JP5630861B2 - Disturbance magnetic field measurement sensor and active magnetic shield system - Google Patents

Description

  The present invention relates to a disturbance magnetic field measurement sensor and an active magnetic shield system, and more particularly to an active magnetic shield system for protecting a magnetoless device from a fluctuating magnetic field and a disturbance magnetic field measurement sensor suitable for the system.

  When installing electron beam application devices such as electron microscopes, EB exposure devices, and EB steppers in semiconductor manufacturing facilities, etc., due to the influence of disturbance magnetic fields (environmental magnetic fields) generated from railways, automobiles, elevators, electrical rooms, etc. inside and outside the facilities There arises a problem of magnetic disturbance in which the original specification performance cannot be secured. For example, an electron microscope or the like, which is one of the EB devices, disturbs the electron trajectory due to the influence of a fluctuating disturbance magnetic field and degrades the resolution (resolution) of the image. In addition, when a SQUID (superconducting quantum interference device) application device such as an MRI apparatus, NMR apparatus, magnetoencephalograph or magnetocardiograph is installed in a medical facility, etc., the same applies because of the high sensitivity of the apparatus to minute magnetic field fluctuations. In addition, the magnetic disturbance of the device becomes a problem. In order to assure normal operation by suppressing / reducing magnetic disturbance of a device that hates the influence of such a magnetic field (magnetomagnetic device), it is required to provide a magnetic shield space (shield room) in the facility.

  The magnetic shield space can be broadly classified into a passive magnetic shield system (hereinafter simply referred to as a passive system) and an active magnetic shield system (hereinafter sometimes simply referred to as an active system). In passive systems, the space is generally covered with a soft magnetic material (ferromagnetic material) such as permalloy or magnetic steel sheet with a high permeability μ, and the soft magnetic material captures and detours the disturbance magnetic field. It is a magnetic shield system that prevents the disturbance magnetic field from entering the space by the shielding effect of electromagnetic induction (eddy current) induced by the magnetic material, and is excellent in that it can shield the disturbance magnetic field in a relatively wide frequency range. There is a problem that the material cost of the soft magnetic material increases. On the other hand, in an active system, a coil for generating a compensation magnetic field (hereinafter sometimes referred to as a compensation coil) is arranged around the space, and an appropriate compensation magnetic field is generated in the compensation coil in accordance with the fluctuation of the disturbance magnetic field. This is a magnetic shield system that cancels out the disturbance magnetic field, and the frequency band of the disturbance magnetic field that can be shielded is limited, but there is an advantage that a magnetic shield space can be realized at a relatively low cost. For this reason, from the viewpoint of cost effectiveness, the magnetic shield space is often combined with a passive type and an active type, and a composite type magnetic shield system with high shielding performance (hereinafter, simply referred to as a composite type system). (See Patent Document 1 and Non-Patent Documents 1 and 2).

  FIG. 6A shows an example of a composite system disclosed in Patent Document 1. FIG. The composite type system of the illustrated example includes a passive type system 5 in which soft magnetic plates 6 and 7 (see FIG. 7A) such as permalloy are arranged without gaps on the inner surfaces of the floor, wall, and ceiling of the space R to be shielded, This is a combination with the active system 1. The active type system 1 in the illustrated example receives compensation coils 2 and 3 arranged around the space R, a magnetic sensor 10 that detects an internal magnetic field (magnetic flux density) in the space R, and a detection signal from the magnetic sensor 10. And a control device 20 that drives the compensation coils 2 and 3. For example, a disturbance magnetic field (internal magnetic field) inside the space R attenuated by the passive system 5 is arranged by aligning the center axis of the compensation coils 2 and 3 with the X axis of the position where the magnetoless device in the space R is installed. ) The Be is detected by the magnetic sensor 10, the compensation magnetic field Bc generated by the compensation coils 2 and 3 is superimposed on the internal magnetic field Be, and the superposition magnetic field Bs (= Be−Bc) approaches zero. Adjust the coil current. The illustrated example shows only the compensation coils 2 and 3 in the X-axis direction. However, by disposing the compensation coils in the Y-axis direction and the Z-axis direction as well, it is possible to deal with disturbance magnetic fields in all directions.

  Non-Patent Document 1 describes the case where the compensation coils 2 and 3 of the active system 1 are arranged outside the soft magnetic plates 6 and 7 of the passive system 5 in the composite system as shown in FIG. Compared with the case where it is arranged, the shield performance is compared, and the arrangement of the compensation coils 2 and 3 outside the passive system 5 and the composite type is more in the shield target space R than the case where it is arranged inside. It is reported that the magnetic field distribution can be made uniform in a wide range. For example, even if the installation position of the anaerobic device and the arrangement position of the magnetic sensor 10 are separated in the space R, the internal magnetic field can be generated in a wide range in the space R by the compensation coils 2 and 3 arranged outside the passive system 5. Can be attenuated uniformly to suppress magnetic disturbance, the degree of freedom of arrangement of the sensor 10 can be increased and the utilization efficiency of the space R can be increased.

JP 2008-282893 A JP 2009-175067 A International Publication No. 2004/084603 Pamphlet JP 2006-351598 A

Keita Yamazaki et al. “Investigation of magnetic field distribution and phase lag for designing an active shield system suitable for a simple magnetic shield room” IEEJ Transactions, Vol. 121, No. 12, 2001, pp 1085-1092 Yusuke Umeda et al. “Application of Active Cancellation to Cylindrical Magnetic Shield” IEICE Transactions, Vol. 123, No. 8, 2003, pp 790-796 Edited by the Architectural Institute of Japan “Environmental Magnetic Field Measurement Techniques—In-Situ Measurement Examples” Maruzen Corporation, July 15, 1998, pp23-57

