JP2009229325A - Method and device of evaluating performance of active magnetic shield - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate the performance of an active magnetic shield combined with a passive magnetic shield. <P>SOLUTION: In a magnetic shield room 1 in which an environmental magnetic field measurement sensor 12 and a compensation coil 10 for generating a compensation magnetic field to cancel out the environmental magnetic field are arranged, an disturbance coil 11 with the same shape for generating an disturbance magnetic field is disposed at the same position as the compensation coil 10, a test magnetic field signal V is applied to the disturbance coil 11 when the drive of the compensation coil 10 is stopped, and a magnetic field amount ratio Pv/Sv of a sensor position S and an object position P is detected. Thereafter, a magnetic field amount St after the compensation at the sensor position S is measured by driving the compensation coil 10 while applying to the disturbance coil an environmental magnetic field signal E according to an environmental magnetic field amount Se upon the design of shield. A compensation magnetic field amount Sc at the sensor position S is calculated from the magnetic field amount St after the compensation and the environmental magnetic field amount Se upon the design. A compensation magnetic field amount Pc at the object position P is calculated from the compensation magnetic field amount Sc and the magnetic field amount ratio Pv/Sv. The shield performance at the object position P is evaluated from the compensation magnetic field amount Pc and the environmental magnetic field amount Pe upon the design. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for evaluating the performance of an active magnetic shield, and more particularly to a method and apparatus for evaluating the shielding performance of an active magnetic shield room in which a compensation coil for generating a compensation magnetic field that cancels an environmental magnetic field is arranged.

  Buildings that use strong magnetism, such as electron beam (EB) devices such as electron microscopes, MRI (magnetic resonance imaging) devices, NMR (nuclear magnetic resonance) devices, SQUID (superconducting quantum interference device) devices, etc. For the purpose of protecting the surrounding people and equipment from the leakage magnetic field from the installation room and ensuring the normal operation by protecting the device from the environmental magnetic field (magnetic noise) around the building when installed inside The installation room may be magnetically shielded. For example, in medical facilities and semiconductor-related facilities, the installation room for MRI equipment, EB equipment, etc. is passively surrounded by magnetic material plates (hereinafter sometimes referred to as magnetic plates) such as high magnetic permeability steel plates and permalloy. ) Magnetic shield room. In general, a passive magnetic shield room is a sealed type that blocks the influence of an environmental magnetic field by covering the wall surface with a magnetic plate without any gap (see Patent Document 1), but the sealed magnetic shield room has no air or light permeability. As shown in FIG. 6, a plurality of rectangular strip-shaped magnetic plates 5 are laminated in a bowl shape at a required interval in the plate thickness direction so that the longitudinal center axes thereof are arranged in parallel on the same plane ( An open type magnetic shield room with a gap using the walls 2 and 3 as wall surfaces has also been developed (refer to Patent Document 2).

  FIG. 6 shows an open-type passive magnetic shield chamber 1 surrounded by six shield housings 2a, 2b, 2c, 2d, 2e and 3. The five shield housings 2a, 2b, 2c, 2d, and 2e are joined to form a side wall of the shield chamber 1 by overlapping the edge 6 of the corresponding magnetic plate 5 in a row, and the shield housing 2a on one end side thereof. The shield housing 3 is arranged between the shield housing 2e on the other end side and serves as an opening / closing part (door, window, etc.) of the shield chamber 1. In order to prevent a leakage magnetic field from occurring in the thickness direction of the magnetic plates 5 of the housings 2 and 3, the interval is compared with the ease of passing the magnetic flux of the magnetic plate 5 (permeance of the magnetic plate). The design is such that the ease of magnetic flux passage (permeance of spacing) is sufficiently small. Further, in order not to generate a leakage magnetic field from the gap between the shield housings 2a, 2e and the shield housing 3, the edge of the magnetic plate 5 of each of the housings 2a, 2e, 3 facing the gap is A magnetic expansion plate 7 that expands the area in the plate thickness direction is attached, and the housings 2a and 3 and the housings 2e and 3 are designed to be magnetically coupled by the magnetic expansion plate 7 via a gap. If necessary, magnetic leakage 8 is provided in the gap to further reduce the leakage magnetic field from the gap. According to the shield chamber 1 of the illustrated example, the leakage magnetic field from the shield chamber 1 can be efficiently reduced with a minimum magnetic material while ensuring the permeability of air and light by the interval in the thickness direction of the housings 2 and 3. It can be suppressed economically.

  However, since all of the conventional passive magnetic shields have static performance and structure, they are effective for countermeasures against leakage magnetic fields from the shield room 1, but MRI from the fluctuating environmental magnetic field generated by the operation of the railway around the building, etc. In some cases, the device and the EB device cannot be protected efficiently and economically. For example, even if the peak of the environmental magnetic field fluctuation is temporary, it is necessary to provide a shield structure using a large number of magnetic materials in order to cope with the peak, and problems such as a thick wall of the shield chamber 1 occur. Therefore, in addition to or instead of a passive magnetic shield, as shown in FIG. 4, active magnetism that generates a compensation magnetic field having the same amplitude and opposite phase according to the environmental magnetic field fluctuation and cancels the environmental magnetic field fluctuation. A shield is used (see Patent Documents 3 and 4).

