Magnetic sensor

Abstract

A magnetic sensor (1A) comprises an electroconductive excitation body (21) through which an intermittent current is supplied, a magnetic body (22) that is provided on the surface of the excitation body (21) and has lower electroconductivity than the excitation body (21), a coil (3) wound around the excitation body (21) and the magnetic body (22), and a detection unit (9) for detecting an external magnetic field by detecting a voltage generated in the coil 3 by the external magnetic field in a state in which the intermittent current is supplied through the excitation body (21). The coil (3) includes a first coil part (31) wound around a first excitation part (51) of the excitation body (21), and a second coil part (32) wound around a second excitation part (52) of the excitation body (21). The first excitation part (51) and the second excitation part (52) are connected in series, and the first coil part (31) and the second coil part (32) are connected in parallel. The detection unit 9 detects the external magnetic field by detecting a common voltage generated in the first coil part (31) and the second coil part (32).

Description

magnetic sensor

[0001] The present invention relates to a magnetic sensor.

[0002] A magneto-impedance (MI) sensor is known as a magnetic sensor that utilizes the magneto-impedance phenomenon. The MI element described in Patent Document 1 includes an amorphous magnetic wire and a coil wound around the magnetic wire. When a pulse current is applied to the magnetic wire, a voltage corresponding to the strength of an external magnetic field is generated in the coil. The MI element detects the strength of the external magnetic field by amplifying and detecting the voltage generated in the coil.

[0003] Patent No. 3693119

[0004] One method for achieving good sensitivity in an MI sensor is to increase the conductivity of the conductor through which the pulse current flows. Increasing the conductivity of the conductor allows the pulse current to flow smoothly, which allows the conductor to be extended and results in good sensitivity. However, in the MI element described in Patent Document 1, the pulse current flows through an amorphous magnetic wire. The conductivity of amorphous materials is lower than that of general conductors. Therefore, as the magnetic wire is extended, the pulse current cannot flow smoothly. Therefore, the MI element described in Patent Document 1 has the problem of making it difficult to achieve good magnetic resolution.

[0005] An object of the present invention is to provide a magnetic sensor that can achieve good magnetic resolution.

[0006] The magnetic sensor of the present invention comprises a conductive exciter through which an intermittent current is passed, a magnetic body provided on the surface of the exciter and having a lower conductivity than the exciter, a coil wound around the exciter and the magnetic body, and a detection unit that detects the external magnetic field by detecting a voltage generated in the coil by an external magnetic field while the intermittent current is passed through the exciter, wherein the coil includes a first coil portion wound around a first excitation portion of the exciter, and a second coil portion wound around a second excitation portion of the exciter that is different from the first excitation portion, wherein the first excitation portion and the second excitation portion are connected in series, and the first coil portion and the second coil portion are connected in parallel, and the detection unit detects the external magnetic field by detecting a common voltage generated in the first coil portion and the second coil portion.

[0007] In a magnetic sensor, the direction of the magnetic moment of a magnetic body is influenced by an external magnetic field and tilts toward the external magnetic field. When an intermittent current is passed through a conductive exciter in this state, the magnetic field generated by the exciter causes the magnetic moment of the magnetic body to align in the circumferential direction of the exciter. A voltage corresponding to this change in the direction of the magnetic moment is then generated in the coil. The detection unit detects the external magnetic field by measuring the voltage generated in the coil.

[0008] The magnetic sensor includes a first coil wound around a first excitation unit and a second coil wound around a second excitation unit. By connecting the first and second coil units in parallel, the magnetic sensor can average out random noise generated by each coil unit, thereby reducing noise detected by the detection unit. Furthermore, because the excitation body through which the intermittent current flows is conductive, the intermittent current can be effectively passed even when the first and second excitation units are connected in series. Therefore, even when multiple excitation units need to be connected in series by connecting multiple magnetic bodies in parallel, the magnetic sensor can prevent a reduction in the magnitude of the intermittent current flowing through each excitation unit. Therefore, by connecting the first and second coil units in parallel, the magnetic sensor can reduce noise while maintaining sensitivity and improving magnetic resolution.

[0009] In the present invention, the first coil portion includes a first partial coil portion wound around a first partial excitation portion of the first excitation portion, and a second partial coil portion wound around a second partial excitation portion of the first excitation portion that is different from the first partial excitation portion, and the first partial excitation portion and the second partial coil portion are connected in series, and the first partial coil portion and the second partial coil portion are connected in series or in parallel, and a first direction indicating the direction in which the intermittent current flows through the first partial excitation portion and a second direction indicating the direction in which the intermittent current flows through the second partial excitation portion may be opposite to each other.

[0010] When the first direction and the second direction are opposite to each other, the polarity of the voltage offset generated in the first partial coil section and the voltage offset generated in the second partial coil section can be reversed. In this case, the detection unit can increase the measured voltage while eliminating the influence of the offset by detecting a value obtained by adding or averaging the respective voltages. Note that when the voltage is amplified in the output unit, the amplified offset may exceed the voltage range measurable in the detection unit circuit. In contrast, by eliminating the influence of the offset using the above method, the voltage range measurable in the detection unit circuit can be prevented from being exceeded, thereby increasing the amplification factor of the detection unit. Therefore, the magnetic sensor can achieve good sensitivity characteristics to external magnetic fields and improve magnetic resolution. This allows the magnetic sensor to improve its signal-to-noise ratio.

