JP5328599B2 - Composite magnetic shield structure and system - Google Patents

Description

  The present invention relates to a composite magnetic shield structure and system, and more particularly, to a composite magnetic shield structure and system combining a passive (active) magnetic shield and an active (active) magnetic shield.

  Electron beam application devices such as electron microscopes, EB exposure devices, and EB steppers used in semiconductor manufacturing facilities, etc., maintain the quality of the product because the trajectory of the electron beam is distorted even by weak magnetic noise of about 100 nT (1 mG). It is necessary to avoid the influence of environmental magnetic field (disturbance magnetic field). In addition, SQUID (superconducting quantum interference device) application devices such as magnetoencephalographs and magnetocardiographs used in medical facilities and the like have an effect of 1 nT (0. 01 mG) or less is necessary. In order to protect such a device from a weak environmental magnetic field and ensure normal operation, it is required to provide a magnetic shield space (shield room) in a building such as a semiconductor manufacturing facility or medical facility.

  The magnetic shield space is constructed, for example, as a passive magnetic shield structure in which the inner surface of the target space S is covered with a magnetic material plate (hereinafter sometimes referred to as a magnetic plate) such as permalloy or electromagnetic steel plate having a high magnetic permeability μ. be able to. However, since passive magnetic shields use magnetic plates such as permalloy, which are generally expensive, and tend to be over-specified in accordance with the temporary peak of the environmental magnetic field, they are magnetic for the required shielding performance. There is a problem that the cost of the material increases. On the other hand, a coil for generating a compensation magnetic field (hereinafter sometimes referred to as a compensation coil) is arranged around the target space S, and an appropriate compensation magnetic field is generated in the compensation coil in accordance with a change in the environment magnetic field to thereby generate an environment magnetic field. An active type (active type) magnetic shield structure has been developed that cancels the fluctuations (for example, Patent Document 1). In order to construct a magnetic shield space that can respond to a changing environmental magnetic field, a composite magnetic shield combining a passive magnetic shield and an active magnetic shield is advantageous in terms of performance and economy.

  Patent Documents 2 and 3 combine a passive magnetic shield (hereinafter sometimes referred to as a hermetically sealed shield) and an active magnetic shield that surround each inner surface of the floor, wall, and ceiling of the target space S with a magnetic plate without a gap. A composite magnetic shield structure is disclosed. The active magnetic shield requires a magnetic sensor for detecting the environmental magnetic field in the target space S. In the composite magnetic shield structure of Patent Document 2, a compensation coil is arranged on the outer surface of each magnetic plate surrounding the target space S, a magnetic sensor is arranged so as to face the outer surface, and the magnetic plate opposed by each magnetic sensor. The combined magnetic field of the magnetic field due to the magnetization and the environmental magnetic field (external magnetic field) is detected. Depending on the combined magnetic field detected by each sensor, a compensation magnetic field that cancels the change in magnetization of each magnetic plate is generated in the compensation coil of each magnetic plate, and by keeping the degree of magnetization of each magnetic plate constant, Degradation of the shielding performance of the target space S in the sealed shield structure surrounded by each magnetic plate is prevented.

  Further, as shown in FIG. 8, the composite magnetic shield structure of Patent Document 3 has a compensation coil 34 around an axial direction passing through a specific position O in the target space S (for example, an X-axis direction passing through the arrangement position O of the SQUID device). (For example, a Helmholtz type coil) is disposed along the outer peripheral surface (upper and lower in the illustrated example) of the target space S, and the magnetic plate 31 of the hermetic shield 30 surrounding the target space S is provided with a through hole 32 and the same axis A magnetic detection coil 36 in the direction (X-axis direction) is arranged, and the detection coil 36 detects an induced voltage corresponding to a change in the environmental magnetic field as a change in magnetic flux density in the magnetic plate 31. The compensation coil 34 and the detection coil 36 are connected to the control device 40, and the applied current of the compensation coil 34 is negatively fed back so that the detection value of the detection coil 36 is almost minimized (that is, the fluctuation of the environmental magnetic field is canceled). By controlling, the environmental magnetic field in the X-axis direction in the target space S surrounded by the hermetic shield 30 is minimized. Similarly, in the Y-axis direction and the Z-axis direction, the compensation coil 34 and the detection coil 36 are arranged to minimize the environmental magnetic field in the Y-axis direction and the Z-axis direction. The environmental magnetic field at the position of the SQUID device is minimized. Further, as in the illustrated example, a plurality of detection coils 36a and 36b are arranged in each axial direction of the target space S, and the compensation coil 34 is applied in each axial direction based on the difference between the detection values of the plurality of detection coils 36a and 36b. By controlling the current, the magnetic field gradient in each axial direction can be corrected.

JP 2004-349431 A JP 2002-094280 A Japanese Patent No. 3824142 International Publication No. 2004/084603 Pamphlet JP 2006-351598 A

Sunagawa Shigenobu "Theoretical Electromagnetism 3rd Edition" Kinokuniya, September 16, 1999, pp222-225 Ichiro Hamada “Cubic 3-coil System for Uniform Magnetic Field Generation”, Journal of Japan Society of Applied Electrical Engineers, Vol. 27, no. 4, April 2003, pp612-615

  However, although the composite magnetic shield structures of Patent Documents 2 and 3 can control the magnetic field (magnetic flux density) at a specific position (for example, one point) in the magnetic shield target space S, There is a problem that the distribution of the magnetic field over a wide range cannot be appropriately controlled. In general, the environmental magnetic field inside the target space S is not uniform and differs depending on the position. Moreover, the magnetization distribution (distribution of magnetic flux density) of each magnetic plate surrounding the space S is not uniform and is different for each part. In the composite magnetic shield structure of Patent Document 2, the magnetization state of each magnetic plate surrounding the target space S is detected by a facing magnetic sensor. In such a magnetic sensor, the magnetization state of a specific part of the magnetic plate is detected. It is not possible to grasp the entire magnetization distribution of the magnetic plate. In addition, although the magnetization state of each magnetic plate around the target space S is individually controlled, in such individual control of the magnetization state of each magnetic plate, the target space S generated by the interaction of the magnetization states of each magnetic plate. It is difficult to control the magnetic field distribution inside.

