JP2006184116A - Device for detecting magnetism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the magnetic field generated by an object to be measured, without being affected by the environmental magnetic field. <P>SOLUTION: An environmental magnetic field is detected by a normal conductor coil (24), used for detecting environmental magnetic fields. A signal, corresponding to the detected environmental magnetic field, is fed back by a compensating/adjusting circuit (8) to a magnetic field measuring section (25), including a magnetic sensor (SQUID) and an FLL circuit, thereby compensating with respect to the environmental magnetic field for the measured magnetic field. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic detection device that detects a magnetic field from a detection target object, and more particularly to a magnetic detection device that uses a superconducting quantum interference device (SQUID) as a magnetic sensor. More specifically, the present invention relates to a configuration for accurately detecting a magnetic field from a detection target object while suppressing the influence of an environmental magnetic field with a simple magnetic shield.

  A quantum magnetic interference element (hereinafter referred to as SQUID) is known as a highly sensitive magnetic sensor. SQUID utilizes a phenomenon that allows a current to flow through a Josephson junction without causing a voltage difference. When a magnetic field is externally applied to the SQUID with a bias current larger than the superconducting critical current, a voltage modulated by the externally applied magnetic field appears at both ends of the SQUID. By detecting this SQUID voltage externally, an externally applied magnetic field can be detected. A SQUID that uses a high-temperature superconductor that normally becomes a superconductor at a liquid nitrogen temperature has a sensitivity of 10 ^ (-13) Tesla / √Hz, and a low-temperature superconductor that becomes a superconductor at a liquid helium temperature. The SQUID that uses is sensitive to 10 ^ (-14) Tesla / √Hz. Here, the symbol “^” indicates a power.

  Since the voltage in the SQUID periodically changes in units of quantized magnetic flux (flux quanta) according to the externally applied magnetic field, an extremely weak magnetic field can be detected.

  As an application using such a SQUID as a magnetic sensor, it is used in a medical device for detecting a biomagnetic field, a non-destructive inspection device for detecting a magnetic foreign object, and the like.

  As described above, since the output voltage of the SQUID magnetic sensor periodically changes in units of quantized magnetic flux, the characteristic curve indicating the correspondence relationship between the voltage V and the magnetic field φ is represented by a multi-value function. Therefore, in order to detect the absolute value of the magnetic field from the measurement target object, it is necessary to lock the operating point of the SQUID magnetic sensor. For this purpose, a drive circuit called an FLL (magnetic flux locked loop) circuit is used. An example of the configuration of a magnetic detection device using a SQUID magnetic sensor having such an FLL circuit is shown in Patent Document 1 (Japanese Patent Laid-Open No. 2000-292511).

Further, in order to accurately detect a weak magnetic field, it is required to eliminate the influence of an external noise magnetic field such as an environmental magnetic field. The configuration of magnetic shielding for suppressing the influence of such an external noise magnetic field is disclosed in Patent Document 2 (US Patent Publication No. 2003-0218872) and Non-Patent Document 1 (Kurijo, “Study on High-Temperature Superconductor SQUID”. , Electronic Science Research, No. 8, pages 18-23, 2000).
JP 2000-292511 A US Patent Publication No. 2003-0218872 "Research on high-temperature superconductor SQUID", Kurijo, Electronic Science Research, No. 8, pp. 18-23, 2000

  The configuration disclosed in Patent Document 1 shows a configuration in which the position at which the slope of the voltage-magnetic field characteristic curve (V-Φ characteristic curve) is the largest is set as the operating point as the operating point of the FLL circuit. However, in the configuration shown in Patent Document 1, it is difficult to distinguish between a magnetic field (signal magnetic field) from an object to be detected and an external magnetic field (noise magnetic field such as an environmental magnetic field). Does not discuss the effects of environmental magnetic fields on measurements.

