since the detection signal has the same polarity as the voltage output from the first detection coil and the voltage output from the second detection coil in this case, as a result of the differential coupling between the first detection coil and the second detection coil, the peak value may become small. Further, in this gradient magnetic field sensor, when the detection object passes near the tip of the magnetic core, the waveform of the detection signal may become a unimodal waveform having wave heights with different polarities and magnitudes. Thus, in this gradient magnetic field sensor, the waveform of the detection signal may differ depending on the passing position of the detection object. This means that the sensitivity of the gradient magnetic field sensor changes depending on the passing position of the detection object, which is not desirable.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a gradient magnetic field sensor and a magnetic object detection device that can suppress fluctuations in sensitivity according to the passing position of a detection object while suppressing the occurrence of a dead zone.

Means for Solving the Problems

[0009] One aspect of the present invention is a gradient magnetic field sensor including a first magnetic core having a linear portion, a second magnetic core having a linear portion, N first coils sequentially arranged on the linear portion of the first magnetic core, N second coils sequentially arranged on the linear portion of the second magnetic core, and a main body portion provided with the first magnetic core and the second magnetic core, wherein the nth first coil from the tip side of the first magnetic core among the N first coils is differentially connected to the nth second coil from the tip side of the second magnetic core among the N second coils, N is an integer of 2 or more, and n is an integer within a range of 1 or more and N or less.

Effects of the Invention

[0010] According to the present invention, it is possible to suppress the occurrence of a dead zone and suppress fluctuations in sensitivity according to the passing position of the detection target.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] <Embodiment> Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] <Outline of the Magnetic Substance Detection Device> First, the outline of the magnetic substance detection device according to the present embodiment will be described.

[0014] The magnetic substance detection device according to the embodiment includes a gradient magnetic field sensor according to the embodiment. The gradient magnetic field sensor according to the embodiment includes a first magnetic core, a second magnetic core, N first coils, N second coils, and a main body portion. The first magnetic core has a linear portion. The second magnetic core has a linear portion. The N first coils are sequentially arranged on the linear portion of the first magnetic core. The N second coils are sequentially arranged on the linear portion of the second magnetic core. The main body portion is provided with the first magnetic core and the second magnetic core. Among the N first coils, the n-th first coil from the tip side of the first magnetic core is differentially connected to the n-th second coil from the tip side of the second magnetic core among the N second coils. However, N is an integer of 2 or more. And n is an integer within the range of 1 or more and N or less.

[0015] As a result, the gradient magnetic field sensor according to the embodiment and the magnetic object detection device according to the embodiment can suppress the occurrence of a dead zone and suppress fluctuations in sensitivity according to the passing position of the detection target object.

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

[0017] <Configuration of Magnetic Object Detection Device> Hereinafter, as an example of the magnetic object detection device, the magnetic object detection device 1 will be taken as an example to describe the configuration of the magnetic object detection device according to the embodiment. Here, in the embodiment, a conductor that transmits an electrical signal corresponding to direct current power or an electrical signal corresponding to alternating current power will be described as a transmission line. The transmission line may be, for example, a conductor printed on a substrate, a wire in which the conductor is formed linearly, or other conductors. Also, in the embodiment, when referring to voltage, it means the potential difference from a predetermined reference potential, and the illustration and description of the reference potential are omitted. Here, the reference potential may be any potential. In the embodiment, as an example, the case where the reference potential is the ground potential will be described. Also, in the embodiment, when referring to ground, the same ground is indicated. Also, in this specification, the terminal with a dot among the two terminals of the coil in each circuit diagram will be described as the hot side terminal. Also, in this specification, the terminal without a dot among the two terminals of the coil in each circuit diagram will be described as the cold side terminal.

[0018] FIG. 1 is a diagram showing an example of the configuration of the magnetic object detection device 1.

[0019] The magnetic object detection device 1 is a device that detects a detection target object by a magnetic field. The detection target object is an object capable of changing a magnetic field. The detection target object is, for example, a magnetic body or the like.

[0020] The magnetic object detection device 1 includes, 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 includes two sensor heads, a first sensor head S1 and a second sensor head S2. In FIG. 1, in order to prevent the figure from becoming complicated, the cable connecting the information processing device 20 and other members in the magnetic object detection device 1 is omitted. Further, the magnetic object detection device 1 may be configured not to include 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. Further, the magnetic object detection device 1 may be configured to include, together with the gradient magnetic field sensor 12, other members, other devices, etc. 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. Further, the magnetic object detection device 1 may be configured to include, together with the gradient magnetic field sensor 12, other members, other devices, etc. in addition to all of the frame CS, the first roller RL1, the second roller RL2, the magnetization device 11, and the information processing device 20.

[0021] Each member of the magnetic object detection device 1 is attached to the frame CS. The frame CS is mainly composed of a top plate (not shown), a bottom plate (not shown), and a plurality of columns connecting the top plate and the bottom plate. In the example shown in FIG. 1, the outer shape of the frame CS is substantially rectangular parallelepiped. Note that the outer shape of the frame CS may be any shape.

[0022] The first roller RL1 and the second roller RL2 are provided inside the frame CS.

[0023] The first roller RL1 is a roller around which a sheet member ST, which is an object to be inspected for the presence or absence of adhesion of a detection target, is wound in a roll shape. The second roller RL2 is a roller that winds up the sheet member ST drawn from the first roller RL1 while conveying it along a predetermined path. The second roller RL2 is rotated by a servo motor (not shown) or the like. Thereby, the second roller RL2 can wind up the sheet member ST drawn from the first roller RL1. That is, the second roller RL2 is a driving roller. And the first roller RL1 is a driven roller that rotates while the sheet member ST is being wound up in response to the rotation of the second roller RL2. Note that the servo motor is controlled by, for example, an information processing apparatus 20 described later.

[0024] The sheet member ST is conveyed through a magnetic field generated by the magnetization device 11 until it is drawn from the first roller RL1 and wound up by the second roller RL2. Thereby, the detection target attached to the sheet member ST is magnetized. After the sheet member ST is conveyed through the magnetic field, it is conveyed to a predetermined detection region where the gradient magnetic field sensor 12 can detect the presence or absence of the detection target. And the sheet member ST is wound around the second roller RL2.

[0025] Here, the magnetization device 11 is a device that generates a magnetic field of a predetermined intensity in a predetermined magnetization region and magnetizes a magnetic body that has entered the magnetization region. Since the magnetization device 11 is a known device, further detailed description thereof is omitted.

[0026] The gradient magnetic field sensor 12 detects the gradient of the magnetic field strength at two different points in the aforementioned detection region by means of sensor heads, namely, the first sensor head S1 and the second sensor head S2, arranged at each of the two different points. Thereby, the information processing device 20 that acquires the detection signal output from the gradient magnetic field sensor 12 can determine whether or not a detection object is attached to the sheet member ST conveyed through the detection region based on the detection signal. In the following, for the sake of convenience in explanation, the gradient of the magnetic field strength at the two points, i.e., the point where the first sensor head S1 is arranged and the point where the second sensor head S2 is arranged, will be simply referred to as the gradient for explanation.

[0027] The information processing device 20 is communicably connected to the gradient magnetic field sensor 12. And as described above, the information processing device 20 determines whether or not a detection object is attached to the sheet member ST conveyed through the detection region based on the detection signal output from the gradient magnetic field sensor 12.

[0028] For example, when the information processing device 20 determines that a detection object is attached to the sheet member ST conveyed through the detection region, the information processing device 20 controls the aforementioned servo motor to stop the winding of the sheet member ST by the second roller RL2 and performs a notification process for notifying that a detection object is attached to the sheet member ST. The notification process is, for example, a process of displaying information indicating that a detection object is attached to the sheet member ST on the display of the information processing device 20. Thereby, the user of the magnetic object detection device 1 can remove the detection object from the sheet member ST, identify the sheet member ST as a defective product, and so on. Note that the notification process may be a process of outputting sound, vibration, light, etc. indicating the information instead of such a display process.

[0029] The information processing device 20 is, for example, a notebook PC (Personal Computer), a tablet PC, a desktop PC, a workstation, a multifunctional mobile phone terminal (smartphone), a mobile phone terminal, a PDA (Personal Digital Assistant), or the like. Note that the information processing device 20 may be another information processing device such as a microcomputer.

[0030] In the magnetic object detection device 1, a part or all of the magnetization device 11, the gradient magnetic field sensor 12, and the information processing device 20 may be integrally configured.

[0031] Further, the object for which the magnetic object detection device 1 inspects the attachment of the detection object may be another object capable of inspecting the presence or absence of the detection object instead of the sheet member ST. For example, a magnetic object detector equipped with a gradient magnetic field sensor 12 detects the presence or absence of a magnetic object in the ground. In this case, the magnetic object detector is an example of the magnetic object detection device 1. Also, the magnetic object in the ground is an example of the detection object in this case.

[0032] <Circuit configuration of the gradient magnetic field sensor> Hereinafter, with reference to FIG. 2, the circuit configuration of the gradient magnetic field sensor 12 will be described. FIG. 2 is a diagram showing an example of the circuit configuration of the gradient magnetic field sensor 12.

[0033] 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 DT1, a detection circuit DT2, a detection circuit DT3, a detection circuit DT4, a signal processing unit PR, and a detection signal output terminal CT2.

[0034] The first sensor head S1 includes a first magnetic core CR1 having a linear portion and N detection coils CL11 to CL1N of the detection coils CL1. And these N detection coils CL1 are sequentially arranged on the linear portion of the first magnetic core CR1. In other words, these N detection coils CL1 are wound around the linear portion of the first magnetic core CR1 in order from the tip side of the first magnetic core CR1. In this case, each of the N detection coils CL1 is magnetically coupled to the first magnetic core CR1. And when a magnetic field is applied to the first sensor head S1, the magnetic fluxes linked to each of the N detection coils CL1 are equal to each other (or substantially equal to each other). This is because each of these N detection coils CL1 is wound around the first magnetic core CR1 which is a magnetic material, and the magnetic resistance of the magnetic material is lower than the magnetic resistance of air. Note that the first magnetic core CR1 is made of, for example, amorphous ribbon, but is not limited thereto. Also, in addition to these N detection coils CL1, one or more other coils may be arranged on the linear portion of the first magnetic core CR1. In this case, on the linear portion of the first magnetic core CR1, these one or more other coils are arranged on the tip side or the base end side of the first magnetic core CR1 with respect to the N detection coils CL1.

[0035] The second sensor head S2 includes a second magnetic core CR2 having a linear portion, and N detection coils CL21 to CL2N of the detection coils CL2. That is, the second sensor head S2 includes the same number of detection coils CL2 as the number of detection coils CL1 included in the first sensor head S1. And these N detection coils CL2 are sequentially arranged on the linear portion of the second magnetic core CR2. In other words, these N detection coils CL2 are wound around the linear portion of the second magnetic core CR2 in order from the tip side of the second magnetic core CR2. In this case, each of the N detection coils CL2 is magnetically coupled to the second magnetic core CR2. And when a magnetic field is applied to the second sensor head S2, the magnetic fluxes linked to each of the N detection coils CL2 are equal to each other (or substantially equal to each other). This is because each of these N detection coils CL2 is wound around the second magnetic core CR2 which is a magnetic material, and the magnetic resistance of the magnetic material is lower than the magnetic resistance of air. Note that the second magnetic core CR2 is made of, for example, amorphous ribbon, but is not limited thereto. Also, in addition to these N detection coils CL2, one or more other coils may be arranged on the linear portion of the second magnetic core CR2. In this case, in the linear portion of the second magnetic core CR2, these one or more other coils are arranged on the tip side or the base end side of the second magnetic core CR2 with respect to the N detection coils CL2.

[0036] Here, N may be any integer as long as it is an integer of 2 or more. Hereinafter, as an example, the case where N is 4 will be described. In this case, as shown in FIG. 2, the first sensor head S1 includes a first magnetic core CR1 and four detection coils of detection coils CL11 to detection coils CL14. Also, in this case, the second sensor head S2 includes a second magnetic core CR2 and four detection coils of detection coils CL21 to detection coils CL24.

[0037] The 0th phase shift circuit PS0 has two terminals, an input terminal PS01 and an output terminal PS02.

[0038] The alternating current control unit CC1 has an input terminal CC11, an input terminal CC12, an output terminal CC13, and an output terminal CC14. The alternating current control unit CC1 also includes a first phase-shifting circuit PS1, a first variable resistor VR11, a first capacitor C1, a second phase-shifting circuit PS2, a second variable resistor VR12, and a second capacitor C2.

[0039] The detection circuit DT1 has three terminals: an input terminal DT11, an input terminal DT12, and an output terminal DT13.

[0040] The detection circuit DT2 has three terminals: an input terminal DT21, an input terminal DT22, and an output terminal DT23.

[0041] The detection circuit DT3 has three terminals: an input terminal DT31, an input terminal DT32, and an output terminal DT33.

[0042] The detection circuit DT4 has three terminals: an input terminal DT41, an input terminal DT42, and an output terminal DT43.

[0043] The signal processing unit PR has five terminals: an input terminal PR1, an input terminal PR2, an input terminal PR3, an input terminal PR4, and an output terminal PR5.

[0044] Further, the gradient magnetic field sensor 12 is connected to the AC power supply P1 via a transmission line. More specifically, the AC power supply connection terminal CT1 of the gradient magnetic field sensor 12 is connected to the first power supply terminal P11, which is one of the two power supply terminals of the AC power supply P1, via a transmission line. And the second power supply terminal P12, which is the other of the two power supply terminals of the AC power supply P1, is grounded via a transmission line. Here, the AC power supply P1 can be any AC power supply. Note that other circuit elements, other devices, etc. may be connected between the AC power supply connection terminal CT1 and the first power supply terminal P11 as long as the function of the gradient magnetic field sensor 12 is not impaired. Also, other circuit elements, other devices, etc. may be connected between the second power supply terminal P12 and the ground as long as the function of the gradient magnetic field sensor 12 is not impaired.