[0011] In the present invention, the second coil portion may include a third partial coil portion wound around a third partial excitation portion of the second excitation portion, and a fourth partial coil portion wound around a fourth partial excitation portion of the second excitation portion that is different from the third partial excitation portion, the third partial excitation portion and the fourth partial excitation portion being connected in series, and the third partial coil portion and the fourth partial coil portion being connected in series or in parallel, and a third direction indicating the direction in which the intermittent current flows in the third partial excitation portion and a fourth direction indicating the direction in which the intermittent current flows in the fourth partial excitation portion may be opposite to each other. In this case, by connecting in parallel components for increasing the detected voltage, the magnetic sensor can further reduce noise, thereby further improving magnetic resolution.

[0012] In the present invention, the exciter may include a plurality of parallel excitation portions extending parallel to each other, and the direction of the intermittent current may be the same for each of the parallel excitation portions. In this case, the magnetic sensor can obtain even better sensitivity characteristics to external magnetic fields. Furthermore, the magnetic sensor can average out random noise generated in the parallel excitation portions, thereby reducing noise.

[0013] In the present invention, the material of the exciter may be any one of copper, silver, aluminum, tin, and zinc, or an alloy containing at least one of copper, silver, aluminum, tin, and zinc. In this case, an exciter that can effectively pass an intermittent current can be easily produced.

[0014] In the present invention, the magnetic body may be made of a nickel-iron alloy or an amorphous material, which makes it easy to produce a magnetic body that appropriately changes the direction of its magnetic moment when it is subjected to the influence of an external magnetic field or a magnetic field generated in response to an intermittent current flowing through an exciter.

[0015] In the present invention, the magnetic body may be plated on the surface of the exciter. In this case, the magnetic sensor can appropriately change the direction of the magnetic moment of the magnetic body by passing an intermittent current through the exciter.

[0016] In the present invention, the conductivity of the exciter may be 20 times or more the conductivity of the magnetic body, in which case the magnetic sensor can effectively pass an intermittent current through the exciter.

[0017] FIG. 1 is a diagram illustrating a magnetic sensor 1A. It shows a state in which an external magnetic field Bc is not acting on a magnetic body 22. It shows a state in which an external magnetic field Bc is acting on a magnetic body 22. It shows a state in which a pulse current is passed through an exciter 21. It is a diagram for explaining current noise in the magnetic sensor 1A. It is a diagram for explaining current noise in the magnetic sensor 10. It is a first explanatory diagram for explaining the principle of how an offset occurs. It is a second explanatory diagram for explaining the principle of how an offset occurs. It is a third explanatory diagram for explaining the principle of how an offset occurs. It is a diagram illustrating a magnetic sensor 1B. It is a diagram illustrating a magnetic sensor 1C. It is a table showing noise evaluation results. It is a diagram illustrating a magnetic sensor 1D.

[0018] A magnetic sensor 1 (1A, 1B, 1C, 1D) according to one embodiment of the present invention will be described below with reference to the drawings. The drawings are used to explain technical features that may be adopted by the present invention. The device configurations described are merely illustrative examples and are not intended to be limiting. The magnetic sensor 1 is a sensor that detects magnetism based on changes in the magnetic moment of a magnetic material.

[0019] <Magnetic Sensor 1A> As shown in FIG. 1, the magnetic sensor 1A includes a wire unit 2, a coil 3, and a detection unit 9.

[0020] The wire unit 2 is an elongated body. In FIG. 1 , a predetermined extension direction D is defined. One direction of the extension directions D is referred to as a first extension direction D1, and the other direction of the extension directions D is referred to as a second extension direction D2. In FIG. 1 , the first extension direction D1 is the rightward direction, and the second extension direction D2 is the leftward direction, so that the extension direction D is the left-right direction. The wire unit 2 extends while bending alternately from the first extension direction D1 to the second extension direction D2 and from the second extension direction D2 to the first extension direction D1. The wire unit 2 has copper wires 20 and wires 2A and 2B arranged alternately.

[0021] The wires 2A and 2B have the same configuration and extend parallel to each other. Each of the wires 2A and 2B includes an exciter 21 and a magnetic body 22.

[0022] The exciter 21 is electrically conductive. The exciter 21 is a rod-shaped member with a circular cross section. The conductivity of the exciter 21 is, for example, 30 to 70 MS / m. The material of the exciter 21 is preferably any one of copper, silver, aluminum, tin, and zinc, or an alloy containing at least any one of copper, silver, aluminum, tin, and zinc. A specific example of the alloy that constitutes the exciter 21 is aluminum copper.

[0023] The magnetic body 22 is provided on the surface of the exciter 21. The magnetic body 22 has a thin film shape and covers the exciter 21 from the outside. The magnetic body 22 is coated on the surface of the exciter 21 by plating. The conductivity of the magnetic body 22 is, for example, 0.01 to 2.00 MS / m. The conductivity of the magnetic body 22 is at least less than 1 / 20 of the conductivity of the exciter 21, more specifically, less than 1 / 100. The conductivity of the magnetic body 22 is lower than the conductivity of the exciter 21. A nickel-iron alloy or an amorphous material is preferably used as the material of the magnetic body 22.

[0024] In each of the exciters 21 of the wires 2A and 2B, a first partial excitation portion 511, a second partial excitation portion 512, a third partial excitation portion 523, and a fourth partial excitation portion 524 are defined. The first partial excitation portion 511, the second partial excitation portion 512, the third partial excitation portion 523, and the fourth partial excitation portion 524 each extend linearly along the extension direction D.