  Moreover, in patent document 2, as a prior art of the structure of magnetic shielding, an external magnetic field (environmental magnetic field) is detected using a flux gate or SQUID, and a magnetic field having a phase opposite to the detected external magnetic field is generated via a coil. A configuration of an active filter type magnetic shield that cancels an external magnetic field is described. As an example of the configuration of this active filter type magnetic shielding, a configuration is described in which a large Helmholtz coil is provided outside the magnetic shielding chamber, and this Helmholtz coil is combined with the permalloy of the magnetic shielding layer of the magnetic shielding chamber to realize an active shield. Has been.

  In this patent document 2, when the entire magnetic shielding room is used, the phase delay of the shielding magnetic field occurs due to the time delay until the reverse-phase magnetic field is generated by the output of the sensor that detects the external magnetic field, and the external magnetic field is accurately detected. States that it cannot be compensated. In Patent Document 2, an external noise magnetic field for a measurement coil that detects a magnetic field to be detected is used to generate a compensation magnetic field for the external magnetic field, cancel the external magnetic field, and transfer to the measurement coil. Try to prevent the external magnetic field from affecting. However, this active shield system assumes a magnetic shielding room as a whole, which increases the cost of the equipment and the scale of the equipment.

  In this patent document 2, in order to interpret such a problem, superconducting rings are respectively arranged at both ends of a cylindrical magnetic shield having open ends at both ends, and a measuring magnetic sensor is placed at an intermediate position of the superconducting ring pair. The arrangement to be arranged is shown. The surface of the magnetic sensor is arranged so as to be parallel to the axial direction of these superconducting rings, and the intrusion of an external magnetic field is suppressed by the Meissner effect of the superconducting ring. However, in this configuration, a dedicated superconducting ring is used to cancel the influence of the external magnetic field, which increases the device price and the device scale. In particular, when the object to be measured is large, such as meat, the opening of the magnetic shield of the magnetic sensor for measurement becomes large, and a superconducting ring is placed in such a large opening to provide an external magnetic field due to the Meissner effect. It is difficult to suppress the intrusion of

  In Non-Patent Document 1, coils are wound around the upper, middle, and lower portions of the magnetic shield, and the output signal of the center coil is applied to the upper and lower coils to cancel the external magnetic field. Thus, a configuration for preventing the external noise magnetic field from entering the magnetic shield is shown. In the configuration of Non-Patent Document 1, a large magnetic shield chamber is assumed as the magnetic shield, and the facility becomes large.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic detection device capable of accurately measuring the magnetic field (signal magnetic field) from a measurement target while suppressing the influence of an external magnetic field (environmental magnetic field) under a simple magnetic shield environment. That is.

  The magnetic detection device according to the present invention includes a magnetic sensor for detecting a magnetic field to be measured, a normal conducting coil arranged separately from the magnetic sensor, and a compensation magnetic field for the detected magnetic field of the magnetic sensor according to the detection output of the normal conducting coil. A magnetic compensation circuit that is generated and supplied to the magnetic sensor, and a detection circuit that generates a signal corresponding to the magnetic field to be measured in accordance with an output signal of the magnetic sensor.

  An environmental magnetic field (external noise magnetic field) is detected using an inexpensive normal conducting coil, and a compensation magnetic field corresponding to the detected environmental magnetic field is supplied to the magnetic sensor. It is possible to compensate, and the magnetic field to be measured can be accurately detected. In addition, a normal conducting coil is used to detect the environmental magnetic field, and the apparatus price can be reduced.

[Embodiment 1]
FIG. 1 schematically shows an overall configuration of a magnetic detection device according to the first embodiment of the present invention. In FIG. 1, the magnetic detection device includes a magnetic sensor 1 that detects a magnetic field from an object to be measured (not shown), a bias current source 2 that supplies the magnetic sensor 1 with a bias current Ib having a constant magnitude, An amplifier 3 that amplifies the voltage across the magnetic sensor 1, an integrator 4 that integrates the output signal of the amplifier 3 to generate a detection output voltage Vout, and a feedback resistance element 5 that converts the output voltage of the integrator 4 into a current. And a modulation coil 6 that generates a compensation magnetic field according to the current from the feedback resistance element 5.