[0045] Further, 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 as long as the function of the gradient magnetic field sensor 12 is not impaired.

[0046] Also, the AC power connection terminal CT1 is connected to each of the input terminal PS01 of the 0th phase shift circuit PS0, the input terminal DT11 of the detection circuit DT1, the input terminal DT21 of the detection circuit DT2, the input terminal DT31 of the detection circuit DT3, and the input terminal DT41 of the detection circuit DT4 via transmission lines. And the output terminal PS02 of the 0th phase shift circuit PS0 is connected to each of the input terminal CC11 and the input terminal CC12 of the AC current control unit CC1 via transmission lines. Note that, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the AC power connection terminal CT1 and the input terminal PS01. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the AC power connection terminal CT1 and the input terminal DT11. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the AC power connection terminal CT1 and the input terminal DT21. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the AC power connection terminal CT1 and the input terminal DT31. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the AC power connection terminal CT1 and the input terminal DT41. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the output terminal PS02 and the input terminal CC11. Also, within a range that does not impair the function of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the output terminal PS02 and the input terminal CC12.

[0047] Also, in the AC current control unit CC1, between the input terminal CC11 and the output terminal CC13, a first phase shift circuit PS1, a first variable resistor VR11, and a first capacitor C1 are connected in series via a transmission line. Also, in the AC current control unit CC1, between the input terminal CC12 and the output terminal CC14, a second phase shift circuit PS2, a second variable resistor VR12, and a second capacitor C2 are connected in series via a transmission line. Note that between the input terminal CC11 and the output terminal CC13, within a range that does not impair the function of the gradient magnetic field sensor 12, a configuration may be adopted in which other circuit elements, other devices, etc. are connected together with the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1. Also, between the input terminal CC11 and the 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. Also, between the input terminal CC12 and the output terminal CC14, within a range that does not impair the function of the gradient magnetic field sensor 12, a configuration may be adopted in which other circuit elements, other devices, etc. are connected together with the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2. Also, between the input terminal CC12 and the 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.

[0048] Also, between the output terminal CC13 of the alternating current control unit CC1 and the ground, the first magnetic core CR1 of the first sensor head S1 is connected via a transmission line. Also, between the output terminal CC14 of the alternating current control unit CC1 and the ground, the second magnetic core CR2 of the second sensor head S2 is connected via a transmission line. Hereinafter, for convenience of explanation, the alternating current flowing from the output terminal CC13 to the first magnetic core CR1 will be described as the first alternating excitation current AC1 as indicated by the arrow in FIG. 2. Also, hereinafter, for convenience of explanation, the alternating current flowing from the output terminal CC14 to the second magnetic core CR2 will be described as the second alternating excitation current AC2 as indicated by the arrow in FIG. 2. Note that, between the output terminal CC13 of the alternating current control unit CC1 and the ground, other circuit elements, other devices, etc. may be connected together with the first magnetic core CR1 within a range that does not impair the function of the gradient magnetic field sensor 12. Also, between the output terminal CC14 of the alternating current control unit CC1 and the ground, other circuit elements, other devices, etc. may be connected together with the second magnetic core CR2 within a range that does not impair the function of the gradient magnetic field sensor 12.

[0049] Also, the input terminal DT12 of the detection circuit DT1 is connected via a transmission line to the hot-side terminal of the two terminals of the detection coil CL11. Also, the cold-side terminal of the two terminals of the detection coil CL11 is connected via a transmission line to the cold-side terminal of the two terminals of the detection coil CL21. And the hot-side terminal of the two terminals of the detection coil CL21 is grounded to the ground via a transmission line. That is, the detection coil CL11 and the detection coil CL21 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DT12 and the detection coil CL11 as long as the function of the gradient magnetic field sensor 12 is not impaired. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL11 and the detection coil CL21 as long as the function of the gradient magnetic field sensor 12 is not impaired. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL21 and the ground as long as the function of the gradient magnetic field sensor 12 is not impaired.

[0050] Here, the self-inductance of the detection coil CL11 is the same (or approximately the same) as the self-inductance of the detection coil CL21. Thereby, the gradient magnetic field sensor 12 can match the sensitivities of the detection coil CL11 and the detection coil CL21 with respect to their respective uniform magnetic fields. In other words, in this case, the voltage output from the detection coil CL11 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 is made to be a voltage with the opposite polarity and the same magnitude as the voltage output from the detection coil CL21 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2. As a result, the gradient magnetic field sensor 12 can suppress detecting a uniform magnetic field due to the combination of the detection coil CL11 and the detection coil CL21. Note that a uniform magnetic field, in this specification, is a magnetic field whose strength changes uniformly regardless of position within a region where no magnetic field other than the uniform magnetic field is applied, and is, for example, geomagnetism, a remote disturbance magnetic field, or the like. Also, the self-inductance of the detection coil CL11 may have a configuration different from the self-inductance of the detection coil CL21. In this case, the gradient magnetic field sensor 12 suppresses detecting a uniform magnetic field by performing signal processing such that, for example, the magnitude of the voltage output from the detection coil CL11 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 matches the magnitude of the voltage output from the detection coil CL21 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2.

[0051] Also, the input terminal DT22 of the detection circuit DT2 is connected via a transmission line to the hot-side terminal of the two terminals of the detection coil CL12. Also, the cold-side terminal of the two terminals of the detection coil CL12 is connected via a transmission line to the cold-side terminal of the two terminals of the detection coil CL22. And, the hot-side terminal of the two terminals of the detection coil CL22 is grounded to the ground via a transmission line. That is, the detection coil CL12 and the detection coil CL22 are differentially connected. Note that, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal DT22 and the detection coil CL12. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the detection coil CL12 and the detection coil CL22. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the detection coil CL22 and the ground.

[0052] Here, the self-inductance of the detection coil CL12 is the same (or approximately the same) as the self-inductance of the detection coil CL22. Thereby, the gradient magnetic field sensor 12 can match the sensitivities of the detection coil CL12 and the detection coil CL22 with respect to their respective uniform magnetic fields. In other words, in this case, the voltage output from the detection coil CL12 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 can be made to have the same magnitude but opposite polarity as the voltage output from the detection coil CL22 when a magnetic field of the predetermined magnitude X1 is applied to the second sensor head S2. As a result, the gradient magnetic field sensor 12 can suppress detecting a uniform magnetic field due to the combination of the detection coil CL12 and the detection coil CL22. Note that the self-inductance of the detection coil CL12 may have a configuration different from that of the self-inductance of the detection coil CL22. In this case, the gradient magnetic field sensor 12 suppresses detecting a uniform magnetic field, for example, by performing signal processing to match the magnitude of the voltage output from the detection coil CL12 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 with the magnitude of the voltage output from the detection coil CL22 when a magnetic field of the predetermined magnitude X1 is applied to the second sensor head S2.

[0053] Also, the input terminal DT32 of the detection circuit DT3 is connected via a transmission line to the hot-side terminal of the two terminals of the detection coil CL13. Also, the cold-side terminal of the two terminals of the detection coil CL13 is connected via a transmission line to the cold-side terminal of the two terminals of the detection coil CL23. And, the hot-side terminal of the two terminals of the detection coil CL23 is grounded via a transmission line. That is, the detection coil CL13 and the detection coil CL23 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DT32 and the detection coil CL13 within a range that does not impair the functions of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL13 and the detection coil CL23 within a range that does not impair the functions of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL23 and the ground within a range that does not impair the functions of the gradient magnetic field sensor 12.

[0054] Here, the self-inductance of the detection coil CL13 is the same (or approximately the same) as the self-inductance of the detection coil CL23. Thereby, the gradient magnetic field sensor 12 can make the sensitivities of the detection coil CL13 and the detection coil CL23 with respect to their respective uniform magnetic fields coincide. In other words, in this case, the voltage output from the detection coil CL13 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 can be made a voltage having the opposite polarity and the same magnitude as the voltage output from the detection coil CL23 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2. As a result, the gradient magnetic field sensor 12 can suppress detecting a uniform magnetic field due to the combination of the detection coil CL13 and the detection coil CL23. Note that the self-inductance of the detection coil CL13 may have a configuration different from the self-inductance of the detection coil CL23. In this case, the gradient magnetic field sensor 12 suppresses detecting a uniform magnetic field by performing signal processing such that, for example, the magnitude of the voltage output from the detection coil CL13 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 coincides with the magnitude of the voltage output from the detection coil CL23 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2.

[0055] Also, the input terminal DT42 of the detection circuit DT4 is connected via a transmission line to the hot-side terminal of the two terminals of the detection coil CL14. Also, the cold-side terminal of the two terminals of the detection coil CL14 is connected via a transmission line to the cold-side terminal of the two terminals of the detection coil CL24. And, the hot-side terminal of the two terminals of the detection coil CL24 is grounded via a transmission line. That is, the detection coil CL14 and the detection coil CL24 are differentially connected. Note that other circuit elements, other devices, etc. may be connected between the input terminal DT42 and the detection coil CL14 within a range that does not impair the function of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL14 and the detection coil CL24 within a range that does not impair the function of the gradient magnetic field sensor 12. Also, other circuit elements, other devices, etc. may be connected between the detection coil CL24 and the ground within a range that does not impair the function of the gradient magnetic field sensor 12.

[0056] Here, the self-inductance of the detection coil CL14 is the same as (or approximately the same as) the self-inductance of the detection coil CL24. Thereby, the gradient magnetic field sensor 12 can match the sensitivities of the detection coil CL14 and the detection coil CL24 with respect to their respective uniform magnetic fields. In other words, in this case, the voltage output from the detection coil CL14 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 can be made into a voltage with the opposite polarity and the same magnitude as the voltage output from the detection coil CL24 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2. As a result, the gradient magnetic field sensor 12 can suppress detecting a uniform magnetic field due to the combination of the detection coil CL14 and the detection coil CL24. Note that the self-inductance of the detection coil CL14 may have a configuration different from the self-inductance of the detection coil CL24. In this case, the gradient magnetic field sensor 12 suppresses detecting a uniform magnetic field by performing signal processing such that, for example, the magnitude of the voltage output from the detection coil CL14 when a magnetic field of a predetermined magnitude X1 is applied to the first sensor head S1 matches the magnitude of the voltage output from the detection coil CL24 when a magnetic field of a predetermined magnitude X1 is applied to the second sensor head S2.

[0057] Note that some or all of the self-inductances of detection coil CL11 and detection coil CL21, the self-inductances of detection coil CL12 and detection coil CL22, the self-inductances of detection coil CL13 and detection coil CL23, and the self-inductances of detection coil CL14 and detection coil CL24 may be the same as each other or may be different from each other. However, if all of the self-inductances of detection coil CL11 and detection coil CL21, the self-inductances of detection coil CL12 and detection coil CL22, the self-inductances of detection coil CL13 and detection coil CL23, and the self-inductances of detection coil CL14 and detection coil CL24 are the same as each other, the gradient magnetic field sensor 12 can make the sensitivities of the combination of detection coil CL11 and detection coil CL21, the combination of detection coil CL12 and detection coil CL22, the combination of detection coil CL13 and detection coil CL23, and the combination of detection coil CL14 and detection coil CL24 coincide with each other. As a result, the gradient magnetic field sensor 12 can suppress detecting a uniform magnetic field and, as will be described later, can suppress detecting a uniform gradient magnetic field such as that generated by a gradient magnetic field coil or the like. In a region where a certain uniform gradient magnetic field is applied, the magnetic field strength at each position in the region is a uniform magnetic field, and moreover, it is a magnetic field whose intensity periodically changes uniformly at each position in the region. Examples of factors that generate a uniform gradient magnetic field include vibrations caused by a motor or the like that drives a production line. For example, the gradient magnetic field sensor 12 provided on the production line may be used in a state covered with a magnetic material such as a magnetic shield. In this case, the magnetic material also vibrates in response to the vibration of the production line, generating a fluctuating magnetic field. Such a fluctuating magnetic field may be detected as a uniform gradient magnetic field by the gradient magnetic field sensor 12. The uniform gradient magnetic field generated in this way acts as magnetic noise and may interfere with the detection of the object to be detected by the gradient magnetic field sensor 12.The gradient magnetic field sensor 12 can suppress detection of such a uniform gradient magnetic field.

[0058] Here, the inductance of the detection coil CL1n and the inductance of the detection coil CL2n can be made to match, for example, by matching the number of turns per unit length of the detection coil CL1n and the number of turns per unit length of the detection coil CL2n, and by matching the length in the central axis direction of the detection coil CL1n and the length in the central axis direction of the detection coil CL2n. Note that the method of matching the inductance of the detection coil CL1n and the inductance of the detection coil CL2n may be other methods.

[0059] Also, the input terminal PR1 of the signal processing unit PR is connected to the output terminal DT13 of the detection circuit DT1 via a transmission line. Also, the input terminal PR2 of the signal processing unit PR is connected to the output terminal DT23 of the detection circuit DT2 via a transmission line. Also, the input terminal PR3 of the signal processing unit PR is connected to the output terminal DT33 of the detection circuit DT3 via a transmission line. Also, the input terminal PR4 of the signal processing unit PR is connected to the output terminal DT43 of the detection circuit DT4 via a transmission line. Also, the output terminal PR5 of the signal processing unit PR is connected to the detection signal output terminal CT2 via a transmission line. Note that, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal PR1 and the output terminal DT13. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal PR2 and the output terminal DT23. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal PR3 and the output terminal DT33. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the input terminal PR4 and the output terminal DT43. Also, within a range that does not impair the functions of the gradient magnetic field sensor 12, other circuit elements, other devices, etc. may be connected between the output terminal PR5 and the detection signal output terminal CT2.