  In the composite magnetic shield structure of Patent Document 3, the magnetic detection coil 36 is arranged in the through hole 32 of each magnetic plate 31 surrounding the target space S and the magnetic flux density in the magnetic plate 31 is measured. Since the magnetic flux density in the magnetic plate 31 is two-dimensionally spread in the shield 30, such a detection coil 36 must grasp the magnetic flux density (magnetic flux vector) including the internal direction of the magnetic plate 31. I can't. Even when a plurality of magnetic detection coils 36a and 36b are arranged, the gradient of the magnetic flux density in a specific direction can be estimated to some extent from the difference between the detected values, but the magnetic flux density including the orientation in the magnetic plate 31 is also possible. It is still difficult to detect the distribution of. In the magnetic shield structure of Patent Document 3 in which the distribution of the magnetic flux density in the magnetic plate 31 cannot be grasped, even if the environmental magnetic field at a specific position (for example, one point) in the target space S can be minimized, It is difficult to control the magnetic field distribution over a wide range.

  For example, in a semiconductor manufacturing facility (factory) or the like, electron beam devices may be arranged or moved at a plurality of locations such as a manufacturing line, and the entire or a wide range of a relatively wide space including such a manufacturing line is desired. There is a demand for shielding performance. Also, in medical facilities and the like, the SQUID device or the like may be used while being moved, and there is a demand for making the entire or wide range within the movable space of the device a desired shielding performance. In the magnetic shield structure in which a desired shield performance can be obtained only at a specific position in the target space S as in Patent Documents 2 and 3, the arrangement or movement of the device in the target space S is limited, and the target space is limited. The utilization efficiency of S will fall significantly. In order to construct a magnetic shield space in which desired shield performance can be obtained over a wide range according to demands, it is necessary to develop a composite magnetic shield structure capable of appropriately controlling the magnetic field distribution in the space.

  Accordingly, an object of the present invention is to provide a composite magnetic shield structure and system capable of controlling the magnetic field distribution inside the target space.

In general, the electromagnetic field distribution in a closed space can be uniquely determined by the governing equation (Maxwell's equation) and boundary conditions, and the magnetic field distribution inside the magnetic shield target space S is determined by the Maxwell's equation and boundary conditions. It can be expressed by the Kirchoff integral display of the considered equation (1) or the approximate equation of the equation (1) based on the Maxwell equation and the boundary condition excluding the term relating to the displacement current (see Non-Patent Document 1). In the expression (1), the left side ψ (x, t) represents a magnetic field vector (magnetic flux density vector) at an arbitrary position x in the space S at time t, and the right side is on the surface (boundary surface) S ′ of the space S. This represents a boundary condition determined by the magnetic field vector (magnetic flux density vector) ψ (x ′, t ′) at the initial time t ′ at the position x ′ or its temporal change ∂ψ (x ′, t ′) / ∂t ′. N ′ on the right side represents a unit normal vector of the surface S ′, and R represents a vector or distance connecting the internal position x of the space S and the position x ′ on the surface S ′. That is, if the magnetic field vector (magnetic flux density distribution) at the position x ′ on the surface (inner surface) S ′ that is the boundary condition in the target space S can be detected, the magnetic field vector (magnetic field at an arbitrary position x inside the space S). Can be calculated by the equation (1) or its approximation.

  However, in the composite magnetic shield structure, the inner surface S ′ of the target space S is covered with a magnetic plate (passive magnetic shield structure). As described above with reference to FIG. 8, when the sealed shield structure 30 that covers the inner surface S ′ with a magnetic plate without a gap is used, the magnetic field vector on the inner surface S ′, that is, the two-dimensional expansion in the magnetic plate 31. It is generally difficult to detect the distribution of magnetic flux density (direction of magnetic flux density) with a limited number of magnetic detection coils 36. Theoretically, it is conceivable to arrange a large number of magnetic detection coils on the magnetic plate 31 to detect the internal magnetic flux density distribution. In this case, however, it is necessary to provide a large number of through holes 32 in the magnetic plate 31 in FIG. As a result, the shield performance of the sealed shield structure 30 itself may be deteriorated, and it is difficult to put it into practical use in consideration of mounting of the detection coil 36 and wiring. In order to obtain the magnetic field distribution in the target space S in the composite magnetic shield structure, it is necessary to use a passive magnetic shield structure that can detect the magnetic flux density distribution in the magnetic plate covering the inner surface S ′ of the space S.

  As shown in FIG. 6, the inventor has a passive magnetic shield structure (hereinafter referred to as a sealed shield) using a group of strip-shaped magnetic plates (hereinafter referred to as a shield housing) arranged in a cage or louver shape. (See Patent Documents 4 and 5). In the open type shield structure, as shown in FIG. 6 (A), a plurality of strip-like magnetic plates 2 having a predetermined width (for example, about 30 to 100 mm) are arranged so that their longitudinal center axes C are arranged substantially in parallel on the same saddle surface F. The shield housing 3 laminated with a predetermined gap d is used as a basic structure, or a plurality of shield housings 3a, 3b, 3c, 3d are formed on the corresponding strip-like magnetic plates 2 of each housing 3 as shown in FIG. A row-like structure is formed by magnetically joining by overlapping edges (surface contact, see reference numeral 9 in the figure). As shown in FIG. 6B, the row-shaped shield housing 3 surrounds the target space S by overlapping and joining the unjoined edge on one end side with the corresponding unjoined edge on the other end side. A magnetically closed annular structure (hereinafter sometimes referred to as an annular shield housing 5) may be employed.