  As an example, the magnetic sensor 1 includes a DC-SQUID having two Josephson junctions 1a and 1b. The magnetic sensor 1 may be an RF-SQUID having one other Josephson junction, or may be another magnetic sensor such as an MI sensor using an MI (magnetic impedance) effect.

  The superconducting current flows when a Cooper pair that creates a superconducting state moves through the Josephson coupling by a tunnel phenomenon. When a bias current Ib is passed through the SQUID, a normal conducting current is generated when the critical value (superconducting critical current value) of the superconducting current limited by the Josephson junction is exceeded, and a voltage Vs is generated across the SQUID. On the other hand, when a magnetic field is applied to the SQUID, a shielding current is generated in the superconducting ring so as to prohibit the penetration of the magnetic field into the inside. At this time, the phase difference Δφ of the Cooper pair in the Josephson junction changes depending on the strength of the magnetic field applied from the outside. When the superconducting critical current value is Ic, the shielding current Is is limited by the Josephson junction and is given by the following equation.

Is = Ic · sinΔφ
In the superconductor, the magnetic field is quantized, and the minimum unit is called a quantized magnetic flux (flux quantum) φ0. The phase difference Δφ is expressed by the following equation using an externally applied magnetic field φ and a quantized magnetic flux (magnetic flux quantum) φc.

Δφ = 2 · n · π + 2 · π · (φ / φ0)
That is, the shield current Is periodically changes in units of quantized magnetic flux φ0 (2 · 10 ^ (− 15) Wb). Here, the symbol “^” indicates a power. Therefore, when a magnetic field is applied to the SQUID, the bias current value that can maintain the superconducting state is changed by the shielding current, and the current-voltage curves are Δφ = 2 · n · π and Δφ = (2n + 1) · φ. Move between. At this time, if the bias current Ib is a constant value, the voltage Vs generated at both ends of the SQUID also changes periodically.

  The voltage Vs generated at both ends of the SQUID 1 has a magnitude of about μV, is amplified using the amplifier 3, and the high frequency component is removed by the integrator 4 to generate a detection output voltage Vout corresponding to the measurement magnetic field. To do.

  Since the voltage-magnetic field characteristic curve (V-φ characteristic curve) periodically changes with the quantized magnetic flux φ0 as a unit as described above, the linear region of the characteristic curve is narrow. Therefore, in order to increase the dynamic range of the detection voltage, negative feedback is performed using the integrator 4, the feedback resistance element 5, and the modulation coil 6, and magnetic field detection is performed according to the so-called “zero detection method (zero method)”. Do. A magnetic field is generated from the modulation coil 6 so as to cancel the external magnetic field applied to the SQUID 1. When the magnetic coupling coefficient (transconductance) between the modulation coil 6 and the SQUID is Mf and the resistance value of the feedback resistance element 5 is Rf, the voltage at both ends of the feedback resistance element 5, that is, the detected output voltage Vout is (Rf / Mf) Φ, which is proportional to the signal flux φ.

  In FIG. 1, an operating point setting circuit for adjusting the bias current applied to the modulation coil 6 and setting the operating point of the SQUID is provided. In FIG. The circuit to supply is not shown. By fixing the operating point of this SQUID, the magnetic field-voltage correspondence can be set uniquely, and the signal magnetic field can be detected according to the detection voltage Vout.

  The magnetic field-voltage characteristic curve of the SQUID changes periodically with the quantized magnetic flux as a unit, and a magnetic field weaker than the quantized magnetic flux φ0 can be detected. A SQUID using a high-temperature superconductor has a sensitivity of 10 ^ (-13) Tesla / √Hz, and a SQUID using a low-temperature superconductor has a sensitivity of 10 ^ (-14) Tesla / √Hz. It can be measured.

