JP2011146621A - Active magnetic shielding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active magnetic shielding device capable of solving the problem, wherein when a compensation coil is large, a heavy drive current is required to pass to the compensation coil at all times, and low power consumption of the active magnetic shielding device in conventional methods, or low power consumption for the large active magnetic shielding device cannot be attained. <P>SOLUTION: The active magnetic shielding device 1 includes magnetic materials 101, 102; magnetic field compensation coil 201, 202 arranged contacting magnetic materials 101, 102; a magnetic sensor 300 for measuring an environmental magnetic field; and a drive signal control section 400 for controlling the drive signal Ib which drives magnetic field compensation coil 201, 202, based on a measuring signal Vb from the magnetic sensor 300. When variation in the measuring signal Vb lies within a prescribed range, the drive signal Ib is turned off by the drive signal control section 400, after an interval required for magnetizing the magnetic materials 101, 102. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an active magnetic shield device in which a compensation coil for generating a compensation magnetic field that cancels an environmental magnetic field is arranged.

  A superconducting quantum interference device (SQUID), magnetic resonance imaging (MRI) device, nuclear magnetic resonance (NMR) device for measuring a heart magnetic field, a brain magnetic field, and the like that are smaller than the geomagnetism. A device such as a Nuclear Magnetic Resonance Scanner device needs to shield the influence of an environmental magnetic field (magnetic noise) around the building as much as possible. Therefore, it is necessary to install a device such as SQUID in a passive magnetic shield room surrounded by a magnetic material plate such as a high magnetic permeability magnetic steel plate or permalloy for shielding from an environmental magnetic field.

  However, such a passive magnetic shield room has a problem that a strong environmental magnetic field from the outside due to a car or a train passing near the building cannot be coped with.

  In order to solve this problem, for example, Patent Document 1 discloses an active magnetic shield in which a compensation magnetic field having the same amplitude and antiphase is generated by a compensation coil in accordance with a change in the environmental magnetic field to cancel the change in the environmental magnetic field. The method is described.

Japanese Patent Laying-Open No. 2002-232182 (FIG. 1)

  However, in the conventional method, when the compensation coil is large, it is necessary to always flow a large amount of drive current, and there is a problem that the power consumption of the active magnetic shield device cannot be reduced.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 In the active magnetic shield device according to this application example, a magnetic material, a magnetic field compensation coil disposed so as to be in contact with the magnetic material, a magnetic sensor that measures an environmental magnetic field, and a magnetic sensor A drive signal control unit that controls a drive signal that drives the magnetic field compensation coil based on a measurement signal, and the drive signal control unit magnetizes the magnetic material if the variation of the measurement signal is within a predetermined range. The active magnetic shield device is characterized in that the drive signal is turned off after a time required for the operation.

  According to this configuration, the drive signal control unit applies a drive signal for canceling a stable environmental magnetic field such as geomagnetism to the magnetic field compensation coil for a predetermined time so that the magnetic material is magnetized, and thereafter the drive signal is turned off. However, since the environmental magnetic field can be continuously canceled by the magnetized magnetic material, power consumption can be reduced.

  Application Example 2 In the active magnetic shield device described above, the magnetic material is a hard magnetic material.

  According to this configuration, since the hard magnetic material has a high holding force, the drive signal control unit applies a drive signal for canceling a stable environmental magnetic field such as geomagnetism to the magnetic field compensation coil for a predetermined time. Even if the drive signal is turned off after that, the ambient magnetic field can be stably canceled by the magnetized magnetic material, so that power consumption can be reduced.

  Application Example 3 In the active magnetic shield device described above, the active magnetic shield device includes a first surface and a second surface including the magnetic material and the magnetic field compensation coil, and the first surface. And the second surface are arranged in parallel, and the magnetic field compensation coil included in the first surface and the magnetic field compensation coil included in the second surface are electrically connected in series. An active magnetic shield device characterized by that.

  According to this configuration, since the Helmholtz coil can be configured by the first surface and the second surface, a magnetic field environment with a small gradient magnetic field can be realized.

Schematic which shows the structure of the active magnetic shielding apparatus which concerns on 1st Embodiment. The timing diagram which shows operation | movement of the active magnetic shielding apparatus which concerns on 1st Embodiment.

  Hereinafter, embodiments of an active magnetic shield device will be described with reference to the drawings.

(First embodiment)
<Configuration of active magnetic shield device>
First, the configuration of the active magnetic shield device 1 according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of the active magnetic shield device according to the first embodiment.

  As shown in FIG. 1, the active magnetic shield device 1 includes magnetic materials 101 and 102, magnetic field compensation coils 201 and 202, a magnetic sensor 300, and a drive signal control unit 400.

  The magnetic materials 101 and 102 are obtained by processing a hard magnetic material such as a ferrite magnet into a plate shape. The magnetic field compensation coil 201 is disposed so as to be in contact with the magnetic material 101, and similarly, the magnetic field compensation coil 202 is disposed so as to be in contact with the magnetic material 102. In FIG. 1, the magnetic field compensation coils 201 and 202 have a circular shape, but may be a polygonal shape such as a square in accordance with the shape of the magnetic materials 101 and 102.

  The magnetic sensor 300 is composed of a flux gate sensor, a magnetic impedance element, a Hall element, a magnetoresistive effect element, and the like, and converts an environmental magnetic field into a voltage value and outputs a measurement signal Vb. The drive signal control unit 400 controls the amount of current for driving the magnetic field compensation coils 201 and 202 based on the measurement signal Vb and outputs it as a drive signal Ib.