  The shield housing 3 shown in FIG. 6 imparts openness (transparency, translucency, heat dissipation) to the target space by the gaps d between the strip-shaped magnetic plates 2. The gap d is set such that the magnetic flux passing through the magnetic plate 2 (permeance of the magnetic plate) is larger than the magnetic flux passing through the gap d (permeance of the interval), that is, the gap d orthogonal to the longitudinal direction. The ratio (Sm · μs / Sa) of the product (Sm · μs) of the cross-sectional area Sm of the magnetic plate 2 and the relative magnetic permeability μs to the cross-sectional area Sa is designed to be greater than 1. Actually, the ratio (Sm · μs / Sa) can be made sufficiently larger than 1 in accordance with the required shield performance. The shield housing 3 secures high magnetic continuity at the joint portion of the magnetic plate 2 by overlapping the edges, and the magnetic plate 2 joined in a row or ring shape (in FIG. 6 (B), a square shape). Can be a magnetic path through which magnetic flux easily passes (magnetic flux is less likely to leak). For example, the annular shield housing 5 in FIG. 6 (B) concentrates the magnetic flux on the closed magnetic circuit (magnetic circuit) formed by the annular magnetic plate 2 and suppresses magnetic leakage (deterioration of shield performance) from the gap d. A higher shielding performance is given to the target space S than the sealed shield structure 30 of FIG. 8 using the same amount of magnetic material (see Patent Document 4).

  FIG. 7A is a color-coded display of the magnetization distribution (magnetic flux density distribution) when the annular shield housing 5 of FIG. 6B is exposed to a disturbance magnetic field in the Z-axis direction. FIG. 7B shows the distribution of magnetic flux density in each annular magnetic plate 2 constituting the annular shield housing 5, and further, the gradient of magnetic flux density (magnetic flux density vector) in each part is indicated by an arrow. It is. As can be seen from FIG. 7A, in the open shield structure, the magnetic flux density of the magnetic plate 2 is different for each part, as in the sealed shield structure 30 in FIG. However, if the distribution of the magnetic flux density is viewed as a magnetic field flow as shown by the arrow in FIG. 7B, the magnetic flux density in each part of the open shield structure has a gradient along the substantially longitudinal direction of the magnetic plate 2. It can be seen that the distribution is not a two-dimensional distribution like the sealed shield structure 30 but a one-dimensional distribution.

  That is, in the open type shield structure, the magnetic flux concentrates on the magnetic plates 2 (magnetic paths) joined in a row or ring shape, so that the distribution of the magnetic flux density in the magnetic plate 2 is limited to the longitudinal direction of the magnetic plate 2. be able to. If a composite magnetic shield structure is constructed using an open shield structure having such characteristics, boundary conditions necessary for calculating the magnetic field distribution in the target space S, that is, the magnetic flux density distribution on the inner surface S ′ of the space S will be described. Can be expected to detect. The present invention has been completed through research and development based on this idea.

Referring to FIG. 1, in the composite magnetic shield structure according to the present invention, a plurality of belt-like magnetic plates 2 are arranged on the inner surface of a magnetic shield target space S so that the longitudinal center axes C thereof are arranged in parallel with a predetermined gap d. The magnetic shield housing 3 (see FIG. 6) disposed, a plurality of compensation magnetic field generating coils 10 respectively disposed in each of the divided areas, and a magnetic plate attached to a plurality of positions on the shield housing 3 2, and a magnetic flux density distribution on the inner surface of the target space S and the inside of the target space S from the longitudinal direction of the shield housing 3 and the position and detection value of each sensor 14. And the compensation current i corresponding to the deviation between the calculated value and the predetermined magnetic field distribution is selectively applied to the coil 10 in each region to control the target space S to the predetermined magnetic field distribution. is there.

Referring also to FIG. 1, in the composite magnetic shield system according to the present invention, a plurality of strip-like magnetic plates 2 are arranged on the inner surface of the magnetic shield target space S so that the longitudinal center axes C thereof are arranged in parallel with a predetermined gap d. The magnetic shield housing 3 (see FIG. 6) disposed on the inner surface of the magnetic plate 2, the compensation magnetic field generating coil 10 disposed in each of the areas divided into a plurality of areas, and the magnetic shield 2 attached to a plurality of positions on the shield housing 3. a magnetic sensor 14 for detecting the magnetic flux density, and calculates the internal magnetic field distribution of the magnetic flux density distribution and the space S on the inner surface of the target space S from the longitudinal position and the detection value of each sensor of the shield blind body 3 The control means 20 is provided for selectively applying a compensation current i corresponding to the calculated value and the predetermined magnetic field distribution to the coil 10 in each region.

  Preferably, as shown in the drawing, the magnetic shield housing 3 is an annular shield housing 5 (see FIG. 6B) disposed while being magnetically coupled along the inner surface of the target space S. The magnetic field generating coil 14 is arranged adjacent to the outside or the inside of the annular shield housing 5. The magnetic sensor 14 can be, for example, an induction coil 14a wound around the magnetic plate 2 of the shield housing 3 as shown in FIG. 3, or can be attached to the gap facing surface of the magnetic plate 2 of the shield housing 3. . The compensation magnetic field generating coil 10 disposed in each region can be an annular coil disposed around a vertical axis passing through the center of the region.

In the composite magnetic shield structure and system of the present invention, a magnetic shield housing 3 is disposed on the inner surface of the target space S as a passive magnetic shield, and the inner surface is divided into a plurality of regions for generating a compensation magnetic field. The coil 10 is disposed to form an active magnetic shield, and the magnetic flux density in the magnetic plate 2 is detected by magnetic sensors 14 attached to a plurality of positions on the shield housing 3, and the position and detected value of the magnetic sensor 14 and the shield The magnetic flux density distribution on the inner surface of the target space S and the magnetic field distribution inside the target space S are calculated from the longitudinal direction of the body 3, and the compensation current i corresponding to the deviation between the calculated magnetic field distribution and the predetermined magnetic field distribution is calculated for each region. By selectively applying to the coil 10, the inside of the target space S is controlled to have a predetermined magnetic field distribution, and the following effects are produced.

