JP5589355B2 - Active magnetic shield - Google Patents

Description

  The present invention relates to an active magnetic shield.

  According to the environmental magnetic noise shielding magnetic field applying device described in Patent Document 1, by supplying the same current to a pair of coils that satisfy the Helmholtz coil condition, a magnetic field having an opposite phase to the environmental magnetic noise is generated. It is said that a uniform magnetic field region in which environmental magnetic noise is canceled can be generated between both coils.

JP 2005-217341 A

  However, in the above technique, it is necessary to increase the diameter of the coil in order to form a uniform magnetic field region over a wide range. The present invention provides an active magnetic shield capable of forming a uniform magnetic field region over a wide range without increasing the diameter of the coil by solving the above-described problems.

  In order to solve the above-described problem, the active magnetic shield according to the first aspect of the present invention supplies a current to each of the Helmholtz coil unit in which a plurality of Helmholtz coils are coaxially arranged, and the plurality of Helmholtz coils. And a control unit that controls the current supply unit so as to switch the Helmholtz coil to be supplied with the current and supply the current to the Helmholtz coil after switching. Features. According to such a configuration, a plurality of uniform magnetic field regions can be formed in the axial direction by a plurality of Helmholtz coils. Therefore, a uniform magnetic field region can be formed over a wide range without increasing the diameter of the coil. it can.

  In the active magnetic shield, the plurality of Helmholtz coils include at least one part of a uniform magnetic field region formed by one adjacent Helmholtz coil and one uniform magnetic field region formed by the other adjacent Helmholtz coil. They may be arranged side by side with an interval that satisfies the condition that they overlap each other. According to such a configuration, since a non-uniform magnetic field region is not formed between a plurality of uniform magnetic field regions formed by a plurality of Helmholtz coils, a uniform magnetic field region can be formed over a wide range.

  In the active magnetic shield, the control unit is configured to supply the current to the Helmholtz coil with a period shorter than a measurement period of a measurement apparatus that measures an object to be measured in a uniform magnetic field region formed by the active magnetic shield. And the current supply unit may be instructed to supply the current to the Helmholtz coil after switching. According to such a configuration, a uniform and wide magnetic field region can be formed by generating a uniform magnetic field region in the plurality of Helmholtz coils within one measurement period by the measuring apparatus.

  In the active magnetic shield, the Helmholtz coil unit may be provided for each of two different axial directions. According to such a configuration, a uniform magnetic field region can be formed over a wide range in the biaxial direction.

  In the active magnetic shield, the Helmholtz coil unit may be provided for each of three different axial directions. According to such a configuration, a uniform magnetic field region can be formed over a wide range in the triaxial direction.

1 shows an external appearance of an active magnetic shield 10 according to a first embodiment. 1 shows a configuration of an active magnetic shield 10 according to a first embodiment. An example of the magnetic field region 114 formed by the active magnetic shield 10 is shown. The current supply timing by the current supply unit 160 is shown. The external appearance of the active magnetic shield 10 which concerns on 2nd Embodiment is shown. The external appearance of the active magnetic shield 10 which concerns on 3rd Embodiment is shown.

  FIG. 1 shows an appearance of an active magnetic shield 10 according to the first embodiment. FIG. 2 shows the configuration of the active magnetic shield 10 according to the first embodiment. The active magnetic shield 10 can form a uniform and wide magnetic field region 114. For example, the active magnetic shield 10 is used in a biological measurement system such as a cardiac magnetic measurement system, but can be used in systems other than the biological measurement system as long as it is a system that measures magnetism.

  The active magnetic shield 10 includes a substrate 12, a Helmholtz coil unit 100, and a control device 150. The Helmholtz coil unit 100 and the control device 150 are provided on the substrate 12. The Helmholtz coil unit 100 has a plurality of Helmholtz coils 110. For example, the Helmholtz coil unit 100 of the present embodiment includes a Helmholtz coil 110A and a Helmholtz coil 110B as shown in FIG. That is, the Helmholtz coil unit 100 of the present embodiment has two Helmholtz coils 110.

