JP4919873B2 - Magnetic shield device - Google Patents

Description

  The present invention relates to a magnetic shield device using both a passive type and an active type magnetic shield.

  An electron beam drawing apparatus, an electron microscope, and the like that are easily affected by environmental magnetic noise (hereinafter referred to as magnetic noise) are generally installed and used in a passive magnetic shield room that attenuates the magnetic noise. Normally, a passive magnetic shield room is covered with a highly permeable wall represented by permalloy.

  Main components of magnetic noise include a low frequency magnetic field (30 Hz or less) generated from a train, automobile, elevator, etc., a commercial frequency magnetic field, a commercial frequency double frequency magnetic field, and a commercial frequency triple frequency magnetic field.

  In addition, the value of the commercial frequency is 50 Hz on the east side and 60 Hz on the west side from the boundary line connecting Itoigawa to Fujigawa. Therefore, the double frequency on the east side is 100 Hz, the triple frequency is 150 Hz, the double frequency on the west side is 120 Hz, and the triple frequency is 180 Hz.

  In recent magnetic shield rooms, higher magnetic shielding properties are required. In addition, the magnetic flux density of magnetic noise of 50 Hz or higher that can be expected to be magnetically shielded by eddy current in a passive magnetic shield room is generally large.

  Therefore, in the case of a passive magnetic shield room, it is necessary to increase the number of layers and thickness of the highly permeable material constituting the wall in order to improve the magnetic shielding properties. However, increasing the number of layers and thickness of the high magnetic permeability increases the cost and labor of construction.

  Therefore, the active magnetic shield devices 204, 206, 208, and 210 are used in combination with the passive magnetic shield room 200 as shown in FIGS. A method for improving the performance has been proposed.

  In the active magnetic shield devices 204, 206, 208, and 210, the magnetic compensation coil 202 is disposed in the passive magnetic shield room 200.

As shown in FIG. 8A, a magnetic noise measurement reference sensor (hereinafter referred to as a magnetic sensor 212) provided in the active magnetic shield devices 204, 206, 208, 210 in FIGS. 7A to 7D. ) Is caused to flow through the magnetic compensation coil 202 by the controller 214 so as to generate an antiphase magnetic field (signal R ₂ ) that cancels the magnetic noise based on the magnetic noise (signal R ₁ ). Thereby, the magnetic shielding property of the passive type magnetic shield room 200 can be improved.

  7A, 7B, and 7D, the magnetic compensation coil 202 is disposed outside the magnetic shield room 200 so as to surround the outer wall of the magnetic shield room 200, and in FIG. The magnetic compensation coil 202 is disposed inside the magnetic shield room 200 along the inner wall of the magnetic shield room 200.

  7A, the magnetic sensor 212 is disposed outside the magnetic shield room 200, and in FIG. 7B, the magnetic sensor 212 is disposed outside the vicinity of the ceiling wall of the magnetic shield room 200. 7C and 7D, the magnetic sensor 212 is disposed inside the magnetic shield room 200.

Here, the active magnetic shield devices 204, 206, 208, and 210 are less affected by the phase delay of the anti-phase magnetic field (signal R ₂ ) that cancels the magnetic noise because the frequency is low for the low-frequency magnetic field. The magnetic shielding effect shown in FIG. 8A can be sufficiently exhibited.

However, as shown in FIG. 8B, the active magnetic shield devices 204, 206, and 210 have a high frequency magnetic noise component higher than the commercial frequency due to the eddy current effect generated on the wall surface of the magnetic shield room 200. In some cases, the phase delay of the magnetic field (signal R ₃ ) that cancels the magnetic noise becomes large, so that a sufficient magnetic shielding effect cannot be obtained, and the magnetic noise is amplified.

  In particular, in a magnetic shield room for biomagnetism measurement, in order to improve the magnetic shielding properties as a passive magnetic shield room, use a wall that combines a highly permeable layer such as permalloy with a conductive layer such as aluminum or copper. Therefore, the eddy current effect increases, and the phase of the magnetic field that cancels magnetic noise is greatly delayed.

FIG. 9 shows a phase delay with respect to the frequency when a magnetic field is generated from a magnetic compensation coil provided outside the magnetic shield room in a 1.8 m square magnetic shield room surrounded by a 1 mm thick permalloy wall. Is shown. FIG. 9 shows a calculated value S ₁ obtained by a three-dimensional magnetic field analysis using a finite element method and an experimentally measured value S ₂ .

From the calculated value S ₁ and the measured value S ₂ , the frequency of the magnetic field that cancels the magnetic noise generated from the magnetic compensation coil increases and the phase lag also increases. In particular, it rapidly increases from a frequency exceeding 10 Hz. I understand.

  As shown in FIG. 7C, in the active magnetic shield device 208, since the magnetic compensation coil 202 is inside the magnetic shield room 200, a large phase delay does not occur in the magnetic field generated from the magnetic compensation coil 202. The compensation coil 202 itself becomes a new magnetic noise source.

  In addition, since a power line for supplying power to the magnetic compensation coil 202 is drawn from the outside to the inside of the magnetic shield room 200, high-frequency electromagnetic noise that greatly affects biomagnetism measurement and the like is induced in the magnetic shield room 200. Is a problem.

  Furthermore, in the active magnetic shield device 208, the magnetic field generated from the magnetic compensation coil 202 is uniformly distributed over a wide area in the magnetic shield room 200 as compared with the case where the magnetic compensation coil 202 is disposed outside the magnetic shield room 200. I can't. Therefore, in the magnetic shield room 200, the installation location of a device that requires magnetic shielding is limited.

  Thus, the active magnetic shield device 208 is not suitable as a magnetic shield room using a biomagnetic measuring device or an electron beam drawing device that requires magnetic shielding in a wide area.

  As shown in FIG. 10, in the active magnetic shield device 226 of Patent Document 1, Helmholtz coils 230 </ b> A and 230 </ b> B are disposed outside the vicinity of the magnetic shield room 228. In addition, a fluxgate magnetometer 232 is disposed far from the magnetic shield room 228.

  Then, the fluctuation component of the environmental magnetic field is measured by the fluxgate magnetometer 232, and the sensitivity direction of the measured magnetic field and the magnetic field generation direction generated from the Helmholtz coils 230A and 230B are matched to cancel the environmental magnetic field. Thereby, the magnetic shielding property of the magnetic shield room 228 can be improved.

  However, when magnetic noise sources such as electric wires and devices that generate magnetic noise of a relatively high frequency such as a commercial frequency magnetic field are scattered around the magnetic shield room 228, magnetic noise generated from these magnetic noise sources Is not spatially uniform compared to low-frequency magnetic noise generated from a train or automobile traveling far away from the magnetic shield room 228.