  However, the composite system in which the compensation coils 2 and 3 are arranged outside the passive system 5 as shown in FIG. 6A is affected by the influence of eddy currents induced on the soft magnetic plates 6 and 7 of the passive system 5. In addition, a phase delay (phase delay) occurs in the superimposed magnetic field Bs (= inner magnetic field Be−compensation magnetic field Bc) with respect to the disturbance magnetic field B outside the shield target space R, and the shielding performance of the active system 1 is deteriorated. There is a point. The graph of FIG. 9 shows the shielding rate and phase delay measured in the central part of the AC magnetic field generated by the compensation coils 2 and 3 outside the passive system 5 in the composite system as shown in FIG. The frequency characteristic measurement results are shown (see Non-Patent Document 1). FIG. 9 also shows the analysis results of the frequency characteristics of the phase lag and shielding rate in consideration of eddy currents induced in the soft magnetic plates 6 and 7. Both the measurement results and the analysis results of FIG. 9 show that the shielding rate of the passive system 5 is increased and the phase delay of the compensation coils 2 and 3 is also increased due to the eddy current shielding effect of the soft magnetic plates 6 and 7 as the frequency increases. Represents that.

The block diagram of the active system 1 in FIG. 6A shows the frequency characteristics Go (ω) of the magnetic sensor 10 and the control device 20 (including a filter circuit, a current drive amplifier, and other electronic circuits), and the compensation coils 2, 3. Can be expressed as a solid line in FIG. 6B using the frequency characteristic Gc (ω). The shield performance (cancellation performance) SEs can be defined as the ratio of the internal magnetic field Be to the superposed magnetic field Bs (= Be / Bs). It can be evaluated using the function G (ω) (= Go (ω) · Gc (ω)). As can be seen from the equation (3), the shielding performance SEs of the active system 1 increases as the one-round transfer function G (ω) increases.

  In the block diagram of FIG. 6B, the frequency characteristic Go (ω) of the magnetic sensor 10 and the control device 20 has a phase delay characteristic (a characteristic in which the phase delay increases as the frequency increases) as shown in FIG. Yes. 6A, the frequency characteristics Gc (ω) of the compensation coils 2 and 3 exhibit the phase lag characteristics as shown in FIG. 9, and the circular transfer function G of the active system 1 In (ω), the phase delay of Go (ω) and the phase delay of Gc (ω) are accumulated. When this phase delay increases, the active system 1 operates based on the delayed signal, and the transfer function G (ω) decreases and the shield performance SEs decreases. In general, as the frequency of the magnetic field increases, the magnitude of the loop transfer function decreases, so that the influence of the phase delay becomes more prominent and the shield performance SEs is further deteriorated. In the worst case, the phase delay is 180. As a result, the shield performance SEs = 0, that is, an oscillation phenomenon occurs.

  In order to avoid a decrease in shielding performance due to the phase delay of such an active system 1 (particularly, deterioration of shielding performance in a high frequency region), Patent Document 1 discloses an active system 1 as shown in FIG. Proposed to provide a high-frequency signal processing circuit 22 and a low-frequency signal processing circuit 23 in the control device 20, and to perform signal processing by dividing a wideband detection signal detected by the magnetic sensor 10 into a high-frequency band and a low-frequency band. Yes. That is, for the low frequency band (for example, 30 Hz or less) of the detection signal of the magnetic sensor 10 having a relatively small phase delay, the DC component is removed from the buffer 21 via the high pass filter 23a and then the low pass filter 23b. The extracted signal is directly converted into an antiphase signal by the integrator 23c and the amplification degree adjusting circuit 23e. On the other hand, a high-frequency signal (for example, 50 Hz) having a relatively large phase delay is extracted by the band pass filters 22a and 22c, converted into an antiphase signal by the amplification adjustment circuit 22d, and then the phase delay time is adjusted by the phase adjustment circuit 22e. Adjust and convert to phase adjustment signal. The anti-phase signal of the low-frequency signal processing circuit 23 and the phase adjustment signal of the high-frequency signal processing circuit 22 are combined by the adder 24 and added to the compensation coils 2 and 3, so that the shielding performance can be improved due to the phase delay in the high frequency region. Prevent decline.

  However, as shown in FIG. 9, the phase delay times of the compensation coils 2 and 3 differ for each frequency, whereas the high-frequency signal processing circuit 22 (phase adjustment circuit 22e) in FIG. 6C has a specific frequency (for example, 50 Hz). In order to cope with a plurality of different magnetic field disturbance fields B (for example, 50 Hz, 100 Hz, 150 Hz, etc.) in the control device 20 of Patent Document 1, a complex combination of a plurality of high-frequency signal processing circuits 22 is possible. Signal processing is required. Further, a disturbance magnetic field whose frequency is known in advance can be dealt with by providing a high-frequency signal processing circuit 22 corresponding to the frequency, but there is a problem that the control device 20 of Patent Document 1 cannot deal with a disturbance magnetic field whose frequency is unknown. is there.

  Further, in the general active type system 1, the disturbance magnetic field is detected by using the fluxgate type magnetic sensor 10 or the like, but the response speed of the fluxgate type magnetic sensor 10 is about several kHz, which is limited to a wide band. There is also a problem that it is difficult to cope with a high-frequency signal exceeding the response speed of the magnetic sensor 10. In order to realize a composite system having high shielding performance against various disturbance magnetic fields, it is desirable to make an active system in which the shielding performance is hardly deteriorated due to the phase delay regardless of the frequency of the disturbance magnetic field.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an active magnetic shield system in which a reduction in shield performance due to phase delay hardly occurs regardless of the frequency of a disturbance magnetic field.