The active magnetic shield shown in FIG. 4 (B) has the central axis direction aligned with the three orthogonal axes (X axis, Y axis, Z axis) passing through the central portion of the shield chamber 1 as shown in FIG. 4 (A). Three sets of compensation coils 10 _X , 10 _Y , and 10 _Z , a magnetic sensor 12 that measures an environmental magnetic field in the shield chamber 1, and a signal processing means that calculates a compensation magnetic field signal according to the measurement signal of the sensor 12 15 and a drive power supply 14 for driving the compensation coils 10 _X , 10 _Y , and 10 _Z according to the compensation magnetic field signal. The illustrated example shows a compensation coil 10 _X in the X-axis direction including two Helmholtz coils 10 _X1 and 10 _X2 , but the compensation coils 10 _Y and 10 _{Z in} the Y-axis direction and the Z-axis direction have the same configuration. The signal processing means 15 calculates a compensation magnetic field signal necessary for canceling the fluctuation of the environmental magnetic field (magnetic flux density) measured by the sensor 12, and the power corresponding to the signal is supplied from the drive power supply 14 to the compensation coils _10Y , _10Z. The compensation of the environmental magnetic field is canceled by generating a compensation magnetic field. For example, by combining (using together) the passive magnetic shield of FIG. 6 and the active magnetic shield of FIG. 4, it can be expected to efficiently and economically design the shield chamber 1 that can cope with a fluctuating environmental magnetic field.

JP 09-162585 A JP 2006-351598 A JP 2002-232182 A JP 2006-324651 A

  However, the conventional active magnetic shield has a problem that it is difficult to evaluate (verify) whether or not the shield performance of the shield chamber 1 conforms to the design specification. Generally, the environmental magnetic field fluctuations before the shield construction is measured to determine the design specifications of the shield performance, and the environmental magnetic field fluctuations are measured again after the shield construction to evaluate the performance of the shield room 1 (conformity of the design specifications). However, since the environmental magnetic field fluctuations are usually not reproducible, compatibility evaluation must be performed using environmental magnetic field fluctuations different from those at the time of design specification determination. In this way, with the performance evaluation method using the environmental magnetic field, even if the proximity of the environmental magnetic field fluctuation is increased over a long time, accurate shielding performance evaluation based on the environmental magnetic field fluctuation directly reflected in the design specifications is not possible. Have difficulty. In particular, when the active magnetic shield is used in combination with the passive magnetic shield, the environmental magnetic field is affected by the magnetic material of the passive magnetic shield, making it difficult to accurately evaluate the performance of the active magnetic shield alone.

  When the cause of the environmental magnetic field fluctuation exists sufficiently far away and a variable magnetic field having a substantially uniform magnetic field distribution can be assumed, a disturbance coil installed outside the shield chamber 1 as shown in FIG. 11 may artificially generate an environmental magnetic field (disturbance magnetic field) to evaluate the performance of the active magnetic shield. However, in order to reproduce a uniform environmental magnetic field, it is necessary to install a large-diameter disturbance coil 11 far enough as compared to the shield chamber 1, and such an installation is practically difficult. Even with the performance evaluation method using the coil 11, it is difficult to perform a highly reliable evaluation of the active magnetic shield. Even if the disturbance coil 11 can be installed, when it is used together with the passive magnetic shield, the magnetic field distribution intended by the disturbance coil 11 is different from the distribution due to the influence of the magnetic material of the passive magnetic shield. This makes it impossible to accurately evaluate the active magnetic shield. There is a demand for the development of a system that can appropriately evaluate and verify the performance of an active magnetic shield even when combined with a passive magnetic shield.

  Further, when the active magnetic shield is combined with the passive magnetic shield, it is difficult to evaluate the active magnetic shield performance at a position away from the sensor 12 in the shield chamber 1. For example, in the shield room 1 in which the MRI apparatus is installed, it is desirable to evaluate the shielding performance at the installation position of the MRI apparatus (Dewar part) that is the shield target. Since a strong magnetic field is generated, it is difficult to install a sensor 12 at such a target position and measure a slight fluctuation (for example, 100 nT or less) of the environmental magnetic field (accuracy of about 100 nT in a few T). There is no sensor 12 with a wide dynamic range having In addition, in the EB apparatus such as an electron microscope, since the shield target is in the lens barrel portion, the sensor 12 cannot be disposed at the target position in the first place. For this reason, in the active magnetic shield chamber 1 in which an MRI apparatus, an EB apparatus, or the like is installed, it is often necessary to evaluate the shield performance with the sensor 12 at the sensor position S far from the evaluation target position P.

  When the active magnetic shield is combined with the passive magnetic shield, the environmental magnetic field (or the artificial environmental magnetic field generated by the disturbance coil 11) at the sensor position S and the target position P that are separated from each other in the shield chamber 1 is As shown in FIG. 5 (P1) and (S1), it differs depending on the influence of the magnetic material of the passive magnetic shield. Further, the compensation magnetic field generated by the compensation coil 10 of the active magnetic shield also deviates from the design specification due to the influence of the magnetic material, as shown in FIGS. Therefore, as shown in FIGS. (P3) and (S3), even in the same shield chamber 1, the shield performance at the target position P and the sensor position S is completely different, leaving the shield performance at the target position P apart. It is difficult to estimate from the shielding performance of the sensor position S. In order to appropriately evaluate and verify the performance of the active magnetic shield combined with the passive magnetic shield, it is possible to appropriately evaluate the shielding performance of the target position P even if the target position P and the sensor position S are separated. desirable.

  Accordingly, an object of the present invention is to provide an evaluation method and apparatus capable of appropriately evaluating the performance of an active magnetic shield even when combined with a passive magnetic shield.