  Therefore, when the active magnetic shield device 226 of Patent Document 1 is used in an environment where such high-frequency magnetic noise sources are scattered, the flux gate magnetometer 232 as a magnetic sensor disposed outside has this flux. Magnetic noise caused by a magnetic noise source at a point away from the gate magnetometer 232 cannot be accurately measured.

  Further, when the fluxgate magnetometer 232 is disposed outside the wall in the vicinity of the magnetic shield room 228, the fluxgate magnetometer 232 is disposed on the opposite space (for example, the Helmholtz coil 230A side) via the magnetic shield room 228. In this case, magnetic noise existing in the space on the Helmholtz coil 230B side cannot be measured.

  As shown in FIG. 11, in the active magnetic shield device 234 of Patent Document 2, a magnetic sensor 240 is disposed inside a magnetic shield room 238 covered with an electromagnetic shield wall 236 made of a highly permeable material. In addition, electromagnetic coils 242 are provided on each surface of the magnetic shield room 238 so as to suppress magnetic fluctuations inside the magnetic shield room 238. A desired current can be independently passed through each electromagnetic coil 242.

  Then, based on the amount of magnetic fluctuation obtained by the measurement by the magnetic sensor 240, a controller causes a desired current to flow independently through each electromagnetic coil 242 so as to cancel out the magnetic fluctuation. Thereby, the magnetic fluctuation inside the magnetic shield room 238 can be suppressed.

  However, similarly to the active magnetic shield devices 204, 206, and 210 shown in FIGS. 7A, 7B, and 7D, the magnetic shield room 238 shown in FIG. Due to the eddy current effect generated on the wall of the magnetic field, the phase delay of the magnetic field generated from the electromagnetic coil 242 to cancel the magnetic noise increases, and sufficient magnetic shielding properties cannot be obtained.

Here, it is conceivable that a current in consideration of the phase delay due to the eddy current effect generated on the wall surface is caused to flow through the electromagnetic coil 242. However, since this phase lag varies greatly from frequency to frequency, in order to exert a magnetic shielding effect against wideband magnetic noise, a plurality of electromagnetic coils are arranged for each frequency, and a current that takes into account the phase lag for each frequency. Must flow through each electromagnetic coil. Therefore, the cost is increased, and the control of flowing a current through the electromagnetic coil is complicated.
JP 2002-257914 A JP 2003-243874 A

  In consideration of such facts, the present invention provides a low-cost and easy-to-control magnetic shield device that exhibits a magnetic shielding effect against broadband magnetic noise by using both a passive and active magnetic shield. Is an issue.

  According to the first aspect of the present invention, a magnetic shielding space covered with a magnetic shielding wall that shields magnetism, a coil provided outside the magnetic shielding wall, an inside of the magnetic shielding space, and the magnetic A magnetic sensor that measures the magnetic field strength of magnetic noise in the shielded space and outputs the magnetic signal as a reference signal; and a control unit that controls a magnetic field generated from the coil by causing a current to flow through the coil. Low-pass filter means for extracting a low-frequency signal having a frequency equal to or lower than a first predetermined value from the reference signal, and a low-frequency signal for converting the low-frequency signal into a low-frequency reverse phase signal obtained by inverting the phase of the low-frequency signal Phase inversion means, bandpass filter means for extracting a high-frequency signal having a frequency equal to a second predetermined value larger than the first predetermined value from the reference signal, and the high-frequency signal as the high-frequency signal. A high-frequency phase inverting means for converting the phase to a high-frequency anti-phase signal, and prediction of the phase delay time of the magnetism that occurs when magnetism enters from the outside to the inside of the magnetic shielding space through the magnetic shield wall From the value that is equal to or greater than the phase delay prediction time that is the sum of the value and the predicted value of the phase delay time caused by the output delay of the magnetic field generated from the coil, and that is a time that is an integral multiple of the period of the high-frequency antiphase signal Phase adjustment means for delaying the phase of the high-frequency anti-phase signal by the phase adjustment time minus the delay prediction time and converting the high-frequency anti-phase signal into a phase adjustment signal, the low-frequency anti-phase signal, and the phase adjustment signal, And a current supply means for converting a signal obtained by combining the signals into a current to flow through the coil.

  According to the first aspect of the present invention, the magnetic sensor is provided inside the magnetic shielding space covered by the magnetic shielding wall that shields magnetism. This magnetic sensor measures the magnetic field strength of magnetic noise in the magnetic shielding space and outputs it as a reference signal.

  A coil is provided outside the magnetic shield wall.

  And a control means controls the magnetic field which flows an electric current through this coil and is generated from this coil.

  The control means includes low-pass filter means, low-frequency phase inversion means, band-pass filter means, high-frequency phase inversion means, phase adjustment means, and current supply means.

  The low-pass filter means extracts a low-frequency signal having a frequency equal to or lower than the first predetermined value from the reference signal output from the magnetic sensor.

  The low frequency phase inversion means converts the low frequency signal into a low frequency opposite phase signal which is a signal obtained by inverting the phase of the low frequency signal.

  The band pass filter means extracts a high frequency signal having a frequency equal to a second predetermined value larger than the first predetermined value from the reference signal output from the magnetic sensor.

  The high frequency phase reversing means converts the high frequency signal into a high frequency reverse phase signal which is a signal obtained by inverting the phase of the high frequency signal.

  In the phase adjusting means, the predicted value of the magnetic phase delay time that occurs when the magnet enters the magnetic shield space from the outside through the magnetic shield wall and the phase delay time caused by the output delay of the magnetic field generated from the coil A value obtained by summing the predicted values is set as a phase delay predicted time.

  Then, the phase adjustment time is obtained by subtracting the phase delay prediction time from the value that is equal to or longer than the phase delay prediction time and is a time obtained by multiplying the period of the high-frequency antiphase signal by an integer, and the high-frequency antiphase signal is output by this phase adjustment time Is delayed to convert the high-frequency anti-phase signal into a phase adjustment signal. Thereby, the phase adjustment signal becomes a signal having a waveform as if the phase of the high-frequency anti-phase signal is advanced by the phase delay prediction time.

  In the current supply means, a signal obtained by synthesizing the low frequency antiphase signal and the phase adjustment signal is converted into a current, and this current is passed through the coil.

  Therefore, the magnetic shielding wall can exert a magnetic shielding effect against magnetic noise generated outside the magnetic shielding space and entering the magnetic shielding space.