[0060] Next, referring to FIG. 3, the circuit configurations of detection circuits DT1 to DT4 will be described. Hereinafter, as an example, the case where each of detection circuits DT1 to DT4 has the same configuration as each other will be described. For this reason, hereinafter, the configuration of detection circuit DT1 will be taken as an example to describe the configurations of detection circuits DT1 to DT4, and the description of the configurations of detection circuits DT2 to DT4 will be omitted. FIG. 3 is a diagram showing an example of the configuration of detection circuit DT1. Note that some or all of detection circuits DT1 to DT4 may have different configurations from each other as long as the functions of gradient magnetic field sensor 12 are not impaired.

[0061] Detection circuit DT1 includes a phase detection circuit PD, a low-pass filter LF, an error amplifier EA, and a resistor R1. The phase detection circuit PD has three terminals: an input terminal PD1, an input terminal PD2, and an output terminal PD3.

[0062] In the detection circuit DT1, the input terminal DT11 is connected to the input terminal PD1 of the phase detection circuit PD via a transmission line. Also, the output terminal PD3 of the phase detection circuit PD is connected to the input terminal of the low-pass filter LF via a transmission line. Further, the output terminal of the low-pass filter LF is connected to the inverting input terminal of the error amplifier EA via a transmission line. Also, the non-inverting input terminal of the error amplifier EA is grounded via a transmission line. Moreover, the output terminal of the error amplifier EA is connected to the output terminal DT13 of the detection circuit DT1 and one of the two terminals of the resistor R1 via a transmission line respectively. Also, the other of the two terminals of the resistor R1 is connected to the input terminal DT12 of the phase detection circuit PD and one of the two terminals of the third capacitor C3 via a transmission line. Further, the other of the two terminals of the third capacitor C3 is connected to the input terminal PD2 of the phase detection circuit PD via a transmission line. Thus, the detection circuit DT1 is a PSD (Phase Sensitive Detector) circuit. Note that other circuit elements, other devices, etc. may be connected between the input terminal DT11 and the phase detection circuit PD within a range that does not impair the functions of the detection circuit DT1. Also, other circuit elements, other devices, etc. may be connected between the phase detection circuit PD and the low-pass filter LF within a range that does not impair the functions of the detection circuit DT1. Also, other circuit elements, other devices, etc. may be connected between the low-pass filter LF and the error amplifier EA within a range that does not impair the functions of the detection circuit DT1. Also, other circuit elements, other devices, etc. may be connected between the error amplifier EA and the ground within a range that does not impair the functions of the detection circuit DT1. Also, other circuit elements, other devices, etc. may be connected between the error amplifier EA and the output terminal DT13 within a range that does not impair the functions of the detection circuit DT1. Also, other circuit elements, other devices, etc. may be connected between the error amplifier EA and the resistor R1 within a range that does not impair the functions of the detection circuit DT1.Also, between the resistor R1 and the third capacitor C3, within a range that does not impair the functions of the detection circuit DT1, other circuit elements, other devices, etc. may be connected. Also, between the third capacitor C3 and the phase detection circuit PD, within a range that does not impair the functions of the detection circuit DT1, other circuit elements, other devices, etc. may be connected. Also, between the transmission line connecting the resistor R1 and the third capacitor C3 and the input terminal DT12, within a range that does not impair the functions of the detection circuit DT1, other circuit elements, other devices, etc. may be connected.

[0063] Next, referring to FIG. 4, the circuit configuration of the signal processing unit PR will be described. FIG. 4 is a diagram showing an example of the circuit configuration of the signal processing unit PR.

[0064] The signal processing unit PR includes four buffers B1 to B4, four amplifying units A1 to A4, six arithmetic units O1 to O6, a differential amplifier DA, four high-pass filters HF1 to HF4, three full-wave rectifiers FR1 to FR3, a hysteresis comparator HC, and an inverter IV.

[0065] Each of the four buffers B1 to B4 is, for example, a voltage follower or the like, but is not limited thereto.

[0066] Each of the four amplifying units A1 to A4 is, for example, an operational amplifier or the like, but is not limited thereto.

[0067] Each of the six arithmetic units O1 to O6 is, for example, an adder, but is not limited thereto.

[0068] In the signal processing unit PR, the input terminal of the buffer B1 is connected to the input terminal PR1 of the signal processing unit PR via a transmission line. Also, the output terminal of the buffer B1 is connected to the input terminal of the amplifier unit A1 via a transmission line. Also, the output terminal of the amplifier unit A1 is connected to one of the two input terminals of the arithmetic unit O1 and one of the two input terminals of the arithmetic unit O4 via a transmission line, respectively. Also, the input terminal of the buffer B2 is connected to the input terminal PR2 of the signal processing unit PR via a transmission line. Also, the output terminal of the buffer B2 is connected to the input terminal of the amplifier unit A2 via a transmission line. Also, the output terminal of the amplifier unit A2 is connected to the other of the two input terminals of the arithmetic unit O1 and one of the two input terminals of the arithmetic unit O2 via a transmission line, respectively. Also, the input terminal of the buffer B3 is connected to the input terminal PR3 of the signal processing unit PR via a transmission line. Also, the output terminal of the buffer B3 is connected to the input terminal of the amplifier unit A3 via a transmission line. Also, the output terminal of the amplifier unit A3 is connected to the other of the two input terminals of the arithmetic unit O2 and one of the two input terminals of the arithmetic unit O3 via a transmission line, respectively. Also, the output terminal of the buffer B4 is connected to the input terminal of the amplifier unit A4 via a transmission line. Also, the output terminal of the amplifier unit A4 is connected to the other of the two input terminals of the arithmetic unit O3 and the other of the two input terminals of the arithmetic unit O4 via a transmission line, respectively. Note that other circuit elements, other devices, etc. may be connected between the input terminal PR1 and the buffer B1 within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the buffer B1 and the amplifier unit A1 within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the amplifier unit A1 and the arithmetic unit O1 within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the amplifier unit A1 and the arithmetic unit O4 within a range that does not impair the functions of the signal processing unit PR.Also, between the input terminal PR2 and the buffer B2, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the buffer B2 and the amplification unit A2, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A2 and the operation unit O1, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A2 and the operation unit O2, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the input terminal PR3 and the buffer B3, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the buffer B3 and the amplification unit A3, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A3 and the operation unit O2, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A3 and the operation unit O3, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the input terminal PR4 and the buffer B4, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the buffer B4 and the amplification unit A4, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A4 and the operation unit O3, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected. Also, between the amplification unit A4 and the operation unit O4, within a range that does not impair the functions of the signal processing unit PR, other circuit elements, other devices, etc. may be connected.

[0069] Also, in the signal processing unit PR, the output terminal of the arithmetic unit O1 is connected via a transmission line to one of the two input terminals of the differential amplifier DA. Also, the output terminal of the arithmetic unit O3 is connected via a transmission line to the other of the two input terminals of the differential amplifier DA. The output terminal of the differential amplifier DA is connected via a transmission line to the input terminal of the high-pass filter HF1. Also, the output terminal of the high-pass filter HF1 is connected via a transmission line to the input terminal of the full-wave rectifier FR1. Note that other circuit elements, other devices, etc. may be connected between the arithmetic unit O1 and the differential amplifier DA within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the arithmetic unit O3 and the differential amplifier DA within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the differential amplifier DA and the high-pass filter HF1 within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the high-pass filter HF1 and the full-wave rectifier FR1 within a range that does not impair the functions of the signal processing unit PR.

[0070] Also, in the signal processing unit PR, the output terminal of the arithmetic unit O2 is connected via a transmission line to the input terminal of the high-pass filter HF2. Also, the output terminal of the high-pass filter HF2 is connected via a transmission line to the input terminal of the full-wave rectifier FR2. Note that other circuit elements, other devices, etc. may be connected between the arithmetic unit O2 and the high-pass filter HF2 within a range that does not impair the functions of the signal processing unit PR. Also, other circuit elements, other devices, etc. may be connected between the high-pass filter HF2 and the full-wave rectifier FR2 within a range that does not impair the functions of the signal processing unit PR.

[0071] Also, in the signal processing unit PR, the output terminal of the full-wave rectifier FR1 is connected via a transmission line to one of the two input terminals of the arithmetic unit O5. Also, the output terminal of the full-wave rectifier FR2 is connected via a transmission line to the other of the two input terminals of the arithmetic unit O5. Note that other circuit elements, other devices, etc. may be connected between the full-wave rectifier FR1 and the arithmetic unit O5 as long as the functions of the signal processing unit PR are not impaired. Also, other circuit elements, other devices, etc. may be connected between the full-wave rectifier FR2 and the arithmetic unit O5 as long as the functions of the signal processing unit PR are not impaired.

[0072] Also, in the signal processing unit PR, the output terminal of the arithmetic unit O4 is connected via a transmission line to the input terminal of the high-pass filter HF3. Also, the output terminal of the high-pass filter HF3 is connected via a transmission line to the input terminal of the full-wave rectifier FR3. Note that other circuit elements, other devices, etc. may be connected between the arithmetic unit O4 and the high-pass filter HF3 as long as the functions of the signal processing unit PR are not impaired. Also, other circuit elements, other devices, etc. may be connected between the high-pass filter HF3 and the full-wave rectifier FR3 as long as the functions of the signal processing unit PR are not impaired.

[0073] Also, in the signal processing unit PR, the output terminal of the arithmetic unit O5 is connected via a transmission line to one of the two input terminals of the arithmetic unit O6. Also, the output terminal of the full-wave rectifier FR3 is connected via a transmission line to the other of the two input terminals of the arithmetic unit O6. Also, the output terminal of the arithmetic unit O6 is connected via a transmission line to the input terminal of the high-pass filter HF4. Also, the output terminal of the high-pass filter HF4 is connected via a transmission line to the input terminal of the hysteresis comparator HC. The output terminal of the hysteresis comparator HC is connected via a transmission line to the input terminal of the inverter IV. Also, the output terminal of the inverter IV is connected via a transmission line to the output terminal PR5 of the signal processing unit PR. Note that between the arithmetic unit O5 and the arithmetic unit O6, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted. Also, between the full-wave rectifier FR3 and the arithmetic unit O6, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted. Also, between the arithmetic unit O6 and the high-pass filter HF4, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted. Also, between the high-pass filter HF4 and the hysteresis comparator HC, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted. Also, between the hysteresis comparator HC and the inverter IV, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted. Also, between the inverter IV and the output terminal PR5, within a range that does not impair the functions of the signal processing unit PR, a configuration in which other circuit elements, other devices, etc. are connected may be adopted.

[0074] With the above configuration, the gradient magnetic field sensor 12 can detect the presence or absence of a detection target using the first sensor head S1 and the second sensor head S2. More specifically, the gradient magnetic field sensor 12 can detect the presence or absence of a detection target according to the voltages output from each of the four detection coils CL1 of the first sensor head S1 and the voltages output from the four detection coils CL2 of the second sensor head S2.

[0075] Here, referring to FIG. 5, a more detailed configuration of the first sensor head S1 and the second sensor head S2 will be described. FIG. 5 is a diagram showing an example of a more detailed configuration of the first sensor head S1 and the second sensor head S2. Further, FIG. 5 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 including both the central axis AX1 of the first magnetic core CR1 and the central axis AX2 of the second magnetic core CR2.

[0076] As shown in FIG. 5, the gradient magnetic field sensor 12 includes a first sensor head S1, a second sensor head S2, and a main body portion MB. Here, the main body portion MB is a housing in which the first magnetic core CR1 and the second magnetic core CR2 are provided. The main body portion MB is provided with at least a part of an AC power connection terminal CT1, a 0th phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT1, a detection circuit DT2, a detection circuit DT3, a detection circuit DT4, a signal processing unit PR, and a detection signal output terminal CT2. Hereinafter, as an example, the case where the main body portion MB is provided with all of the AC power connection terminal CT1, the 0th phase shift circuit PS0, the AC current control unit CC1, the detection circuit DT1, the detection circuit DT2, the detection circuit DT3, the detection circuit DT4, the signal processing unit PR, and the detection signal output terminal CT2 will be described. However, in FIG. 5, for the sake of simplifying the drawing, the internal configuration of the main body portion MB is omitted.

[0077] The linear portion of the first magnetic core CR1 is parallel (or substantially parallel) to the linear portion of the second magnetic core CR2. In the example shown in FIG. 5, the first magnetic core CR1 has a linear shape that extends entirely along the central axis AX1. Also, in this example, the second magnetic core CR2 has a linear shape that extends entirely along the central axis AX2. That is, in this example, the first magnetic core CR1, which is entirely linear, is parallel (or substantially parallel) to the second magnetic core CR2, which is also entirely linear. Note that the linear portion of the first magnetic core CR1 may be non-parallel to the linear portion of the second magnetic core CR2.

[0078] Also, in the example shown in FIG. 5, each of the first magnetic core CR1 and the second magnetic core CR2 projects in a predetermined direction from the main body portion MB such that their linear portions are substantially parallel to each other. The predetermined direction is to the left in the plane of FIG. 5, but is not limited to this. Note that the linear portion of the first magnetic core CR1 and the linear portion of the second magnetic core CR2 may be coaxially (or substantially coaxially) positioned.