  Each of the plurality of Helmholtz coils 110 includes a pair of coils 112 that satisfy the Helmholtz coil condition. In order to satisfy the Helmholtz coil condition, a pair of coils 112 having substantially the same size and number of turns are used. Further, in order to satisfy the Helmholtz coil condition, the pair of coils 112 are arranged such that the radius of the coil 112 and the distance between the pair of coils 112 are substantially the same. For example, in the Helmholtz coil unit 100 of the present embodiment, the Helmholtz coil 110A has a pair of coils 112A that satisfy the Helmholtz coil condition. The Helmholtz coil 110B has a pair of coils 112B that satisfy the Helmholtz coil condition. The coils 112A and the coils 112B are alternately arranged in the direction of the axis A.

  Here, the actual coil 112 has multiple coils wound around the coil bobbin. Further, the actual coil 112 is installed in a standing state on the substrate 12 and is supported by a support member or the like. In FIG. 1 and FIG. 2, in order to make the configuration of the active magnetic shield 10 easy to understand, these are not shown. Although the active magnetic shield 10 of the present embodiment uses the circular coil 112, the present invention is not limited thereto, and a coil 112 other than a circular shape such as a quadrangle, other polygons, or an ellipse may be used. .

  Each of the plurality of Helmholtz coils 110 is supplied with the same current to each of the pair of coils 112, thereby forming a uniform magnetic field region 114 around the intermediate point of the pair of coils 112. For example, the Helmholtz coil 110A forms a uniform magnetic field region 114A around an intermediate point Pa between the pair of coils 112A. The Helmholtz coil 110B forms a uniform magnetic field region 114B around the intermediate point Pb of the pair of coils 112B. Here, the uniform magnetic field region 114 indicates a region where the change in magnetic field accompanying the change in position is minimal. The region with the smallest change in magnetic field may be a region where the change in magnetic field is zero as long as it is a region where the change in magnetic field is smaller than other regions. The uniform magnetic field region 114 is not limited to the region where the magnetic field change accompanying the change in position is the smallest, but may include a region within the range of the minimum to a predetermined value.

  The plurality of Helmholtz coils 110 are arranged on the same axis. Specifically, the plurality of Helmholtz coils 110 includes at least a part of a uniform magnetic field region 114 formed by one adjacent Helmholtz coil 110 and a uniform magnetic field region 114 formed by the other adjacent Helmholtz coil 110. They are arranged side by side on the same axis with an interval that satisfies the condition that they partially overlap. For example, in the example shown in FIG. 2, the Helmholtz coil 110A and the Helmholtz coil 110B include a part of the uniform magnetic field region 114A formed by the Helmholtz coil 110A and a part of the uniform magnetic field region 114B formed by the Helmholtz coil 110B. They are arranged side by side on the axis A with an interval D that satisfies the condition of overlapping.

  The control device 150 includes a current supply unit 160, a magnetic field detection unit 170, and a control unit 180. The current supply unit 160 supplies a current to each of the plurality of Helmholtz coils 110. The magnetic field detector 170 detects the magnetic field of each of the plurality of Helmholtz coils 110. For example, the magnetic field detection unit 170 uses, for each of the plurality of Helmholtz coils 110, a magnetic sensor such as a fluxgate magnetometer provided in the vicinity of the magnetic field region 114 formed by the Helmholtz coil 110. Is detected.

  The control unit 180 controls the current supply unit 160. Specifically, for each of the plurality of Helmholtz coils 110, the control unit 180, based on the magnetic field detected by the magnetic field detection unit 170, the environmental magnetism necessary for the Helmholtz coil 110 to form a uniform magnetic field region. The current supply unit 160 is controlled so that a current for generating a magnetic field having a phase opposite to that of the noise is supplied to the Helmholtz coil 110. The control unit 180 controls the current supply unit 110 to switch the Helmholtz coil 110 to be supplied with current and supply current to the Helmholtz coil 110 after switching. In particular, the control unit 180 switches the Helmholtz coil 110 to be supplied with current at a cycle shorter than the measurement cycle of the measurement device that measures the object to be measured in the uniform magnetic field region formed by the active magnetic shield 10. The current supply unit 110 is controlled to supply current to the Helmholtz coil 110.