[0025] The copper wire 20 is a copper conductor that is thicker than the wires 2A and 2B. The copper wire 20 has connecting portions 561, 562, and 563, an input portion 571, and an output portion 572. The connecting portion 561 is interposed between the ends of the first partial excitation portion 511 and the second partial excitation portion 512 in the first extension direction D1. The connecting portion 562 is interposed between the ends of the second partial excitation portion 512 and the third partial excitation portion 523 in the second extension direction D2. The connecting portion 563 is interposed between the ends of the third partial excitation portion 523 and the fourth partial excitation portion 524 in the first extension direction D1. The input portion 571 is connected to the end of the first partial excitation portion 511 in the second extension direction D2. The output portion 572 is connected to the end of the fourth partial excitation portion 524 in the second extension direction D2. The first partial magnetic excitation unit 511 , the second partial magnetic excitation unit 512 , the third partial magnetic excitation unit 523 , and the fourth partial magnetic excitation unit 524 are connected in series by connecting units 561 , 562 , and 563 .

[0026] An external pulse current is applied to the input portion 571. The pulse current flows in this order through the input portion 571, the first partial excitation portion 511 of the exciter 21, the connecting portion 561, the second partial excitation portion 512 of the exciter 21, the connecting portion 562, the third partial excitation portion 523 of the exciter 21, the connecting portion 564, the fourth partial excitation portion 524 of the exciter 21, and the output portion 572. The direction of the pulse current flow is the same in the exciter 21 of the wire 2A and the exciter 21 of the wire 2B.

[0027] The direction of the pulse current flowing in the first partial excitation unit 511 (the direction of arrow Y1) coincides with the first extension direction D1. The direction of the pulse current flowing in the second partial excitation unit 512 (the direction of arrow Y2) coincides with the second extension direction D2. Therefore, the direction of the pulse current flowing in the first partial excitation unit 511 and the direction of the pulse current flowing in the second partial excitation unit 512 are opposite to each other.

[0028] The direction of the pulse current flowing in the third partial excitation unit 523 (the direction of arrow Y3) coincides with the first extension direction D1. The direction of the pulse current flowing in the fourth partial excitation unit 524 (the direction of arrow Y4) coincides with the second extension direction D2. Therefore, the direction of the pulse current flowing in the third partial excitation unit 523 and the direction of the pulse current flowing in the fourth partial excitation unit 524 are opposite to each other.

[0029] The coil 3 is wound around the excitation body 21 and the magnetic body 22 of the wire unit 2. The portion of the coil 3 wound around the first partial excitation part 511 is called the first partial coil part 311. The portion of the coil 3 wound around the second partial excitation part 512 is called the second partial coil part 312. The portion of the coil 3 wound around the third partial excitation part 523 is called the third partial coil part 323. The portion of the coil 3 wound around the fourth partial excitation part 524 is called the fourth partial coil part 324.

[0030] The ends of the first partial coil portion 311 and the second partial coil portion 312 in the first extension direction D1 are connected by a connection line 361. The ends of the first partial coil portion 311 and the second partial coil portion 312 in the second extension direction D2 are connected by a connection line 362. Therefore, the first partial coil portion 311 and the second partial coil portion 312 are connected in parallel.

[0031] The ends of the third partial coil portion 323 and the fourth partial coil portion 324 in the first extension direction D1 are connected by a connection line 363. The ends of the third partial coil portion 323 and the fourth partial coil portion 324 in the second extension direction D2 are connected by a connection line 364. Therefore, the third partial coil portion 323 and the fourth partial coil portion 324 are connected in parallel.

[0032] The connection lines 361 and 363 are connected by a connection line 365. The connection lines 362 and 364 are connected by a connection line 366. Therefore, the first partial coil portion 311, the second partial coil portion 312, the third partial coil portion 323, and the fourth partial coil portion 324 are connected in parallel.

[0033] A portion of the exciter 21 that includes the first partial excitation unit 511 and the second partial excitation unit 512 is referred to as the first excitation unit 51. A portion of the exciter 21 that includes the third partial excitation unit 523 and the fourth partial excitation unit 524 is referred to as the second excitation unit 52. The first excitation unit 51 is interposed between the input unit 571 and the connecting unit 562, and the second excitation unit 52 is interposed between the connecting unit 562 and the output unit 572. Therefore, the first excitation unit 51 and the second excitation unit 52 are connected in series by the connecting unit 562.

[0034] The first partial coil portion 311 and the second partial coil portion 312 correspond to the portion of the coil 3 wound around the first excitation portion 51. The portion of the coil 3 including the first partial coil portion 311 and the second partial coil portion 312 is referred to as the first coil portion 31. The third partial coil portion 323 and the fourth partial coil portion 324 correspond to the portion of the coil 3 wound around the second excitation portion 52. The portion of the coil 3 including the third partial coil portion 323 and the fourth partial coil portion 324 is referred to as the second coil portion 32.

[0035] The first coil portion 31 and the second coil portion 32 are connected in the first extension direction D1 by a connection line 365 and in the second extension direction D2 by a connection line 366. Therefore, the first coil portion 31 and the second coil portion 32 are connected in parallel.

[0036] The connection line 365 is connected to the ground and is thus grounded. The connection line 366 is connected to the detection unit 9.

[0037] The detection unit 9 detects the external magnetic field by detecting a common voltage generated in the first coil unit 31 and the second coil unit 32. The principle by which the detection unit 9 detects the external magnetic field is as follows.