  In the hybrid system as shown in FIG. 6A, the reason why the phase delay as shown in FIG. 9 occurs in the frequency characteristics Gc (ω) of the compensation coils 2 and 3 of the active system 1 is that the compensation coils 2 and 3 are generated. This is because eddy current is induced in the soft magnetic plates 6 and 7 of the passive system 5 that covers the periphery of the shield target space R by the compensation magnetic field Bc (and the disturbance magnetic field B) (see Non-Patent Documents 1 and 2). For example, if the disturbance magnetic field Bx in the X-axis direction is exposed to the passive system 5 that seals the space R as shown in FIG. 7A, the front and back YZ planes perpendicular to the X-axis are shown in FIG. 7B. In the soft magnetic plates 6a and 6b, an induced electromotive force (rotating electric field) and an eddy current E in an annular direction that prevent the magnetic field Bx entering the YZ plane are induced. As shown in FIG. 7C, the rectangular cylindrical soft magnetic plates 7a, 7b, 7c, and 7d on the peripheral XY plane and XZ plane parallel to the X axis are caused by time fluctuation of the magnetic field Bx (magnetic flux density). A macro-circular eddy current E is induced in a direction that prevents the magnetic field Bx from entering.

  The magnetization characteristic of a soft magnetic material when an eddy current is induced by a fluctuating disturbance magnetic field B is known as an AC magnetization characteristic. This is mainly caused by a phase delay caused by an apparent fluctuation of magnetization with respect to the disturbance magnetic field B due to an action of an eddy current induced by the changing disturbance magnetic field B (AC hysteresis). As shown in FIGS. 7B and 7C, a large annular eddy current E induced on the surface of the soft magnetic plates 6 and 7 is generated in the outer disturbance magnetic field B in the inner region surrounded by the soft magnetic plates 6 and 7. A secondary magnetic field that is delayed in phase is generated, and a phase delay is generated in the internal magnetic field Be of the passive system 5 with respect to the external disturbance magnetic field B by superposition with the secondary magnetic field that is delayed in phase.

  The inventor has arranged a soft magnetic material in which a large annular eddy current E as shown in FIG. 7 is not induced on the surface by the disturbance magnetic field B, for example, parallel to the arrival direction of the disturbance magnetic field B as shown in FIG. Attention was paid to the secondary magnetic field generated by the soft magnetic plate 12a. First, when the disturbance magnetic field B is a static magnetic field or a variable magnetic field having a low frequency, the soft magnetic plate 12a of FIG. 3A parallel to the disturbance magnetic field B is magnetized in phase with the disturbance magnetic field B and is at the end. Magnetic poles are generated. This magnetic pole generates a demagnetizing field inside the soft magnetic plate 12a, acts in the direction of weakening the magnetization, and also generates a secondary magnetic field outside. This secondary magnetic field can be expressed as a magnetic field generated by an equivalent magnet as shown in FIG. 3B, and is opposite to the direction of the disturbance magnetic field B. It becomes. When the disturbance magnetic field B fluctuates, an eddy current is induced in the cross section of the soft magnetic plate 12a as shown in FIG. 3C, and a secondary magnetic field whose phase is delayed with respect to the disturbance magnetic field B is generated (AC hysteresis). The phase of this secondary magnetic field is further delayed by the amount of the hysteresis effect than that of the above-described reverse phase, so that it becomes a secondary magnetic field whose phase is advanced with respect to the disturbance magnetic field B as a whole.

  That is, if the soft magnetic plate 12a is arranged in parallel to the direction of arrival of the external magnetic field B, a secondary magnetic field whose phase is advanced with respect to the external magnetic field B can be generated around the soft magnetic plate 12a. In the active system 1 as shown in FIG. 6, as described above, (i) a phase delay is generated by the system components (the magnetic sensor 10 and the control device 20) (see FIG. 8), and (ii) the composite system In this case, the phase delay due to the induced eddy current of the passive type system 5 is accumulated and the shielding performance is deteriorated (see FIG. 9). However, FIG. If a secondary magnetic field whose phase is advanced with respect to the disturbance magnetic field B is generated around the magnetic sensor 10 by attaching a soft magnetic plate 12a as shown in FIG. It can be expected that i) and (ii) are reduced or compensated to suppress a decrease in shield performance of the active system 1. The present invention has been completed as a result of research and development based on this idea.

Referring to the embodiment of FIG. 1B, a disturbance magnetic field measuring sensor 10 according to the present invention includes a probe 11 for detecting a varying disturbance magnetic field B, and a probe detection axis A and a gap around the probe 11 via a gap. A soft magnetic material 12 attached in parallel is provided, and a disturbance magnetic field on which a secondary magnetic field with an advanced phase generated around the soft magnetic material 12 is superimposed is detected by the probe 11.

Referring to the block diagram of FIG. 1A, the active magnetic shield system according to the present invention includes a compensating magnetic field generating coil 2 disposed around a shielded space R to be protected from a fluctuating disturbance magnetic field B. 3, a disturbance magnetic field B having a probe 11 for detecting the disturbance magnetic field B and a soft magnetic material 12 attached around the probe 11 in parallel with the probe detection axis A through a gap and arranged in the shielded space R The compensation magnetic field generated by the coils 2 and 3 is controlled in accordance with the detection value of the sensor 10 for detecting the disturbance magnetic field on which the secondary magnetic field with an advanced phase generated around the measurement sensor 10 and the soft magnetic material 12 is superimposed. The control device 20 is provided.

Preferably, as shown in FIG. 1C, a plurality of soft magnetic materials 12a and 12b are attached around the probe 11 of the sensor 10 in parallel with the probe detection axis A via a gap . Desirably, soft magnetic plates 12a and 12b parallel to the probe detection axis A and soft magnetic plates 12c and 12d with slits 13 intersecting the probe detection axis A are arranged around an axis V perpendicular to the probe detection axis A of the sensor 10. Are attached in a cylindrical shape.

  Alternatively, as shown in FIGS. 2B and 2C, a plurality of strip-shaped soft magnetic plates 14 having longitudinal axes parallel to the probe detection axis A are arranged around the probe 11 of the sensor 10 as the probe detection axis A. It may be arranged side by side with a predetermined interval d in the vertical direction. Desirably, as shown in FIG. 2 (E), the sensor 10 is arranged around a plurality of parallel planes intersecting the vertical axis V at a predetermined interval d around the axis V perpendicular to the probe detection axis A. A group of annular soft magnetic plates 16 is attached.