  Also, magnetic noise generated outside the magnetic shielding space is suppressed by generating a magnetic field from the coil. Further, magnetic noise that enters the inside of the magnetic shielding space from the outside of the magnetic shielding space is suppressed by a magnetic field that is generated from the coil and enters the inside of the magnetic shielding space. As a result, the magnetic shielding effect can be improved.

  In addition, when magnetic noise is generated inside the magnetic shielding space, a magnetic field generated from a coil provided outside the magnetic shielding wall enters the magnetic shielding space, and this magnetic field enters the magnetic shielding space. Since the generated magnetic noise is suppressed, the magnetic noise in the magnetic shielding space can be reduced.

  The magnetic field generated from the coil to suppress the magnetic noise outside or inside the magnetic shielding space is caused by the magnetic phase delay that occurs when the magnet enters the inside from the outside of the magnetic shielding space through the magnetic shielding wall, And the phase of this magnetism that occurs when magnetism enters from the outside to the inside of the magnetic shielding space through the magnetic shielding wall because it is a phase-corrected magnetic field that compensates for the phase delay caused by the output delay of the magnetic field generated from the coil. Even if a delay or a phase delay caused by the output delay of the magnetic field generated from the coil occurs, sufficient magnetic shielding properties can be obtained.

  In addition, magnetic noise of a frequency that has a large phase lag caused by the magnetic phase lag that occurs when magnetism enters from the outside to the inside of the magnetic shielding space through the magnetic shield wall, or the output delay of the magnetic field generated from the coil ( A high-frequency signal equal to the frequency of the second predetermined value) and a phase delay of the magnetism that occurs when magnetism enters the magnetic shield space from the outside through the magnetic shield wall, or an output delay of the magnetic field generated from the coil Separate processing (for high-frequency signals) according to the magnetic noise characteristics of each frequency and frequency band for magnetic noise (low-frequency signal in the frequency band below the first predetermined value) in the frequency band where the phase delay caused by The phase adjustment is performed after the phase is reversed, and the phase adjustment is not performed for the low frequency signal after the phase is reversed. It produces a suppressing signal magnetic noise respectively. Therefore, the magnetic noise of each frequency and frequency band can be effectively reduced, and a magnetic shielding effect can be exhibited against broadband magnetic noise.

  In addition, since a signal obtained by synthesizing the low-frequency reverse phase signal and the phase adjustment signal is converted into a current and passed through the coil, it is not necessary to separately install a coil for each frequency and frequency band, and one to be reduced. One coil (one pair of two connected in series) can be used in common with respect to magnetic noise in the direction (for example, magnetic noise in one direction of X, Y, Z can be reduced) In order to reduce magnetic noise in all directions of X, Y, and Z, it is sufficient to provide one coil (a pair of two connected in series). A pair of 2 coils × 3 sets of coils). As a result, the cost can be reduced, the construction labor can be reduced, and the control of flowing a current through the coil becomes easy.

  Further, a high frequency signal having a frequency equal to the second predetermined value larger than the first predetermined value is a relatively high frequency, and therefore has a relatively stable period and amplitude characteristic that does not change rapidly with time.

  Since the magnetic sensor is provided inside the magnetic shielding space, real-time feedback control by the control means cannot be performed, but the high-frequency signal has a relatively stable period and amplitude characteristic that does not change rapidly with time. Even if feedback control by the control means is performed based on the reference signal measured by the magnetic sensor before the time when the magnetic field is generated from the magnetic field, the magnetism generated outside or inside the magnetic shielding space at the time when the magnetic field is generated from the coil Noise can be suppressed.

  As a result, magnetic noise sources such as commercial power lines and devices (transformers, distribution boards) that generate magnetic noise of a relatively high frequency such as a commercial frequency magnetic field are scattered around the magnetic shield space. Even in this case, a magnetic field suitable for suppressing magnetic noise can be generated from the coil.

  In addition, since the magnetic sensor can be provided inside the magnetic shielding space, the magnetic sensor can be installed at a position where the magnetic noise is most desired to be reduced inside the magnetic shielding space.

  Further, since the coil is provided outside the magnetic shield wall, the magnetic field generated from the coil is uniformly distributed over a wide area in the magnetic shielding space along the wall surface of the magnetic shield wall. Thereby, the freedom degree of the installation place of the apparatus which requires a magnetic shielding becomes large inside a magnetic shielding space. Therefore, it can be used for a magnetic shield room using a biomagnetic measuring device or an electron beam drawing device that requires magnetic shielding in a wide area.

  The invention according to claim 2 is characterized in that the frequency of the first predetermined value is 30 Hz.

  According to the second aspect of the present invention, the magnetic noise of 30 Hz or less can be effectively reduced by setting the frequency of the first predetermined value to 30 Hz.

  The invention described in claim 3 is characterized in that it has a plurality of the second predetermined values.

  In the third aspect of the invention, by having a plurality of second predetermined values, a large number of high frequency signals can be extracted and a magnetic field that suppresses the high frequency signals can be generated from the coil. On the other hand, a magnetic shielding effect can be exhibited.

  The invention according to claim 4 is characterized in that at least one of a commercial frequency, a frequency twice the commercial frequency, and a frequency triple the commercial frequency is the frequency of the second predetermined value.

  In the invention according to claim 4, the frequency of the second predetermined value is at least one of a commercial frequency, a frequency twice the commercial frequency, and a frequency three times the commercial frequency, which is a main component of magnetic noise. At least one of a commercial frequency magnetic field, a commercial frequency double frequency magnetic field, and a commercial frequency triple frequency magnetic field can be reduced.

  According to a fifth aspect of the present invention, there is provided a predicted value of a phase delay time of the magnetism that is generated when magnetism enters the inside of the magnetic shield space from the outside through the magnetic shield wall, and a magnetic field generated from the coil. As a predicted value of the phase delay time caused by the output delay, a value measured by a prior experiment in which a magnetic field of a predetermined frequency is generated from the coil or a value calculated by magnetic field analysis is used.

  According to the fifth aspect of the present invention, the predicted value of the phase delay time of the magnetism that occurs when the magnetism enters the magnetic shield space from the outside through the magnetic shield wall, and the output of the magnetic field generated from the coil By using a value measured by a prior experiment in which a magnetic field of a predetermined frequency is generated from the coil or a value calculated by magnetic field analysis, as a predicted value of the phase delay time caused by the delay, these predicted values are obtained. A value close to the actual phase delay time can be obtained. Therefore, a magnetic field more suitable for suppressing magnetic noise can be generated from the coil.

  Since the present invention has the above-described configuration, a low-cost and easy-to-control magnetic shield device that exhibits a magnetic shielding effect against wide-band magnetic noise by using both a passive magnetic shield and an active magnetic shield is provided. Can do.