[0038] An overview of the operating principle of the magnetic sensor 1A will be explained with reference to Figures 2 to 4. The coil 3 and detection unit 9 are omitted from Figures 2 to 4. The arrows in the magnetic body 22 indicate magnetic moments. Figure 2 shows a magnetic field-free state in which the component of the external magnetic field in the extension direction D (hereinafter referred to as the external magnetic field Bc) is not acting on the magnetic body 22. Figure 3 shows a state in which the external magnetic field Bc acts on the magnetic body 22. Figure 4 shows a state in which a pulse current is applied to the exciter 21.

[0039] 2, when no external magnetic field Bc is applied, the magnetic moment in the magnetic body 22 coincides with the orthogonal direction V that is perpendicular to the extension direction D. The magnetic moment faces one side of the orthogonal direction V. In other words, a magnetic moment facing one side of the orthogonal direction V and a magnetic moment facing the other side of the orthogonal direction V coexist.

[0040] 3, in response to the application of an external magnetic field Bc to the magnetic body 22, the magnetic moment in the magnetic body 22 is tilted in the extension direction D with respect to the orthogonal direction V. In other words, the magnetic moment includes a component in the extension direction D.

[0041] As shown in Fig. 4, when a pulse current flows through the exciter 21, the exciter 21 generates an induced magnetic field having a component in the orthogonal direction V in response to the pulse current. Hereinafter, the component in the orthogonal direction V of the induced magnetic field generated in response to the flow of the pulse current will be referred to as the induced magnetic field Be. In this case, the magnetic moments in the magnetic body 22 are aligned in the circumferential direction along the direction of the induced magnetic field Be. As a result, the magnetic moments in the magnetic body 22 coincide with the direction of one of the orthogonal directions V, and their respective directions are aligned.

[0042] When a pulse current is applied to the exciter 21 and the magnetic moment of the magnetic body 22 is aligned, a magnetic field is temporarily generated. Hereinafter, the magnetic field temporarily generated by the induced magnetic field Be is referred to as a transient magnetic field. Hereinafter, in the state shown in FIG. 2 , the magnetic moment does not include a component in the extension direction D. Therefore, when the state shown in FIG. 2 changes from the state shown in FIG. 4 , the extension direction D of the magnetic moment does not change over time, and therefore the transient magnetic field does not include a component in the extension direction D. On the other hand, in the state shown in FIG. 3 , the magnetic moment includes a component in the extension direction D. Therefore, when the state shown in FIG. 3 changes from the state shown in FIG. 4 , the extension direction D of the magnetic moment changes over time, and therefore the transient magnetic field includes a component in the extension direction D. In other words, the magnitude of the component in the extension direction D of the transient magnetic field when the magnetic body 22 changes from the state shown in FIG. 2 to the state shown in FIG. 4 is different from the magnitude of the component in the extension direction D of the transient magnetic field when the magnetic body 22 changes from the state shown in FIG. 3 to the state shown in FIG. 4 .

[0043] When the component of the extension direction D of the transient magnetic field changes, a voltage E is generated in the coil 3. The magnitude of the voltage E reflects the external magnetic field Bc. Therefore, the detection unit 9 detects the voltage E generated in the coil 3 and can calculate the magnitude of the external magnetic field Bc based on the detected voltage E.

[0044] The magnitude of the induced magnetic field Be generated in the exciter 21 by the application of the pulse current changes periodically. As a result, an excited state period in which the magnetic moments of the magnetic body 22 are aligned and a relaxed state period in which the application of current is stopped and the magnetic moments return to their original state are repeated in a short cycle. Therefore, the detector 9 detects the difference between the excited state period and the relaxed state period of the voltage E in the coil 3. For example, the detector 9 can calculate the average value by repeatedly calculating the difference between the excited state period and the relaxed state period multiple times.

[0045] <Functions and Effects of Magnetic Sensor 1A> In magnetic sensor 1A, the direction of the magnetic moment of magnetic body 22 is influenced by an external magnetic field Bc and tilts toward the external magnetic field Bc. When a pulse current is passed through conductive exciter 21 in this state, the induced magnetic field Be generated by exciter 21 aligns the magnetic moments of magnetic body 22 in the circumferential direction. A voltage E corresponding to this change in the direction of the magnetic moment is then generated in coil 3. The detection unit 9 detects the external magnetic field Bc by measuring the voltage E generated in coil 3.

[0046] Here, in the magnetic sensor 1A, the first coil portion 31 and the second coil portion 32 of the coil 3 are connected in parallel. This has the effect of reducing current noise caused by the preamplifier 90 included in the detection unit 9. Details are as follows. Note that in Figures 5 and 6, the first partial coil portion 311 and the second partial coil portion 312 (see Figure 1) included in the first coil portion 31, and the third partial coil portion 323 and the fourth partial coil portion 324 (see Figure 1) included in the second coil portion 32 are both shown as a single common coil.

[0047] 5, the detection unit 9 includes a preamplifier 90 having an input terminal with an input impedance R. In this case, a current I flowing from the preamplifier 90 to the coil 3 connected to the input terminal of the preamplifier 90 generates current noise N with a magnitude of R×I×r / (r+2R) (unit: V / √Hz), where r represents the coil impedance of each of the first coil portion 31 and the second coil portion 32. Here, in order for the detection unit 9 to accurately detect the voltage E generated in the coil 3, it is preferable that the current noise N is small.