  In order to suppress the influence of the external magnetic field (environmental magnetic field) on the weak magnetic field from the measurement object, the environment magnetic field detection coil 7 that detects the environment magnetic field, and amplification, integration, attenuation, and the like according to the output signal of the environment magnetic field detection coil 7 A compensation adjustment circuit 8 that performs a necessary process such as phase adjustment to generate a current signal, and a compensation coil 9 that generates a compensation magnetic field according to an output signal of the compensation adjustment circuit 8 and supplies the compensation magnetic field to the magnetic sensor (SQUID) 1 are provided. It is done.

  The normal conducting coil 7 is made of a normal conducting material such as enameled wire or copper wire.

  The output signal of the environmental magnetic field detection coil 7 is a differential signal of the environmental magnetic field. In the compensation adjustment circuit 8, the differential signal is amplified and integrated to generate a voltage signal corresponding to the detected environmental magnetic field, and then the signal amplitude considering the mutual coupling between the compensation coil 9 and the modulation coil 1. The phase adjustment is performed so that the magnetic field having a negative phase and the magnetic field having exactly opposite phases are applied to the modulation coil 1. As a result, a magnetic field having a phase opposite to that of the environmental magnetic field detected by the environmental magnetic field detection coil 7 is generated by the compensation coil 9 and supplied to the magnetic sensor 1. Accordingly, in the magnetic sensor 1, the environmental magnetic field is canceled out, and the magnetic field from the measurement target object can be accurately detected.

  In particular, as shown in FIG. 1, a negative feedback magnetic field having a phase opposite to that of the environmental magnetic field is generated by the compensation coil 9 and directly applied to the magnetic sensor 1. The influence can be suppressed. In addition, the compensation adjustment circuit 8 generates a magnetic field having a phase opposite to that detected by the environmental magnetic field detection coil 7 by the compensation coil 9, and generates a compensation magnetic field that follows the change in the environmental magnetic field, thereby generating a magnetic sensor. 1 and the influence of the environmental magnetic field can be accurately suppressed in the magnetic sensor 1 with almost no delay in response.

  As described above, according to the first embodiment of the present invention, the environmental magnetic field is detected using the normal conducting coil, and the negative feedback compensation magnetic field corresponding to the detected environmental magnetic field is generated and applied to the magnetic sensor. Even under an insufficient magnetic shield environment, the influence of the environmental magnetic field can be suppressed and the magnetic field from the measurement detection target can be accurately detected.

[Embodiment 2]
FIG. 2 schematically shows a configuration of a magnetic detection device according to the second embodiment of the present invention. The magnetic detection device shown in FIG. 2 differs from the magnetic detection device shown in FIG. 1 in the following points. That is, a core with high magnetic permeability is inserted as the magnetic core of the environmental magnetic field detection coil 7 composed of a normal conducting coil. Permalloy (Ni—Fe alloy), amorphous metal or amorphous alloy can be used as the core material with high magnetic permeability. Fe-B-Si-Cu, Co-Fe-Si-B, Co-Fe-Ni-Si-B or Fe-Cu-Nb-Si-B is used as the high magnetic permeability soft magnetic amorphous alloy material. be able to.

  The other configuration of the magnetic detection device shown in FIG. 2 is the same as the configuration of the magnetic detection device shown in FIG. 1, and corresponding portions are denoted by the same reference numerals, and detailed description thereof is omitted.

  By using a high magnetic permeability material as the core of the environmental magnetic field detection coil 7 composed of a superconducting coil, the detection magnetic flux in the environmental magnetic field detection coil 7 can be increased. The sensitivity of the configured environmental magnetic field detection sensor can be increased, and the magnetic field from the measurement target object can be detected more accurately while suppressing the influence of the environmental magnetic field.

  As described above, according to the second embodiment of the present invention, the high magnetic permeability material is used for the core of the normal conducting coil as the environmental magnetic field detection sensor, and the sensitivity of the environmental magnetic field detection sensor can be increased. It is possible to reliably detect the measurement target magnetic field while suppressing the influence of the environmental magnetic field.

[Embodiment 3]
FIG. 3 schematically shows an overall configuration of the magnetic detection apparatus according to the third embodiment of the present invention. In the magnetic detection device shown in FIG. 3, the output signal (current) of the compensation adjustment circuit 8 is added to the current from the feedback resistance element 5 and supplied to the modulation coil 6.