(B) As a passive magnetic shield structure, by using the magnetic shield housing 3 that can limit the direction of the magnetic flux density in the magnetic plate 2 to the longitudinal direction of the magnetic plate 2, the detected value of the magnetic flux density on the magnetic plate 2 The magnetic flux density distribution of the inner surface S ′ of the target space S is obtained from the above, and the magnetic flux density distribution of the inner surface S ′ is used as a boundary condition, not the magnetic flux density at a specific position (for example, one point) in the target space S, but the entire or wide range Can be calculated.
(B) In addition, by using the magnetic shield housing 3 in which magnetic flux concentrates on the magnetic plate 2 (magnetic path), the magnetic flux density on the magnetic plate 2 when calculating the magnetic field distribution inside the target space S The contribution can be increased, and the magnetic field distribution in the target space can be accurately calculated from the magnetic flux density on the magnetic plate 2 that is relatively easy to detect.

(C) Furthermore, by using the magnetic shield housing 3 having the gap d between the magnetic plates 2, the magnetic sensor 14 and the wiring cable thereof can be arranged using the gap d, and the passive type The magnetic flux density in the magnetic plate 2 can be detected without impairing the shield performance of the magnetic shield structure itself (deteriorating the shield performance).
(D) The inner surface of the target space S is divided into a plurality of areas, the compensation magnetic field generating coil 10 is arranged in each area, and the magnetic field distribution in the space S calculated from the magnetic flux density distribution of the magnetic shield housing 3 and a predetermined magnetic field distribution ( For example, by selectively driving only the necessary coil 10 in accordance with the deviation from the environmental magnetic field distribution allowed at each position x in the space S, the magnetic field distribution over a wide area inside the target space S is minimized. It is possible to control with the driving power.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
It is explanatory drawing of one Example of the composite-type magnetic shield structure by this invention. It is an example of the flowchart of the method of controlling the magnetic field distribution in the object space S using the composite type magnetic shield structure of FIG. It is explanatory drawing of the other Example of the composite type magnetic-shield structure by this invention. It is explanatory drawing of an example of the arrangement | positioning method of the coil for compensation magnetic field generation used by this invention. It is explanatory drawing of an example of the arrangement | positioning method of the magnetic shield housing | casing used by this invention. It is explanatory drawing of an example of the conventional open type shield structure. It is explanatory drawing of an example of magnetic flux density distribution in the open type shield structure of FIG. It is explanatory drawing of an example of the conventional composite type magnetic-shield structure.

  FIG. 1 shows an embodiment of a composite magnetic shield structure of the present invention in which a passive magnetic shield using an open shield structure and an active magnetic shield are combined. The open type shield structure of the illustrated example has a plurality of strip-like magnetic plates on the inner peripheral surface (four inner surfaces in the Y-axis direction and the Z-axis direction) surrounding the central axis X of the target space S, as in FIG. 2 are arranged such that the central axis C in the longitudinal direction is aligned in parallel with a predetermined gap d in the Y-axis direction or the Z-axis direction to form magnetic shield housings 3a, 3b, 3c, 3d. 3b, 3c, and 3d are joined by overlapping edges to form an annular shield housing 5. In addition, the active type magnetic shield in the illustrated example includes a group of compensation coils 10 arranged in each region obtained by dividing the inner peripheral surface (four inner surfaces in the Y-axis direction and Z-axis direction) of the space S into a plurality of regions, and an annular shield. And a group of magnetic sensors 14 respectively attached to a plurality of predetermined positions on the housing 5. Each magnetic sensor 14 is connected to the control device 20, and each compensation coil 10 is connected to the drive device 26, and the control device 20 and the drive device 26 are included to constitute a composite magnetic shield system that drives the active magnetic shield.

  The control device 20 in the illustrated example includes a storage unit 21 and a calculation unit 22 that calculates a magnetic field distribution in the target space S. The storage means 21 stores parameters of the magnetic shield structure necessary for controlling the active magnetic shield, for example, a predetermined magnetic field distribution required in the target space S (for example, a maximum magnetic field distribution allowed at each position x in the target space S). ), The longitudinal direction of each magnetic plate 2 of the shield housing 5 (arrangement direction, Y-axis direction and Z-axis direction in the illustrated example), the mounting position of each magnetic sensor 14 on the annular shield housing 5 (the surface of the space S) The position x ′) on S ′ is stored. The calculation means 22 inputs the detection value of each magnetic sensor 14 (the magnetic flux density in the magnetic plate 2 on the shield housing 5) and the parameter stored in the storage means 21 (the longitudinal direction of each magnetic plate 2). The magnetic flux density distribution on the inner surface S ′ of the target space S is calculated based on the position of each magnetic sensor 14 and the like, and further, the magnetic flux density distribution on the inner surface S ′ is used as a boundary condition in the target space S. Calculate the magnetic field distribution. Further, the control unit 20 in the illustrated example includes a detection unit 23 that detects a deviation between the magnetic field distribution in the target space S calculated by the calculation unit 21 and the predetermined magnetic field distribution in the target space S stored in the storage unit 21, and the deviation. Correspondingly, a selection means 24 for selecting a region of the compensation coil 10 to be driven and a compensation current i to be applied to the compensation coil 10 is provided. By inputting the region selected by the selection means 24 to the driving device 26, the plurality of compensation coils 10 of the active magnetic shield are selectively driven to control the target space S to have a predetermined magnetic field distribution.

  In the illustrated example, the annular shield housing 5 is used as the passive magnetic shield. However, the shield housing 3 used in the present invention is not limited to the annular structure, and for example, the influence of the environmental magnetic field on the inner peripheral surface of the target space S. A specific inner surface (for example, an inner surface in the Y-axis direction or the Z-axis direction) having a large height or a planar or row-shaped shield housing 3 (see FIG. 6A) covering only a part thereof may be used. In this case, the magnetic flux density distribution (boundary condition) on the inner surface S ′ where the shield housing 3 is not disposed cannot be detected, but the inner surface S that is less influenced by the environmental magnetic field in calculating the magnetic field distribution inside the target space S. Since the degree of contribution of ′ is relatively small, the magnetic field distribution in the target space S can be calculated with sufficient accuracy based on the magnetic flux density detected on the planar or columnar shield housing 3.