  Referring to the embodiment of FIG. 1 and the flowchart of FIG. 2, the active magnetic shield performance evaluation method according to the present invention includes an environmental magnetic field measurement sensor 12 and a compensation coil 10 for generating a compensation magnetic field that cancels the environmental magnetic field. In the method for evaluating the shielding performance at the evaluation target position P in the active magnetic shield chamber 1, the disturbance coil 11 for generating a disturbance magnetic field having the same shape is arranged at the same position as the compensation coil 10 (step S002 in FIG. 2). S005), when the driving of the compensation coil 10 is stopped, the test magnetic field signal V is applied to the disturbance coil 11 to detect the magnetic field amount ratio Pv / Sv between the sensor position S and the target position P (steps S006 to S007). The compensation coil 10 is driven while the environmental magnetic field signal E corresponding to the environmental magnetic field amount Se at the time of designing the shield at the sensor position S is applied to the sensor position S. The post-compensation magnetic field amount St is measured (step S008), and the compensation magnetic field amount Sc at the sensor position S is calculated from the difference (= St−Se) between the compensated magnetic field amount St at the sensor position S and the design environment magnetic field amount Se. In addition, the compensation magnetic field amount Pc at the target position P is calculated from the compensation magnetic field amount Sc and the magnetic field amount ratio Pv / Sv (step S009), and the environment at the time of the shield design of the compensation magnetic field amount Pc at the target position P and the target position P is calculated. The shield performance at the target position P is evaluated based on the magnetic field amount Pe (step S012).

  Referring to the block diagram of FIG. 1, the active magnetic shield performance evaluation apparatus according to the present invention is an active magnetism in which an environmental magnetic field measurement sensor 12 and a compensation coil 10 for generating a compensation magnetic field that cancels the environmental magnetic field are arranged. In the apparatus for evaluating the shielding performance at the evaluation target position P in the shield chamber 1, the disturbance coil 11 for generating a disturbance magnetic field, the sensor position S, and the target position, which are arranged in the same position as the compensation coil 10 in the shield chamber 1 Storage means 23 for recording the amount of environmental magnetic field Se, Pe at the time of shield design of P, and the amount of magnetic field between sensor position S and target position P by applying test magnetic field signal V to disturbance coil 11 when driving of compensation coil 10 is stopped An environmental magnetic field signal E corresponding to the amount of environmental magnetic field Se at the sensor position S at the time of design is applied to the detecting means 24 for detecting the ratio Pv / Sv and the disturbance coil 11. Measuring means 25 for driving the compensation coil 10 to measure the post-compensation magnetic field amount St at the sensor position S, from the difference (= St−Se) between the post-compensation magnetic field amount St at the sensor position S and the design environment magnetic field amount Se. The calculating means 26 for calculating the compensation magnetic field amount Sc at the sensor position S and calculating the compensation magnetic field amount Pc at the target position P from the compensation magnetic field amount Sc and the magnetic field amount ratio Pv / Sv, and the compensation magnetic field amount Pc at the target position P And an evaluation means 27 for evaluating the shield performance of the target position P based on the amount of environmental magnetic field Pe at the target position P at the time of design.

  Preferably, as shown in steps S010 to S011 in FIG. 2, the measurement of the compensated magnetic field amount St at the sensor position S (step S008) and the calculation of the compensation magnetic field amount Pc at the target position P (step S009) are repeated a plurality of times. Then, the shielding performance of the target position P is evaluated based on the average value of the compensation magnetic field amount Pc at the target position P for a plurality of times. More preferably, as shown in FIG. 1, an inspection position R is defined inside or outside the shield chamber 1, and a magnetic field amount ratio Sv / Rv between the inspection position R and the sensor position S when the test magnetic field signal V is applied. (Step S007 in FIG. 2), when the environmental magnetic field signal E is applied, the compensated magnetic field amount Rt at the inspection position R is measured instead of the compensated magnetic field amount St at the sensor position S, and the compensated magnetic field amount Rt A post-compensation magnetic field amount St at the sensor position S is calculated from the magnetic field amount ratio Sv / Rv (step S008).

  The method and apparatus for evaluating the performance of an active magnetic shield according to the present invention are arranged in the same position in the shield chamber 1 at the same position as the compensation coil 10 for generating a compensation magnetic field and the disturbance coil 11 for generating a disturbance magnetic field, and driving the compensation coil 10. The test magnetic field signal V is applied to the disturbance coil 11 at the time of stopping to detect the magnetic field amount ratio Pv / Sv between the sensor position S and the target position P, and then the environmental magnetic field at the time of designing the shield at the sensor position S in the disturbance coil. The compensation coil 10 is driven while applying the environmental magnetic field signal E corresponding to the quantity Se to measure the compensated magnetic field quantity St at the sensor position S, and the compensated magnetic field quantity St at the sensor position S and the environmental magnetic field quantity Se at the time of design. The compensation magnetic field amount Sc at the sensor position S is calculated from the difference between the compensation position (= St−Se), and the compensation magnetic field amount Pc at the target position P is calculated from the compensation magnetic field amount Sc and the magnetic field amount ratio Pv / Sv. P Since evaluating the shielding performance of the target position P by the environmental magnetic field amount Pe when the shield design of 償磁 field amount Pc and the target position P, exhibits the following advantageous effects.

(A) Since the compensation coil 10 and the disturbance coil 11 are arranged at the same position and in the same shape, the compensation magnetic field distribution generated by the compensation coil 10 and the environmental magnetic field distribution generated by the disturbance coil 11 are made to coincide with each other from the target position P. The shield performance of the target position P can be appropriately evaluated based on the measured value of the separated sensor position S.
(B) In addition, because the shield performance is evaluated by reproducing the environmental magnetic field quantities Se and Pe directly reflected in the design specifications of the active magnetic shield, accurate evaluation and verification (acceptance) of the shield performance based on the design specifications is possible. It becomes possible.
(C) Even in the active magnetic shield chamber 1 combined with a passive magnetic shield, it is possible to directly evaluate the shield performance by matching the environmental magnetic field distribution and the compensation magnetic field distribution affected by the magnetic material. The reliability of the evaluation result can be improved as compared with the performance evaluation method using the magnetic field distribution (for example, uniform magnetic field distribution).