  The magnetic material 101 and the magnetic field compensation coil 201 constitute a first surface 210, and the magnetic material 102 and the magnetic field compensation coil 202 constitute a second surface 220. The first surface 210 and the second surface 220 are arranged in parallel so as to face each other so that the center of the surface comes on the X axis. The magnetic field compensation coil 201 and the magnetic field compensation coil 202 are connected so that the drive signal Ib of the drive signal control unit 400 flows in series. By arranging the magnetic field compensation coil 201 and the magnetic field compensation coil 202 in this manner, a Helmholtz coil is configured on the X axis. The magnetic sensor 300 is disposed at the center of the magnetic field compensation coil 201 and the magnetic field compensation coil 202 on the X axis.

<Operation of active magnetic shield device>
Next, the operation of the active magnetic shield device 1 according to the first embodiment will be described with reference to FIG. FIG. 2 is a timing chart showing the operation of the active magnetic shield device according to the first embodiment.

  FIG. 2 shows changes in the measurement signal Vb, the control signal Ib, and the magnetic flux density FB magnetized by the magnetic materials 101 and 102 along the time axis. The magnetic sensor 300 outputs a measurement signal Vb having a positive voltage value when the magnetic flux density is generated in the positive direction on the X axis in FIG. 1, and the magnetic flux density is generated in the negative direction. If it is, the measurement signal Vb having a negative voltage value is output. Further, the drive signal control unit 400 controls the control signal Ib that drives the magnetic field compensation coils 201 and 202 so that the magnetic flux density is generated in the negative direction when the measurement signal Vb is a positive voltage value, and the measurement signal Vb. When is a negative voltage value, the control signal Ib for driving the magnetic field compensation coils 201 and 202 is controlled so that the magnetic flux density is generated in the positive direction.

  FIG. 2 shows an example in which the magnetic flux density is generated in the negative direction of the X axis due to the influence of geomagnetism, which is an environmental magnetic field, at time t0, and the measurement signal Vb outputs a negative voltage value v1.

  At time t1, the drive signal control unit 400 controls the current value of the drive signal Ib to a positive current value i1 so that the measurement signal Vb becomes 0V. Along with this, the measurement signal Vb transits to 0 V, while the value of the magnetic flux density FB gradually rises to the positive magnetic flux density b1, and saturates at time t2.

  At time t2, the drive signal control unit 400 turns off the drive signal Ib because the fluctuation of the measurement signal Vb is within a predetermined range (for example, a range of −0.01 V to +0.01 V). Since the magnetic flux density b1 is coerced in the positive direction of the X axis in 101 and 102, the measurement signal Vb remains 0 V after time t2.

  At time t3, a disturbance magnetic field in the positive direction of the X axis is generated due to an external influence on the environmental magnetic field, and the voltage value of the measurement signal Vb jumps to the positive voltage value v2, so that the drive signal control unit 400 The current value of the drive signal Ib is controlled to a negative current value i2 so that Vb becomes 0V. Accordingly, since the measurement signal Vb transits to 0V, the current value of the drive signal Ib also transits to 0A.

  At time t4, a disturbance magnetic field in the negative direction of the X-axis is generated due to the external influence on the environmental magnetic field, and the voltage value of the measurement signal Vb has dropped to the negative voltage value v3. The current value of the drive signal Ib is controlled to a positive current value i3 so that Vb becomes 0V. Accordingly, since the measurement signal Vb transits to 0V, the current value of the drive signal Ib also transits to 0A.

  According to the present embodiment described above, the following effects can be obtained.

  In this embodiment, the drive signal control unit 400 applies a drive signal Ib for canceling a stable environmental magnetic field such as geomagnetism to the magnetic field compensation coils 201 and 202 for a predetermined time (period from time t1 to time t2 in FIG. 2). As a result, the magnetic materials 101 and 102 are magnetized to the magnetic flux density b1, and the environmental magnetic field can be continuously canceled by the magnetized magnetic materials 101 and 102 even after the drive signal Ib is turned off, thereby reducing power consumption. be able to.

  As mentioned above, although embodiment of the active magnetic shield apparatus was described, it is not limited to such embodiment at all, It can implement in various forms within the range which does not deviate from the meaning. Hereinafter, a modification will be described.

(Modification 1)
A modification of the active magnetic shield device will be described. In the above-described embodiment, the Helmholtz coil composed of the first surface 210 and the second surface 220 is arranged on the X axis. However, the Helmholtz coil is also constructed on the Y axis and the Z axis. , The Z-axis three-axis magnetic sensor 300 can cancel geomagnetism and disturbance magnetic fields in all directions of the X, Y, and Z axes.

  DESCRIPTION OF SYMBOLS 1 ... Active magnetic shield apparatus, 101, 102 ... Magnetic material, 201, 202 ... Magnetic field compensation coil, 210 ... 1st surface, 220 ... 2nd surface, 300 ... Magnetic sensor, 400 ... Drive signal control part.

Claims (3)

Magnetic materials,
A magnetic field compensation coil disposed in contact with the magnetic material;
A magnetic sensor that measures the environmental magnetic field;
A drive signal controller for controlling a drive signal for driving the magnetic field compensation coil based on a measurement signal from the magnetic sensor;
Including
The drive signal control unit turns off the drive signal after a time necessary for the magnetic material to be magnetized if the variation of the measurement signal is within a predetermined range.
An active magnetic shield device.   2. The active magnetic shield device according to claim 1, wherein the magnetic material is a hard magnetic material.   3. The active magnetic shield device according to claim 1, comprising a first surface and a second surface including the magnetic material and the magnetic field compensation coil, wherein the first surface and the second surface are The active magnetism is characterized in that the magnetic field compensation coil included in the first surface and the magnetic field compensation coil included in the second surface are arranged in parallel, and are electrically connected in series. Shield device.

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