  More preferably, as shown in FIGS. 1B to 1D and FIGS. 2B, 2C, and 2E, the soft magnetic material 12 (or the soft magnetic plate 14 or 16) is relative to the probe 11. A position adjusting mechanism 17 for adjusting the position in the direction perpendicular to the probe detection axis A is provided.

The disturbance magnetic field measurement sensor and the active magnetic shield system according to the present invention are provided with a soft magnetic material 12 attached in parallel to the probe detection axis A through a gap around a probe 11 for detecting a fluctuating disturbance magnetic field B. The probe 11 detects the disturbance magnetic field B on which the secondary magnetic field with an advanced phase generated around the soft magnetic material 12 is superimposed.

(A) By making the probe detection axis A coincide with the arrival direction of the external magnetic field B, a secondary magnetic field having a phase advanced around the soft magnetic material 12 is generated, and the probe having a phase advanced with respect to the disturbance magnetic field B The disturbance magnetic field measurement sensor 10 can output 11 detection values.
(B) In addition, by incorporating the disturbance magnetic field measurement sensor 10 that outputs a detection value whose phase is advanced with respect to the disturbance magnetic field B into the active system, the phase delay due to the system components is reduced or compensated, and the phase delay is reduced. It can be an active system that is small and does not easily cause a decrease in shield performance.
(C) Furthermore, by incorporating a disturbance magnetic field measurement sensor 10 that outputs a detection value whose phase is advanced with respect to the disturbance magnetic field B into the composite system, the phase delay due to the eddy current induced in the passive system 5 is reduced. It is possible to reduce or compensate for a composite system that has a small phase delay and is unlikely to cause a reduction in shield performance.

(D) A plurality of soft magnetic materials 12a and 12b are attached around the probe 11, and a phase-advanced magnetic field is generated in the plurality of soft magnetic materials 12a and 12b. The disturbance magnetic field measurement sensor 10 can output a large detection value.
(E) In addition, a plurality of soft magnetic materials 12 are attached in a cylindrical or annular shape around an axis V perpendicular to the probe detection axis A to form a magnetic circuit, and eddy currents easily flow through each soft magnetic material 12. By doing so, the disturbance magnetic field measurement sensor 10 having a larger phase advance of the detection value with respect to the external magnetic field B can be obtained.
(F) Although the magnitude of the phase advance with respect to the external magnetic field B can be adjusted by the shape and permeability of the soft magnetic material 12 to be attached, the relative position of the soft magnetic material 12 with respect to the probe 11 is determined by the probe detection axis A. The disturbance magnetic field measurement sensor 10 can easily adjust the phase advance of the detected value.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
These are explanatory drawings of one Example of the active type magnetic shielding system and disturbance magnetic field measurement sensor by this invention. These are explanatory drawings of other Examples of the active type magnetic shield system and disturbance magnetic field measurement sensor by this invention. These are explanatory drawings of an effect | action of the disturbance magnetic field measurement sensor by this invention. These are the graphs which show the experimental result which confirmed the phase advance characteristic of the disturbance magnetic field measurement sensor of this invention. These are the graphs which show the experimental result which confirmed the relationship between the distance of the probe from the center of the soft magnetic material of the disturbance magnetic field measurement sensor of this invention, and a phase advance characteristic. These are explanatory drawings of an example of the conventional composite type magnetic shield system. These are explanatory drawings of the eddy current induced in the composite magnetic shield system of FIG. These are an example of the graph which shows the phase lag (phase advance) characteristic of the frequency characteristic Go ((omega)) of the magnetic sensor 10 of FIG. 6, and the control apparatus 20. FIG. These are an example of the graph which shows the phase delay characteristic of the frequency characteristic Gc ((omega)) of the compensation coils 2 and 3 of FIG.

  FIG. 1A shows an embodiment of an active system 1 of the present invention. The active type system 1 in the illustrated example is arranged around a shield target position P (for example, an installation position of the anaerobic device 4) P in the shield target space R, similarly to the conventional active type system 1 shown in FIG. Compensation coils 2 and 3, a disturbance magnetic field measurement sensor 10 installed at a sensor position S in the space R, and a controller 20 that inputs the detection value of the sensor 10 and drives the compensation coils 2 and 3. Yes. The compensation coils 2 and 3 in the illustrated example are arranged around the space R so as to be aligned with the X axis passing through the shield target position P, respectively, and in the same way as in the case of FIG. The disturbance magnetic field (internal magnetic field) near the target position P is attenuated by superimposing the compensation magnetic field Bc. Similarly, in the Y-axis direction and the Z-axis direction, compensation coils can be arranged to make the system 1 capable of dealing with disturbance magnetic fields in all directions. However, the arrangement position and shape of the compensation coils 2 and 3 are not limited to the illustrated example. For example, the inner surface of the space R may be divided into a plurality of areas and the compensation coils 2 and 3 may be arranged in the respective regions. Although the sensor position S is preferably close to the target position P, even if the sensor position S is separated from the target position P, for example, the control device 20 appropriately corrects the detection value of the sensor 10 to correct the target position P. It is possible to attenuate nearby disturbance magnetic fields (see Patent Document 2).

  A disturbance magnetic field measurement sensor 10 in FIG. 1A includes a disturbance magnetic field B detection probe 11 connected to a control device 20, and a soft magnet attached around the magnetic probe 11 in parallel with the probe detection axis A. Material 12. The magnetic probe 11 is not particularly limited as long as it outputs a detection value of a disturbance magnetic field (or magnetic flux density) in at least one axial direction (X-axis direction in the illustrated example) of the sensor position S to the control device 20. Same as active system, for example, search coil type, Hall element type, fluxgate type, magnetic oscillation type magnetic probe, high sensitivity micro magnetic probe (MI sensor), magnetic probe using magnetoresistive effect element (MR) Sensor), a high-frequency drive type magnetic probe (TMF sensor) using a magnetic thin film, and the like (see Non-Patent Document 3). The soft magnetic material 12 attached to the probe 11 is a magnetic member such as permalloy or electromagnetic steel plate that generates eddy currents due to fluctuations in the disturbance magnetic field B and causes a magnetization delay (AC hysteresis) associated with the eddy currents. It can be a plate-like one as in (A) or a rod-like one as in FIG.