  FIG. 3 shows an example of the magnetic field region 114 formed by the active magnetic shield 10. In the graph shown in FIG. 3, the vertical axis indicates the strength of the magnetic field formed by the active magnetic shield 10. The horizontal axis indicates the position of the magnetic field formed by the active magnetic shield 10 in the direction of the axis A. Among the Helmholtz coil units 100 included in the active magnetic shield 10, the Helmholtz coil 110A is front and rear in the direction of the axis A around the intermediate point Pa of the pair of coils 112A as shown by the dotted line in the graph shown in FIG. In addition, a region where the change in the strength of the magnetic field accompanying the change in position is the lowest, that is, a uniform magnetic field region 114A is formed. In the Helmholtz coil unit 100, the Helmholtz coil 110B is positioned over the front and rear in the direction of the axis A around the intermediate point Pb of the pair of coils 112B, as indicated by a one-dot chain line in the graph shown in FIG. A region where the change in the magnetic field strength due to the change is lowest, that is, a uniform magnetic field region 114B is formed. In this way, the active magnetic shield 10 can form a uniform magnetic field region 114com including the uniform magnetic field region 114A and the uniform magnetic field region 114B, as indicated by the solid line in the graph shown in FIG. .

  According to the active magnetic shield 10 according to the first embodiment, a plurality of uniform magnetic field regions 114 can be formed in the direction of the axis A by the plurality of Helmholtz coils 100, so that the coils can be uniformly formed without increasing the diameter of the coils. A wide magnetic field region 114com can be formed. Here, a part of the uniform magnetic field region 114A formed by the Helmholtz coil 110A and a part of the uniform magnetic field region 114B formed by the Helmholtz coil 110B overlap each other. As described above, according to the active magnetic shield 10 according to the first embodiment, a non-uniform magnetic field region is not formed between the plurality of uniform magnetic field regions 114 formed by the plurality of Helmholtz coils 110. A magnetic field region 114com can be formed.

  FIG. 4 shows current supply timing by the current supply unit 160. The timing chart of FIG. 4 shows (a) measurement timing of the measuring device, (b) current supply timing to the Helmholtz coil 110A, and (c) current supply timing to the Helmholtz coil 110B. (A) At the measurement timing of the measurement apparatus, the measurement period is indicated by Hi level, and the non-measurement period is indicated by Low level. In (b) the current supply timing to the Helmholtz coil 110A and (c) the current supply timing to the Helmholtz coil 110B, the period during which the current is supplied is indicated by Hi level, and the period during which no current is supplied is indicated. Shown at Low level.

  As shown in the timing chart of FIG. 4, the current supply unit 160 alternately supplies current to the Helmholtz coil 110 </ b> A and the Helmholtz coil 110 </ b> B under the control of the control unit 180. In addition, the current supply unit 160 switches the Helmholtz coil 110 to be supplied with current at a cycle shorter than the measurement cycle of the measurement device under the control of the control unit 180 and supplies current to the Helmholtz coil 110 after switching. For example, if the measurement cycle of the measurement device is 100 Hz, such as a cardiac magnetic measurement device, the cycle for switching the Helmholtz coil 110 to be supplied with current is preferably several tens of kHz. Thereby, the active magnetic shield 10 can form a uniform and wide-range magnetic field region 114 for the measuring device to accurately measure the living body. As described above, according to the active magnetic shield 10 according to the first embodiment, uniform magnetic field regions 114 are alternately generated for each Helmholtz coil 110 within one measurement period of the measurement apparatus. A uniform and wide magnetic field region 114 can be formed. Further, by alternately supplying current to the Helmholtz coil 110 </ b> A and the Helmholtz coil 110 </ b> B, it is possible to suppress the synthesis of the plurality of magnetic field regions 114 formed by both Helmholtz coils 110. The current supply period to the Helmholtz coil 110 </ b> A and the current supply period to the Helmholtz coil 110 </ b> B may partially overlap or be spaced apart.