  A magnetic shield device according to an embodiment of the present invention will be described with reference to the drawings.

  First, the magnetic shield device according to the first embodiment of the present invention will be described.

  As shown in FIG. 1, in the magnetic shield device 10, a magnetic sensor 14 is provided inside a substantially cubic magnetic shield space V that is entirely covered with a magnetic shield wall 12 that shields magnetism.

  The magnetic sensor 14 measures the magnetic field strength of the magnetic noise in the magnetic shielding space V and outputs it as a reference signal.

  In addition, one coil 16 is provided on the outside of the magnetic shield wall 12 so as to surround the magnetic shield wall 12 provided on the side surface of the magnetic shield space V.

  The coil 16 is connected to a control device 18 as control means. Then, the control device 18 controls the magnetic field generated from the coil 16 by causing a current to flow from the control device 18 to the coil 16.

  As shown in the block diagram of FIG. 2, the signal processing circuit 20 of the control device 18 is a circuit in which a high frequency signal processing circuit 28 and a low frequency signal processing circuit 38 are connected in parallel.

  In the high frequency signal processing circuit 28, a band pass filter 22A having a pass frequency of 50 Hz as a band pass filter means, an amplification degree adjusting circuit 24A, a band pass filter 22B having a pass frequency of 50 Hz as band pass filter means, and an amplification as a high frequency phase inverting means. A degree adjusting circuit 24B and a phase adjusting circuit 26 as a phase adjusting means are connected in series in this order.

  In the low-frequency signal processing circuit 38, a high-pass filter 30 having a cutoff frequency of 0.05 Hz, a low-pass filter 32 having a cutoff frequency of 30 Hz as a low-pass filter means, an integrator 34, and an amplification as a low-frequency phase inversion means. The degree adjustment circuit 36 is connected in series in this order.

  The reference signal output from the magnetic sensor 14 is sent to the high frequency signal processing circuit 28 and the low frequency signal processing circuit 38 via the buffer 40 and processed by the high frequency signal processing circuit 28 and the low frequency signal processing circuit 38. The signals are synthesized by an adder 42 as current supply means.

  Next, the operation and effect of the magnetic shield device according to the first embodiment of the present invention will be described.

  When magnetic noise occurs outside the magnetic shielding space V covered by the magnetic shielding wall 12 and magnetic noise enters the magnetic shielding space V from the outside of the magnetic shielding space V, first, as shown in FIG. The magnetic sensor 14 measures the magnetic field intensity of the magnetic noise in the magnetic shielding space V and outputs it as a reference signal.

  Next, the reference signal output from the magnetic sensor 14 is sent to the low frequency signal processing circuit 38 via the buffer 40 as shown in the block diagram of FIG. The buffer 40 is provided to receive the reference signal from the magnetic sensor 14 with a high input impedance and resistance, and to send the reference signal to the low frequency signal processing circuit 38 and the high frequency signal processing circuit 28 without loss.

  In the low-frequency signal processing circuit 38, first, the DC component included in the reference signal sent to the low-frequency signal processing circuit 38 is removed by the high-pass filter 30 having a cutoff frequency of 0.05 Hz.

Next, a low-frequency signal P ₁ (refer to FIG. 3A) having a frequency of 30 Hz or less as a first predetermined value from the reference signal from which the DC component has been removed by the low-pass filter 32 having a cutoff frequency of 30 Hz. Extract.

Next, the low frequency signal P ₁ integrated by the integrator 34 is subjected to a process for adjusting the amplification degree and inverting the phase by the amplification degree adjusting circuit 36. Thus, converting the low-frequency signals P ₁ to the low frequency antiphase signal P ₂ (see FIG. 3 (B)).

In this way, it is possible to produce a low frequency antiphase signals P ₂ to cancel out the low-frequency signal P _1.

  Further, the reference signal output from the magnetic sensor 14 is sent to the low frequency signal processing circuit 38 via the buffer 40, and at the same time, the same reference signal is sent to the high frequency signal processing circuit 28.

Here, among the magnetic noise generated outside the magnetic shielding space V covered by magnetic shield wall 12, 50 Hz component of the second predetermined value is in the waveform such as an external signal Q ₀ (FIG. 4 ( See A).

When magnetic noise enters from the outside of the magnetic shielding space V through the magnetic shield wall 12, the phase of the external signal Q ₀ is a phase delay time D ₁ due to the eddy current generated in the magnetic shield wall 12. Only late. As a result, the external signal Q ₀ changes to the internal signal Q ₁ (see FIG. 4B).

For example, if measurement is started from time T ₁ by the magnetic sensor 14, the magnetic noise measured at time T ₁ by the magnetic sensor 14 is delayed by the phase delay time caused by the output delay of the reference signal from the magnetic sensor 14. The reference signal is output to the high-frequency signal processing circuit 28.

At this time, the internal signal Q ₁ changes to a 50 Hz reference signal Q ₂ delayed by the phase delay time D ₂ , and this 50 Hz reference signal Q ₂ is sent to the high frequency signal processing circuit 28 at time T ₂ (= T ₁ + D ₂ ). Is output (see FIG. 4C).

In the high-frequency signal processing circuit 28, first, the band-pass filter 22A of the pass frequency 50Hz, a high-frequency signal _{Q 3} is equal to the frequency of 50Hz from the reference signal as a second predetermined value greater than 30Hz frequency as a first predetermined value Extract.

Next, with respect to high-frequency signals Q _3, adjusts the amplification factor in the amplification factor adjustment circuit 24A.

  Then, the signal whose amplification is adjusted by the amplification adjustment circuit 24A is subjected to the same processing as the band-pass filter 22A and amplification adjustment circuit 24A via the band-pass filter 22B and amplification adjustment circuit 24B. .

The high frequency signal Q ₃ becomes a signal in which the phase of the 50 Hz reference signal Q ₂ is delayed by the phase delay time D ₃ caused by the extraction delay of the high frequency signal Q ₃ by the band pass filters 22A and 22B, and the time T ₃ (= T ₂ + D ₃ ) Is output to the amplification adjustment circuit 24B (see FIG. 4D).

  As described above, the same processing is performed twice in the band pass filter 22A and the amplification degree adjustment circuit 24A, and in the band pass filter 22B and the amplification degree adjustment circuit 24B, thereby improving the extraction accuracy of the 50 Hz component.