  FIG. 1B shows an example of a disturbance magnetic field measurement sensor 10 in which a soft magnetic plate (plate-like magnetic member) 12 a is attached around the probe 11 in parallel with the probe detection axis A. For example, as shown in FIG. 1A, in the shield target space R exposed to the disturbance magnetic field Bx that fluctuates in the X-axis direction, the probe detection axis A of the sensor 10 is set to face the arrival direction (X-axis) of the external magnetic field Bx. Then, the side surface (thickness direction cross section) of the soft magnetic plate 12a parallel to the detection axis A is crossed with the disturbance magnetic field Bx. When the surface of the soft magnetic plate 12a intersects with the disturbance magnetic field Bx as shown in FIG. 7B, an annular eddy current E is induced on the surface, and a secondary magnetic field whose phase is delayed with respect to the disturbance magnetic field Bx is generated. Although generated around the soft magnetic plate 12a, if the soft magnetic plate 12a is arranged parallel to the arrival direction of the disturbance magnetic field Bx as shown in FIG. 1B, a large annular eddy current E is generated on the surface of the soft magnetic plate 12. And a secondary magnetic field whose phase is advanced with respect to the disturbance magnetic field Bx is generated around the soft magnetic plate 12a as described above with reference to FIGS. 3 (A) and 3 (C). Can be made. Although the magnitude and phase advance of the secondary magnetic field generated in the surroundings are different depending on the shape, magnetic permeability, etc. of the soft magnetic plate 12a, the secondary magnetic field having the advanced phase is superimposed on the disturbance magnetic field Bx around the probe 11. Therefore, the superposed magnetic field can be detected by the probe 11 and a detected value whose phase is advanced from the disturbance magnetic field Bx can be output.

  Instead of the soft magnetic plate 12a of FIG. 1B, for example, as shown in FIG. 3D, a rod-shaped soft magnetic material 12 having a circular or rectangular cross section is attached in parallel to the probe detection axis A for measuring a disturbance magnetic field. The sensor 10 can also be used. Similarly to the soft magnetic plate 12a of FIGS. 3A and 3C, the phase around the magnetic field Bx is also increased around the rod-shaped soft magnetic material 12 arranged in parallel with the arrival direction of the magnetic field Bx. Since the secondary magnetic field is generated, the disturbance magnetic field Bx on which the secondary magnetic field is superimposed is detected by the probe 11, and thereby the disturbance magnetic field measurement sensor 10 that outputs a detection value whose phase is advanced with respect to the disturbance magnetic field Bx; can do.

  However, as will be described later, the phase of the secondary magnetic field generated around the soft magnetic material 12 is most advanced in the vicinity of the center of the cross section (side surface) intersecting the disturbance magnetic field Bx of the soft magnetic material 12. As the magnetic field shifts from the vertical direction to the direction perpendicular to the magnetic field arrival, the phase advance gradually decreases (see FIG. 5). In order to stably obtain the detection value of the sensor 10 having the advanced phase, as shown in FIG. 3D, the cross-sectional length in the direction perpendicular to the magnetic field arrival direction is smaller than that of the rod-shaped soft magnetic material 12 shown in FIG. It is desirable to attach a soft magnetic plate 12a having a large cross-sectional length D in the direction perpendicular to the magnetic field arrival direction as in FIG. That is, by using a soft magnetic plate 12a having a sufficiently large cross-sectional length D in the direction perpendicular to the probe detection axis A and attaching the vicinity of the center of the cross-sectional length D adjacent to the probe 11, a detection value with a advanced phase is obtained. Can be obtained as a sensor 10 that stably outputs. The length L of the soft magnetic plate 12a in the probe detection axis direction (see FIG. 1B) can be appropriately designed so that a detection value with an advanced phase can be stably obtained.

  Preferably, as shown in FIG. 1C, a plurality of soft magnetic materials 12 a and 12 b are attached around the probe 11 in parallel with the detection axis A. For example, a pair of soft magnetic materials 12a and 12b are attached to each other with the probe 11 interposed therebetween. When a plurality of soft magnetic materials 12a and 12b are attached, as shown in FIG. 3E, secondary magnetic fields with advanced phases generated around the respective soft magnetic materials 12a and 12b become disturbance magnetic fields Bx. Since they are superimposed, the phase advance of the detected value of the probe 11 with respect to the external magnetic field B can be expanded as compared with the case where only the single soft magnetic material 12a (or 12b) is attached.

  More preferably, as shown in FIG. 1D, the soft magnetic plates 12a and 12b parallel to the probe detection axis A and the slit 13 intersecting with the probe detection axis A around the axis V perpendicular to the probe detection axis A. The attached soft magnetic plates 12c and 12d are joined together in a cylindrical shape. By linking the soft magnetic plates 12a to 12d into a cylindrical shape to form an annular magnetic path (magnetic circuit) in which eddy currents easily flow, excitation of eddy currents in each soft magnetic material 12 is promoted and soft magnetism is increased. The phase advance of the secondary magnetic field generated around the plates 12a and 12b with respect to the external magnetic field B can be further expanded. In addition, when the probe detection axis A is installed in the direction of arrival of the external magnetic field Bx (X axis), the surfaces of the soft magnetic plates 12c and 12d coupled in a cylindrical shape intersect the disturbance magnetic field Bx. By providing the slits 13 in the soft magnetic plates 12c and 12d to suppress the induction of a large annular eddy current E, a secondary magnetic field having a delayed phase is generated around the soft magnetic plates 12c and 12d. Thus, it is possible to prevent the magnetic field from being superimposed on the disturbance magnetic field Bx around the probe 11.