[0079] Also, in the example shown in FIG. 5, when viewed from the orthogonal direction (i.e., the direction orthogonal to each of the central axis AX1 and the central axis AX2 and along the plane including the central axis AX1 and the central axis AX2) that is orthogonal to each of the linear portion of the first magnetic core CR1 and the linear portion of the second magnetic core CR2, the linear portion of the second magnetic core CR2 entirely (or substantially entirely) overlaps with the linear portion of the first magnetic core CR1. Note that in this case, the linear portion of the first magnetic core CR1 may be configured such that a part of it overlaps with the linear portion of the second magnetic core CR2.

[0080] Also, in the example shown in FIG. 5, the n-th detection coil CL1n among the N detection coils CL1 overlaps all (or substantially all) of the n-th detection coil CL2n among the N detection coils CL2 when viewed from the orthogonal direction. Therefore, in this example, in the gradient magnetic field sensor 12, the shape (structure) of the first sensor head S1 is the same (or substantially the same) as the shape (structure) of the second sensor head S2. In other words, in the gradient magnetic field sensor 12, the first magnetic core CR1 around which the four detection coils CL1 are wound and the second magnetic core CR2 around which the four detection coils CL2 are wound are arranged in line symmetry. Thereby, the gradient magnetic field sensor 12 can suppress the occurrence of fluctuations in the sensitivity of the gradient magnetic field sensor 12 due to the difference between the shape of the first sensor head S1 and the shape of the second sensor head S2. In other words, thereby, the gradient magnetic field sensor 12 can ensure the symmetry between the sensitivity distribution of the first sensor head S1 and the sensitivity distribution of the second sensor head S2.

[0081] Here, the winding direction of the n-th detection coil CL1n among the N detection coils CL1 with respect to a predetermined direction is opposite to the winding direction of the n-th detection coil CL2n among the N detection coils CL2 with respect to the predetermined direction. And the cold-side terminal among the two terminals of the detection coil CL1n is connected to the cold-side terminal among the two terminals of the detection coil CL2n. Thereby, the detection coil CL1n is differentially connected to the detection coil CL2n as described above. As a result, the polarity of the voltage output from the detection coil CL1n is opposite to the polarity of the voltage output from the detection coil CL2n. Note that the differential connection between the detection coil CL1n and the detection coil CL2n may be realized by other methods. For example, the detection coil CL1n and the detection coil CL2n may be configured to be differentially connected via an element (such as an inverter or the like) that inverts the polarity of the voltage. In this case, the winding direction of the detection coil CL1n with respect to the predetermined direction and the winding direction of the detection coil CL2n with respect to the predetermined direction are the same, and the cold-side terminal of the detection coil CL1n is connected to the hot-side terminal of the detection coil CL2n via an element that inverts the polarity of the voltage. As a result, in this case, the polarity of the voltage output from the detection coil CL1n is the same as the polarity of the voltage output from the detection coil CL2n. Also, inverting the polarity of the voltage may be performed, for example, by the signal processing unit PR or the like in each of the detection circuits DT1 to DT4.

[0082] Also, in the example shown in FIG. 5, among the N detection coils CL1, two adjacent detection coils CL1 are insulated from each other and in contact. Also, in this example, among the N detection coils CL2, two adjacent detection coils CL2 are insulated from each other and in contact. In other words, in the gradient magnetic field sensor 12, among the N detection coils CL1, two adjacent detection coils CL1 are wound around the first magnetic core CR1 so that there is no gap between them. Also, in the gradient magnetic field sensor 12, among the N detection coils CL2, two adjacent detection coils CL2 are wound around the second magnetic core CR2 so that there is no gap between them. As a result, the gradient magnetic field sensor 12 can efficiently take in the magnetic flux generated from the detection object into the first magnetic core CR1 and the second magnetic core CR2, and as a result, the detection accuracy of the detection object can be improved. Also, as a result, the gradient magnetic field sensor 12 can make the period of the sensitivity distribution with respect to the magnetic moment of each of the four detection coils CL1 in the first sensor head S1 coincide with the period of the arrangement intervals of these four detection coils CL1. Also, the gradient magnetic field sensor 12 can make the period of the sensitivity distribution with respect to the magnetic moment of each of the four detection coils CL2 in the second sensor head S2 coincide with the period of the arrangement intervals of these four detection coils CL2. As a result, the gradient magnetic field sensor 12 can accurately remove the influence of noise.

[0083] <Operation of the gradient magnetic field sensor according to the embodiment> Next, the operation of the gradient magnetic field sensor 12 will be described.

[0084] In the gradient magnetic field sensor 12 having the circuit configuration as described above, an alternating current power supply P1 inputs an alternating current to an alternating current power supply connection terminal CT1. The alternating current input to the alternating current power supply connection terminal CT1 is branched into two. One of the two branched alternating currents is input to a 0th phase shift circuit PS0 as an alternating excitation current. The other of the two branched alternating currents is input as a reference signal to each of an input terminal DT11 of a detection circuit DT1, an input terminal DT21 of a detection circuit DT2, an input terminal DT31 of a detection circuit DT3, and an input terminal DT41 of a detection circuit DT4.

[0085] The alternating excitation current input to the 0th phase shift circuit PS0 is branched into two alternating excitation currents, a 1st alternating excitation current AC1 and a 2nd alternating excitation current AC2, after being phase-shifted by the 0th phase shift circuit PS0.

[0086] The 1st alternating excitation current AC1 flows through a 1st magnetic core CR1 via a 1st phase shift circuit PS1, a 1st variable resistor VR11, and a 1st capacitor C1. For this reason, the 1st alternating excitation current AC1 is phase-shifted by the 1st phase shift circuit PS1 and the amplitude is adjusted by the 1st variable resistor VR11. As a result, a voltage corresponding to the 1st alternating excitation current AC1 that has flowed through the 1st magnetic core CR1 and the strength of the magnetic field applied to the nth detection coil CL1n among the four detection coils CL1 is induced in the nth detection coil CL1n. That is, a voltage is output from the detection coil CL1n. And the voltage changes according to the strength of the magnetic field applied to the detection coil CL1n from the outside. Hereinafter, for convenience of explanation, the voltage induced in the detection coil CL1n will be described as the 1st induced voltage. Note that the 1st capacitor C1 is a capacitor for AC (Alternating Current) coupling. Due to the presence of the 1st capacitor C1, in the gradient magnetic field sensor 12, it is possible to suppress a direct current from flowing from the output terminal CC13 to the input terminal CC11.

[0087] The second alternating excitation current AC2 flows through the second magnetic core CR2 via the second phase-shifting circuit PS2, the second variable resistor VR12, and the second capacitor C2. Therefore, the second alternating excitation current AC2 is phase-shifted by the second phase-shifting circuit PS2 and its amplitude is adjusted by the second variable resistor VR12. As a result, a voltage corresponding to the second alternating excitation current AC2 flowing through the second magnetic core CR2 and the strength of the magnetic field applied to the n-th detection coil CL2n among the four detection coils CL2 is induced in the n-th detection coil CL2n. That is, a voltage is output from the detection coil CL2n. Then, the voltage changes according to the strength of the magnetic field applied to the detection coil CL2n from the outside. Hereinafter, for convenience of explanation, the voltage induced in the detection coil CL2n will be described as the second induced voltage. Note that the second capacitor C2 is a capacitor for AC coupling. The presence of the second capacitor C2 can suppress the direct current from flowing from the output terminal CC14 to the input terminal CC12 in the gradient magnetic field sensor 12.

[0088] In the gradient magnetic field sensor 12, signals corresponding to the first induced voltage induced in the detection coil CL11 and the second induced voltage induced in the detection coil CL21 are input to the input terminal DT12 of the detection circuit DT1 as the differential signal Vout1. Also, in the gradient magnetic field sensor 12, signals corresponding to the first induced voltage induced in the detection coil CL12 and the second induced voltage induced in the detection coil CL22 are input to the input terminal DT22 of the detection circuit DT2 as the differential signal Vout2. Also, in the gradient magnetic field sensor 12, signals corresponding to the first induced voltage induced in the detection coil CL13 and the second induced voltage induced in the detection coil CL23 are input to the input terminal DT32 of the detection circuit DT3 as the differential signal Vout3. Also, in the gradient magnetic field sensor 12, signals corresponding to the first induced voltage induced in the detection coil CL14 and the second induced voltage induced in the detection coil CL24 are input to the input terminal DT42 of the detection circuit DT4 as the differential signal Vout4.

[0089] Here, each of the detection circuits DT1 to DT4 performs the same operation, differing only in the differential signals input thereto. Therefore, hereinafter, the operation of the detection circuit DT1 will be taken as an example to explain the operations of the detection circuits DT1 to DT4 respectively. In the present embodiment, the descriptions of the operations of the detection circuits DT2 to DT4 are omitted.

[0090] The phase detection circuit PD of the detection circuit DT1 inputs a signal corresponding to the deviation between the input differential signal Vout1 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 obtained by removing components having a frequency equal to or higher than a predetermined first frequency 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 the resistor R1 respectively. Note that the third capacitor C3 is a capacitor for AC coupling. Also, a buffer circuit (for example, a voltage follower or the like) is connected to the terminal of the third capacitor C3 opposite to the terminal connected to the phase detection circuit PD. For the sake of simplifying the drawing, the illustration of this buffer circuit is omitted.

[0091] Due to the presence of a buffer circuit (not shown), the detection signal input to the resistor R1 flows as a feedback current from the input terminal DT12 toward the detection coil CL11 without being input to the third capacitor C3.

[0092] By adjusting the detection circuit DT1 that performs such an operation, when the signal level of the differential signal Vout1 is 0 [V], a detection signal with a signal level of 0 [V] can be output from the detection signal output terminal CT2, and when the signal level of the differential signal Vout1 is not 0 [V], a detection signal with a signal level not equal to 0 [V] can be output from the detection signal output terminal CT2. Note that since the adjustment of the detection circuit DT1 is known, further detailed description thereof is omitted.

[0093] In this way, each of the detection circuits DT1 to DT4 outputs a detection signal from the output terminal. That is, the detection circuit DT1 outputs a detection signal corresponding to the differential signal Vout1 to the signal processing unit PR. Also, the detection circuit DT2 outputs a detection signal corresponding to the differential signal Vout2 to the signal processing unit PR. The detection circuit DT3 outputs a detection signal corresponding to the differential signal Vout3 to the signal processing unit PR. Also, the detection circuit DT4 outputs a detection signal corresponding to the differential signal Vout4 to the signal processing unit PR. Here, at this time, each of the detection circuits DT1 to DT4 synchronizes the output timing of the detection signal. The method of synchronizing the output timing may be a known method or a method to be developed in the future.

[0094] The signal processing unit PR performs various signal processes on the detection signals input from each of the detection circuits DT1 to DT4. Some or all of the functions of the signal processing unit PR may be realized by hardware or by software. However, when some or all of the functions of the signal processing unit PR are realized by software, each detection signal input to the signal processing unit PR is converted into digital data by an A (Analog) / D (Digital) converter. Hereinafter, as an example, the case where all of the signal processing unit PR is realized by hardware will be described.

[0095] Specifically, in the signal processing unit PR, for example, the detection signal input from the detection circuit DT1 is temporarily stored by the buffer B1. In the example shown in FIG. 4, the detection signal is indicated by a symbol with 1 in the circle. Hereinafter, for convenience of explanation, the symbol is indicated by ○1. After the detection signal is stored in the buffer B1, the amplification unit A1 reads out the detection signal stored in the buffer B1 and amplifies the read detection signal based on a predetermined gain. The detection signal amplified by the amplification unit A1 is input to each of the arithmetic unit O1 and the arithmetic unit O4. Note that the signal processing unit PR may not include the buffer B1. In this case, in the signal processing unit PR, the detection signal input from the detection circuit DT1 is input to the amplification unit A1.

[0096] Also, in the signal processing unit PR, for example, the detection signal input from the detection circuit DT2 is temporarily stored by the buffer B2. In the example shown in FIG. 4, the detection signal is indicated by a symbol with 2 in the circle. Hereinafter, for convenience of explanation, the symbol is indicated by ○2. After the detection signal is stored in the buffer B2, the amplification unit A2 reads out the detection signal stored in the buffer B2 and amplifies the read detection signal based on a predetermined gain. The detection signal amplified by the amplification unit A2 is input to each of the arithmetic unit O1 and the arithmetic unit O2. Note that the signal processing unit PR may not include the buffer B2. In this case, in the signal processing unit PR, the detection signal input from the detection circuit DT2 is input to the amplification unit A2.

[0097] Also, in the signal processing unit PR, for example, the detection signal input from the detection circuit DT3 is temporarily stored by the buffer B3. In the example shown in FIG. 4, the detection signal is indicated by a symbol with 3 in the circle. Hereinafter, for convenience of explanation, the symbol is indicated by ○3. After the detection signal is stored in the buffer B3, the amplification unit A3 reads out the detection signal stored in the buffer B3 and amplifies the read detection signal based on a predetermined gain. The detection signal amplified by the amplification unit A3 is input to each of the arithmetic units O2 and O3. Note that the signal processing unit PR may be configured not to include the buffer B3. In this case, in the signal processing unit PR, the detection signal input from the detection circuit DT3 is input to the amplification unit A3.