Next, it inverts the phase of the high-frequency signal Q ₃ by an amplification factor adjustment circuit 24B as a high frequency phase inverting means. Thus, converting the high-frequency signal Q ₃ to the high-frequency antiphase signal Q _4. The high-frequency antiphase signal Q ₄ is output to the phase adjustment circuit 26 at time T ₃ (= T ₂ + D ₃ ) (see FIG. 4E).

Next, as shown in FIG. 4 (F), the phase adjustment circuit 26, the phase of the high-frequency antiphase signal Q ₄ is delayed by the phase adjustment time D _5, the high-frequency reverse phase signal Q ₄ to the phase adjustment signal Q ₅ Convert.

Phase adjustment time D ₅ at this time, the period of the phase delay is at the estimated time or more and a high frequency anti-phase signal Q ₄ from the value which is integer times the time, the time obtained by subtracting the phase delay prediction time.

Further, the phase delay prediction time, the predicted value of the phase delay time D ₁ that occurs when the magnetic noise into the interior enters from the outside of the magnetic shielding space V through the magnetic shield wall 12 actually took phase delay time The sum of D ₂ and D ₃ and the predicted value of the phase delay time D ₄ caused by the output delay of the magnetic field generated from the coil is taken as the total time.

Thus, the phase adjustment signal Q _5, as if the signal waveform as the phase was advanced by a phase delay estimated time of the high-frequency anti-phase signal Q _4.

The phase adjustment time D ₅ is the period of the phase delay is at the estimated time or more and a high frequency anti-phase signal Q ₄ from the minimum value of the value which is integer times the time, that a time obtained by subtracting the phase delay prediction time preferable.

The phase delay times D ₂ and D ₃ are delay times generated in the electrical signal processing process, and are extremely small values compared to the predicted values of the phase delay times D ₁ and D _4. It may not be included in the phase delay prediction time. In actual implementation, if any of the phase delay times D ₂ and D ₃ has a value that cannot be ignored, the value may be included in the phase delay prediction time.

Next, a signal obtained by synthesizing the low-frequency reverse phase signal P ₂ generated by the low-frequency signal processing circuit 38 and the phase adjustment signal Q ₅ generated by the high-frequency signal processing circuit 28 by the adder 42 is converted into a current. This current is passed through the coil 16.

Phase of the phase adjustment signal Q ₅ is delayed by the phase delay time D ₄ when it is output from the coil. Thereby, the phase adjustment signal _{Q 5,} changes in the coil output signal _{Q 6} (FIG. 4 (G) see).

The coil output signal Q ₆ becomes an antiphase signal that cancels the external signal Q ₀ that is a 50 Hz component of the magnetic noise generated outside the magnetic shielding space V, and the coil is output at time T ₄ (= T ₃ + D ₄ ). 16 is output. That is, the external signal Q ₀ that is a 50 Hz component of the magnetic noise generated outside the magnetic shielding space V is suppressed by the coil output signal Q ₆ .

Further, the 50 Hz component of the magnetic noise that has entered the inside of the magnetic shielding space V from the outside of the magnetic shielding space V and has become the internal signal Q ₁ is output from the coil 16 and the coil output that enters the inside of the magnetic shielding space V. It is inhibited by the signal _{Q 6.} That is, when the coil output signal Q ₆ output from the coil 16 passes through the magnetic shield wall 12 and enters the magnetic shield space V from the outside to the inside, the phase of the coil output signal Q ₆ is changed to the phase delay time D _1. changes in signal delayed by, thereby, the changed signal is antiphase to cancel the 50Hz component of the magnetic noise becomes internal signals Q ₁ to penetrate from the outside of the magnetic shielding space V inside the magnetic shielding space V Signal.

In addition, when an experimental device or a medical device installed in the magnetic shielding space V becomes a magnetic noise generation source, and magnetic noise is generated in the magnetic shielding space V, the second predetermined one of the magnetic noises. 50Hz component as the value becomes the waveform as shown in the internal signals _{Q 1,} through the process of FIG. 4 (B) ~ (G) . Then, the coil output signal Q ₆ in FIG. 4G enters the inside of the magnetic shielding space V and suppresses the 50 Hz component (internal signal Q ₁ ) of the magnetic noise generated inside the magnetic shielding space V.

When the coil output signal Q ₆ output from the coil 16 passes through the magnetic shield wall 12 and enters the magnetic shield space V from the outside to the inside, the phase of the coil output signal Q ₆ is delayed by the phase delay time D _1. The signal changes. Thus, a signal of opposite phase that this changed signal cancels the internal signal Q _1.

Note that the frequency of the external signal Q _0, which is a 50 Hz component of magnetic noise, and the coil output signal Q ₆ output from the coil 16 are both 50 Hz and are equal, so that the external signal Q ₀ passes through the magnetic shield wall 12. The magnetic noise phase delay time D ₁ generated when the magnetic shield space V enters from the outside to the inside and the coil output signal Q ₆ pass through the magnetic shield wall 12 and enter the magnetic shield space V from the outside to the inside. the phase delay time D ₁ of the coil output signal Q ₆ which occurs when approximately equal.

  Therefore, the magnetic shielding wall 12 can exert a magnetic shielding effect against magnetic noise generated outside the magnetic shielding space V and entering the inside of the magnetic shielding space V.

  Further, the magnetic noise generated from the coil 16 provided outside the magnetic shield wall 12 can suppress magnetic noise inside or outside the magnetic shielding space V, and can reduce magnetic noise in the magnetic shielding space V. The magnetic shielding effect can be improved.

  The magnetic field generated from the coil 16 to suppress magnetic noise inside or outside the magnetic shielding space V is generated when the magnetism enters the magnetic shielding space V from the outside through the magnetic shielding wall 12. Therefore, the magnetic field penetrates from the outside to the inside of the magnetic shield space V through the magnetic shield wall 12 because the magnetic field has been subjected to phase correction to compensate for the phase delay caused by the output delay of the magnetic field generated from the coil 16. Sufficient magnetic shielding can be obtained even if this magnetic phase lag that occurs sometimes or a phase lag caused by the output delay of the magnetic field generated from the coil 16 occurs.

Further, the magnetic phase lag that occurs when the magnetism enters from the outside to the inside of the magnetic shielding space V through the magnetic shield wall 12 and the frequency of the phase lag that is caused by the output delay of the magnetic field generated from the coil 16 is large. Magnetic noise (a high-frequency signal Q ₃ equal to the frequency of 50 Hz as the second predetermined value) and the phase delay of this magnetism that occurs when magnetism enters the magnetic shield space V from the outside through the magnetic shield wall 12 In addition, with respect to magnetic noise (low frequency signal P _{1 in} a frequency band of 30 Hz or less as a first predetermined value) in a frequency band with a small phase delay caused by an output delay of a magnetic field generated from the coil 16, each frequency and frequency It performs phase adjustment after the antiphase for separate processing to match the magnetic noise characteristics of the band (high-frequency signals Q _3, the low-frequency signal P ₁ Is against the not performed the phase adjustment) from reversed phase subjected by the controller 18, produces a suppressing signal to each of the magnetic noise. Therefore, the magnetic noise of each frequency and frequency band can be effectively reduced, and a magnetic shielding effect can be exhibited against broadband magnetic noise.