  In FIG. 2B, a plurality of strip-shaped soft magnetic plates 14 having a longitudinal axis C parallel to the probe detection axis A are arranged around the probe 11 in a direction perpendicular to the probe detection axis A at a predetermined interval d. The other Example of the sensor 10 for disturbance magnetic field measurement of this invention is shown. For example, the longitudinal axis C of the plurality of strip-shaped soft magnetic plates 14 having a predetermined width W is arranged on the same plane (or curved surface) F parallel to the probe detection axis A so as to be arranged in parallel at a predetermined interval d. 15, the magnetic casing 15 is attached around the probe 11. The mutual spacing d of the strip-shaped soft magnetic plates 14 is specifically determined so that the magnetic flux 15 in the spacing d can pass through (the permeance of the spacing) so that the plane (or curved surface) F of the magnetic casing 15 functions as a magnetic shield surface. ) Can be designed to be smaller than the ease of passing the magnetic flux in the magnetic plate 14 (permeance of the magnetic plate). For example, the ratio (Sm · μ) of the product (Sm · μ) of the cross sectional area Sm of the magnetic plate 14 and the relative magnetic permeability μ to the cross sectional area Sa of the interval d orthogonal to the longitudinal direction line C of the magnetic housing 15. / Sa) is designed to be greater than 1.

  When the sensor 10 in FIG. 2B is installed with the probe detection axis A facing the direction of arrival of the external magnetic field Bx (X-axis) as shown in FIG. As in the soft magnetic plate 12a in FIG. 1B, a secondary magnetic field having a phase advanced as compared with the disturbance magnetic field Bx is generated. Further, by attaching a plurality of strip-shaped soft magnetic plates 14 as magnetic housings 15 having a predetermined interval d, secondary magnetic fields generated around the respective magnetic plates 14 are respectively disturbed magnetic fields as shown in FIG. Since it is superimposed on Bx, the sensor 10 can output a detection value with an expanded phase advance with respect to the external magnetic field B as compared with the soft magnetic plate 12a of FIG. The cross-sectional length D perpendicular to the probe detection axis A and the length L in the probe detection axis direction of the magnetic housing 15 are advanced in phase as in the case of the soft magnetic plate 12a of FIG. The detection value can be designed to be obtained stably.

  Further, as shown in FIG. 2C, by attaching the pair of magnetic housings 15a and 15b to each other with the probe 11 interposed therebetween, the single magnetic housing 15 is attached as shown in FIG. It can be expected that the phase advance of the detected value of the probe 11 with respect to the external magnetic field B is further expanded as compared with the case of the above. The configuration of the magnetic housing 15 and the magnetic shielding performance are described in detail in Patent Documents 3 and 4, for example.

  Preferably, as shown in FIG. 2 (E), an annular soft magnetic material arranged on a plurality of parallel surfaces that intersect the vertical axis V at a predetermined interval d around the axis V perpendicular to the probe detection axis A. A group of plates 16 is attached in a cylindrical shape. By attaching an annular soft magnetic plate 16 (magnetic circuit) in which eddy current easily flows, excitation of eddy current in each soft magnetic material 16 is promoted, and a secondary magnetic field generated around the soft magnetic plate 16. It can be expected that the phase advance with respect to the external magnetic field B will be further expanded. 2 (E) includes a strip-shaped soft magnetic plate 14 (magnetic casing 15) arranged in parallel with the probe detection axis A in the X-axis direction as shown in FIG. 2 (C), and FIG. As shown in (D), it can be configured by combining the strip-shaped soft magnetic plate 14 (magnetic housing 15) arranged in parallel with the probe detection axis A in the Y-axis direction, and the external magnetic field Bx and Y-axis in the X-axis direction. A secondary magnetic field with an advanced phase can be generated for any external magnetic field By. That is, a group of annular soft magnetic plates 16 as shown in FIG. 2 (E) is attached around the probe 11 to detect the phase advanced with respect to the external magnetic field B from any direction on the XY plane. It can be set as the sensor 10 corresponding to two axes which outputs a value.

[Experimental Example 1]
A disturbance magnetic field measurement sensor 10 as shown in FIG. 2E is made using a flux gate type magnetic probe 11 and a group of permalloy annular soft magnetic plates 16, and the detection value of the sensor 10 for the external magnetic field B is measured. An experiment was conducted to confirm the phase advance. In this experiment, a strip-shaped soft magnetic plate 14 having a length L as shown in FIG. 2B is joined in a square shape by overlapping edges to form an annular soft magnetic plate 16. A plurality of sheets are stacked in parallel at a predetermined interval d to form a cylindrical laminate having a stacking length D as shown in FIG. 2 (E), and an equal distance (= D / 2) from both ends of the cylindrical laminate. The probe 11 is locked at the center position to obtain a disturbance magnetic field measurement sensor 10. Further, the central axis (cylinder axis) of the cylindrical laminate and the vertical axis V of the probe detection axis A are aligned, and the probe detection axis A is arranged in parallel with each annular soft magnetic plate 16. The disturbance magnetic field B was exposed to the sensor 10 attached with the cylindrical laminate while sweeping the disturbance magnetic field B in parallel with the probe detection axis A, and the phase advance of the detection value of the probe 11 with respect to the exposed disturbance magnetic field Bx was detected for each frequency. The same experiment was repeated while switching the intensity of the disturbance magnetic field Bx to be exposed to 0.1 μT, 1 μT, 10 μT, and 40 μT.