[0098] Also, in the signal processing unit PR, for example, the detection signal input from the detection circuit DT4 is temporarily stored by the buffer B4. In the example shown in FIG. 4, the detection signal is indicated by a symbol with 4 in the circle. Hereinafter, for convenience of explanation, the symbol is indicated by ○4. After the detection signal is stored in the buffer B4, the amplification unit A4 reads out the detection signal stored in the buffer B4 and amplifies the read detection signal based on a predetermined gain. The detection signal amplified by the amplification unit A4 is input to each of the arithmetic units O3 and O4. Note that the signal processing unit PR may be configured not to include the buffer B4. In this case, in the signal processing unit PR, the detection signal input from the detection circuit DT4 is input to the amplification unit A4.

[0099] Also, in the signal processing unit PR, the arithmetic unit O1 adds, for example, the detection signal amplified by the amplification unit A1 and the detection signal amplified by the amplification unit A2. The arithmetic unit O1 inputs the detection signal after addition to the differential amplifier DA. In the example shown in FIG. 4, the detection signal is indicated by "○1 + ○2".

[0100] Also, in the signal processing unit PR, the arithmetic unit O2 adds, for example, the detection signal amplified by the amplifier A2 and the detection signal amplified by the amplifier A3. The arithmetic unit O2 inputs the detection signal after addition to the high-pass filter HF2. In the example shown in FIG. 4, the detection signal is indicated by "○2 + ○3".

[0101] Also, in the signal processing unit PR, the arithmetic unit O3 adds, for example, the detection signal amplified by the amplifier A3 and the detection signal amplified by the amplifier A4. The arithmetic unit O3 inputs the detection signal after addition to the differential amplifier DA. In the example shown in FIG. 4, the detection signal is indicated by "○3 + ○4".

[0102] Also, in the signal processing unit PR, the arithmetic unit O4 adds, for example, the detection signal amplified by the amplifier A1 and the detection signal amplified by the amplifier A4. The arithmetic unit O4 inputs the detection signal after addition to the high-pass filter HF3. In the example shown in FIG. 4, the detection signal is indicated by "○1 + ○4".

[0103] Also, in the signal processing unit PR, the differential amplifier DA generates, for example, a differential signal between the detection signal input from the arithmetic unit O1 and the detection signal input from the arithmetic unit O3 as a new detection signal, and inputs the generated detection signal to the high-pass filter HF1. Thereby, the high-pass filter HF1 removes the DC component from the detection signal. That is, the high-pass filter HF1 inputs a signal obtained by removing components having a frequency of a predetermined first frequency or less from the detection signal to the full-wave rectifier FR1 as a new detection signal.

[0104] Also, in the signal processing unit PR, the full-wave rectifier FR1 full-wave rectifies the detection signal input from the high-pass filter HF1, and inputs the signal after full-wave rectification to the arithmetic unit O5 as a new detection signal.

[0105] Also, in the signal processing unit PR, the high-pass filter HF2 removes the DC component from the detection signal input from the arithmetic unit O2. That is, the high-pass filter HF2 inputs a signal obtained by removing components with a frequency of the first frequency or lower from the detection signal to the full-wave rectifier FR2 as a new detection signal.

[0106] Also, in the signal processing unit PR, the full-wave rectifier FR2 full-wave rectifies the detection signal input from the high-pass filter HF2, and inputs the signal after full-wave rectification to the arithmetic unit O5 as a new detection signal.

[0107] Also, in the signal processing unit PR, the arithmetic unit O5 adds the detection signal input from the full-wave rectifier FR1 and the detection signal input from the full-wave rectifier FR2. The arithmetic unit O5 inputs the detection signal after addition to the arithmetic unit O6.

[0108] Also, in the signal processing unit PR, the high-pass filter HF3 removes the DC component from the detection signal input from the arithmetic unit O4. That is, the high-pass filter HF3 inputs a signal obtained by removing components with a frequency of the first frequency or lower from the detection signal to the full-wave rectifier FR3 as a new detection signal.

[0109] Also, in the signal processing unit PR, the full-wave rectifier FR3 full-wave rectifies the detection signal input from the high-pass filter HF3, and inputs the signal after full-wave rectification to the arithmetic unit O6 as a new detection signal.

[0110] Also, in the signal processing unit PR, the arithmetic unit O6 adds the detection signal input from the arithmetic unit O5 and the detection signal input from the full-wave rectifier FR3. The arithmetic unit O6 inputs the detection signal after addition to the high-pass filter HF4.

[0111] Also, in the signal processing unit PR, the high-pass filter HF4 removes the DC component from the detection signal input from the arithmetic unit O6. That is, the high-pass filter HF4 inputs a signal obtained by removing components with a frequency of the first frequency or lower from the detection signal to the hysteresis comparator HC as a new detection signal.

[0112] Further, the hysteresis comparator HC has two thresholds, i.e., a first threshold and a second threshold lower than the first threshold. In the signal processing unit PR, when the signal level of the detection signal input from the high-pass filter HF4 is greater than the first threshold or less than the second threshold, the hysteresis comparator HC determines that it is a signal and inputs an L-level signal to the inverter IV. On the other hand, when the signal level of the detection signal input from the high-pass filter HF4 is within the range between the first threshold and the second threshold, the hysteresis comparator HC determines that it is noise and inputs an H-level signal to the inverter IV. Thereby, the gradient magnetic field sensor 12 can determine whether the detection signal is noise, and as a result, can accurately detect the object to be detected.

[0113] Also, in the signal processing unit PR, when an H-level signal is input from the hysteresis comparator HC, the inverter IV outputs an L-level signal from the output terminal PR5 as a non-detection signal. On the other hand, when an L-level signal is input from the hysteresis comparator HC, the inverter IV outputs an H-level signal from the output terminal PR5 as a detection signal. Therefore, when the gradient magnetic field sensor 12 detects an object to be detected, it outputs an H-level signal as a detection signal. Note that since it is considered that it is easier to handle on the information processing device 20 side when the inverter IV outputs an H-level signal as a detection signal to the information processing device 20, it is provided in the gradient magnetic field sensor 12. For this reason, the gradient magnetic field sensor 12 may have a configuration without the inverter IV. In this case, the gradient magnetic field sensor 12 outputs an L-level signal as a detection signal.

[0114] Note that in the signal processing unit PR, the hysteresis comparator HC may be configured to determine that the detection signal input from the high-pass filter HF4 is a signal when the signal level of the detection signal exceeds the first threshold and is large, or when it is less than the second threshold and is small, and output an H-level signal as a detection signal from the output terminal PR5. In this case, when the signal level of the detection signal input from the high-pass filter HF4 is within the range between the first threshold and the second threshold, the hysteresis comparator HC determines that it is noise and outputs an L-level signal as a non-detection signal from the output terminal PR5. And in this case, the signal processing unit PR does not include the inverter IV.

[0115] Also, in the signal processing unit PR, the hysteresis comparator HC may be configured to determine that the detection signal input from the high-pass filter HF4 is a signal when the signal level of the detection signal exceeds the first threshold and is large, or when it is less than the second threshold and is small, and input an H-level signal to the inverter IV. In this case, when the signal level of the detection signal input from the high-pass filter HF4 is within the range between the first threshold and the second threshold, the hysteresis comparator HC determines that it is noise and inputs an L-level signal to the inverter IV. And in this case, when an L-level signal is input from the hysteresis comparator HC, the inverter IV outputs an H-level signal as a non-detection signal from the output terminal PR5, and when an H-level signal is input from the hysteresis comparator HC, the inverter IV outputs an L-level signal as a detection signal from the output terminal PR5.

[0116] Also, in the signal processing unit PR, the hysteresis comparator HC may be configured to determine that the signal is a signal when the signal level of the detection signal input from the high-pass filter HF4 is greater than the first threshold or less than the second threshold, and output an L-level signal as the detection signal from the output terminal PR5. In this case, the hysteresis comparator HC determines that the signal is noise when the signal level of the detection signal input from the high-pass filter HF4 is within the range between the first threshold and the second threshold, and outputs an H-level signal as the non-detection signal from the output terminal PR5. And in this case, the signal processing unit PR does not include the inverter IV.

[0117] Here, the relationship between the voltage of the differential signal output from the detection coil CL1n differentially connected to the detection coil CL2n and the dead zone of the gradient magnetic field sensor 12 will be described. FIG. 6 is a diagram showing an example of a graph in which the voltage of the differential signal output from the detection coil CL1n differentially connected to the detection coil CL2n is plotted while changing the relative position of the object to be detected with respect to the gradient magnetic field sensor 12. The horizontal axis of the graph shown in FIG. 6 has the boundary between the detection coil CL12 and the detection coil CL13 when viewed from the first sensor head S1 and the second sensor head S2 in the orthogonal direction as the origin of the horizontal axis, and indicates the distances in the positive and negative directions from the origin of the horizontal axis. The vertical axis of the graph indicates the voltages of the differential signals output from the detection coil CL11 differentially connected to the detection coil CL21, the detection coil CL12 differentially connected to the detection coil CL22, the detection coil CL13 differentially connected to the detection coil CL23, and the detection coil CL14 differentially connected to the detection coil CL24, respectively. However, the polarities of these differential signal voltages are defined by Peak to Peak. Specifically, in this example, the polarities of these differential signal voltages when the polarity of the induced voltage of the detection coil CL1n is positive are defined as positive. The curve F1 in the graph is a curve obtained by sequentially connecting the points at which the voltage of the differential signal output from the detection coil CL11 differentially connected to the detection coil CL21 is plotted when the object to be detected is moved from the tip side to the base end side of the first sensor head S1 and the second sensor head S2 while keeping the distances between the first sensor head S1 and the second sensor head S2 and the object to be detected constant. The curve F2 in the graph is a curve obtained by sequentially connecting the points at which the voltage of the differential signal output from the detection coil CL12 differentially connected to the detection coil CL22 is plotted in this case. The curve F3 in the graph is a curve obtained by sequentially connecting the points at which the voltage of the differential signal output from the detection coil CL13 differentially connected to the detection coil CL23 is plotted in this case. The curve F4 in the graph is a curve obtained by sequentially connecting the points at which the voltage of the differential signal output from the detection coil CL14 differentially connected to the detection coil CL24 is plotted in this case.

[0118] As shown in FIG. 6, in the gradient magnetic field sensor 12, there is no dead zone that conventionally existed at the origin position of the horizontal axis. For example, at a position of -25 [mm] from the origin of the horizontal axis, as shown by the curve F1, the voltage of the differential signal output from the detection coil CL11 differentially connected to the detection coil CL21 is 0 [mVpp]. However, at this position, the voltages of the differential signals output from the detection coil CL12 differentially connected to the detection coil CL22, the detection coil CL13 differentially connected to the detection coil CL23, and the detection coil CL14 differentially connected to the detection coil CL24 are not 0 [mVpp]. That is, this indicates that in the gradient magnetic field sensor 12, this position is not a dead zone. Also, for example, at a position of -10 [mm] from the origin of the horizontal axis, as shown by the curve F2, the voltage of the differential signal output from the detection coil CL12 differentially connected to the detection coil CL22 is 0 [mVpp]. However, at this position, the voltages of the differential signals output from the detection coil CL11 differentially connected to the detection coil CL21, the detection coil CL13 differentially connected to the detection coil CL23, and the detection coil CL14 differentially connected to the detection coil CL24 are not 0 [mVpp]. That is, this indicates that in the gradient magnetic field sensor 12, this position is also not a dead zone. Also, for example, at a position of +5 [mm] from the origin of the horizontal axis, as shown by the curve F3, the voltage of the differential signal output from the detection coil CL13 differentially connected to the detection coil CL23 is 0 [mVpp]. However, at this position, the voltages of the differential signals output from the detection coil CL11 differentially connected to the detection coil CL21, the detection coil CL12 differentially connected to the detection coil CL22, and the detection coil CL14 differentially connected to the detection coil CL24 are not 0 [mVpp]. That is, this indicates that in the gradient magnetic field sensor 12, this position is also not a dead zone. Also, for example, at a position of +20 [mm] from the origin of the horizontal axis, as shown by the curve F4, the voltage of the differential signal output from the detection coil CL14 differentially connected to the detection coil CL24 is 0 [mVpp].However, at this position, the voltages of the differential signals output from the detection coils CL11 differentially connected to the detection coil CL21, the detection coils CL12 differentially connected to the detection coil CL22, and the detection coils CL13 differentially connected to the detection coil CL23 are not 0 [mVpp]. That is, this indicates that this position is not a dead zone in the gradient magnetic field sensor 12.

[0119] Thus, in the gradient magnetic field sensor 12, even if the voltage of one of the four differential signals may become 0 [mVpp], the remaining three voltages of the four differential signals do not become 0 [mVpp]. For this reason, there is no dead zone in the gradient magnetic field sensor 12. Also, in the gradient magnetic field sensor 12, since the shape of the first sensor head S1 is the same as the shape of the second sensor head S2, the sensitivity distribution of the first sensor head S1 coincides with the sensitivity distribution of the second sensor head S2. These are not peculiar to the case where N is 4 as in this example, but the same applies when N is 2, 3, etc., and the same also applies when N is 5 or more.

[0120] Further, FIG. 7 is a diagram showing an example of a graph in which the voltage of the detection signal output from the arithmetic unit O6 is plotted while changing the relative position of the object to be detected with respect to the gradient magnetic field sensor 12. The horizontal axis of the graph shown in FIG. 7 has the boundary between the detection coil CL12 and the detection coil CL13 when viewing the first sensor head S1 and the second sensor head S2 from the orthogonal direction as the origin of the horizontal axis, and shows the distances in the positive and negative directions from the origin of the horizontal axis. The vertical axis of the graph shows the voltage of the detection signal output from the arithmetic unit O6. The curve F5 in the graph is a curve obtained by sequentially connecting the points plotted with the voltage of the detection signal output from the arithmetic unit O6 when the object to be detected is moved from the tip side to the base end side of the first sensor head S1 and the second sensor head S2 while keeping the distance between each of the first sensor head S1 and the second sensor head S2 and the object to be detected constant. In other words, the curve F5 shows the sensitivity distribution of the gradient magnetic field sensor 12. On the other hand, the curve F6 plotted in the graph shows the sensitivity distribution of a conventional gradient magnetic field sensor.