  In the illustrated example, the control device 20 is a computer (PC), and the calculation means 22, the detection means 23, the selection means 24, and the like are programs built in the computer. However, as the control device 20, other control means belonging to the prior art, for example, A digital signal processor (DSP), a programmable logic device (FPGA or the like), an analog signal processing circuit, or the like can be used. If necessary, a preamplifier, a filter circuit or the like (not shown) may be added between the magnetic sensor 14 and the control device 20 to improve the S / N ratio of the detected value of the magnetic sensor 14.

  FIG. 2 shows an example of a flowchart of a method for controlling the magnetic field distribution in the target space S using the composite magnetic shield system of FIG. The operation of the composite magnetic shield structure shown in FIG. 1 will be described below with reference to the flowchart of FIG. Steps S001 to S003 show a procedure for constructing a composite magnetic shield structure. First, in step S001, as shown in FIG. 1 or FIG. 6 (A), the shield housing 3 is constructed on the inner surface of the target space S that is greatly affected by the environmental magnetic field. For example, the predetermined magnetic field distribution required in the target space S (for example, the distribution of the environmental magnetic field allowed at each position x) is determined, and the environmental magnetic field distribution in the target space S before construction of the shield housing 3 and its The variation is measured, and the arrangement position of the shield housing 3, the cross-sectional area Sm orthogonal to the longitudinal direction of each magnetic plate 2, the relative permeability μs, and the gap so that a predetermined magnetic field distribution is obtained when the environmental magnetic field is minimum. Design d etc. The predetermined magnetic field distribution of the designed target space S and the longitudinal direction of the shield housing 3 that has been constructed are stored in the storage means 21 of the control device 20.

  In step S002, magnetic sensors 14 for detecting the magnetic flux density in the magnetic plate 2 are attached to a plurality of predetermined positions on the shield housing 3, respectively. The magnetic sensors 14 and the wiring cables 16 that connect them to the control device 20 can be arranged in the gaps d between the magnetic plates 2 of the shield housing 3 so as not to impair the shielding performance of the shield housing 3. The magnetic sensor 14 is not particularly limited as long as it can be attached to the gap d. For example, as shown in FIG. 3, the magnetic sensor 14 is an induction coil 14a wound around the magnetic plate 2 of the shield housing 3, and the induced voltage of the coil 14a. Thus, the magnetic flux density in the magnetic plate 2 at the mounting position is detected. Alternatively, a high-sensitivity micromagnetic sensor (MI sensor) that can attach the magnetic sensor 14 to the gap facing surface of the magnetic plate 2 of the shield housing 3, a magnetic sensor using a Hall element, and a magnetic sensor using a magnetoresistive element ( MR sensor), a high-frequency drive type magnetic sensor (TMF sensor) using a magnetic thin film, and the like. If necessary, the induction coil 14a and another magnetic sensor 14 may be used in combination.

  The mounting position and number (mounting interval) of the magnetic sensor 14 are designed according to the magnetization distribution (magnetic flux density distribution) that can be generated in the magnetic plate 2 of the shield housing 3. It can be determined according to the environmental magnetic field distribution. For example, when the exposure direction of the environmental magnetic field is constant as shown in FIG. 7A (Z-axis direction in the illustrated example), the magnetic plate 2 in the longitudinal direction is intensively magnetized and the gradient of the magnetic flux density (see FIG. The arrow in the Z-axis direction in the middle increases, so that the magnetic sensor 14 is intensively attached at short intervals to the longitudinal shield housing 3 that coincides with the exposure direction of the environmental magnetic field, and other longitudinal shield housings. It is sufficient if the magnetic sensor 14 is attached to 3 at a relatively coarse interval. On the other hand, when it is necessary to cope with an environmental magnetic field in an arbitrary direction, it is desirable to attach a plurality of magnetic sensors 14 to all the magnetic plates 2 constituting the shield housing 3 as shown in FIG. The mounting position of each magnetic sensor 14 is also stored in the storage means 21 of the control device 20.

  Next, in step S003, the inner surface of the target space S in which the shield housing 3 is disposed is divided into a plurality of regions, and the compensation coils 10 are disposed so as to be adjacent to the outside or the inside of the shield housing 3 in each of the divided regions, Each compensation coil 10 is connected to the control device 20 via the drive device 26. By adjusting the compensation magnetic field generated by the compensation coil 10 in each region by the control device 20, the target space S is controlled to have a predetermined magnetic field distribution. The arrangement position and shape of the compensation coil 10 (the method for dividing the inner surface of the space S) are designed so that the magnetic field distribution in the target space S can be freely controlled by the compensation magnetic field generated by the compensation coil 10. According to the distribution of the environmental magnetic field obtained at the time of designing the body 3, it can be determined by numerical simulation so that the predetermined magnetic field distribution can be reproduced in the target space S. Since the cause and the source of the environmental magnetic field are different for each target space S, the arrangement position and shape of the compensation coil 10 can be designed and constructed according to the target space S in the field where the present invention is actually applied. desirable. The wiring cable 28 of each compensation coil 10 can also be arranged using the gap d of the shield housing 3.

  FIG. 1 shows an example of an arrangement position and a shape of a compensation coil 10 that can cope with an environmental magnetic field in an arbitrary direction, and an inner peripheral surface (four inner surfaces in the Y-axis direction and the Z-axis direction) surrounding the central axis X of the target space S. ) Are divided into grid-like regions (16 regions in the illustrated example), and the compensation coils 10 are arranged so as to circumscribe the shield housing 3 in each region (64 regions in total) (FIG. 4A). See also). Each compensation coil 10 includes, for example, an annular Helmholtz type coil arranged around a vertical axis passing through the center of each region, and a Merritt that generates a highly uniform compensation magnetic field near the center of each region by combining a plurality of annular coils. As disclosed in Non-Patent Document 2, a three-dimensional annular coil or the like that generates a compensation magnetic field with a primary gradient in the vicinity of the center of each region can be used. The distribution of the compensation magnetic field generated by each compensation coil 10 can be obtained from the center position of each region and the compensation current i applied to the compensation coil 10 according to Biot-Savart's law.