Further, since it converts the combined signal and a low frequency antiphase signals P ₂ and the phase adjustment signal Q ₅ to the current flowing through the coil 16, there is no need to install a coil 16 separately for each frequency and the frequency band , One (two in one pair connected in series) coils 16 can be commonly used for magnetic noise in one direction to be reduced (for example, one of X, Y, and Z directions) In the case where the magnetic noise is to be reduced, one coil 16 (one pair connected in series) may be provided, and the magnetic noise in all X, Y, and Z directions is to be reduced. 3 may be provided with three coils 16 (one pair × two sets connected in series). As a result, the cost can be reduced, the construction labor can be reduced, and the control of flowing a current through the coil 16 becomes easy.

Also, because 30Hz second frequency higher the frequency of the high frequency signal Q ₃ equal to 50Hz as a predetermined value greater than as a first predetermined value, unlike the low-frequency signal P _1, compared not to abruptly change with time Stable period and amplitude characteristics. In general, train sending / returning current and movement of magnetic materials such as elevators, automobiles, and carts are sources of constantly changing low-frequency magnetic fields (low-frequency signals P ₁ ), An outdoor transmission line or the like becomes a generation source of a high-frequency magnetic field (high-frequency signal Q ₃ ) with little temporal change.

Since the magnetic sensor 14 is provided in the magnetic shielding space V, real-time feedback control by the control device 18 cannot be performed, but the high-frequency magnetic field (high-frequency signal Q ₃ ) is relatively stable and does not change rapidly with time. Since it has the period and amplitude characteristics, even if feedback control by the control device 18 is performed based on the reference signal (50 Hz reference signal Q ₂ ) measured by the magnetic sensor 14 before the time point when the magnetic field is generated from the coil 16, Magnetic noise outside or inside the magnetic shielding space V can be suppressed at the time when the magnetic field is generated from the coil 16.

  As a result, magnetic noise sources such as commercial power lines and devices (transformers, distribution boards) that generate magnetic noise of a relatively high frequency such as a commercial frequency magnetic field are scattered around the magnetic shielding space V. Even in this case, a magnetic field suitable for suppressing these magnetic noises can be generated from the coil 16.

  In addition, since the magnetic sensor 14 can be provided inside the magnetic shielding space V, the magnetic sensor 14 can be installed in the magnetic shielding space V at a position where the magnetic noise is most desired to be reduced.

  In addition, since the coil 16 is provided outside the magnetic shield wall 12, the magnetic field generated from the coil 16 is uniformly distributed over a wide area inside the magnetic shield space V along the wall surface of the magnetic shield wall 12. Thereby, in the magnetic shielding space V, the freedom degree of the installation place of the apparatus which requires a magnetic shielding becomes large. Therefore, it can be used for a magnetic shield room using a biomagnetic measuring device or an electron beam drawing device that requires magnetic shielding in a wide area.

  Moreover, magnetic noise below 30 Hz can be effectively reduced by setting the first predetermined value to 30 Hz.

  Further, by setting the frequency of the second predetermined value to 50 Hz which is a commercial frequency, it is possible to reduce a commercial frequency magnetic field which is a main component of magnetic noise.

  Next, a magnetic shield device according to a second embodiment of the present invention will be described.

  In the second embodiment, three high-frequency signal processing circuits are provided in the signal processing circuit 20 of the first embodiment. Therefore, in the following description, the same components as those in the first embodiment are denoted by the same reference numerals and are appropriately omitted.

  As shown in the block diagram of FIG. 5, the signal processing circuit 44 of the control device 18 is a circuit in which high-frequency signal processing circuits 28, 46, and 48 and a low-frequency signal processing circuit 38 are connected in parallel.

  The configurations of the high-frequency signal processing circuit 28 and the low-frequency signal processing circuit 38 are the same as those in FIG.

  The high-frequency signal processing circuit 46 includes a band-pass filter 50A having a pass frequency of 100 Hz as a band-pass filter unit, an amplification degree adjusting circuit 52A, a band-pass filter 50B having a pass frequency of 100 Hz as a band-pass filter unit, and amplification as a high-frequency phase inverting unit. A degree adjusting circuit 52B and a phase adjusting circuit 54 as a phase adjusting means are connected in series in this order.

  The high-frequency signal processing circuit 48 includes a band-pass filter 56A having a pass frequency of 150 Hz as a band-pass filter unit, an amplification degree adjusting circuit 58A, a band-pass filter 56B having a pass frequency of 150 Hz as a band-pass filter unit, and an amplification as a high-frequency phase inverting unit. The degree adjusting circuit 58B and the phase adjusting circuit 60 as the phase adjusting means are connected in series in this order.

  The reference signal output from the magnetic sensor 14 is sent to the high-frequency signal processing circuits 28, 46, 48 and the low-frequency signal processing circuit 38 via the buffer 40, and the high-frequency signal processing circuits 28, 46, 48, and The signal processed by the low frequency signal processing circuit 38 is synthesized by an adder 42 and adders 62 and 64 as current supply means.

  Next, operations and effects of the magnetic shield device according to the second embodiment of the present invention will be described.

  In the high-frequency signal processing circuit 28, the high-frequency signal equal to the frequency of 50 Hz as the second predetermined value larger than the frequency of 30 Hz as the first predetermined value is extracted from the reference signal by the band-pass filters 22A and 22B having the pass frequency of 50 Hz. .

  Further, in the high frequency signal processing circuit 46, a high frequency signal equal to a frequency of 100 Hz as a second predetermined value larger than a frequency of 30 Hz as the first predetermined value from the reference signal is obtained by the band pass filters 50A and 50B having a pass frequency of 100 Hz. Extract.

  Further, in the high frequency signal processing circuit 48, the high frequency signal equal to the frequency of 150 Hz as the second predetermined value is larger than the frequency of 30 Hz as the first predetermined value from the reference signal by the band pass filters 56A and 56B having the pass frequency of 150 Hz. Extract.

  That is, the signal processing circuit 44 can extract many high-frequency signals by having a plurality of second predetermined values.