  The compensation adjustment circuit 8 includes an amplifier 12 that amplifies the detection voltage of the environmental magnetic field detection coil 7, an integrator 13 that integrates the output signal of the amplifier 12, and an attenuator 14 that attenuates the output signal of the integrator 13 at a predetermined rate. And a phase adjuster 16 that adjusts the phase of the output signal of the attenuator 14, and a compensation resistor element 18 that converts the output signal of the phase adjuster 16 into a current signal and supplies the current signal to the modulation coil 6.

  The other configuration of the magnetic detection device shown in FIG. 3 is the same as the configuration of the magnetic detection device shown in FIG. 1, and corresponding portions are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the configuration of the magnetic detection device shown in FIG. 3, the environmental magnetic field compensation coil and the measurement magnetic field canceling coil are shared. Therefore, it is not necessary to adjust the arrangement position of the environmental magnetic field compensation coil provided separately from the modulation coil 6, and the adjustment for environmental magnetic field compensation is simplified.

  Further, in this compensation adjustment circuit 8, by using the amplifier 12 and the attenuator 14, a magnetic field corresponding to the magnitude of the environmental magnetic field in the magnetic sensor 1 constituted by the SQUID is generated according to the output voltage of the environmental magnetic field detection coil 7. Thus, the amount of current supplied to the modulation coil 7 can be adjusted. Further, by using the phase adjuster 16, a compensation magnetic field having a phase opposite to that detected by the environmental magnetic field detection coil 7 can be generated, and a magnetic field that accurately compensates the environmental magnetic field is generated in the modulation coil 6. Can do.

  The output voltage of the environmental magnetic field detection coil 7 is amplified by the amplifier 12, and the output signal of the amplifier 12 corresponds to the time differential component of the environmental magnetic field. Therefore, in order to generate a voltage corresponding to the environmental magnetic field, an integrator 13 that performs an integration process opposite to the differentiation process is arranged at the next stage of the amplifier 12. Thereby, the signal corresponding to the environmental magnetic field detected correctly can be generated.

  In the configuration of the magnetic detection device shown in FIG. 3, a high magnetic permeability material may be used as the core in the environmental magnetic field detection coil 7.

  The phase adjuster 16 may have any configuration as long as the phase of the signal can be adjusted in the modulation coil 6 so that a magnetic field opposite in phase to the accurately detected environmental magnetic field is generated. Configuration can be utilized.

  As described above, according to the third embodiment of the present invention, the magnetic field corresponding to the environmental magnetic field is compensated by using the FLL circuit for the SQUID magnetic sensor, and the circuit scale can be reduced. The environmental magnetic field compensation coil and the detection magnetic field canceling modulation coil can be shared, and the environmental magnetic field compensation can be adjusted efficiently.

[Embodiment 4]
FIG. 4 schematically shows a configuration of a magnetic detection device according to the fourth embodiment of the present invention. In FIG. 4, the magnetic inspection unit 25 including the SQUID is disposed in the magnetic shield body 20. The magnetic detection unit 25 includes, for example, a SQUID cooled by liquid nitrogen filled in a dewar, an FLL circuit for the SQUID, a modulation coil 6, a circuit for supplying a bias current for the SQUID, an integrator 32, and the like. Including.

  The magnetic shield body 20 is a measurement method in which a hollow rectangular conveyance path shielding portion 21 to which a measurement target object is conveyed and a substantially central portion of the conveyance path shielding portion 21 are disposed, and a magnetic measurement unit 25 is disposed therein. The part shielding part 22 is included.

  The conveyance path shielding part 21 is provided with openings 23 a and 23 b at both ends, and a relatively large object to be measured is conveyed in the conveyance path shielding part 21. The substantially inverted T-shaped magnetic shield 20 is made of a material having a high magnetic permeability such as permalloy, amorphous metal, or amorphous alloy, and realizes a magnetic shield function for the magnetic measurement unit 25.