[0121] As shown in FIG. 7, the voltage indicated by curve F6 is equal to or greater than half of the maximum value of the voltage indicated by curve F6 over the range from the tips of the first sensor head S1 and the second sensor head S2 to the base ends of the first sensor head S1 and the second sensor head S2 (that is, in the range of -30 [mm] to +30 [mm]). This means that, unlike the sensitivity distribution of the conventional gradient magnetic field sensor indicated by curve F6, there is no dead zone in the sensitivity distribution of the gradient magnetic field sensor 12. Also, the sensitivity distribution indicated by curve F6 shows that there is no dead zone corresponding to the passing position of the detection object with respect to the gradient magnetic field sensor 12. In other words, in this sensitivity distribution, the drop in sensitivity according to the passing position of the detection object with respect to the gradient magnetic field sensor 12 is suppressed, and the difference in sensitivity due to the difference in the passing position of the detection object with respect to the gradient magnetic field sensor 12 is smaller compared to the sensitivity distribution of the conventional gradient magnetic field sensor (it is approaching a uniform sensitivity distribution compared to the sensitivity distribution of the conventional gradient magnetic field sensor). That is, the gradient magnetic field sensor 12 can suppress fluctuations in sensitivity according to the passing position of the detection object while suppressing the occurrence of a dead zone. Also, because the gradient magnetic field sensor 12 has such characteristics, a plurality of gradient magnetic field sensors 12 can also be arrayed by arranging the sensor heads so as not to overlap in the orthogonal direction.

[0122] In this example, the signal processing unit PR of the gradient magnetic field sensor 12 generates four signals, namely ○1 + ○2, ○2 + ○3, ○3 + ○4, and ○1 + ○4, based on the detection signal ○1 output from the detection circuit DT1, the detection signal ○2 output from the detection circuit DT2, the detection signal ○3 output from the detection circuit DT3, and the detection signal ○4 output from the detection circuit DT4. Subsequently, signal processing is performed to add three signals, namely |(○1 + ○2) - (○3 + ○4)|, |○2 + ○3|, and |○1 + ○4|. This signal processing is obtained through a triad error. Compared with other signal processing, in addition to improving the sensitivity of the gradient magnetic field sensor 12, the variation in sensitivity according to the passing position of the detection object with respect to the gradient magnetic field sensor 12 is also small. However, the signal processing unit PR may be configured to perform other signal processing. This other signal processing may include subtraction of some or all of the signals indicated by ○1, ○2, ○3, and ○4 respectively. In this case, the signal processing unit PR includes a subtractor. For example, in this case, some or all of the arithmetic units O1 to O6 included in the signal processing unit PR may be subtractors.

[0123] Here, by the gradient magnetic field sensor 12 including adders or subtractors such as the arithmetic units O1 to O6, the gradient magnetic field sensor 12 can virtually reduce the value of N. That is, in this case, the gradient magnetic field sensor 12 can virtually reduce the number of each of the detection coils CL1 and CL2. As a result, the gradient magnetic field sensor 12 can detect the detection object with a sensitivity distribution in the shape desired by the user.

[0124] Also, by the gradient magnetic field sensor 12 including the amplifying units A1 to A4, the gradient magnetic field sensor 12 can perform balance adjustment of the detection signals output from each of the detection circuits DT1 to DT4.

[0125] Also, by the gradient magnetic field sensor 12 including the full-wave rectifiers FR1 to FR3, the gradient magnetic field sensor 12 can suppress the cancellation of detection signals due to differences in polarity.

[0126] <Modification Example 1 of the Embodiment> The following describes Modification Example 1 of the embodiment. In Modification Example 1 of the embodiment, the same reference numerals are given to the same components as in the embodiment, and the description thereof is omitted. In Modification Example 1 of the embodiment, the gradient magnetic field sensor 12 includes a differential amplifier DF instead of the signal processing unit PR. Further, in this modification example 1, as an example, the case where N = 2 is described. That is, in this modification example 1, the gradient magnetic field sensor 12 does not include the detection coils CL13 and CL14 among the detection coils CL11 to CL14, does not include the detection coils CL23 and CL24 among the detection coils CL21 to CL24, and does not include the detection circuits DT3 and DT4 among the detection circuits DT1 to DT4. FIG. 8 is a diagram showing an example of the configuration of the gradient magnetic field sensor 12 according to Modification Example 1 of the embodiment. Hereinafter, for convenience of explanation, the gradient magnetic field sensor 12 according to this modification example 1 is described as the gradient magnetic field sensor 12A.

[0127] As shown in FIG. 8, in Modification Example 1 of the embodiment, the output terminal DT13 of the detection circuit DT1 is connected to the input terminal DF1 of the differential amplifier DF via a transmission line. Further, the output terminal DT23 of the detection circuit DT2 is connected to the input terminal DF2 of the differential amplifier DF via a transmission line. And the output terminal DF3 of the differential amplifier DF is connected to the detection signal output terminal CT2 via a transmission line. Note that other circuit elements, other devices, etc. may be connected between the detection circuit DT1 and the differential amplifier DF as long as the functions of the gradient magnetic field sensor 12A are not impaired. Also, other circuit elements, other devices, etc. may be connected between the detection circuit DT2 and the differential amplifier DF as long as the functions of the gradient magnetic field sensor 12A are not impaired.

[0128] In the gradient magnetic field sensor 12A having such a configuration, the detection circuit DT1 inputs a detection signal corresponding to the input differential signal Vout1 to the differential amplifier DF.

[0129] Also, in the gradient magnetic field sensor 12A, the detection circuit DT2 inputs a detection signal corresponding to the input differential signal Vout2 to the differential amplifier DF.

[0130] The differential amplifier DF outputs, as a new detection signal, the differential signal between the detection signal input from the detection circuit DT1 and the detection signal input from the detection circuit DT2 to the detection signal output terminal CT2.

[0131] By such an operation, the gradient magnetic field sensor 12A can suppress fluctuations in sensitivity according to the passing position of the detection object while suppressing the occurrence of a dead zone, similar to the gradient magnetic field sensor 12 according to the embodiment. Also, the gradient magnetic field sensor 12A can suppress detecting a uniform gradient magnetic field generated by a gradient magnetic field coil or the like, similar to the gradient magnetic field sensor 12 according to the embodiment.

[0132] FIG. 9 is a diagram showing an example of detection signals output from a detection circuit DT1, a detection circuit DT2, and a differential amplifier DF when a predetermined magnetic moment moving in an orthogonal direction is detected by a gradient magnetic field sensor 12 arranged in a region where a uniform gradient magnetic field is applied. However, FIG. 9 shows detection signals obtained by simulation. The horizontal axis of the graph shown in FIG. 9 indicates the elapsed time. However, the origin of the horizontal axis of the graph indicates the timing when the magnetic moment passed through a position equidistant from both the first sensor head S1 and the second sensor head S2. The vertical axis of the graph indicates the voltage of the detection signals output from the detection circuit DT1, the detection circuit DT2, and the differential amplifier DF, respectively. Also, the curve F7 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT1. Also, the curve F8 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT2. Also, the curve F9 plotted on the graph indicates the change in the detection signal output from the differential amplifier DF. As shown in FIG. 9, outside the vicinity of the origin of the horizontal axis of the graph, the curves F7 and F8 almost overlap. And outside the vicinity of the origin of the horizontal axis of the graph, the curves F7 and F8 are sinusoidal curves. This is because each of the detection coils CL11, CL12, CL21, and CL22 detects a uniform gradient magnetic field. On the other hand, around the origin of the horizontal axis of the graph, the curves F7 and F8 form peaks in response to the detection of the magnetic moment. Here, the differential amplifier DF outputs a differential signal between the detection signal indicated by the curve F7 and the detection signal indicated by the curve F8. For this reason, the curve F9 is the difference between the curve F7 and the curve F8. As a result, in the curve F9, the voltage is 0 [V] outside the vicinity of the origin of the horizontal axis of the graph. This indicates that the gradient magnetic field sensor 12A does not detect a uniform gradient magnetic field and only detects the magnetic moment.

[0133] FIG. 10 is a diagram showing another example of detection signals output from a detection circuit DT1, a detection circuit DT2, and a differential amplifier DF when a gradient magnetic field sensor 12 is disposed in a region where a uniform gradient magnetic field is applied. However, in the example shown in FIG. 10, a sine-wave signal estimated to be generated in the uniform gradient magnetic field is output as a test detection signal from the detection circuit DT1 and the detection circuit DT2. The horizontal axis of the graph shown in FIG. 10 indicates the elapsed time. The vertical axis of the graph indicates the voltage of the detection signals output from the detection circuit DT1, the detection circuit DT2, and the differential amplifier DF, respectively. Also, a curve F10 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT1. A curve F11 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT2. A curve F12 plotted on the graph indicates the change in the detection signal output from the differential amplifier DF. Also in this case, as shown in the graph, a curve F12, which is a curve indicating the change in the detection signal output from the differential amplifier DF, is the difference between the curve F10 and the curve F11. As a result, in the curve F12, the voltage is 0 [V] in the entire visible range in FIG. 10.

[0134] FIG. 11 is a diagram showing still another example of detection signals output from the detection circuit DT1, the detection circuit DT2, and the differential amplifier DF when the gradient magnetic field sensor 12 is disposed in a region where a uniform gradient magnetic field is applied. However, in the example shown in FIG. 11, the detection signals output from the detection circuit DT1, the detection circuit DT2, and the differential amplifier DF when a uniform gradient magnetic field is actually detected by the first sensor head S1 and the second sensor head S2 are shown. The horizontal axis of the graph shown in FIG. 11 indicates the elapsed time. Also, the vertical axis of the graph indicates the voltage of the detection signals output from the detection circuit DT1, the detection circuit DT2, and the differential amplifier DF, respectively. Also, the curve F13 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT1. Also, the curve F14 plotted on the graph indicates the change in the voltage of the detection signal output from the detection circuit DT2. Also, the curve F15 plotted on the graph indicates the change in the detection signal output from the differential amplifier DF. Also in this case, as shown in the graph, the curve F15, which is a curve indicating the change in the detection signal output from the differential amplifier DF, is the difference between the curve F13 and the curve F14. As a result, in the curve F15, the voltage is 0 [V] over the entire range visible in FIG. 11. This indicates that the actual gradient magnetic field sensor 12A does not detect a uniform gradient magnetic field either.

[0135] As described above, the gradient magnetic field sensor 12A can be suppressed from detecting a uniform gradient magnetic field such as that generated by a gradient magnetic field coil or the like.

[0136] Here, the principle by which the detection of a uniform gradient magnetic field is suppressed in the gradient magnetic field sensor 12A will be described. Note that this principle is the same as the principle by which the detection of a uniform gradient magnetic field is suppressed in the gradient magnetic field sensor 12 according to the embodiment.

[0137] <Principle by which detection of a uniform gradient magnetic field is suppressed in the gradient magnetic field sensor 12> Hereinafter, as an example, consider a case where a uniform magnetic field and a uniform gradient magnetic field are applied to the gradient magnetic field sensor 12A, and a predetermined magnetic moment is conveyed within the detection region of the gradient magnetic field sensor 12A. Also, hereinafter, for convenience of explanation, the strength of the magnetic field applied from the magnetic moment to the first sensor head S1 at time t is denoted as B1(t), the strength of the magnetic field applied from the magnetic moment to the second sensor head S2 at time t is denoted as B2(t), the strength of the uniform magnetic field applied to the first sensor head S1 and the second sensor head S2 at time t is denoted as B u (t), the strength of the uniform gradient magnetic field applied to the first sensor head S1 at time t is denoted as B g1 (t), and the strength of the uniform gradient magnetic field applied to the second sensor head S2 at time t is denoted as B g2 (t).

[0138] In this case, the first induced voltage V 11 (t) induced in the detection coil CL11 at time t, and the first induced voltage V 12 (t) induced in the detection coil CL12 at time t are represented by the following equation (1). The second induced voltage V 21 (t) induced in the detection coil CL21 at time t, and the second induced voltage V 22 (t) induced in the detection coil CL22 at time t are represented by the following equation (2).

[0139]

Equation

Equation

[0140] Here, κ in the above equations (1) and (2) represents a proportionality constant that converts the strength of the magnetic field into voltage. Also, N in the above equations (1) and (2) crepresents the number of turns of each of the detection coils CL11, CL12, CL21, and CL22. Also, S in the above equations (1) and (2) represents the cross-sectional area of the coil surface of each of the detection coils CL11, CL12, CL21, and CL22. The coil surface of a certain coil is a virtual plane having a thickness including the conductor wound as the coil and the opening of the coil. And the cross-sectional area of the coil surface is the area of the upper or lower surface of the plane.

[0141] When the detection sensitivity of the magnetic moment by the detection coil CL11 according to the passing position x of the object to be detected is α 11 and the detection sensitivity of the magnetic moment by the detection coil CL12 according to the passing position x of the object to be detected is α 12 and the detection sensitivity of the magnetic moment by the detection coil CL21 according to the passing position x of the object to be detected is α 21 and the detection sensitivity of the magnetic moment by the detection coil CL22 according to the passing position x of the object to be detected is α 22 are represented by, when the detection sensitivities of the detection coils CL11, CL12, CL21, and CL22 are equal, the following equation (3) holds. Note that α 11 α 12 α 21 α 22 each is a function of the passing position x of the object to be detected.