  An experimental result is shown in FIG. 4 as a graph according to the intensity of the disturbance magnetic field Bx. Each graph in FIG. 4 shows that the phase of the detection value of the sensor 10 advances with respect to the disturbance magnetic field B regardless of the intensity and frequency of the external magnetic field Bx, and the probe as shown in FIG. It was confirmed that the phase of the detected value of the disturbance magnetic field B was advanced by the incidental of the strip-shaped soft magnetic plate 14 (or the soft magnetic plate 12a as shown in FIG. 1B) parallel to the detection axis A. 4 shows that the phase advance of the detection value of the sensor 10 increases as the frequency of the disturbance magnetic field Bx increases. That is, the frequency characteristic Gs (ω) of the disturbance magnetic field measurement sensor 10 of the present invention has a phase delay that increases as the frequency increases, as shown in FIG. 8, and the frequency of the magnetic sensor 10 and the control device 20 of the conventional active system 1. It can be seen that the characteristic is adjusted to a characteristic almost opposite to the characteristic Go (ω), and the influence of the phase delay is compensated. Therefore, if the active system 1 as shown in FIG. 1A or FIG. 2A is configured using the sensor 10 of the present invention, the phase delay characteristic Go (ω) of the system components (such as the control device 20). Can be reduced or phase-compensated by the frequency characteristic Gs (ω) of the sensor 10, so that the active system 1 is less likely to cause a reduction in shield performance due to phase delay regardless of the frequency of the disturbance magnetic field B.

  Further, the frequency characteristic Gs (ω) of the disturbance magnetic field measuring sensor 10 of the present invention shown in FIG. 4 is almost opposite to the frequency characteristic Gc (ω) of the compensation coils 2 and 3 of the conventional composite system as shown in FIG. For example, by constructing a composite system as shown in FIG. 6A using the sensor 10 of the present invention, the accumulation of phase delay due to the eddy current of the passive system 5 is reduced. It is also possible to prevent a decrease in the shielding performance SEs of the composite system. As shown by a dotted line in FIG. 6B, the shield performance SEs of the composite system incorporating the sensor 10 of the present invention is the frequency characteristic Gs (ω) of the sensor 10 and the frequency characteristic Go (ω) of the control device 20. And the frequency characteristic Gc (ω) of the compensation coils 2 and 3 can be evaluated by a round transfer function G (ω) (= Gs (ω) · Go (ω) · Gc (ω)).

  For example, when the phase delay reaches 180 degrees, | G (ω) | = 1, that is, the shield performance SEs = 0, and an oscillation phenomenon occurs. This phase delay is caused by the phase advance Gs (ω) of the sensor 10 of the present invention. If it can be completely compensated, the shield performance SEs = 2 can be improved. The magnitude of the round transfer function G (ω) varies depending on the number of windings, the configuration of the compensation coils 3 and 4 and the connection method according to the size of the shield target space R, and is difficult to show in general. Assuming the case where (ω) | = 1, the phase delay when the sensor 10 of the present invention is not used is about 65 degrees (see FIG. 8) and the shield performance SEs = 1.68. Since the phase advance of the sensor 10 of the present invention is about 45 degrees (see FIG. 4), the phase delay is compensated to about 20 degrees by incorporating the sensor 10 of the present invention, and the shield performance SEs = 1.97. Can be improved. Similarly, assuming that | G (ω) | = 1 at 200 Hz, the shield performance SEs is about 1.92 by incorporating the sensor 10 of the present invention into a system in which the shield performance SEs is about 1.53. Can be improved up to.

  In this way, it is possible to provide an “active magnetic shield system” that is less likely to cause a reduction in shield performance due to phase delay regardless of the frequency of the disturbance magnetic field, which is an object of the present invention.

  Note that the sensor 10 of the present invention outputs a detection value whose phase is advanced with respect to the disturbance magnetic field B, and the amplitude (gain) of the detection value is different from that of the disturbance magnetic field B. The deterioration of the detected value of the amplitude (gain) can be estimated or corrected by a calibration process similar to that of the conventional active system. In other words, the sensor 10 of the present invention is not only used for constructing a new active system or composite system, but also for improving shield performance by compensating for the phase delay of an existing active system or composite system. Is also beneficial.

  As described above, when the active system or the composite system is constructed by incorporating the disturbance magnetic field measurement sensor 10 of the present invention, the frequency characteristic Go (ω) of the control device 20 of the system and the frequency characteristics of the compensation coils 2 and 3 are used. Taking into account Gc (ω), the shape and size of the soft magnetic material 12 (or the strip-shaped soft magnetic plate 14 or the annular soft magnetic plate 16) attached so that the sensor 10 can perform appropriate phase compensation, the magnetic permeability, etc. Can be designed experimentally or by numerical analysis. Furthermore, the inventor makes phase compensation (that is, phase advance of the detected value) by making it possible to adjust the relative position of the soft magnetic material 12 to the probe 11 in the direction perpendicular to the probe detection axis A in the sensor 10 of the present invention. It was found experimentally that it can be adjusted dynamically.

[Experiment 2]
Using the same disturbance magnetic field measurement sensor 10 as in Experimental Example 1 and changing the relative position between the cylindrical laminated body of the annular soft magnetic plate 16 and the probe 11, the phase advance of the detection value of the sensor 10 with respect to the external magnetic field B is increased. An experiment to confirm was conducted. In this experiment, the probe 11 is locked on the cylindrical laminate via the position adjusting mechanism 17 as shown in FIG. 2B or (E), and the probe 11 on the cylindrical laminate is moved by the position adjusting mechanism 17. The locking position can be adjusted. The position adjusting mechanism 17 in the illustrated example locks the probe 11 at a specific position on the moving rail 18 that extends in the direction perpendicular to the probe detection axis A between both ends on the cylindrical laminate. And a locking member 18. First, the probe 11 is positioned at the center of the cylindrical laminate, and a disturbance magnetic field B having a frequency of 1 Hz is exposed parallel to the probe detection axis A, and the locking member 18 is moved on the moving rail 18 to move the cylindrical laminate. The exposure of the disturbance magnetic field B was repeated while changing the distance of the probe 11 from the center position, and the phase advance of the detection value of the probe 11 was detected for each distance from the center. Further, the same experiment was repeated while switching the frequency of the disturbance magnetic field Bx to be exposed to 10 Hz, 60 Hz, and 200 Hz.