[0048] Here, a magnetic sensor 10 having only one coil portion 30 is defined as shown in FIG. 6 . In the magnetic sensor 10, the current noise N′ is R×I×r / (r+R) (unit: V / √Hz). Assuming that R is much larger than r, the current noise N′ is approximately twice as large as the current noise N (see FIG. 5 ) of the magnetic sensor 1A having the first coil portion 31 and the second coil portion 32. In other words, by providing the first coil portion 31 and the second coil portion 32 connected in parallel in the magnetic sensor 1A, the current noise can be reduced to approximately half compared to the magnetic sensor 10 having only one coil portion 30.

[0049] According to a similar calculation, a magnetic sensor having N coil portions can reduce current noise to 1 / N compared to a magnetic sensor having only one coil portion.

[0050] It is also known that magnetic noise resulting from the magnetic properties of the magnetic body 22 affects the detection accuracy of the voltage E by the detection unit 9. In contrast, in the magnetic sensor 1A, the first coil portion 31 and the second coil portion 32 are connected in parallel. This also reduces magnetic noise. This is because magnetic noise generated in each coil portion or partial coil portion occurs randomly, and therefore, in the case of the magnetic sensor 1A in which multiple coil portions or multiple partial coils are connected in parallel, the magnetic noise can be averaged, thereby reducing the magnetic noise detected by the detection unit 9. Note that in a magnetic sensor having N coil portions, magnetic noise can be reduced to 1 / √N compared to a magnetic sensor having only one coil portion.

[0051] Furthermore, in the magnetic sensor 1A, the first partial coil portion 311 and the second partial coil portion 312 are connected in parallel in the first coil portion 31, and the third partial coil portion 323 and the fourth partial coil portion 324 are connected in parallel in the second coil portion 32. Therefore, in the magnetic sensor 1A, the first partial coil portion 311, the second partial coil portion 312, the third partial coil portion 323, and the fourth partial coil portion 324 are connected in parallel. Therefore, compared to a magnetic sensor having only one partial coil portion, the magnetic sensor 1A can reduce current noise to approximately ¼ and magnetic noise to ½ (=√4). Note that, in a magnetic sensor having M partial coil portions, compared to a magnetic sensor having only one partial coil portion, current noise can be reduced to 1 / M and magnetic noise can be reduced to 1 / √M.

[0052] 5 and 6, the waveform of the voltage E detected by the detection unit 9 does not change between the magnetic sensor 1A having the first coil portion 31 and the second coil portion 32 connected in parallel and the magnetic sensor 10 having only one coil portion 30. The same is true for magnetic sensors having three or more coil portions. Therefore, the peak change amount ΔV (unit: V) of the voltage E in response to a change in the magnetic field also does not change regardless of the number of coil portions.

[0053] The reason for this is that in the magnetic sensor 1A shown in FIG. 5, the frequency of the voltage E is expressed as 1 / [√{(L / 2)×(2×C)}]=1 / {√(L×C)}, whereas in the magnetic sensor 10 shown in FIG. 6, the frequency of the voltage E is expressed as 1 / {√(L×C)}, which is common to both. Note that L represents the inductance of each of the first coil portion 31 and the second coil portion 32. C represents the stray capacitance of each of the first coil portion 31 and the second coil portion 32. In other words, the sensitivity A (unit: V / μT) does not change between the magnetic sensor 1A and the magnetic sensor 10. According to a similar calculation, the peak change ΔV of the voltage E does not change between a magnetic sensor having N coil portions and a magnetic sensor having only one coil portion, and therefore the sensitivity A does not change either.

[0054] That is, in the magnetic sensor 1A, by increasing the number of coil portions while maintaining the sensitivity A, it is possible to suppress current noise and magnetic noise caused by the preamplifier 90 of the detection unit 9. Furthermore, in the magnetic sensor 1A, by increasing the number of partial coil portions included in the coil portion while maintaining the sensitivity A, it is possible to suppress current noise and magnetic noise caused by the preamplifier 90 of the detection unit 9.

[0055] The exciter 21, through which the pulse current is passed, is conductive. Therefore, even when the total number of excitation units is increased by connecting the first excitation unit 51 and the second excitation unit 52 in series, as in the case of the exciter 21, the pulse current can be passed through the exciter 21 satisfactorily. Therefore, in the magnetic sensor 1A, even if the number of coil units or partial coil units connected in parallel to reduce current noise and magnetic noise is increased, the magnitude of the pulse current flowing through the exciter 21 does not change. Therefore, the magnetic sensor 1A can improve the magnetic resolution by reducing current noise and magnetic noise by increasing the number of coil units or partial coil units connected in parallel while maintaining the sensitivity A.

[0056] Furthermore, when the voltage E generated in the coil 3 is amplified by the detector 9, the offset component is also amplified. In this case, there is a possibility that the voltage may exceed the measurable voltage range in the circuit of the detector 9. For this reason, it is preferable to reduce the offset component, since this allows for a correspondingly higher amplification factor.

[0057] The principle behind the occurrence of offset is as follows. Figures 7 to 9 schematically show the magnetic moment Q in the magnetic body 22 in a magnetic field-free state. The magnetic moment Q includes a first magnetic moment Qa and a second magnetic moment Qb that face in opposite directions. Figure 7 shows a state in which no pulse current is passed through the exciter 21. Figure 8 shows a state in which a pulse current is passed through the exciter 21 in a first extension direction D1. Figure 9 shows a state in which a pulse current is passed through the exciter 21 in a second extension direction D2. One of the orthogonal directions V is referred to as a first orthogonal direction V1, and the other orthogonal direction V is referred to as a second orthogonal direction V2.