[0142]

Equation

[0143] In this case, the differential signal V1(t) between the first induced voltage induced in the detection coil CL11 at time t and the second induced voltage induced in the detection coil CL21 at time t is expressed as the following equation (4). Also, in this case, the differential signal V2(t) between the first induced voltage induced in the detection coil CL12 at time t and the second induced voltage induced in the detection coil CL22 at time t is expressed as the following equation (5).

[0144] [Number] [Number]

[0145] As shown in Equation (4), the differential signal V1(t) at time t is the difference between the first induced voltage V 11 (t) induced in the detection coil CL11 at time t and the second induced voltage V 21 (t) induced in the detection coil CL21 at time t. Therefore, in the differential signal V1(t), the component of the uniform magnetic field strength B u (t) is canceled out. Also, as shown in Equation (5), the differential signal V2(t) at time t is the difference between the first induced voltage V 12 (t) induced in the detection coil CL12 at time t and the second induced voltage V 22 (t) induced in the detection coil CL22 at time t. Therefore, also in the differential signal V2(t), the component of the uniform magnetic field strength B u (t) is canceled out.

[0146] And the detection signal V0(t) output from the differential amplifier DF at time t is obtained by the difference between the differential signal V1(t) shown in Equation (4) and the differential signal V2(t) shown in Equation (5), as shown in the following Equation (6).

[0147] [Number]

[0148] As shown in the above Equation (6), in the detection signal V0(t), the strength B of the uniform gradient magnetic field g1 (t) and the strength B of the uniform gradient magnetic field g2(t) both cancel out. This indicates that in the gradient magnetic field sensor 12A, the detection of a uniform magnetic field is suppressed, and the detection of a uniform gradient magnetic field is suppressed. Based on the above principle, the gradient magnetic field sensor 12A can suppress the detection of a uniform magnetic field and can suppress the detection of a uniform gradient magnetic field.

[0149] <Modification Example 2 of the Embodiment> Hereinafter, Modification Example 2 of the embodiment will be described. In Modification Example 2 of the embodiment, the same components as those in the embodiment are denoted by the same reference numerals, and the description thereof will be omitted. Also, hereinafter, for convenience of explanation, the gradient magnetic field sensor 12 according to Modification Example 2 of the embodiment will be described as the gradient magnetic field sensor 12B. Further, the matters described in Modification Example 2 of the embodiment may be applied not only to the embodiment but also to Modification Example 1 of the embodiment.

[0150] FIG. 12 is a diagram showing an example of the circuit configuration of the gradient magnetic field sensor 12B.

[0151] The gradient magnetic field sensor 12B includes an AC power supply connection terminal CT1, a first sensor head S1, a second sensor head S2, a 0th phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT1, a detection circuit DT2, a detection circuit DT3, a detection circuit DT4, a signal processing unit PR, and a detection signal output terminal CT2. In addition, it includes a DC power supply connection terminal CT3 and a DC current control unit CC2. The DC current control unit CC2 has an input terminal CC21, an output terminal CC22, and an output terminal CC23. 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.

[0152] Further, the gradient magnetic field sensor 12B is also connected to a DC power supply P2 in addition to the AC power supply P1 via a transmission line. More specifically, a DC power supply connection terminal CT3 of the gradient magnetic field sensor 12B is connected to the positive power supply terminal of the DC power supply P2 via a transmission line. And the negative power supply terminal of the DC power supply P2 is grounded via a transmission line. Here, the DC power supply P2 can be any DC power supply. Note that other circuit elements, other devices, etc. may be connected between the DC power supply connection terminal CT3 and the positive power supply terminal as long as the functions of the gradient magnetic field sensor 12B are not impaired. Also, other circuit elements, other devices, etc. may be connected between the negative power supply terminal and the ground as long as the functions of the gradient magnetic field sensor 12B are not impaired.

[0153] Also, the DC power supply connection terminal CT3 is connected to an input terminal CC21 of the DC current control unit CC2 via a transmission line. Note that other circuit elements, other devices, etc. may be connected between the DC power supply connection terminal CT3 and the DC current control unit CC2 as long as the functions of the gradient magnetic field sensor 12A are not impaired.

[0154] Also, in the DC current control unit CC2, between the input terminal CC21 and the output terminal CC22, a first variable resistor VR21 and a first inductor L1 are connected in series via a transmission line. Also, in the DC current control unit CC2, between the input terminal CC21 and the output terminal CC23, a second variable resistor VR22 and a second inductor L2 are connected in series via a transmission line. Note that between the input terminal CC21 and the output terminal CC22, within a range that does not impair the function of the gradient magnetic field sensor 12A, other circuit elements, other devices, etc. may be connected together with the first variable resistor VR21 and the first inductor L1. Also, between the input terminal CC21 and the output terminal CC22, the first variable resistor VR21 and the first inductor L1 may be connected in series in any order. Also, between the input terminal CC21 and the output terminal CC23, within a range that does not impair the function of the gradient magnetic field sensor 12A, other circuit elements, other devices, etc. may be connected together with the second variable resistor VR22 and the second inductor L2. Also, between the input terminal CC21 and the output terminal CC23, the second variable resistor VR22 and the second inductor L2 may be connected in series in any order.

[0155] Also, the output terminal CC22 of the DC current control unit CC2 is connected via a transmission line connecting the output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1, and other transmission lines. Note that between the output terminal CC22 and the transmission line connecting the output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1, within a range that does not impair the function of the gradient magnetic field sensor 12A, other circuit elements, other devices, etc. may be connected.

[0156] Also, the output terminal CC23 of the direct current control unit CC2 is connected via a transmission line that connects the output terminal CC14 of the alternating current control unit CC1 and the second magnetic core CR2, and via another transmission line. Note that other circuit elements, other devices, etc. may be connected between the output terminal CC23 and the transmission line that connects the output terminal CC14 of the alternating current control unit CC1 and the second magnetic core CR2, as long as the function of the gradient magnetic field sensor 12 is not impaired.

[0157] Next, the operation of the gradient magnetic field sensor 12B will be described.

[0158] In the gradient magnetic field sensor 12B having the circuit configuration as described above, the direct current power supply P2 inputs a direct current to the direct current power supply connection terminal CT3. The direct current input to the direct current power supply connection terminal CT3 is input to the direct current control unit CC2 as a direct current excitation current.

[0159] The direct current excitation current input to the direct current control unit CC2 is branched into two direct current excitation currents, a first direct current excitation current DC1 and a second direct current excitation current DC2.

[0160] In the direct current control unit CC2, the magnitude of the first direct current excitation current DC1 is adjusted by the first variable resistor VR21. Then, the first direct current excitation current DC1 is input from the output terminal CC22 to the first magnetic core CR1. As a result, in the n-th detection coil CL1n among the four detection coils CL1, a voltage corresponding to the first alternating current excitation current AC1 flowing through the first magnetic core CR1, the first direct current excitation current DC1 flowing through the first magnetic core CR1, and the strength of the magnetic field applied to the detection coil CL1n is induced. That is, also in the gradient magnetic field sensor 12B, the voltage changes according to the strength of the magnetic field externally applied to the detection coil CL1n. Hereinafter, for convenience of explanation, the voltage will be described as the third induced voltage. Note that the first inductor L1 is an inductor for DC (Direct Current) coupling. Due to the presence of the first inductor L1, in the gradient magnetic field sensor 12B, it is possible to suppress the alternating current from flowing from the output terminal CC22 to the input terminal CC21.

[0161] On the other hand, in the DC current control unit CC2, the magnitude of the second DC excitation current DC2 is adjusted by the second variable resistor VR22. Then, the second DC excitation current DC2 is input from the output terminal CC23 to the second magnetic core CR2. As a result, in the n-th detection coil CL2n among the four detection coils CL2, a voltage corresponding 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 detection coil CL2n is induced. That is, also in the gradient magnetic field sensor 12B, the voltage changes according to the strength of the magnetic field applied to the detection coil CL2n from the outside. Hereinafter, for convenience of explanation, the voltage will be described as the fourth induced voltage. Note that the second inductor L2 is an inductor for DC coupling. Due to the presence of the second inductor L2, in the gradient magnetic field sensor 12B, it is possible to suppress the alternating current from flowing from the output terminal CC23 to the input terminal CC21.

[0162] In the gradient magnetic field sensor 12B, signals corresponding to the third induced voltage induced in the detection coil CL11 and the fourth induced voltage induced in the detection coil CL21 are input to the input terminal DT12 of the detection circuit DT1 as the differential signal Vout1. Also, in the gradient magnetic field sensor 12B, signals corresponding to the third induced voltage induced in the detection coil CL12 and the fourth induced voltage induced in the detection coil CL22 are input to the input terminal DT22 of the detection circuit DT2 as the differential signal Vout2. Also, in the gradient magnetic field sensor 12B, signals corresponding to the third induced voltage induced in the detection coil CL13 and the fourth induced voltage induced in the detection coil CL23 are input to the input terminal DT32 of the detection circuit DT3 as the differential signal Vout3. Also, in the gradient magnetic field sensor 12B, signals corresponding to the third induced voltage induced in the detection coil CL14 and the fourth induced voltage induced in the detection coil CL24 are input to the input terminal DT42 of the detection circuit DT4 as the differential signal Vout4.

[0163] Note that the operations of the detection circuit DT1, the detection circuit DT2, the detection circuit DT3, the detection circuit DT4, and the signal processing unit PR are the same as those described in the embodiment. Therefore, detailed descriptions of these operations are omitted below.

[0164] Even with the above configuration, the gradient magnetic field sensor 12B can suppress the occurrence of a dead zone and suppress fluctuations in sensitivity according to the passing position of the magnetized foreign object, similar to the gradient magnetic field sensor 12 according to the embodiment.

[0165] Note that each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to the first modification of the embodiment, and the gradient magnetic field sensor 12B according to the second modification of the embodiment may be configured not to include the 0th phase shift circuit PS0.

[0166] Also, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to the first modification of the embodiment, and the gradient magnetic field sensor 12B according to the second modification of the embodiment may be configured not to include either the first phase shift circuit PS1 or the second phase shift circuit PS2.

[0167] Also, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to the first modification of the embodiment, and the gradient magnetic field sensor 12B according to the second modification of the embodiment may be configured not to include either the first variable resistor VR11 or the second variable resistor VR12.

[0168] Also, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to the first modification of the embodiment, and the gradient magnetic field sensor 12B according to the second modification of the embodiment may be configured not to include at least one of the first capacitor C1 and the second capacitor C2. However, as described above, these are capacitors for AC coupling. Therefore, it is desirable for the gradient magnetic field sensor 12 to include both the first capacitor C1 and the second capacitor C2.

[0169] Further, in each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to Modification Example 1 of the embodiment, and the gradient magnetic field sensor 12B according to Modification Example 2 of the embodiment, the alternating current control unit CC1 may be configured to include a first amplification circuit that amplifies the amplitude of the first alternating current excitation current AC1 instead of or in addition to the first variable resistor VR11.

[0170] Further, in each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to Modification Example 1 of the embodiment, and the gradient magnetic field sensor 12B according to Modification Example 2 of the embodiment, the alternating current control unit CC1 may be configured to include a second amplification circuit that amplifies the amplitude of the second alternating current excitation current AC2 instead of or in addition to the second variable resistor VR12.

[0171] Further, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to Modification Example 1 of the embodiment, and the gradient magnetic field sensor 12B according to Modification Example 2 of the embodiment can bring the sensitivity of the first sensor head S1 closer to the sensitivity of the second sensor head S2 by adjusting the phase shift amount of the first phase shift circuit PS1 of the alternating current control unit CC1, the resistance value of the first variable resistor VR11, the phase shift amount of the second phase shift circuit PS2, and the resistance value of the second variable resistor VR12. That is, thereby, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to Modification Example 1 of the embodiment, and the gradient magnetic field sensor 12B according to Modification Example 2 of the embodiment can balance the sensitivity of the first sensor head S1 and the sensitivity of the second sensor head S2 and improve the accuracy of detecting the object to be detected.

[0172] In addition, the first magnetic core CR1 described above may be configured to include two or more magnetic bodies connected in series. In this case, in the first magnetic core CR1, some or all of these two or more magnetic bodies may be configured to be connected in series by a non-magnetic conductor. Here, for example, when the first magnetic core CR1 includes two magnetic bodies, i.e., a magnetic body CR1A and a magnetic body CR1B, in the first magnetic core CR1, the magnetic body CR1A and the magnetic body CR1B are connected by a non-magnetic conductor. Then, a terminal connected to the output terminal CC13 of the alternating current control unit CC1 is provided at an end of the magnetic body CR1A opposite to the end connected to the conductor. Also, a terminal grounded to the ground is provided at an end of the magnetic body CR1B opposite to the end connected to the conductor CR1C.

[0173] In addition, the second magnetic core CR2 described above may be configured to include two or more magnetic bodies connected in series. In this case, in the second magnetic core CR2, some or all of these two or more magnetic bodies may be configured to be connected in series by a non-magnetic conductor. Note that since the configuration of the second magnetic core CR2 including a plurality of magnetic bodies is the same as the configuration of the first magnetic core CR1 including a plurality of magnetic bodies, a detailed description thereof is omitted.