  However, the transport path shielding part 21 is provided with relatively large openings 23a and 23b. The openings 23a and 23b provided at both ends of the transport path shielding part 21 allow an environmental magnetic field to enter the inside. affect.

  In order to suppress the influence of this environmental magnetic field, an environmental magnetic field detection coil 24 composed of a normal conducting coil is wound around a substantially base portion of the measurement unit shielding unit 22. The normal conducting coil 24 is configured using an enameled wire or a copper wire. The number of turns of the environmental magnetic field detection coil 24 is determined to be an appropriate number (for example, 50 turns) in accordance with the shape and size of the magnetic shield body 20 and the size of the measurement unit shielding unit 22. The environmental magnetic field detection coil 24 detects a magnetic field caused by the environmental magnetic field generated in the magnetic shield body 20.

  The ambient magnetic field detection coil 24 is coupled to an amplifier 30, and a signal amplified by the amplifier 30 is supplied to an FLL circuit unit included in the magnetic measurement unit 25 via an integrator 32. The supply form of the output signal of the integrator 32 may be a form in which a current is supplied to the modulation coil 6 shown in FIG. 3 via an environmental magnetic field compensation resistance element provided separately from the feedback resistance element. The output signal of the integrator 32 may be supplied to a compensation coil provided separately from the modulation coil via an environmental magnetic field compensation resistor element. However, in any form, the attenuation process and the phase adjustment operation are performed as necessary (see the configuration shown in FIGS. 1 to 3) as in the first to third embodiments.

  The magnetic shield body 20 is made of a material having a high magnetic permeability, and generates a magnetic field corresponding to an external magnetic field (environmental magnetic field). The magnetic field generated in the magnetic shield body 20 is detected by the environmental magnetic field detection coil 24, and a signal corresponding to the detected environmental magnetic field is generated by the amplifier 30 and the integrator 32, and given to the FLL circuit of the magnetic measurement unit 25. Thereby, the external environmental magnetic field is compensated by the FLL circuit of the magnetic measurement unit 25, and the magnetic measurement unit 25 can accurately detect the magnetic field from the measurement target object. Thereby, openings are provided at both ends, and the magnetic field to be measured can be accurately measured even if the magnetic shield for the magnetic measurement unit is insufficient.

  When environmental magnetic field detection coils are provided at both ends of the openings 23a and 23b at both ends of the conveyance path shielding unit 21, the degree of influence of the detection magnetic field of these environmental magnetic field detection coils on the measurement target magnetic field is adjusted. It becomes difficult and it becomes difficult to cancel the environmental magnetic field accurately. However, the measurement unit shielding unit 22 is disposed at substantially the center of the conveyance path shielding unit 21, and by detecting the external environmental magnetic field at this portion, the relative intensity of the external environmental magnetic field at the measurement position can be determined almost accurately. It is possible to detect and accurately compensate for the environmental magnetic field.

  Further, the environmental magnetic field detection coil 24 is wound around the magnetic shield body 20 made of a high magnetic permeability material, and the measurement part shielding part 22 of the magnetic shield body 20 functions as a core. The environmental magnetic field can be detected with high sensitivity and high sensitivity.

  In the configuration of the magnetic detection device shown in FIG. 4, the measurement unit shielding unit 22 is formed in a rectangular shape. However, the shape of the measurement unit shielding unit 22 may be other shapes such as an elliptical shape or a cylindrical shape, and the magnetic measurement unit is disposed inside and has a magnetic shielding function for the internal magnetic measurement unit. If it has, the shape is arbitrary.

  Also, the shape of the transport path shielding portion 21 may be determined in an appropriate shape depending on the shape of the measurement target object transported through the transport portion, and may be formed in an elliptical shape, for example.

  Further, a phase adjuster may be provided at the next stage of the integrator 32.