[0058] 7, when no pulse current is applied, the first magnetic moment Qa is inclined toward the second extension direction D2 with respect to the second orthogonal direction V2. The second magnetic moment Qb is inclined toward the first extension direction D1 with respect to the first orthogonal direction V1. The inclination angle of the first magnetic moment Qa and the second magnetic moment Qb with respect to the orthogonal direction V is assumed to be θ. In this way, the magnetic moment Q in the magnetic body 22 is slightly inclined with respect to the orthogonal direction V due to the influence of residual stress within the magnetic body 22, etc.

[0059] 8, when a pulse current in the first extension direction D1 is applied to the magnetic exciter 21, the magnetic exciter 21 generates an induced magnetic field having a component in the first orthogonal direction V1 in response to the pulse current. Hereinafter, the component in the first orthogonal direction V1 of the induced magnetic field generated in response to the application of the pulse current will be referred to as the induced magnetic field Be1. At this time, the magnetic moment Q in the magnetic body 22 attempts to align in the circumferential direction along the direction of the induced magnetic field Be1, and performs a precession motion that rotates around the induced magnetic field Be1.

[0060] Here, the difference in angle between the orientation of the second magnetic moment Qb and the induced magnetic field Be1 when no pulse current is applied is small, and the relaxation time of the precession is short. Therefore, even if the pulse width of the pulse current is short, the precession of the second magnetic moment Qb ends within the application time of the pulse current, and the second magnetic moment Qb aligns with the direction of the induced magnetic field Be1. On the other hand, the difference in angle between the orientation of the first magnetic moment Qa and the induced magnetic field Be1 when no pulse current is applied is large, and the relaxation time of the precession is long. Therefore, when the pulse width of the pulse current is short, the precession of the first magnetic moment Qa does not end within the application time of the pulse current, and the first magnetic moment Qa does not align with the direction of the induced magnetic field Be1.

[0061] 9, when a pulse current in the second extension direction D2 is applied to the magnetic exciter 21, the magnetic exciter 21 generates an induced magnetic field having a component in the second orthogonal direction V2 in response to the pulse current. Hereinafter, the component in the second orthogonal direction V2 of the induced magnetic field generated in response to the application of the pulse current will be referred to as the induced magnetic field Be2. At this time, the magnetic moment Q in the magnetic body 22 attempts to align in the circumferential direction along the direction of the induced magnetic field Be2, and performs a precession motion that rotates around the induced magnetic field Be2.

[0062] Here, the difference in angle between the orientation of the first magnetic moment Qa and the induced magnetic field Be2 when no pulse current is applied is small, and the relaxation time of the precession is short. Therefore, even when the pulse width of the pulse current is short, the precession of the first magnetic moment Qa ends within the application time of the pulse current, and the first magnetic moment Qa aligns with the direction of the induced magnetic field Be2. On the other hand, the difference in angle between the orientation of the second magnetic moment Qb and the induced magnetic field Be2 when no pulse current is applied is large, and the relaxation time of the precession is long. Therefore, when the pulse width of the pulse current is short, the precession of the second magnetic moment Qb does not end within the application time of the pulse current, and the second magnetic moment Qb does not align with the direction of the induced magnetic field Be2.

[0063] 8 and 9, an electromotive force is generated in the coil according to the difference in the orientation of the first magnetic moment Qa and the second magnetic moment Qb. Therefore, even in a magnetic field-free state, the voltage E generated in the coil 3 does not become zero and is detected as an offset. Note that the polarity of the offset detected when a pulse current is passed in the first extension direction D1 (see FIG. 8) is opposite to the polarity of the offset detected when a pulse current is passed in the second extension direction D2 (see FIG. 9).

[0064] In contrast, in the first excitation unit 51, the direction of the pulse current flowing through the first partial excitation unit 511 (first extension direction D1) and the direction of the pulse current flowing through the second partial excitation unit 512 (second extension direction D2) are opposite to each other. In this case, the polarity of the offset of the voltage generated in the first partial coil unit 311 wound around the first partial excitation unit 511 can be reversed from the polarity of the offset of the voltage E generated in the second partial coil unit 312 wound around the second partial excitation unit 512. Similarly, in the second excitation unit 52, the direction of the pulse current flowing through the third partial excitation unit 523 (first extension direction D1) and the direction of the pulse current flowing through the fourth partial excitation unit 524 (second extension direction D2) are opposite to each other. In this case, the polarity of the voltage offset generated in the third partial coil portion 323 wound around the third partial excitation portion 523 and the polarity of the voltage offset E generated in the fourth partial coil portion 324 wound around the fourth partial excitation portion 524 can be reversed.

[0065] Therefore, the detection unit 9 can increase the detected voltage while eliminating the influence of offset by calculating an average value of the voltages of the multiple partial coil units. This allows the magnetic sensor 1A to obtain good sensitivity characteristics to the external magnetic field Bc and improve magnetic resolution. Therefore, the magnetic sensor 1A can improve the signal-to-noise ratio by increasing its sensitivity.

[0066] The exciters 21 of the wires 2A and 2B of the wire unit 2 extend parallel to each other. The pulse current flows in the same direction in the exciters 21 of the wires 2A and 2B. In this case, the magnetic sensor 1A can obtain even better sensitivity characteristics to the external magnetic field Bc. Furthermore, random noise generated in the magnetic bodies 22 of the wires 2A and 2B is averaged, thereby reducing noise.