(D) Even when the S / N ratio of the shield performance evaluation deteriorates due to the influence of the magnetic material of the passive magnetic shield, the performance evaluation value can be obtained multiple times by repeating the measurement of the compensated magnetic field amount St at the sensor position S. The S / N ratio can be easily improved by the average operation.
(E) The shield performance of the target position P can be evaluated in a relatively short time of measuring the compensated magnetic field amount St of the sensor position S, and the evaluation and verification work of the active magnetic shield can be speeded up. It can be carried out quickly in a time zone where the environmental magnetic field around the shield room is weak to increase the accuracy of performance evaluation.
(F) The ambient magnetic field distribution of the disturbance coil 11 and the compensation magnetic field distribution of the compensation coil 10 can be matched not only inside the shield chamber 1 but also around the outside, so that the inspection position around the outside without entering the shield chamber 1 It can also be expected that the shield performance evaluation of the target position P is performed with R.
(G) If the environmental magnetic field quantities Se and Pe and the magnetic field quantity ratio Pv / Sv at the time of designing the sensor position S and the target position P are recorded, not only at the time of acceptance but also at the time of periodic maintenance and inspection. The shield performance of the target position P in the shield chamber 1 can be evaluated while the apparatus (MRI apparatus or EB apparatus) in the shield chamber 1 is operating.

FIG. 1 shows an embodiment in which the performance evaluation apparatus of the present invention is applied to a shield chamber 1 in which a passive magnetic shield and an active magnetic shield are used together. The shield chamber 1 in the illustrated example has a peripheral wall composed of a shield housing 2 in which a plurality of magnetic plates 5 are stacked at a required interval in the plate thickness direction, as a passive magnetic shield chamber 1 in FIG. However, the magnetic shield chamber 1 to which the present invention is applied is not limited to the one using the shield housing 2, and is, for example, a shield chamber 1 in which a peripheral wall is configured with a passive magnetic shield without a gap as in Patent Document 1. Also good. The shield chamber 1 in the illustrated example, like the active magnetic shield chamber 1 in FIG. 4, generates a magnetic sensor 12 that measures the environmental magnetic field at the sensor position S in the shield chamber 1 and a compensation magnetic field that cancels the environmental magnetic field. Therefore, the compensation coils (for example, Helmholtz coils) 10 _X , 10 _Y , 10 _Z and the compensation coil 10 _X are arranged so that the central axis direction coincides with the three orthogonal axes (X axis, Y axis, Z axis) of the shield chamber 1. It has a drive power supply 14 for driving 10 _Y and 10 _Z , and a computer 20 connected to the sensor 12 and the drive power supply 14.

In the illustrated example, only the compensation coils 10 _X1 and 10 _{X2 in} the X-axis direction of the active magnetic shield are shown for simplicity of explanation, but the same applies to the compensation coils 10 _Y and 10 _{Z in} the Y-axis direction and the Z-axis direction. It can be configured. The compensation coils 10 _X , 10 _Y , and 10 _Z may be disposed either inside or outside the passive magnetic shield (shield housing in the illustrated example), and are integrally disposed inside or near the passive magnetic shield. Also good. The computer 20 in the illustrated example includes an input unit 21 that inputs a measurement signal of the magnetic sensor 12 and a signal processing unit 15 that calculates a compensation magnetic field signal according to the input signal of the input unit 21 and outputs the signal to the drive power source 14. Have. Further, a switch unit 28 is provided between the input unit 21 and the signal processing unit 15, and the driving / stopping of the compensation coil 10 can be switched by the control of the switch unit 28. The input means 21, the signal processing means 15, and the switch means 28 are programs built in the computer 20, respectively.

The performance evaluation apparatus of the illustrated example includes disturbance coils 11 _X , 11 _Y , 11 _Z for generating a disturbance magnetic field arranged in the same position at the same positions as the compensation coils 10 _X , 10 _Y , 10 _Z of the shield chamber 1, and disturbances The driving power source 16 drives the coils 11 _X , 11 _Y , 11 _Z , the storage unit 23 of the computer 20, and a built-in program to be described later. The disturbance coils 11 _X , 11 _Y , and 11 _Z are Helmholtz coils similar to the compensation coils 10 _X , 10 _Y , and 10 _Z , for example, but in the illustrated example, the disturbance coil 11 is indicated by a dotted line for easy identification from the compensation coil 10. It is represented by Further, for simplification of explanation, only the disturbance coils 11 _X1 and 11 _X2 in the X-axis direction are shown, but the disturbance coils 11 _Y and 11 _{Z in} the Y-axis direction and the Z-axis direction can also have the same configuration. .

  As will be described later, the sensor position S and the environmental magnetic field quantities Se (t) and Pe (t) at the evaluation target position P are recorded in the storage means 23 of the computer 20. The target position P is determined according to the apparatus installed in the shield chamber 1 as described above (for example, the dewar part of the MRI apparatus, the lens barrel part of the electron microscope, etc.). The sensor position S can be an arbitrary position in the shield chamber 1 that does not interfere with the installation / operation of the apparatus. In the illustrated example, the magnetic sensor 12a that measures the environmental magnetic field amount Pe is provided at the target position P. However, the environmental magnetic field amount Pe can be measured by moving the magnetic sensor 12 at the sensor position S to the target position P. Thus, the magnetic sensor 12a is not essential for the performance evaluation apparatus of the present invention. The computer 20 also has a signal processing means 17 for outputting the magnetic field signal of the disturbance coil 11 to the driving power supply 16 as a built-in program for performance evaluation, and the test magnetic field signal V to the disturbance coil 11 via the signal processing means 17. It has a detecting means 24 to be applied, a measuring means 25 for applying the environmental magnetic field signal E to the disturbance coil 11 via the signal processing means 17, a calculating means 26 and an evaluating means 27.