  As described above, according to the fourth embodiment of the present invention, a normal conductive coil is wound around a high permeability material portion that realizes an electrostatic shield of a measurement unit and used as an environmental magnetic field detection coil. The output signal of the conductive coil is fed back to the FLL circuit of the magnetic measurement unit in the magnetic shield via an amplifier and an integrator or phase adjuster. Therefore, even in an environment where the magnetic shield is insufficient, it is possible to accurately detect the environmental magnetic field and generate a magnetic field that cancels the environmental magnetic field, and reliably compensates the environmental magnetic field for the magnetic field of the measurement target object. Can be done.

  The present invention can be applied to an apparatus that performs magnetic field measurement such as biomagnetic field detection and magnetic substance detection. Further, the present invention can be applied to an RF-SQUID as a SQUID, and the present invention can be applied to both a high temperature superconducting SQUID and a low temperature SQUID. Further, as the magnetic sensor, the present invention can be applied to other magnetic sensors such as a fluxgate and an MI (magnetic impedance) sensor.

It is a figure which shows schematically the structure of the magnetic detection apparatus according to Embodiment 1 of this invention. It is a figure which shows schematically the whole structure of the magnetic detection apparatus according to Embodiment 2 of this invention. It is a figure which shows schematically the structure of the magnetic detection apparatus according to Embodiment 3 of this invention. It is a figure which shows roughly the structure of the magnetic measuring device according to Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Magnetic sensor (SQUID), 3 Amplifier, 4 Integrator, 5 Feedback resistance element, 6 Modulation coil, 7 Environmental magnetic field detection coil, 8 Compensation adjustment circuit, 12 Amplifier, 14 Attenuator, 16 Phase adjuster, 18 Compensation resistance Element, 20 Magnetic shield body, 21 Conveyance path shielding part, 22 Measuring part shielding part, 23a, 23b Opening part, 24 Environmental magnetic field detection coil, 25 Magnetic measuring part, 30 Amplifier, 32 Integrator.

Claims (9)

A magnetic sensor for detecting a magnetic field,
A normal conducting coil arranged separately from the magnetic sensor;
A magnetic compensation circuit that generates a compensation magnetic field for the detection magnetic field of the magnetic sensor according to the detection output of the normal conducting coil and supplies the magnetic field to the magnetic sensor, and a detection circuit that generates a signal corresponding to the detection magnetic field according to the output signal of the magnetic sensor A magnetic detection device. The detection circuit includes a magnetic flux locked loop circuit that negatively feeds back an output signal of the magnetic sensor to the magnetic sensor;
The magnetic detection device according to claim 1, wherein the magnetic compensation circuit superimposes a magnetic field corresponding to an output signal of the normal conducting coil on a feedback magnetic field generated by the magnetic flux locked loop circuit. The magnetic compensation circuit includes:
A compensation coil disposed corresponding to the magnetic sensor and magnetically coupled to the magnetic sensor;
The magnetic detection apparatus of Claim 1 provided with the circuit which produces | generates the electrical signal corresponding to the detection signal of the said normal conducting coil, and applies it to the said compensation coil.   The magnetic detection device according to claim 1, wherein the normal conducting coil is wound around a material having high magnetic permeability. The magnetic sensor is disposed in a magnetic shield;
The magnetic detection device according to claim 1, wherein the normal conducting coil is disposed outside the magnetic shield. The magnetic shield is made of a material with high magnetic permeability,
The magnetic detection device according to claim 5, wherein the normal conducting coil is wound around an outer periphery of the magnetic shielding shield. The object to be detected by the magnetic sensor is transferred through a conveyance path shielded by a material with high permeability having openings at both ends,
The magnetic sensor is disposed in a measurement unit that is magnetically shielded by the high permeability material at a predetermined position in the middle of the conveyance path,
The magnetic detection device according to claim 1, wherein the normal conducting coil is wound around an outer periphery of a high magnetic permeability material for shielding an external magnetic field surrounding the measurement unit.   The magnetic detection device according to claim 1, wherein the material having high magnetic permeability is permalloy or amorphous metal.   The magnetic detection apparatus according to claim 1, wherein the magnetic sensor includes a superconducting quantum interference element.

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