  FIG. 5 shows an appearance of the active magnetic shield 10 according to the second embodiment. The active magnetic shield 10 shown in FIG. 5 includes a Helmholtz coil unit 100x and a Helmholtz coil unit 100y. In the Helmholtz coil unit 100x, a plurality of Helmholtz coils 110 are provided side by side on the axis Ax in the X-axis direction. In the Helmholtz coil unit 100y, a plurality of Helmholtz coils 110 are provided side by side on an axis Ay in the Y-axis direction that is substantially orthogonal to the plane direction with respect to the X-axis. Although not shown, each of the plurality of Helmholtz coils 110 is electrically connected to the current supply unit 160 by wiring. The Helmholtz coil unit 100x has the same configuration as the Helmholtz coil unit 100 described in the first embodiment and operates in the same manner. Accordingly, the Helmholtz coil unit 100x forms a uniform magnetic field region 114 in the X-axis direction. The Helmholtz coil unit 100y has the same configuration as the Helmholtz coil unit 100 described in the first embodiment and operates in the same manner. Therefore, the Helmholtz coil unit 100y forms a uniform magnetic field region 114 in the Y-axis direction. Thus, according to the active magnetic shield 10 according to the second embodiment, the Helmholtz coil unit 100 is provided in each of two different axial directions, thereby forming a uniform and wide-range magnetic field region 114 in different two axial directions. can do.

  FIG. 6 shows an appearance of the active magnetic shield 10 according to the third embodiment. The active magnetic shield 10 shown in FIG. 6 is different from the active magnetic shield 10 of the second embodiment in that it further includes a Helmholtz coil unit 100z in addition to the Helmholtz coil unit 100x and the Helmholtz coil unit 100y. In the Helmholtz coil unit 100z, a plurality of Helmholtz coils 110 are provided side by side on an axis Az in the Z-axis direction that is substantially orthogonal to the spatial direction with respect to each of the X-axis and the Y-axis. Although not shown, each of the plurality of Helmholtz coils 110 is electrically connected to the current supply unit 160 by wiring. The Helmholtz coil unit 100z has the same configuration as the Helmholtz coil unit 100 described in the first embodiment and operates in the same manner. Therefore, the Helmholtz coil unit 100z forms a uniform magnetic field region 114 in the Z-axis direction. As described above, according to the active magnetic shield 10 according to the third embodiment, the Helmholtz coil unit 100 is provided in each of three different axial directions, thereby forming a uniform and wide-range magnetic field region 114 in different three axial directions. can do.

  In any of the active magnetic shields 10 described so far, the Helmholtz coil unit 100 includes three or more Helmholtz coils 110, and the plurality of Helmholtz coils 110 may be provided side by side on the same axis. In this case, the control unit 180 may switch the Helmholtz coils 110 to be supplied with current among the three or more Helmholtz coils 110 in order in order, and supply the current to the current supply unit 160. The current supply unit 160 may be supplied with current by switching in this order. For example, the control unit 180 may switch the Helmholtz coils 110 that are current supply targets among the three or more Helmholtz coils 110 in a random order, and cause the current supply unit 160 to supply current.

  DESCRIPTION OF SYMBOLS 10 ... Active magnetic shield, 12 ... Board | substrate, 100 ... Helmholtz coil unit, 110 ... Helmholtz coil, 112 ... Coil, 114 ... Magnetic field area, 150 ... Control apparatus, 160 ... Current supply part, 170 ... Magnetic field detection part, 180 ... Control Part

Claims (5)

A Helmholtz coil unit in which a plurality of Helmholtz coils are coaxially arranged;
A current supply unit for supplying an electric current for the plurality of Helmholtz coils,
Active magnetic shield, characterized in that it comprises a control unit for controlling the pre-SL current supply portion so that switching the supply of current to the previous SL plurality of Helmholtz coils. The plurality of Helmholtz coils are:
At least an interval satisfying a condition that a part of the uniform magnetic field region formed by the one adjacent Helmholtz coil and a part of the uniform magnetic field region formed by the other adjacent Helmholtz coil overlap each other. The active magnetic shield according to claim 1, wherein the active magnetic shield is provided side by side. The controller is
In a period shorter than the measurement period of the measuring device for measuring the object in a homogeneous magnetic field region where the active magnetic shield was formed, so as then switch the supply of current to the plurality of Helmholtz coils, the current supply unit The active magnetic shield according to claim 1, wherein the active magnetic shield is controlled. The active magnetic shield according to any one of claims 1 to 3, wherein the Helmholtz coil unit is provided for each of two different axial directions. The active magnetic shield according to any one of claims 1 to 3, wherein the Helmholtz coil unit is provided for each of three different axial directions.

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