  In the illustrated example, each compensation coil 10 is arranged so as to circumscribe the outside of the shield housing 3, but each compensation coil 10 may be arranged so as to be inscribed inside the shield housing 3. When the compensation coil 10 is arranged outside the shield housing 3, the control device 20 calculates the magnetic field distribution in the target space S by including the compensation magnetic field generated by each compensation coil 10 in the boundary condition, and the predetermined magnetic field distribution is The driving position of the compensation coil 10 and the compensation current i can be selected so that they can be reproduced. When the compensation coil 10 is arranged inside the shield housing 3, the control device 20 uses the compensation magnetic field generated by each compensation coil 10 as a magnetic field generation source (for example, a current source) inside the space S, and the target space S. The driving position of the compensation coil 10 and the compensation current i may be selected so that the predetermined magnetic field distribution can be reproduced.

For example, as shown in FIG. 4A, when the compensation current i is applied to the compensation coils 10 ₃₃ and 10 ₄₄ , the magnetic field distribution in the target space 3 is controlled by the compensation magnetic field generated near the center of those regions. be able to. Further, by applying a compensation current i having the same amplitude and the same phase to the compensation coils 10 ₁₁ , 10 ₁₂ , 10 ₂₁ , and 10 ₂₂ , as shown by a dotted line in FIG. Thus, a compensation magnetic field equivalent to that when the compensation current i is applied can be generated, and the magnetic field distribution in the target space 3 can be controlled by the compensation magnetic field generated near the center of the four regions. Further, the generation distribution of the compensation magnetic field can be changed by changing the phase of the compensation current i of each compensation coil 10 ₁₁ , 10 ₁₂ , 10 ₂₁ , 10 ₂₂ . The magnetic field distribution in the target space 3 can be freely controlled in accordance with the vector addition of the compensation magnetic field generated by each compensation coil 10, and the predetermined magnetic field distribution can be reproduced in the target space S. By increasing the number of divisions of the inner surface of the space S, the degree of freedom in controlling the magnetic field distribution can be further increased.

FIG. 4B shows an example of another arrangement position and shape of the compensation coil 10 in the target space S. The inner peripheral surface of the space S is a corner region where the central region and three surfaces of each inner surface intersect (three regions). In the illustrated example, the rectangular compensation coils 10 ₁₁ , 10 ₁₂ , 10 _13, ... Are arranged in each central region, and triangular compensation coils 10 ₂₁ , 10 ₂₂ are provided in each corner region. 10 ₂₃ ... 10 ₃₁ , 10 ₃₂ , 10 ₃₃ ... are arranged. The compensation coils 10 on each side of the rectangle or triangle need not have the same length, and the rectangle or triangle may be distorted. In the case of FIG. 4B as well, in the same manner as in the case of FIG. 4A, the compensation position is selected by selecting the drive position of the compensation coil 10 and the amplitude / phase of the compensation current i applied to each compensation coil 10. The magnetic field distribution in the target space 3 can be freely controlled in accordance with the vector addition of the compensation magnetic field generated by the coil 10, and the predetermined magnetic field distribution can be reproduced in the target space S. Further, the center area and the corner area are divided into finer rectangular areas and triangular areas (thin areas), respectively, and a small rectangular or triangular compensation coil 10 is provided in each of the narrow areas as shown in FIG. You may arrange. The distribution characteristics of the compensation magnetic field generated according to the arrangement position (divided region) of each compensation coil 10 and the amplitude / phase of the compensation current i are stored in the storage unit 21 of the control device 20.

  Steps S004 to S006 in FIG. 2 show a procedure for controlling the magnetic field distribution in the target space S surrounded by the composite magnetic shield structure constructed in steps S001 to S003. In step S004, the detected value of the magnetic flux density in the magnetic plate 2 detected by each magnetic sensor 14 is input to the control device 20, and the magnetic field distribution (magnetic flux density distribution) in the target space S is calculated by the calculation means 22 of the control device 20. The process which calculates is shown. As described above, since the magnetic flux density distribution in the magnetic plate 2 is limited to the longitudinal direction of the magnetic plate 2 in the magnetic shield housing 3, the mounting position of each magnetic sensor 14 stored in the storage means 21 and each magnetic From the longitudinal direction of the plate 2, the direction of the magnetic flux density at the mounting position can be determined. The calculation means 22 calculates the magnetic field vector (magnetic flux density vector) ψ (x ′, t ′) at the mounting position x ′ from the mounting position x ′ of each magnetic sensor 14, the detected value of the magnetic flux density, and the longitudinal direction of the magnetic plate 2. ) Further, by integrating the magnetic field vectors ψ (x ′, t ′) at a plurality of positions x ′ on the shield housing 3 along the inner surface S ′ of the target space S, the magnetic flux density on the inner surface S ′ of the space S Calculate distribution (boundary conditions). If the magnetic flux density distribution on the inner surface S ′ can be detected, for example, by applying Kirchhoff integral display (equation (1) or an approximation thereof), the magnetic field vector at an arbitrary position x in the target space S, that is, the space S Magnetic field distribution can be calculated.

  Note that the calculation means 22 of the control device 20 can directly or approximately apply the expression (1) or its approximate expression to calculate the magnetic field distribution in the target space S in real time. If the magnetization distribution (boundary condition) on the shield case 3 to be covered can be grasped, the magnetic field distribution in the target space S can be calculated by another appropriate method. For example, the relational expression between the magnetization distribution on the shield housing 3 and the magnetic field distribution in the target space S according to the fluctuation of the environmental magnetic field distribution by numerical simulation based on the environmental magnetic field distribution obtained at the time of designing the magnetic shield housing 3. (Table etc.) is created in advance, and the magnetic field distribution in the target space S can be calculated easily and quickly from the magnetization distribution on the shield housing 3 using the relational expression. When the cause or source of the environmental magnetic field in the target space S can be identified, the magnetization distribution on the shield housing 3 and the magnetic field distribution in the target space S according to the change of the environmental magnetic field generated at the cause or source. And a magnetic field distribution in the target space S can be calculated using the relational expression.