  An experimental result is shown in FIG. 5 as a graph according to the frequency of the disturbance magnetic field Bx. Each graph of FIG. 5 shows that the phase advance (phase advance) of the detection value of the disturbance magnetic field measurement sensor 10 is the largest at the center position of the cylindrical laminate regardless of the frequency of the external magnetic field Bx, and the cylinder is separated from the center position. It shows that the phase advance gradually decreases as it approaches the end of the mold stack. Although the details of the reason for the phase advance variation are unknown, the phase magnetic field B circulates inward from both ends of the cylindrical laminate, and the phase advance increases as it approaches the both ends of the cylindrical laminate due to the influence of the wraparound. Estimated to be smaller. From this experimental result, in order to output a detection value with a stable phase advance by the sensor 10 of the present invention, a direction perpendicular to the probe detection axis A of the cylindrical laminate (or the soft magnetic plate 12a in FIG. 1E). It has been confirmed that it is effective to set the length D to a size that avoids the influence of the disturbance magnetic field B from both ends.

  Further, the disturbance magnetic field measurement sensor 10 of the present invention includes the position adjustment mechanism 17 of the probe 11, and the correspondence relationship between the position of the probe 11 and the phase advance of the detected value of the sensor 10 corresponding to the position of the probe 11 as shown in the graph of FIG. By obtaining the disturbance magnetic field measurement sensor 10, the phase advance of the detection value can be dynamically adjusted so that appropriate phase compensation can be performed according to each site where the active system 1 is constructed. .

DESCRIPTION OF SYMBOLS 1 ... Active type magnetic shield system 2, 3 ... Compensation coil 4 ... Magnetostatic device 5 ... Passive type magnetic shield system 6, 7 ... Soft magnetic plate 10 ... Magnetic detection sensor 11 ... Probe 12 ... Soft magnetic material 13 ... Slit 14 ... Belt-shaped soft magnetic plate 15 ... magnetic housing 16 ... annular soft magnetic plate 17 ... position adjusting mechanism 18 ... moving rail 19 ... locking member 20 ... control device 21 ... buffer 22 ... high frequency signal processing circuits 22a, 22c ... band pass filter 22b , 22d ... amplification adjustment circuit 22e ... phase adjustment circuit 23 ... low frequency signal processing circuit 23a ... high pass filter 23b ... low pass filter 23c ... integrator 23d ... amplification adjustment circuit 24 ... adder A ... probe detection axis B ... Disturbance magnetic field Be ... Internal magnetic field Bc ... Compensation magnetic field Bs ... Superimposed magnetic field R ... Shield target space V ... Vertical axis of probe detection axis Longitudinal axis w ... probe detection axis and a cross-sectional length of the vertical spacing D ... soft plate width d ... soft plate strip soft plate ... shielding object position S ... sensor position C ... belt soft plate

Claims (12)

A probe for detecting a fluctuating disturbance magnetic field, and a soft magnetic material attached in parallel to the probe detection axis through a gap around the probe, and a secondary magnetic field with an advanced phase generated around the soft magnetic material. A disturbance magnetic field measuring sensor formed by detecting a superimposed disturbance magnetic field with the probe. The disturbance magnetic field measurement sensor according to claim 1, wherein a plurality of soft magnetic materials are attached around the probe in parallel to the probe detection axis via a gap . The disturbance magnetic field according to claim 1 or 2, wherein a plurality of strip-shaped soft magnetic plates having a longitudinal axis parallel to the probe detection axis are arranged around the probe and arranged at predetermined intervals in a direction perpendicular to the probe detection axis. Measuring sensor. 4. The sensor according to claim 1, wherein a soft magnetic plate parallel to the probe detection axis and a soft magnetic plate with a slit intersecting with the probe detection axis are formed around an axis perpendicular to the probe detection axis. A disturbance magnetic field measurement sensor that is combined and attached. 5. The sensor according to claim 1, wherein a group of annular soft magnetic plates arranged on a plurality of parallel planes intersecting the vertical axis at a predetermined interval around an axis perpendicular to the probe detection axis. An external disturbance magnetic field measurement sensor. 6. The disturbance magnetic field measurement sensor according to claim 1, further comprising a position adjusting mechanism for adjusting a relative position of the soft magnetic material to the probe in a direction perpendicular to the probe detection axis. A compensating magnetic field generating coil arranged around a space to be shielded to be protected from a fluctuating magnetic field, a probe for detecting the magnetic field, and a soft magnetic material attached around the probe in parallel with the probe detection axis via a gap ; And a detection value of the sensor for detecting a disturbance magnetic field on which a secondary magnetic field with an advanced phase generated around the soft magnetic material is superimposed. An active magnetic shield system comprising a control device for controlling the compensation magnetic field generated by the coil in response. 8. The active magnetic shield system according to claim 7, wherein a plurality of soft magnetic materials are attached around the probe of the sensor in parallel to the probe detection axis via a gap . 9. The system according to claim 7 or 8, wherein a plurality of strip-shaped soft magnetic plates having a longitudinal axis parallel to the probe detection axis are arranged around the probe of the sensor and arranged at predetermined intervals in a direction perpendicular to the probe detection axis. Type magnetic shield system. 10. The system according to claim 7, wherein a soft magnetic plate parallel to the probe detection axis and a soft magnetic plate with a slit intersecting the probe detection axis are arranged around an axis perpendicular to the probe detection axis of the sensor. An active magnetic shield system that is combined and attached. 11. The system according to claim 7, wherein an annular soft magnetic plate disposed on a plurality of parallel surfaces intersecting the perpendicular axis at a predetermined interval around an axis perpendicular to the probe detection axis of the sensor. An accompanying active magnetic shield system. 12. The active magnetic shield system according to claim 7, wherein the sensor is provided with a position adjusting mechanism for adjusting a relative position of the soft magnetic material to the probe in a direction perpendicular to a probe detection axis.