[0067] By using a material for the exciter 21 that is one of copper, silver, aluminum, tin, and zinc, or an alloy containing at least one of copper, silver, aluminum, tin, and zinc, it is possible to easily create an exciter 21 that can effectively conduct pulse current.

[0068] The magnetic body 22 is made of a nickel-iron alloy or an amorphous material. In this case, it is easy to create a magnetic body 22 that appropriately changes the direction of the magnetic moment when it is affected by an external magnetic field Bc or an induced magnetic field Be that is generated in response to a pulse current flowing through the exciter 21.

[0069] The magnetic body 22 is plated on the surface of the exciter 21. In this case, by passing a pulse current through the exciter 21, the direction of the magnetic moment of the magnetic body 22 can be appropriately changed.

[0070] The conductivity of the exciter 21 is 20 times or more the conductivity of the magnetic body 22. This allows the exciter 21 to pass an intermittent current well.

[0071] <Evaluation Results> FIG. 12 shows the results of evaluations performed using the magnetic sensor 1B shown in FIG. 10 and the magnetic sensor 1C shown in FIG.

[0072] 10 includes only the first excitation unit 51 and the first coil unit 31 of the magnetic sensor 1A (see FIG. 1). Therefore, in the magnetic sensor 1B, only the first partial excitation unit 511 and the second partial excitation unit 512 are connected in series, and only the first partial coil unit 311 and the second partial coil unit 312 are connected in parallel.

[0073] 11 includes a third excitation unit 53 and a fourth excitation unit 54 in addition to the first excitation unit 51 and the second excitation unit 52 of the magnetic sensor 1A (see FIG. 1). The third excitation unit 53 and the fourth excitation unit 54 have the same configuration as the first excitation unit 51 and the second excitation unit 52. The third excitation unit 53 includes a fifth partial excitation unit 535 and a sixth partial excitation unit 536. The fourth excitation unit 54 includes a seventh partial excitation unit 547 and an eighth partial excitation unit 548.

[0074] The magnetic sensor 1C further includes a third coil portion 33 and a fourth coil portion 34 in addition to the first coil portion 31 and the second coil portion 32 of the magnetic sensor 1A (see FIG. 1 ). The third coil portion 33 and the fourth coil portion 34 have the same configuration as the first coil portion 31 and the second coil portion 32. The third coil portion 33 includes a fifth partial coil portion 335 and a sixth partial coil portion 336. The fifth partial coil portion 335 is wound around the fifth partial excitation portion 535, and the sixth partial coil portion 336 is wound around the sixth partial excitation portion 536. The fourth coil portion 34 includes a seventh partial coil portion 347 and an eighth partial coil portion 348. The seventh partial coil portion 347 is wound around the seventh partial excitation portion 547, and the eighth partial coil portion 348 is wound around the eighth partial excitation portion 548.

[0075] In magnetic sensor 1C, four excitation units (first excitation unit 51, second excitation unit 52, third excitation unit 53, and fourth excitation unit 54) are connected in series, and eight partial excitation units (first partial excitation unit 511, second partial excitation unit 512, third partial excitation unit 523, fourth partial excitation unit 524, fifth partial excitation unit 535, sixth partial excitation unit 536, seventh partial excitation unit 547, and eighth partial excitation unit 548) are connected in series. In addition, in the magnetic sensor 1C, four partial coil portions (first coil portion 31, second coil portion 32, third coil portion 33, and fourth coil portion 34) are connected in parallel, and eight partial coil portions (first partial coil portion 311, second partial coil portion 312, third partial coil portion 323, fourth partial coil portion 324, fifth partial coil portion 335, sixth partial coil portion 336, seventh partial coil portion 347, and eighth partial coil portion 348) are connected in parallel.

[0076] In magnetic sensors 1B and 1C, the number of turns of each partial coil portion was set to 500. In magnetic sensor 1C, the eight partial coil portions were arranged in an area of ​​1 cm square. The amplification factor of the preamplifier 90 of magnetic sensor 1B was set to 20 times. The amplification factor of the preamplifier 90 of magnetic sensor 1C was set to 20 times or 45 times.

[0077] 12 shows the results of noise (unit: pT / √Hz) measurements performed using magnetic sensors 1B and 1C. These results confirm that, in the case of magnetic sensors 1B and 1C, which share a common amplification factor of 20x for the preamplifier 90, the noise in magnetic sensor 1C, which has eight partial coil sections, is smaller than the noise in magnetic sensor 1B, which has two partial coil sections. This demonstrates that the greater the number of partial coil sections connected in parallel, the greater the noise reduction. Furthermore, it was confirmed that, in magnetic sensor 1C, the noise could be further reduced when the amplification factor of the preamplifier 90 was set to 45x compared to when the amplification factor was set to 20x.

[0078] <Magnetic Sensor 1D> The magnetic sensor 1D will be described with reference to Fig. 13. The magnetic sensor 1D differs from the magnetic sensor 1A (see Fig. 1) in that the first partial coil portion 311 and the second partial coil portion 312 of the first coil portion 31 are connected in series, and the third partial coil portion 323 and the fourth partial coil portion 324 of the second coil portion 32 are connected in series. The other configurations are the same as those of the magnetic sensor 1A.