  In step S005 of FIG. 2, the detection unit 23 of the control device 20 deviates between the magnetic field distribution in the target space S calculated in step S004 and the predetermined magnetic field distribution in the target space S stored in the storage unit 21 (in the space S , And the selection means 24 of the control device 20 detects the drive position of the compensation coil 10 and the compensation current i to be applied to each compensation coil 10 in order to cancel the deviation. The process which selects is shown. For example, the compensation coil 10 in or near the region where the deviation is detected by the detection unit 23 is selected, and the compensation magnetic field generated in the compensation coil 10, that is, the amplitude / phase of the compensation current i is selected by the selection unit 24. Alternatively, the selection means 24 includes the compensation magnetic field generated by the nearby compensation coil 10 in which the deviation is detected in the boundary condition or the magnetic field generation source and applies Kirchoff integral display (equation (1) or an approximation thereof) to apply the target space. By repeating the recalculation of the magnetic field distribution in S, it is possible to select the drive position of the compensation coil 10 that can reproduce the predetermined magnetic field distribution and the amplitude and phase of the compensation current i.

  In step S005, the driving position of the compensation coil 10 and the compensation current i can be selected by another suitable method instead of the method of directly or approximately applying the expression (1). For example, by the numerical simulation based on the environmental magnetic field distribution obtained at the time of designing the magnetic shield housing 3 described above, the deviation that may occur in the magnetic field distribution in the target space S and the position of the compensation coil 10 necessary to cancel the deviation, and A relational expression (table or the like) with the compensation current i is created in advance, and the driving position of the compensation coil 10 and the compensation current i are selected using the relational expression in accordance with the deviation detected by the detecting means 23. Can do. Further, when the cause or source of the environmental magnetic field in the target space S can be specified, the deviation of the magnetic field distribution in the target space S that can be generated according to the variation of the environmental magnetic field generated in the cause or source and the deviation are calculated. It is also possible to create a relational expression between the position of the compensation coil 10 and the compensation current i necessary for cancellation by numerical simulation, and to select the drive position of the compensation coil 10 and the compensation current i using the relational expression.

  In step S006 of FIG. 2, the driving position of the compensation coil 10 and the signal of the compensation current i obtained by the selection unit 24 of the control device 20 are input to the driving device 26, and the compensation coil 10 arranged in each region of the target space 3 is input. The process of selectively driving is shown. The driving device 26 shown in FIG. 1 is connected to each compensation coil 10 via an amplifier or current booster 27, and applies the selected compensation current i to the selected compensation coil 10 via the amplifier or current booster 27. As a result, a compensation magnetic field is generated that cancels the fluctuation of the magnetic field distribution (deviation from the predetermined magnetic field distribution) generated in the target space S. In addition, a plurality of environmental magnetic fields with different causes or sources may be simultaneously exposed to the actual target space S, and a compensation current i corresponding to the environmental magnetic field of a specific cause or source is applied to the compensation coil 10. Only by doing this, there may be a case where the fluctuation of the environmental magnetic field generated in the target space S cannot be sufficiently eliminated. In such a case, the driving device 26 of FIG. 1 includes a multiplexer, a selector (duplexer), etc., and the driving device 26 adjusts (combines or demultiplexes) the signal of the compensation current i of each compensation coil 10 corresponding to different environmental magnetic fields. ) And driving each compensation coil 10 is effective. By applying a compensation current i for a plurality of environmental magnetic fields with different causes or sources to each compensation coil 10, a superimposed compensation magnetic field is generated that cancels fluctuations in the magnetic field distribution of the target space S exposed to such an environmental magnetic field. be able to.

  In step S007, it is determined whether to end the control of the magnetic field distribution in the target space S. When the control is continued, the process returns to step S004, and steps S004 to S006 described above are repeated. According to the flowchart of FIG. 2, not only a magnetic field at a specific position (for example, one point) in the target space S but also a magnetic field at an arbitrary position x can be controlled. Can be controlled. For example, by applying the composite shield structure of the present invention to the magnetic shield space S using an electron beam device, a SQUID device, or the like, the device can be rearranged or moved in the space S, and the space S can be used. Efficiency can be greatly improved. Further, when a deviation occurs in the magnetic field distribution in the target space S, only the compensation coil 10 in the vicinity of the area where the deviation occurs can be selectively driven to cancel the deviation in the magnetic field distribution. It is possible to control the magnetic field distribution in the target space S with the driving power.

  Thus, it is possible to achieve the “composite magnetic shield structure and system capable of controlling the magnetic field distribution inside the target space”, which is an object of the present invention.

  FIG. 5 shows a combination of an annular shield housing 5x surrounding the central axis X of the target space S and an annular shield housing 5y surrounding the central axis Y as shown in FIG. An embodiment of an open shield structure in which a shield housing 5 is disposed on each inner surface of the ceiling will be described. Since the open type shield structure exhibits a great shielding effect when the direction in which the belt-like magnetic plate 2 is arranged is aligned with the direction of the environmental magnetic field, in order to cope with the environmental magnetic field in all directions in the XYZ axis directions, FIG. It is effective to form a two-layer structure by nesting a plurality of annular shield housings 5x and 5y having different installation directions (annular central axis directions) as shown in FIG. In addition, an annular shield housing 5z (not shown) surrounding the central axis Z can be nested in the multilayer structure of FIG. 5A to form a multilayer structure of three or more layers.