[0174] Also, in the first sensor head S1 described above, when a predetermined magnetic field is applied to the first magnetic core CR1, the polarity of the voltage output from the detection coil CL1n is the same as the polarity of the voltage output from the detection coil CL1n+1 when a predetermined magnetic field is applied to the first magnetic core CR1. For this reason, also in the second sensor head S2 described above, when a predetermined magnetic field is applied to the second magnetic core CR2, the polarity of the voltage output from the detection coil CL2n is the same as the polarity of the voltage output from the detection coil CL2n+1 when a predetermined magnetic field is applied to the second magnetic core CR2. This is because it was convenient since the signal processing unit PR could efficiently perform signal processing according to the circuit diagram shown in FIG. 4. From such circumstances, in the first sensor head S1 described above, when a predetermined magnetic field is applied to the first magnetic core CR1, the polarity of the voltage output from a part of the N detection coils CL1 may be different from the polarity of the voltage output from all the remaining N detection coils CL1 when a predetermined magnetic field is applied to the first magnetic core CR1, according to the configuration of the signal processing performed by the signal processing unit PR. In this case, also in the second sensor head S2 described above, when a predetermined magnetic field is applied to the second magnetic core CR2, the polarity of the voltage output from a part of the N detection coils CL2 is also different from the polarity of the voltage output from all the remaining N detection coils CL2 when a predetermined magnetic field is applied to the second magnetic core CR2, according to the configuration of the signal processing performed by the signal processing unit PR. For example, in the first sensor head S1 described above, when a predetermined magnetic field is applied to the first magnetic core CR1, the polarity of the voltage output from the detection coil CL12 may be different from the polarities of the voltages output from the detection coils CL11, CL13, and CL14, respectively, when a predetermined magnetic field is applied to the first magnetic core CR1, according to the configuration of the signal processing performed by the signal processing unit PR.In this case, also in the second sensor head S2 described above, when a predetermined magnetic field is applied to the second magnetic core CR2, the polarity of the voltage output from the detection coil CL22 is different from the polarities of the voltages output from the detection coils CL21, CL23, and CL24, respectively, when a predetermined magnetic field is applied to the second magnetic core CR2. Further, for example, in the first sensor head S1 described above, the polarity of the voltage output from the detection coil CL1n when a predetermined magnetic field is applied to the first magnetic core CR1 may be different from the polarity of the voltage output from the detection coil CL1n+1 when a predetermined magnetic field is applied to the first magnetic core CR1, depending on the configuration of the signal processing performed by the signal processing unit PR. In this case, also in the second sensor head S2 described above, the polarity of the voltage output from the detection coil CL2n when a predetermined magnetic field is applied to the second magnetic core CR2 is different from the polarity of the voltage output from the detection coil CL2n+1 when a predetermined magnetic field is applied to the second magnetic core CR2. As a result, each of the gradient magnetic field sensor 12 according to the embodiment, the gradient magnetic field sensor 12A according to the first modification of the embodiment, and the gradient magnetic field sensor 12B according to the second modification of the embodiment can improve the efficiency of the signal processing of the signal processing unit PR.

[0175] As described above, the gradient magnetic field sensor according to the embodiment (in the example described above, the gradient magnetic field sensors 12, 12A, and 12B) includes a first magnetic core having a linear portion (in the example described above, the first magnetic core CR1), a second magnetic core having a linear portion (in the example described above, the second magnetic core CR2), N first coils arranged in order on the linear portion of the first magnetic core (in the example described above, four detection coils CL1), N second coils arranged in order on the linear portion of the second magnetic core (in the example described above, four detection coils CL2), and a main body portion provided with the first magnetic core and the second magnetic core (in the example described above, the main body portion MB). Among the N first coils, the n-th first coil (in the example described above, the detection coil CL1n) from the tip side of the first magnetic core is differentially connected to the n-th second coil (in the example described above, the detection coil CL2n) from the tip side of the second magnetic core. N is an integer of 2 or more, and n is an integer within the range of 1 to N. Thereby, the gradient magnetic field sensor can suppress fluctuations in sensitivity according to the passing position of the magnetized foreign matter while suppressing the occurrence of a dead zone.

[0176] Further, in the gradient magnetic field sensor, a configuration may be used in which the linear portion of the first magnetic core is substantially parallel to the linear portion of the second magnetic core.

[0177] Further, in the gradient magnetic field sensor, a configuration may be used in which the linear portion of the first magnetic core and the linear portion of the second magnetic core are located substantially coaxially.

[0178] Further, in the gradient magnetic field sensor, a configuration may be used in which each of the first magnetic core and the second magnetic core protrudes in a predetermined direction from the main body portion such that their linear portions are substantially parallel to each other.

[0179] Further, in the gradient magnetic field sensor, a configuration may be used in which the linear portion of the first magnetic core overlaps at least a part of the linear portion of the second magnetic core when viewed from an orthogonal direction that is orthogonal to each of the linear portion of the first magnetic core and the linear portion of the second magnetic core.

[0180] Further, in the gradient magnetic field sensor, a configuration may be used in which the linear portion of the first magnetic core substantially overlaps the linear portion of the second magnetic core when viewed from the orthogonal direction.

[0181] Further, in the gradient magnetic field sensor, a configuration may be used in which the n-th first coil substantially overlaps the n-th second coil when viewed from the orthogonal direction.

[0182] Further, in the gradient magnetic field sensor, a configuration may be used in which two adjacent first coils among the N first coils are insulated from each other and in contact with each other, and two adjacent second coils among the N second coils are insulated from each other and in contact with each other.

[0183] Further, in the gradient magnetic field sensor, a configuration may be used in which the self-inductance of the n-th first coil is substantially the same as the self-inductance of the n-th second coil.

[0184] Further, in the gradient magnetic field sensor, a configuration may be used in which the sum of the self-inductances of each of the N first coils is substantially the same as the sum of the self-inductances of each of the N second coils.

[0185] Further, in the gradient magnetic field sensor, a configuration may be used in which the first magnetic core around which the N first coils are wound and the second magnetic core around which the N second coils are wound are arranged in line symmetry.

[0186] In addition, in the gradient magnetic field sensor, when a predetermined magnetic field is applied to the first magnetic core, the polarity of the voltage output from the n-th first coil is the same as the polarity of the voltage output from the (n + 1)-th first coil among the N first coils from the tip side of the first magnetic core when a predetermined magnetic field is applied to the first magnetic core, and when a predetermined magnetic field is applied to the second magnetic core, the polarity of the voltage output from the n-th second coil is the same as the polarity of the voltage output from the (n + 1)-th second coil among the N second coils from the tip side of the second magnetic core when a predetermined magnetic field is applied to the second magnetic core. Such a configuration may be used.

[0187] In addition, in the gradient magnetic field sensor, when a predetermined magnetic field is applied to the first magnetic core, the polarity of the voltage output from a part of the N first coils is opposite to the polarity of the voltage output from all the remaining N first coils when a predetermined magnetic field is applied to the first magnetic core, and when a predetermined magnetic field is applied to the second magnetic core, the polarity of the voltage output from a part of the N second coils is opposite to the polarity of the voltage output from all the remaining N second coils when a predetermined magnetic field is applied to the second magnetic core. Such a configuration may be used.

[0188] In addition, the gradient magnetic field sensor may further include a signal processing unit (in the example described above, the signal processing unit PR) to which a voltage corresponding to the difference between the voltage output from the n-th first coil and the voltage output from the n-th second coil is input as a voltage signal.

[0189] In addition, in the gradient magnetic field sensor, the signal processing unit may include an arithmetic unit (in the example described above, each of the arithmetic units O1 to O6) that performs addition or subtraction of voltage signals.

[0190] In addition, in the gradient magnetic field sensor, the signal processing unit may include an amplification unit (in the example described above, the amplification units A1 to A4) that amplifies the voltage signal.

[0191] Further, in the gradient magnetic field sensor, a configuration may be used in which the signal processing unit includes an absolute value output unit that outputs the absolute value of the voltage signal (in the example described above, each of the full-wave rectifiers FR1 to FR3).

[0192] Further, in the gradient magnetic field sensor, a configuration may be used in which the signal processing unit includes a discrimination unit that discriminates between a signal and noise (in the example described above, the hysteresis comparator HC).

[0193] Further, the magnetic object detection device according to the embodiment (magnetic object detection device 1 in the example described above) includes the gradient magnetic field sensor described above. Thereby, the magnetic object detection device can suppress fluctuations in sensitivity according to the passing position of the magnetized foreign object while suppressing the occurrence of a dead zone.

[0194] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and may be changed, replaced, deleted, etc. without departing from the gist of the present invention.

Description of Reference Numerals

[0195] 1…Magnetic detection device, 11…Magnetizing device, 12, 12A, 12B…Gradient magnetic field sensors, 20…Information processing device, A1, A2, A3, A4…Amplification units, B1, B2, B3, B4…Buffers, C1…First capacitor, C2…Second capacitor, C3…Third capacitor, CC1…Alternating current control unit, CC2…Direct current control unit, CL1, CL1n, CL1N, CL2, CL2n, CL2N, CL11, CL12, CL13, CL14, CL21, CL22, CL23, CL24…Detection coils, CR1…First magnetic core, CR2…Second magnetic core, CS…Frame body, CT1…Alternating current power supply connection terminal, CT2…Detection signal output terminal, CT3…Direct current power supply connection terminal, DA, DF…Differential amplifiers, DT1, DT2, DT3, DT4…Detection circuits, EA…Error amplifier, FR1, FR2, FR3…Full-wave rectifiers, HC…Hysteresis comparator, HF1, HF2, HF3, HF4…High-pass filters, IV…Inverter, L1…First inductor, L2…Second inductor, LF…Low-pass filter, MB…Main body, O1, O2, O3, O4, O5, O6…Arithmetic units, P1…Alternating current power supply, P2…Direct current power supply, PD…Phase detection circuit, PR…Signal processing unit, PS0…Zero-phase shift circuit, PS1…First-phase shift circuit, PS2…Second-phase shift circuit, R1…Resistor, RL1…First roller, RL2…Second roller, S1…First sensor head, S2…Second sensor head, ST…Sheet member, VR11…First variable resistor, VR12…Second variable resistor, VR21…First variable resistor, VR22…Second variable resistor

Claims

1. a first magnetic core having a linear portion; a second magnetic core having a linear portion; N first coils sequentially arranged on a first linear portion of the first magnetic core; N second coils sequentially arranged on a second linear portion of the second magnetic core; a main body portion in which the first magnetic core and the second magnetic core are provided; comprising among the N first coils, the n-th first coil from the tip side of the first magnetic core is differentially connected to the n-th second coil from the tip side of the second magnetic core among the N second coils; N is an integer of 2 or more; n is an integer within a range of 1 or more and N or less; when a predetermined magnetic field is applied to the first magnetic core, the polarity of the voltage output from a part of the N first coils is opposite to the polarity of the voltage output from all the remaining ones of the N first coils when the predetermined magnetic field is applied to the first magnetic core; when a predetermined magnetic field is applied to the second magnetic core, the polarity of the voltage output from a part of the N second coils is opposite to the polarity of the voltage output from all the remaining ones of the N second coils when the predetermined magnetic field is applied to the second magnetic core; a gradient magnetic field sensor.

2. the first portion is substantially parallel to the second portion; the gradient magnetic field sensor according to Claim 1.

3. the first portion and the second portion are located substantially coaxially; the gradient magnetic field sensor according to Claim 2.

4. each of the first magnetic core and the second magnetic core projects in a predetermined direction from the main body portion such that the first portion and the second portion are substantially parallel; the gradient magnetic field sensor according to Claim 2.

5. when viewed from an orthogonal direction orthogonal to each of the first portion and the second portion, the first portion overlaps at least a part of the second portion; the gradient magnetic field sensor according to Claim 4.

6. when viewed from the orthogonal direction, the first portion substantially overlaps the second portion; the gradient magnetic field sensor according to Claim 5.

7. when viewed from the orthogonal direction, the n-th first coil substantially overlaps the n-th second coil; the gradient magnetic field sensor according to Claim 5 or 6.

8. two adjacent first coils among the N first coils are insulated from each other and in contact with each other; In the N second coils, two adjacent second coils are insulated from each other and in contact with each other. The gradient magnetic field sensor according to any one of claims 1 to 7.

9. The self-inductance of the n-th first coil is substantially the same as the self-inductance of the n-th second coil. The gradient magnetic field sensor according to any one of claims 1 to 8.

10. The sum of the self-inductances of the N first coils is substantially the same as the sum of the self-inductances of the N second coils. The gradient magnetic field sensor according to any one of claims 1 to 9.

11. The first magnetic core around which the N first coils are wound and the second magnetic core around which the N second coils are wound are arranged in line symmetry. The gradient magnetic field sensor according to any one of claims 1 to 10.

12. The gradient magnetic field sensor further includes a signal processing unit to which a voltage corresponding to the difference between the voltage output from the n-th first coil and the voltage output from the n-th second coil is input as a voltage signal. The gradient magnetic field sensor according to any one of claims 1 to 11.

13. The signal processing unit includes an arithmetic unit that performs addition or subtraction of voltage signals. The gradient magnetic field sensor according to claim 12.

14. The signal processing unit includes an amplification unit that amplifies voltage signals. The gradient magnetic field sensor according to claim 12 or 13.

15. The signal processing unit includes an absolute value output unit that outputs the absolute value of a voltage signal. The gradient magnetic field sensor according to any one of claims 12 to 14.

16. The signal processing unit includes a discrimination unit that discriminates between a signal and noise. The gradient magnetic field sensor according to any one of claims 12 to 15.

17. A magnetic object detection device comprising the gradient magnetic field sensor according to any one of claims 1 to 16. Magnetic object detection device.

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