[0079] <Functions and Effects of Magnetic Sensor 1D> In magnetic sensor 1D, like magnetic sensor 1A, the first coil portion 31 and the second coil portion 32 are connected in parallel. Therefore, like magnetic sensor 1A, it has the effect of reducing current noise and magnetic noise while maintaining sensitivity A. Also, in magnetic sensor 1D, like magnetic sensor 1A, the direction of pulse current flow differs in each of the first partial excitation portion 511 and the second partial excitation portion 512, and the direction of pulse current flow differs in each of the third partial excitation portion 523 and the fourth partial excitation portion 524. In this case, the polarity of voltage E can be reversed with respect to the offset, thereby eliminating the effects of the offset.

[0080] Furthermore, in magnetic sensor 1D, the first partial coil portion 311 and the second partial coil portion 312 of the first coil portion 31 are connected in series, and the third partial coil portion 323 and the fourth partial coil portion 324 of the second coil portion 32 are connected in series, so the voltage E generated in coil 3 is larger than in magnetic sensor 1A. For this reason, magnetic sensor 1D can increase the detected voltage while eliminating the effect of offset by calculating a value obtained by adding up the voltages of the multiple partial coil portions in the detection unit 9, thereby improving magnetic resolution. Therefore, magnetic sensor 1D can improve the signal-to-noise ratio by increasing sensitivity.

[0081] The present invention is not limited to the above-described embodiment, and various modifications are possible. In the following, unless otherwise specified, modifications of the magnetic sensor 1A will be described, but the same may be applied to the magnetic sensor 1D as appropriate.

[0082] The waveform of the current passed through the exciter 21 is not limited to a pulse waveform, but may be any other waveform whose value changes intermittently, such as a triangular wave, a sine wave, or a square wave.

[0083] The first coil portion 31 of the magnetic sensor 1A may have one partial coil portion or three or more partial coil portions. The second coil portion 32 of the magnetic sensor 1A may have one partial coil portion or three or more partial coil portions. The magnetic sensor 1A may have one or more coil portions in addition to the first coil portion 31 and the second coil portion 32. The number of partial coil portions included in the first coil portion 31, the second coil portion 32, and the additional coil portion may be the same or different.

[0084] The third partial coil portion 323 and the fourth partial coil portion 324 of the magnetic sensor 1A may be connected in series. When the magnetic sensor 1A has three or more coil portions, the connection method of the multiple partial coil portions included in each coil portion does not have to be the same, and a mixture of series connection and parallel connection may be used. When the same coil portion includes three or more partial coils, the connection method of these partial coils does not have to be the same, and a mixture of series connection and parallel connection may be used.

[0085] The lengths of the plurality of partial coil sections in the extension direction D may all be the same, or at least some may differ. The number of turns of the plurality of partial coil sections may all be the same, or at least some may differ. They may be arranged in a planar manner on a common substrate, or may be arranged in layers perpendicular to the substrate.

Claims

1. A magnetic sensor comprising: a conductive exciter through which an intermittent current is passed; a magnetic body provided on the surface of the exciter and having a lower conductivity than the exciter; a coil wound around the exciter and the magnetic body; and a detection unit that detects the external magnetic field by detecting a voltage generated in the coil by an external magnetic field while the intermittent current is passed through the exciter, wherein the coil includes: a first coil portion wound around a first excitation portion of the exciter; and a second coil portion wound around a second excitation portion of the exciter that is different from the first excitation portion, wherein the first excitation portion and the second excitation portion are connected in series, and the first coil portion and the second coil portion are connected in parallel, and the detection unit detects the external magnetic field by detecting a common voltage generated in the first coil portion and the second coil portion.

2. The magnetic sensor described in claim 1, characterized in that the first coil portion includes a first partial coil portion wound around a first partial excitation portion of the first excitation portion, and a second partial coil portion wound around a second partial excitation portion of the first excitation portion that is different from the first partial excitation portion, the first partial excitation portion and the second partial excitation portion are connected in series, and the first partial coil portion and the second partial coil portion are connected in series or in parallel, and a first direction indicating the direction in which the intermittent current flows in the first partial excitation portion and a second direction indicating the direction in which the intermittent current flows in the second partial excitation portion are opposite to each other.

3. The magnetic sensor described in claim 2, characterized in that the second coil portion includes a third partial coil portion wound around a third partial excitation portion of the second excitation portion, and a fourth partial coil portion wound around a fourth partial excitation portion of the second excitation portion that is different from the third partial excitation portion, the third partial excitation portion and the fourth partial excitation portion being connected in series, and the third partial coil portion and the fourth partial coil portion being connected in series or in parallel, and a third direction indicating the direction in which the intermittent current flows in the third partial excitation portion and a fourth direction indicating the direction in which the intermittent current flows in the fourth partial excitation portion being opposite each other.

4. The magnetic sensor according to claim 1, characterized in that the exciter includes a plurality of parallel excitation parts extending parallel to each other, and the direction in which the intermittent current flows is the same for each of the plurality of parallel excitation parts.

5. The magnetic sensor according to claim 1, characterized in that the material of the exciter is one of copper, silver, aluminum, tin, and zinc, or an alloy containing at least one of copper, silver, aluminum, tin, and zinc.

6. The magnetic sensor according to claim 1, wherein the magnetic material is a nickel-iron alloy or an amorphous material.

7. The magnetic sensor according to claim 1, wherein the magnetic body is plated on the surface of the exciter.

8. The magnetic sensor according to claim 1, wherein the conductivity of said exciter is 20 times or more the conductivity of said magnetic body.

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