  Next, the respective high frequency signals are inverted by the amplification degree adjusting circuits 24B, 52B, and 58B. Thereby, each high frequency signal is converted into a high frequency antiphase signal.

  Next, the phase adjustment circuits 26, 54, and 60 delay the phase of each high-frequency anti-phase signal by the phase adjustment time, and convert each high-frequency anti-phase signal into a phase adjustment signal.

  The phase adjustment time and the phase delay prediction time at this time are obtained for each high-frequency antiphase signal by the same method as in the first embodiment.

  Next, the low frequency antiphase signal generated by the low frequency signal processing circuit 38 and the phase adjustment signal generated by the high frequency signal processing circuits 28, 46, and 48 are synthesized by the adders 62, 64, 42, respectively. The synthesized signal is converted into a current by the adder 42 and is passed through the coil 16.

  Therefore, in the second embodiment, the same effect as that of the first embodiment can be obtained.

  Also, by having a plurality of second predetermined values, it is possible to extract a large number of high-frequency signals and generate a magnetic field that suppresses the high-frequency signals from the coil 16, thereby effectively reducing broadband magnetic noise. it can. In the second embodiment, it is possible to effectively reduce broadband magnetic noise including frequency bands of 50 Hz, 100 Hz, 150 Hz, and 30 Hz or less.

  In addition, by setting the frequency of the second predetermined value to 50 Hz that is a commercial frequency, 100 Hz that is twice the commercial frequency, and 150 Hz that is three times the commercial frequency, it is a main component of magnetic noise. The commercial frequency magnetic field, the commercial frequency double frequency magnetic field, and the commercial frequency triple frequency magnetic field can be reduced.

In the first and second embodiments, the phase lag prediction time is estimated based on the phase lag time D ₁ that occurs when magnetic noise enters the magnetic shield space V from the outside through the magnetic shield wall 12. The sum of the value, the actual phase delay times D ₂ and D _3, and the predicted value of the phase delay time D ₄ generated by the output delay of the magnetic field generated from the coil 16 is the sum of the phase delay times D _1. If the value measured by a prior experiment for generating a magnetic field of a predetermined frequency from the coil 16 or the value calculated by the magnetic field analysis is used as the predicted value of D ₄ , these predicted values are used as the actual phase delay time. The value can be close to. Therefore, since a more suitable magnetic field can be generated from the coil 16 to suppress magnetic noise, the predicted values of the phase delay times D ₁ and D ₄ are calculated by a prior experiment or calculated by magnetic field analysis. It is preferable to use the measured values.

As an experimental method, for example, a current is passed through the coil 16 and the phase delay times D ₁ and D ₄ for each frequency at that time are measured. When the first predetermined value is 30 Hz and the second predetermined value is 50 Hz, 100 Hz, 150 Hz, the predetermined frequency is 0.1 Hz, 0.5 Hz, 10 Hz, 20 Hz, 50 Hz, 100 Hz, and 150 Hz. A magnetic field having a frequency may be generated from the coil 16 and the phase delay characteristic at this time may be measured. In the case of magnetic field analysis, calculation may be performed for similar parameters.

  In the first and second embodiments, the example in which the first predetermined value is 30 Hz has been described. However, the present invention is not limited to this, and may be determined as appropriate according to the frequency of the magnetic noise to be reduced. For example, when the 17 Hz magnetic noise generated from the motor and the 25 Hz magnetic noise generated from the ventilation fan are to be reduced, the first predetermined value may be set to about 5 Hz.

  In addition, assuming that the first or second embodiment is applied in the Kanto region, in the first embodiment, the second predetermined value is set to 50 Hz, which is a commercial frequency in the Kanto region, and the second embodiment. Then, the second predetermined value is 50 Hz, 100 Hz (twice the commercial frequency), and 150 Hz (three times the commercial frequency), but the second predetermined value only needs to be greater than the frequency of the first predetermined value. It may be one value or a plurality of values. It is preferable that at least one of a commercial frequency, a frequency twice the commercial frequency, and a frequency three times the commercial frequency be a frequency of the second predetermined value.

  For example, when the first or second embodiment is applied in the Kansai region, since the commercial frequency is 60 Hz, 60 Hz, 120 Hz (twice the commercial frequency), and 180 Hz (three times the commercial frequency) By setting at least one of the second predetermined value, at least one of the main component of the magnetic noise, the commercial frequency magnetic field, the commercial frequency double frequency magnetic field, and the commercial frequency triple frequency magnetic field is reduced. be able to.

  In the first or second embodiment, an example is shown in which one coil 16 is provided on the outside of the magnetic shield wall 12 in the vertical direction. It is sufficient that at least one coil (a pair of two coils connected in series) is provided. As in the first or second embodiment, it is preferable to provide a pair of coils 16 on the upper and lower sides because the reverse magnetic field generated from the coils 16 becomes uniform.

  Therefore, when magnetic noise in all directions of X, Y, and Z is to be reduced, a pair of coils 16 is provided for each direction, and the coil 16 is composed of a pair of 2 × 3 coils 16. preferable. In this case, three magnetic sensors 14 and three control devices 18 are also required. However, if the magnetic sensor can measure the magnetic field intensity of magnetic noise in three directions, only one magnetic sensor is required.

  Moreover, the magnetic shield wall 12 should just be formed with the material which shields magnetism, and a permalloy, a silicon steel plate, an amorphous, an electromagnetic steel plate etc. can be used for it. The thickness and the number of layers of the magnetic shield wall 12 may be appropriately determined according to the characteristics of magnetic noise to be reduced, the performance of equipment installed in the magnetic shield space V, and the like.

  The magnetic sensor 14 only needs to be able to measure the magnetic field strength of magnetic noise, such as a semiconductor magnetic sensor, an optical fiber magnetic sensor, a SQUID (Superconducting Quantum Interference Device) magnetometer, a fluxgate magnetometer, and the like. Can be used.

  In the first and second embodiments, the example in which the entire surface is covered with the magnetic shield wall 12 so that the magnetic shield space V is substantially cubic is shown. However, the first and second embodiments are various. It may be a magnetic shielding space of any shape or size.

  For example, it may be a magnetic shield room in which a person enters, a magnetic shield space in a small room where an animal experiment is performed, a magnetic shield space covered by a casing 72 as shown in FIG.

  In the magnetic shield device 66 shown in FIG. 6, a permalloy shield box 68 and a pipe 70 are integrated to form a casing 72. The inside of the casing 72 is used as a magnetic shielding space, and an electronic drawing device 74 and a stage 76 are installed in the magnetic shielding space.

  Further, six coils 78 are provided on each surface so as to surround the casing 72 in a substantially rectangular parallelepiped shape.