  FIG. 2 shows an example of a flowchart of the performance evaluation method of the present invention using the performance evaluation apparatus of FIG. The operation of the performance evaluation method of the present invention and the built-in program of the computer 20 will be described below with reference to the flowchart of FIG. First, in step S001, the above-described passive magnetic shield is applied to the shield chamber 1, and then in step S002, the sensor position S in the shield chamber 1 and the environmental magnetic field quantities Se (t) and Pe (t) at the target position P are set to the magnetic sensor 12. The measured environmental magnetic field quantities Se (t) and Pe (t) are input to the computer 20 and recorded in the storage means 23. An example of the waveforms of the environmental magnetic field quantities Se (t) and Pe (t) is shown in FIGS. 3 (P1) and (S1). The recorded environmental magnetic field quantities Se and Pe are used for reproducing the environmental magnetic field at the time of shield performance evaluation in step S008. In addition, when the sensor position S is undecided in step S002, you may respond | correspond by measuring environmental magnetic field amount Se (t) in the several candidate point of the sensor position S. FIG.

In step S003, based on the recorded environmental magnetic field quantities Se (t) and Pe (t), the design specifications of the active magnetic shield (arrangement positions and shapes of the compensation coils 10 _X , 10 _Y , and 10 _Z , the sensor position S of the magnetic sensor 12). After determining the program of the signal processing means 15, etc., the above-described active magnetic shield is applied in step S004. Specifically, the compensation coils 10 _X , 10 _Y , 10 _Z and the magnetic sensor 12 are arranged in the shield chamber 1 according to the design specifications. Further, in step S005, the compensation coil ₁₀ X of the shield room _1, in the same position as 10 Y, 10 _Z, arranged the disturbance coil _{11 X, 11 Y, 11 Z} in the same shape as the compensation coil _{10 X, 10 Y, 10 Z} To do. In the shield chamber 1 that also uses a passive magnetic shield as in the illustrated example, it is assumed that the compensation magnetic field distribution generated by the compensation coils 10 _X , 10 _Y , and 10 _Z is different from the design specification due to the influence of the magnetic plate 5. The disturbance coils 11 _X , 11 _Y , and 11 _Z are arranged in the same position as the compensation coils 10 _X , 10 _Y , and 10 _Z in the same shape, thereby compensating the environmental magnetic field distribution generated by the disturbance coil 11 by the compensation coil 10. It can be matched with the magnetic field distribution.

  After the active magnetic shield is applied and before the compensation coil 10 is driven, a test magnetic field signal V such as a sine wave is applied to the disturbance coil 11 by the detecting means 24 of the computer 20 in step S007, and the sensor position S and the target position P The test magnetic field amounts Sv (t) and Pv (t) are measured by the magnetic sensor 12, and the measured test magnetic field amounts Sv (t) and Pv (t) are input to the detection means 24 to detect the sensor position S and the target position. The magnetic field amount ratio (amplitude ratio) Pv / Sv between P is detected. If the compensation coil 10 has already been driven, the switch means 28 is controlled by the detecting means 24 in step S006 to stop the driving of the compensation coil 10, and then the magnetic field amount ratio Pv / Sv is detected in step S007. . The driving of the compensation coil 10 can be stopped by a manual switch (not shown) provided in the computer 20, for example. An example of the waveforms of the test magnetic field quantities Sv (t) and Pv (t) is shown in FIGS. 3 (P2) and (S2). In the illustrated example, the magnetic field amount ratio Pv / Sv = 1 / 0.7 can be detected from the amplitude ratio of the test magnetic field amounts Sv (t) and Pv (t), for example. The detected magnetic field amount ratio Pv / Sv is recorded in the storage means 23 of the computer 20 and used to calculate the compensation magnetic field amount Pt (t) at the target position P after the active magnetic shield driving in step S009 described later.

  The frequency of the test magnetic field used in step S007 is the environmental magnetic field amount Se (t), Pe measured in step S002 in order to suppress the influence of the environmental magnetic field on the magnetic field amount ratio Pv / Sv as much as possible and increase the S / N ratio. It is desirable to use a frequency band in which the spectral intensity of (t) is sufficiently low. For example, the commercial power supply frequency (50 Hz / 60 Hz) and its harmonic frequencies (100, 150, 200...) According to the waveforms of the environmental magnetic field quantities Se (t) and Pe (t) recorded in the storage unit 23 in step S002. ... Hz / 120, 180, 240 ... Hz) and the frequency band of the test magnetic field used in step S007 by the detection means 24 in order to avoid mixing of noise of about 10 Hz or less due to DC magnetic fields such as railways, automobiles, and elevators. It is determined as 110 Hz.

  Also, the magnitude of the test magnetic field used in step S007 is the compensated magnetic field amount Pt (t) (or sensor position) of the target position P after driving the active magnetic shield so that it is not affected by the nonlinear characteristics of the passive magnetic shield. It is desirable that the magnetic field amount be equal to the post-compensation magnetic field amount St (t)). For example, when the compensation coil 10 of the active magnetic shield is disposed in the vicinity of the passive magnetic shield, the characteristics of the magnetic material of the passive magnetic shield (passive magnetic shield performance) fluctuate due to the influence of the compensation magnetic field generated by the compensation coil 10. There is a possibility that the magnetic field amount ratio (amplitude ratio) Pv / Sv between the sensor position S and the target position P is changed. If the magnetic field amount ratio Pv / Sv is detected using a test magnetic field having the same magnitude as the magnetic field (design magnetic field) after driving the active magnetic shield, the passive magnetic shield drive is performed using the magnetic field amount ratio Pv / Sv. When calculating the subsequent compensation magnetic field amounts Pt and St (step S009 described later), it is possible to suppress the influence of nonlinear characteristic fluctuation of the passive magnetic shield. For example, in the case of a design in which the amount of magnetic field at the target position P is suppressed to about 10 to 100 nT by the active magnetic shield, the magnitude of the test magnetic field is also set to about 10 to 100 nT according to the design specifications.