  FIG. 5B shows an embodiment of the composite magnetic shield structure of the present invention using the two-layer nested annular shield housings 5x and 5y of FIG. 5A. The magnetic shield structure in FIG. 5B is also constructed according to the flow chart of FIG. 2 described above, except that the passive shield structure and the active shield structure are arranged on all six surfaces of the target space S, and is surrounded by the structure. The magnetic field distribution in the target space S can be controlled. That is, after constructing the two-layer nested annular shield housings 5x and 5y on the inner surfaces of the floor, wall, and ceiling of the target space S in step S001, the predetermined inner surfaces of the inner shield housings 5x and 5y are formed in step S002. A magnetic sensor 14 is attached to each position. Since the shield housings 5x and 5y having the two-layer nested structure integrally form the inner surface S ′ of the target space S, the inner surface of the space S where the shield housings 5x and 5y overlap (in the illustrated example, the inner surface in the Z-axis direction). Then, it is sufficient to attach the magnetic sensor 14 on any one of the shield housings 5x and 5y. In step S003, all the inner surfaces of the target space S surrounded by the two-layer nested structure are divided into a plurality of parts, and the compensation coils 10 are arranged in the divided areas. An example of the arrangement of the compensation coil 10 is shown in FIG.

  In step S 004, the detected value of the magnetic flux density in the magnetic plate 2 detected by the magnetic sensor 14 on each inner surface of the target space S is input to the control device 20, and is calculated on all inner surfaces S ′ of the target space S by the calculation means 22. Is calculated, and the magnetic field distribution in the target space S is calculated using the magnetic flux density distribution on all the inner surfaces S ′ as boundary conditions. As described above, for example, the magnetic field distribution can be calculated by applying the expression (1) or its approximate expression, but the magnetic flux density distribution on the two-layer nested structure created in advance and the magnetic field distribution in the target space S The magnetic field distribution in the target space S may be calculated using a relational expression (such as a table). Next, in step S005, the deviation between the magnetic field distribution in the target space S and the predetermined magnetic field distribution is detected by the detecting means 23, and the driving position of the compensation coil 10 necessary for canceling the deviation and the amplitude of the compensation current i to be applied. The phase is selected by the selection means 24. The method for selecting the compensation coil 10 in FIG. 4C is the same as the method described above with reference to FIG. Furthermore, in step S006, the drive position of the compensation coil 10 and the signal of the compensation current i are input to the drive device 26, and the compensation coil 10 disposed on each inner surface of the two-layer nested structure is selectively driven, thereby the target space S It is possible to generate a compensation magnetic field that cancels the fluctuation of the magnetic field distribution (deviation from the predetermined magnetic field distribution) generated in the target space S, and to control the entire or wide range in the target space S to a desired magnetic field distribution.

DESCRIPTION OF SYMBOLS 1 ... Composite type magnetic shield structure 2 ... Strip | belt-shaped magnetic board (strip shape or long type magnetic plate)
DESCRIPTION OF SYMBOLS 3 ... Magnetic shield housing 5 ... Environmental shield housing 9 ... Overlapping part 10 ... Compensation magnetic field generation coil 14 ... Magnetic sensor 14a ... Induction coil 16 ... Cable 20 ... Control apparatus (computer) 21 ... Storage means 22 ... Calculation means 23 ... Detection means 24 ... Selection means 26 ... Driving means (selector) 27 ... Amplifier (amplifier)
28 ... Cable 30 ... Sealed shield structure 31 ... Magnetic plate 32 ... Through-hole 34 ... Compensation coil 36 ... Detection coil 40 ... Control device 41 ... Amplifier 42 ... Integrator 43 ... Adjuster 44 ... Coil drive (drive device) 45 ... adder / subtractor

Claims (8)

A plurality of strip-shaped magnetic plates are arranged on the inner surface of the magnetic shield target space so that each longitudinal central axis is arranged in parallel with a predetermined gap, and the inner surface is arranged in each of the divided areas. A plurality of coils for generating a compensation magnetic field, and a magnetic sensor that is attached to a plurality of positions on the casing and detects a magnetic flux density in the magnetic plate, and includes a longitudinal direction of the casing, a position of each sensor, and a detection value; The magnetic flux density distribution on the inner surface of the target space and the magnetic field distribution inside the target space are calculated, and a compensation current corresponding to the deviation between the calculated value and the predetermined magnetic field distribution is selectively applied to the coils in each region. A composite magnetic shield structure that controls the target space to a predetermined magnetic field distribution. 2. The shield structure according to claim 1, wherein the magnetic shield housing is an annular shield housing disposed while being magnetically coupled along an inner surface of a target space, and the compensation magnetic field generating coil is an annular shield housing. A composite magnetic shield structure arranged adjacent to the outside or inside. 3. The shield structure according to claim 1, wherein the sensor is an induction coil wound on the magnetic plate of the casing or a magnetic sensor attached to a gap facing surface of the magnetic plate of the casing. 4. The composite magnetic shield structure according to claim 1, wherein the compensation magnetic field generating coil in each region is an annular coil arranged around a vertical axis passing through the center of the region. A plurality of strip-shaped magnetic plates are arranged on the inner surface of the magnetic shield target space so that each longitudinal central axis is arranged in parallel with a predetermined gap, and the inner surface is arranged in each of the divided areas. A compensation magnetic field generating coil, a magnetic sensor that is attached to a plurality of positions on the casing and detects the magnetic flux density in the magnetic plate, and an inner surface of the target space from the longitudinal direction of the casing and the position and detection value of each sensor A composite type comprising control means for calculating a magnetic flux density distribution and a magnetic field distribution inside the target space and selectively applying a compensation current according to a deviation between the calculated value and a predetermined magnetic field distribution to the coils in each region Magnetic shield system. 6. The system according to claim 5, wherein the magnetic shield housing is an annular shield housing that is magnetically coupled along the inner surface of the target space, and the compensation magnetic field generating coil is disposed outside the annular shield housing. Alternatively, a composite magnetic shield system arranged adjacent to the inside. 7. The composite magnetic shield system according to claim 5, wherein the sensor is an induction coil wound on a magnetic plate of the casing or a magnetic sensor attached to a gap facing surface of the magnetic plate of the casing. 8. The composite magnetic shield system according to claim 5, wherein the compensation magnetic field generating coil in each region is an annular coil disposed around a vertical axis passing through the center of the region.