  Then, a current is passed through the coil 78 so as to generate a magnetic field that suppresses magnetic noise by the same method as in the first or second embodiment.

  As a result, a magnetic shielding effect can be exerted against magnetic noise entering from the outside to the inside of the housing 72, and the influence of the magnetic noise on the electron beam of the electronic drawing device 74 can be reduced.

  In general, when constructing a magnetic shield room having a large magnetic shielding space, it is difficult to perform sufficient electrical bonding on the floor and side walls, the side walls and the ceiling, and the joints between the side walls. It is not preferred to use flooring, sidewalls and ceiling materials. Therefore, a ferromagnetic material such as permalloy having a thickness of 1 mm or 2 mm is often used as the material for the floor, side walls, and ceiling, or the ferromagnetic material is often used in two or three layers.

  For low-frequency magnetic noise generated from trains, automobiles, etc., the magnetic shielding effect can be exhibited even by such a passive magnetic shielding method using a ferromagnetic material. However, since a ferromagnetic material such as permalloy has a lower conductivity than aluminum, a magnetic shielding effect due to eddy current cannot be expected so much. Therefore, such a passive magnetic shielding method alone can provide a sufficient magnetic shielding effect against commercial high-frequency magnetic noise generated from the wiring of a commercial power supply, transformers, etc. arranged around the magnetic shield room. Can not do it.

  In addition, unlike a measurement apparatus capable of filtering magnetic noise, the electron beam drawing apparatus and the electron beam mask drawing apparatus directly affect the yield in the manufacturing process. Commercial frequency magnetic field, commercial frequency double frequency magnetic field, and commercial frequency triple frequency magnetic field are commercial power lines, equipment (transformers, distribution boards), etc. that are often added after building a magnetic shield room This is a particular problem.

  On the other hand, in the first and second embodiments, the canceling magnetic field subjected to the phase correction based on the measurement result of the magnetic sensor 14 is generated from the coil 16, which is effective in reducing the magnetic noise at the commercial frequency. . In addition, since the number of layers of the magnetic shield wall 12 can be reduced, compared to a passive magnetic shield made of a multi-layered ferromagnetic material such as permalloy, it is possible to save labor and cost, and further increase the cost. A magnetic shielding effect can be exhibited.

  As mentioned above, although 1st and 2nd embodiment of this invention was described, this invention is not limited to such embodiment at all, You may use combining 1st and 2nd embodiment, Needless to say, the present invention can be implemented in various modes without departing from the gist of the present invention.

It is explanatory drawing which shows the magnetic shielding apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the signal processing circuit of the magnetic shielding apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the signal processing method of the magnetic shielding apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the signal processing method of the magnetic shielding apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the signal processing circuit of the magnetic shielding apparatus which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the modification of the magnetic shielding apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the conventional magnetic shield apparatus. It is explanatory drawing which shows the signal processing method of the conventional magnetic shield apparatus. It is the diagram which showed the phase lag with respect to the frequency of the magnetic field generated from the magnetic compensation coil in the magnetic shield room enclosed with the wall of the permalloy. It is explanatory drawing which shows the conventional active magnetic shielding apparatus. It is explanatory drawing which shows the conventional active magnetic shielding apparatus.

Explanation of symbols

10, 66 Magnetic shield device 12 Magnetic shield wall 14 Magnetic sensor 16, 78 Coil 18 Control device (control means)
22A, 22B, 50A, 50B, 56A, 56B Band pass filter (band pass filter means)
24B, 52B, 58B Amplification adjustment circuit (high frequency phase inversion means)
26, 54, 60 Phase adjustment circuit (phase adjustment means)
32 Low-pass filter (low-pass filter means)
36 Amplification adjustment circuit (low frequency phase inversion means)
42 Adder (current supply means)
68 Shield box (magnetic shield wall)
70 pipe (magnetic shield wall)
D ₁ , D ₄ Phase delay time D ₅ Phase adjustment time P ₁ Low frequency signal P ₂ Low frequency reverse phase signal Q ₃ High frequency signal Q ₄ High frequency reverse phase signal Q ₅ Phase adjustment signal V Magnetic shielding space

Claims (5)

A magnetic shielding space covered with a magnetic shielding wall for shielding magnetism;
A coil provided outside the magnetic shield wall;
A magnetic sensor provided inside the magnetic shielding space, measuring a magnetic field intensity of magnetic noise in the magnetic shielding space and outputting as a reference signal;
Control means for controlling a magnetic field generated from the coil by passing a current through the coil;
With
The control means includes
Low-pass filter means for extracting a low-frequency signal having a frequency equal to or lower than a first predetermined value from the reference signal;
Low frequency phase inversion means for converting the low frequency signal into a low frequency antiphase signal obtained by inverting the phase of the low frequency signal;
Bandpass filter means for extracting a high frequency signal having a frequency equal to a second predetermined value larger than the first predetermined value from the reference signal;
High-frequency phase inversion means for converting the high-frequency signal into a high-frequency anti-phase signal obtained by inverting the phase of the high-frequency signal;
Prediction value of the phase delay time of the magnetism generated when magnetism enters from the outside to the inside of the magnetic shielding space through the magnetic shield wall and the prediction of the phase delay time caused by the output delay of the magnetic field generated from the coil The phase of the high-frequency antiphase signal is equal to or more than the phase delay prediction time obtained by subtracting the phase delay prediction time from the value that is equal to or greater than the phase delay prediction time that is the sum of the values and the period of the high-frequency antiphase signal multiplied by an integer. A phase adjusting means for delaying the above and converting the high-frequency anti-phase signal into a phase adjusting signal;
A current supply means for converting a signal obtained by combining the low-frequency reverse phase signal and the phase adjustment signal into a current and flowing the current to the coil;
A magnetic shield device comprising:   The magnetic shield device according to claim 1, wherein the frequency of the first predetermined value is 30 Hz.   The magnetic shield device according to claim 1, wherein the magnetic shield device has a plurality of the second predetermined values.   The frequency according to any one of claims 1 to 3, wherein at least one of a commercial frequency, a frequency twice the commercial frequency, and a frequency triple the commercial frequency is the frequency of the second predetermined value. The magnetic shield device described in 1.   A predicted value of the magnetic phase delay time that occurs when magnetism enters from the outside to the inside of the magnetic shielding space through the magnetic shield wall, and the phase delay time that is generated by the output delay of the magnetic field generated from the coil. The predicted value is a value measured by a prior experiment in which a magnetic field having a predetermined frequency is generated from the coil, or a value calculated by a magnetic field analysis. The magnetic shield device according to item 1.

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