  Next, in step S008, the measurement means 25 of the computer 20 applies an environmental magnetic field signal E corresponding to the environmental magnetic field amount Se at the time of designing the shield at the sensor position S in step S002 to the disturbance coil 11. For example, the disturbance coil 11 is driven while measuring and monitoring the magnetic field waveform data Se (t) at the sensor position S with the magnetic sensor 12, and the magnetic field waveform data Se (t) at the sensor position S as shown in FIG. 3 (S3). Is adjusted to the sensor position S in the shield chamber 1 by adjusting the current of the environmental magnetic field signal E applied to the disturbance coil 11 so as to match the amplitude of the environmental magnetic field amount Se (t) shown in FIG. Reproduces the amount of ambient magnetic field Se when designing a shield. In step S008, after reproducing the environmental magnetic field amount Se in the shield chamber 1, the compensation coil 10 of the active magnetic shield is driven, and the compensated magnetic field amount St (t) at the sensor position S is measured by the magnetic sensor 12. Input to means 25. An example of the waveform of the compensated magnetic field amount St (t) measured by the measuring means 25 is shown in FIG. 3 (S4).

  Further, in step S009, the compensated magnetic field amount St (t) of the sensor position S measured by the measurement unit 25 is input to the calculation unit 26, and the post-compensation magnetic field amount St (t) of the sensor position S is stored in the calculation unit 26. 23, the compensation magnetic field amount Sc (t) of the sensor position S generated by the compensation coil 10 of the active magnetic shield (= St−Se) ) Is calculated. An example of the waveform of the compensation magnetic field amount Sc (t) at the sensor position S calculated by the calculation means 26 is shown in FIG. 3 (S5). Further, the calculation means 26 calculates the compensation magnetic field amount Pc (t) (= Sc (t) at the target position P from the compensation magnetic field quantity Sc (t) at the sensor position S and the magnetic field quantity ratio Pv / Sv recorded in the storage means 23. X Pv / Sv) is calculated. An example of the waveform of the compensation magnetic field amount Pc (t) at the target position P shown in FIG. 3 (P6) is the waveform of the compensation magnetic field amount Sc (t) in FIG. 3 (S5) and the magnetic field amount ratio Pv / Sv = 1/0. Calculated as a product of .7.

  In step S012, the compensation magnetic field amount Pc (t) at the target position P calculated by the calculation unit 26 is input to the evaluation unit 27, and the evaluation unit 27 records the compensation magnetic field amount Pc (t) at the target position P in the storage unit 23. The shield performance of the target position P is evaluated from the environmental magnetic field amount Pe (t) at the time of designing the shield of the target position P. For example, as shown in FIG. 3 (P7), the compensation coil 10 of the active magnetic shield is set as the sum of the compensation magnetic field amount Pc (t) and the environmental magnetic field amount Pe (t) at the target position P by the evaluation means 27 in step S012. The post-compensation magnetic field amount Pt (t) (= Pc + Pe) of the target position P compensated by is calculated. Further, as the ratio of the compensated magnetic field amount Pt (t) to the environmental magnetic field amount Pe (t), the attenuation factor (= Pt (t) / Pe (t) of the magnetic field (magnetic flux density) of the active magnetic shield alone at the target position P ) Is calculated. From the amplitude ratio of FIG. 3 (P1) and (P7), it can be seen that the environmental magnetic field at the target position P in the shield chamber 1 can be attenuated to 1 / 6.4 by the active magnetic shield.

  In the flowchart of FIG. 2, after the compensation magnetic field distribution of the compensation coil 10 at the sensor position S and the target position P is matched with the environmental magnetic field distribution of the disturbance coil 11 (step S005), the disturbance coil 11 at both positions S and P. The magnetic field amount ratio Pv / Sv of the compensation coil 10 is detected (step S007), and the compensation magnetic field amount Pc of the compensation coil 10 at the target position P is determined from the magnetic field amount ratio Pv / Sv and the compensation magnetic field amount Sc of the compensation coil 10 at the sensor position S. Since the calculation is performed (step S009), the active magnetic shield performance (post-compensation magnetic field amount) at the target position P can be appropriately evaluated at the sensor position S away from the target position P. Even when a passive magnetic shield is used in combination, the influence of the magnetic material can be offset by matching the environmental magnetic field distribution and the compensation magnetic field distribution, and the shield performance at the target position P can be directly evaluated. A highly reliable performance evaluation of the shield alone can be performed. Further, by reproducing the ambient magnetic field amount Se at the sensor position S directly reflected in the design specifications of the active magnetic shield by the disturbance coil 11, the shield performance (magnetic field attenuation rate) at the target position P based on the design specifications in step S012. Can be evaluated and verified.

  Thus, it is possible to achieve the “evaluation method and apparatus capable of appropriately evaluating the performance of an active magnetic shield even when combined with a passive magnetic shield”, which is an object of the present invention.

  Steps S010 to S011 in FIG. 2 include the measurement of the post-compensation magnetic field amount St at the sensor position S by the measurement unit 25 in step S008 and the calculation of the compensation magnetic field amount Pc at the target position P by the calculation unit 26 in step S009. A process of obtaining a plurality of average values of the compensation magnetic field amount Pc at the target position P by repeating a plurality of times is shown. In the flowchart of FIG. 2, the compensated magnetic field amount St measured in step S008 is affected by the environmental magnetic field at that time in the shield chamber 1, and the S / N ratio of the shield performance of the target position P obtained in step S012 deteriorates. However, the S / N ratio of the shield performance can be improved by using an average value obtained by measuring the compensated magnetic field amount St a plurality of times. Moreover, the reproduction of the environmental magnetic field amount Se at the time of designing the shield in step S008 can be performed in a relatively short time (several minutes to several tens of minutes), and step S009 is a computer process. The time required will not be too long.

  Further, as described above, the present invention has an advantage that the shield performance at the target position P can be appropriately evaluated even when the passive magnetic shield is used in combination, but the application range of the present invention is that the passive magnetic shield is used together. The present invention is not limited to the shield room 1 but can be applied to the shield room 1 using only the active magnetic shield. Further, the computer 20 stores the ambient magnetic field quantities Se and Pe at the time of designing the shield at the sensor position S and the target position P obtained at step S002 when the active magnetic shield is accepted, and the magnetic field quantity ratio Pv / Sv obtained at step S007. If recorded in the means 23, steps S008 to S012 are carried out during periodic maintenance and inspection, so that the apparatus (MRI apparatus or EB apparatus) in the shield chamber 1 can be operated while the shield chamber 1 is in operation. The shield performance of the target position P can be evaluated.

  The method for evaluating the shield performance of the target position P using the measurement value of the sensor position S inside the shield chamber 1 has been described above. However, in the present invention (step S005 in FIG. 2), not only the inside of the shield chamber 1 but also the inside. Even in the outer periphery, the environmental magnetic field distribution generated by the disturbance coil 11 can be made to coincide with the compensation magnetic field distribution generated by the compensation coil 10, and instead of the sensor position S, the arbitrary position R inside the shield chamber 1 or the outer peripheral area. It is also possible to evaluate the shielding performance of the target position P using the measured value of the arbitrary position R. For example, as shown in FIG. 1, by setting the inspection position R around the outside of the shield room 1 in step S006 of FIG. 2, the object in the shield room 1 can be detected at the inspection position R outside the room without entering the shield room 1. It can be expected that the shield performance evaluation at the position P will be performed.

  When the inspection position R other than the sensor position S is determined in step S006 in FIG. 2, when the test magnetic field signal V is applied to the disturbance coil 11 in step S007, the test is performed at the inspection position R together with the sensor position S and the target position P. The magnetic field amount Rv (t) is measured by the magnetic sensor 13, and the detection unit 24 detects the magnetic field amount ratio (amplitude ratio) Sv / Rv between the inspection position R and the sensor position S. An example of the waveform of the test magnetic field amount Rv (t) is shown in FIG. 3 (R2). In the illustrated example, the magnetic field amount ratio Sv / Rv = 0.7 / 0.5 can be detected from the amplitude ratio of the test magnetic field amounts Sv (t) and Rv (t), for example. The detected magnetic field amount ratio Sv / Rv is recorded in the storage means 23 of the computer 20 together with the magnetic field amount ratio Pv / Sv.

  Further, when the environmental magnetic field signal E is applied to the disturbance coil 11 in step S008 of FIG. 2, the disturbance coil 11 is driven while the magnetic sensor 12 measures and monitors the magnetic field waveform data Re (t) at the inspection position R. For example, the magnetic field waveform data Se (t) (= Re (t) at the sensor position S is obtained by multiplying the magnetic field waveform data Re (t) at the inspection position R and the magnetic field amount ratio Sv / Rv as shown in FIG. 3 (R3). * Sv / Rv, Re (t) * 0.7 / 0.5) in the example of FIG. Then, the current of the environmental magnetic field signal E applied to the disturbance coil 11 so that the calculated amplitude of the magnetic field waveform data Se (t) at the sensor position S coincides with the amplitude of the environmental magnetic field amount Se (t) at the sensor position S. adjust. By doing so, it is possible to reproduce the environmental magnetic field amount Se at the time of designing the shield at the sensor position S in the shield chamber 1 without actually monitoring the magnetic field waveform data Se (t) at the sensor position S.

  Further, in Step S008, after reproducing the environmental magnetic field amount Se at the time of designing the shield in the shield chamber 1, when driving the compensation coil 10 of the active magnetic shield, the inspection position is replaced with the post-compensation magnetic field amount St of the sensor position S. The compensated magnetic field amount Rt (t) of R is measured by the magnetic sensor 12 and input to the measuring means 25. The measuring means 25 calculates the product of the compensated magnetic field amount St at the sensor position S by obtaining the product of the compensated magnetic field amount Rt (t) at the inspection position R and the magnetic field amount ratio Sv / Rv as shown in FIG. (T) (= Rt (t) × Sv / Rv, Rt (t) × 0.7 / 0.5 in the example of FIG. 3) is calculated. In this way, the post-compensation magnetic field amount Rt (t) at the sensor position S is estimated from the post-compensation magnetic field amount Rt at the inspection position R without actually measuring the post-compensation magnetic field amount Rt (t) at the sensor position S. Can be sought. 3 (S3) and 3 (S4), when the measurement values at the inspection position R other than the sensor position S are used, the dotted line frame actually shows the magnetic field waveform data Re (t) and the compensated magnetic field amount Rt at the sensor position S. (T) indicates that there is no need to monitor or measure.

  In step S009, the compensated magnetic field amount St (t) of the sensor position S calculated based on the compensated magnetic field amount Rt (t) of the inspection position R is input to the calculation means 26, and the sensor position S is similar to the above-described processing. The compensation magnetic field amount Sc (t) (= St−Se) is calculated, and the compensation magnetic field amount Pc (t) at the target position P is further calculated. After repeating steps S008 to S010 as necessary, the process proceeds from step S011 to S012, and the shielding performance of the target position P is evaluated based on the compensation magnetic field amount Pc (t) of the target position P in step S012, similarly to the above-described processing. . That is, according to the method for evaluating the shielding performance at the target position P from the measurement value at the inspection position R, it is not necessary to actually measure the magnetic field waveform at the sensor position S. The shield performance in the shield chamber 1 can be evaluated at the position R.

It is a block diagram of one Example of the performance evaluation apparatus by this invention. It is an example of the flowchart which shows the performance evaluation method by this invention. It is explanatory drawing which shows the change of the magnetic flux density of the object position P and the sensor position S (and test | inspection position R) corresponding to the flowchart of FIG. It is explanatory drawing of an example of the conventional active magnetic shielding method. It is explanatory drawing of the shield performance evaluation method of the target position P and the sensor position S in the active magnetic shielding method of FIG. It is explanatory drawing of an example of the conventional passive magnetic shielding method.

Explanation of symbols

1 ... Magnetic shield room 2 ... Magnetic shield wall (shield housing)
3. Magnetic shield opening / closing part (shield housing)
DESCRIPTION OF SYMBOLS 5 ... Magnetic material board (magnetic board) 6 ... Overlapping part 7 ... Expansion part 8 ... Magnetic weathering 10 ... Compensation coil 11 ... Disturbance coils 12, 12a, 13 ... Measurement sensor (magnetic sensor)
DESCRIPTION OF SYMBOLS 14 ... Compensation coil drive power supply 15 ... Compensation coil signal processing means 16 ... Disturbance coil drive power supply 17 ... Disturbance coil signal processing means 20 ... Computer 21, 22 ... Input means 23 ... Storage means 24 ... Detection means 25 ... Measurement Means 26 ... Calculation means 27 ... Evaluation means 28 ... Switch means 29 ... Output means P ... Evaluation target position R ... Inspection position S ... Sensor position E ... Environmental magnetic field signal V ... Test magnetic field signal Pe ... Recording of the amount of environmental magnetic field at the target position Value Se: Recording value Pv / Sv, Sv / Rv: Magnetic field ratio of the environmental magnetic field at the sensor position

Claims (8)

In the method for evaluating the shield performance of the evaluation target position in the active magnetic shield room in which the measurement sensor for the environmental magnetic field and the compensation coil for generating the compensation magnetic field that cancels the environmental magnetic field are arranged, the same shape is formed at the same position as the compensation coil. A disturbance coil for generating a disturbance magnetic field is arranged, and when the driving of the compensation coil is stopped, a test magnetic field signal is applied to the disturbance coil to detect a magnetic field amount ratio between the sensor position and the target position. The compensation coil is driven while applying an environmental magnetic field signal corresponding to the environmental magnetic field amount at the time of shield design to measure the compensated magnetic field amount at the sensor position, and the compensated magnetic field amount at the sensor position and the environmental magnetic field amount at the design time The compensation magnetic field amount at the target position is calculated from the compensation magnetic field amount at the sensor position and the compensation magnetic field amount at the target position from the compensation magnetic field amount and the magnetic field amount ratio. Evaluation method of the active magnetic shield formed by evaluating the shielding performance of the target position by the environmental magnetic field amount at the shield design of the target position. The performance evaluation method according to claim 1, wherein measurement of the compensated magnetic field amount at the sensor position and calculation of the compensation magnetic field amount at the target position are repeated a plurality of times, and an average value of the compensation magnetic field amount at the target position is calculated a plurality of times. A method for evaluating the performance of an active magnetic shield obtained by evaluating the shielding performance at a target position. 3. The performance evaluation method according to claim 1 or 2, wherein an inspection position is set inside or outside the shield chamber, a magnetic field amount ratio between the inspection position and the sensor position is detected when the test magnetic field signal is applied, and the environment Instead of the compensated magnetic field amount at the sensor position when applying the magnetic field signal, the compensated magnetic field amount at the inspection position is measured, and the compensated magnetic field amount at the sensor position is calculated from the compensated magnetic field amount and the magnetic field amount ratio. An active magnetic shield performance evaluation method. 4. The performance evaluation method according to claim 1, wherein a frequency band of the test magnetic field is determined according to an environmental magnetic field when designing a shield at the sensor position and the target position. In the apparatus for evaluating the shield performance of the evaluation target position in the active magnetic shield room in which the measurement sensor of the environmental magnetic field and the compensation coil for generating the compensation magnetic field that cancels the environmental magnetic field are arranged, the apparatus is located at the same position as the compensation coil of the shield room. Disturbing magnetic field generating disturbance coils arranged in the same shape, storage means for recording the amount of environmental magnetic field at the time of designing the shield of the sensor position and target position, and applying a test magnetic field signal to the disturbance coil when driving of the compensation coil is stopped Detecting means for detecting the magnetic field amount ratio between the sensor position and the target position, and driving the compensation coil while applying an environmental magnetic field signal corresponding to the environmental magnetic field amount of the sensor position at the design time to the disturbance coil A measuring means for measuring the amount of magnetic field after compensation of the sensor, and the compensation magnetism of the sensor position from the difference between the amount of magnetic field after compensation of the sensor position and the amount of environmental magnetic field at the design And calculating means for calculating the compensation magnetic field amount at the target position from the compensation magnetic field amount and the magnetic field amount ratio, as well as the compensation magnetic field amount at the target position and the environmental magnetic field amount at the target position at the time of design. An apparatus for evaluating the performance of an active magnetic shield, comprising evaluation means for evaluating the shield performance of a position. 6. The performance evaluation apparatus according to claim 5, wherein measurement of the magnetic field amount after compensation of the sensor position by the measurement unit and calculation of the compensation magnetic field amount of the target position by the calculation unit are repeated a plurality of times, and the evaluation unit calculates the position of the target position. An apparatus for evaluating the performance of an active magnetic shield obtained by evaluating the shielding performance at a target position based on an average value of compensation magnetic field multiple times. 7. The performance evaluation apparatus according to claim 5, wherein a magnetic field amount ratio between an inspection position and a sensor position determined inside or outside the shield chamber is detected by the detection means, and the sensor position is detected by the measurement means. Performance of an active magnetic shield obtained by measuring the compensated magnetic field quantity at the inspection position instead of the compensated magnetic field quantity and calculating the compensated magnetic field quantity at the sensor position from the compensated magnetic field quantity at the examination position and the magnetic field ratio. Evaluation device. 8. The performance evaluation apparatus according to claim 5, wherein a frequency band of the test magnetic field is determined according to an environmental magnetic field at the time of designing a shield at the sensor position and the target position.