JP2021060378A - Magnetic field measuring device - Google Patents

Abstract

To provide a magnetic field measuring device that can reduce a radiated magnetic field noise generated in a magnetic shield room.SOLUTION: A magnetic field measuring device has: a superconducting quantum interference element; and a magnetic flux locked loop circuit including a preceding stage circuit unit that includes an amplifier connected to an output of the superconducting quantum interference element, and a subsequent stage circuit unit that is connected to the preceding stage circuit unit. The preceding stage circuit unit is installed along an inner surface or an outer surface of a shield material that separates the inside and outside of a magnetic shield room in which the superconducting quantum interference element is installed, and the subsequent stage circuit unit is installed on the outside of the magnetic shield room.SELECTED DRAWING: Figure 2

Description

The present invention relates to a magnetic field measuring device.

Measurement of a weak magnetic field such as biomagnetism is generally performed using a superconducting QUantum Interference Device (SQUID) or the like arranged in a magnetic shielding room (MSR). .. Hereinafter, the superconducting quantum interference device is also referred to as SQUID. Since SQUID has a non-linear response to a magnetic field, the magnetic field is measured by linearizing it using an FLL (Flux Locked Loop) circuit. As the FLL circuit, there are known an analog FLL system composed of only an analog circuit and a digital FLL system in which an analog signal is once converted into a digital signal, signal processing is performed, and then converted into an analog signal again.

The magnetic field signal measured by SQUID is weak and susceptible to noise. Therefore, a method is disclosed in which a control circuit for controlling the operation of SQUID is divided into two, one is installed in the magnetic shield room, and the other is installed outside the magnetic shield room (see Patent Document 1).

For example, when a cooling system including SQUID and a headset including a preamplifier are directly connected, the distance between SQUID and the preamplifier is the shortest, so the noise immunity of the signal output from SQUID and before being amplified by the preamplifier. Will improve. On the other hand, the length of the cable connecting the preamplifier and the control circuit arranged outside the magnetic shield room becomes long. In particular, the length of the cable routed in the magnetic shield room is longer than when the preamplifier is installed away from the cooling system.

The cable connecting the preamplifier and the control circuit includes not only a signal cable for transmitting the signal amplified by the preamplifier but also a power cable for supplying power to the preamplifier. Therefore, the longer the cable wired in the magnetic shield room, the larger the radiant magnetic field noise generated in the magnetic shield room, and the larger the radiant magnetic field noise detected by SQUID. Therefore, even if the noise immunity of the signal before being amplified by the preamplifier is improved, the preamplifier amplifies the radiated magnetic field noise detected by SQUID together with the biomagnetic field signal.

The disclosed technique has been made in view of the above problems, and an object of the present invention is to provide a magnetic field measuring device capable of reducing radiated magnetic field noise generated in a magnetically shielded room.

In order to solve the above technical problem, the magnetic field measuring device of one embodiment of the present invention includes a superconducting quantum interference element, a pre-stage circuit unit including an amplifier connected to the output of the superconducting quantum interference element, and the pre-stage circuit. It has a magnetic flux lock loop circuit including a rear circuit unit connected to the unit, and the front circuit unit is a shield material that partitions the inside and the outside of the magnetic shield room in which the superconducting quantum interference element is installed. It is installed along the inner surface or the outer surface, and the subsequent circuit unit is installed outside the magnetic shield room.

It is possible to provide a magnetic field measuring device capable of reducing the radiated magnetic field noise generated in the magnetic shield room.

It is a block diagram which shows an example of the magnetic field measuring apparatus which concerns on 1st Embodiment of this invention. It is a layout diagram which shows an example of installation of the magnetic field measuring apparatus (magnetoencephalography) of FIG. It is a layout diagram which shows another example of the installation of the magnetic field measuring apparatus (spine meter) of FIG. It is a block diagram which shows an example of the magnetic field measuring apparatus which concerns on 2nd Embodiment of this invention. It is a layout diagram which shows an example of installation of the magnetic field measuring apparatus (magnetoencephalography) of FIG. FIG. 5 is a layout diagram showing another example of installation of the magnetic field measuring device (spine meter) of FIG. It is explanatory drawing which shows the example of the wiring path of the magnetic field measuring apparatus of FIG. It is explanatory drawing which shows the example of the wiring path of the magnetic field measuring apparatus of FIG. 1 and FIG. It is a waveform diagram which shows the measurement result of the magnetic field noise in case 1 and case 2 shown in FIG. It is a waveform diagram which shows the measurement result of the magnetic field noise in case 3 and case 4 shown in FIG. It is a waveform diagram which shows the measurement result of the magnetic field noise in case 5 and case 6 shown in FIG. It is a waveform diagram which shows the measurement result of the magnetic field noise in the case 7 shown in FIG. It is a block diagram which shows an example of the magnetic field measuring apparatus which concerns on 3rd Embodiment of this invention. It is a layout figure which shows an example (comparative example) of installation of another magnetic field measuring apparatus. It is a layout figure which shows another example (comparative example) of installation of another magnetic field measuring apparatus.

Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals, and duplicate description may be omitted.

(First Embodiment)
FIG. 1 is a block diagram showing an example of a magnetic field measuring device according to the first embodiment of the present invention. For example, the magnetic field measuring device 100A shown in FIG. 1 employs a digital FLL method and can be applied to a magnetoencephalogram (MEG: Magnetoencephalograph), a magnetoencephalogram (MSG: Magnetospinograph), or a magnetoencephalogram (MCG: Magnetocardiograph). .. The magnetic field measuring device 100A shown in FIG. 1 may be applied to a myomagnetometer.

The magnetic field measuring device 100A includes a superconducting quantum interference element 10, a digital FLL circuit 20, and a feedback coil 36. The SQUID 10 is a highly sensitive magnetic sensor that detects a magnetic field (magnetic flux) generated from a living body and penetrates a superconducting ring having a Josephson junction. For example, the SQUID 10 is configured by providing Josephson junctions at two locations on the superconducting ring.

The SQUID 10 generates a voltage that changes periodically with respect to a change in magnetic flux penetrating the superconducting ring. Therefore, the magnetic flux penetrating the superconducting ring can be obtained by measuring the voltage across the superconducting ring with the bias current flowing through the superconducting ring. Hereinafter, the characteristic of the periodic voltage change in which the SQUID 10 is generated is also referred to as a Φ-V characteristic.

The digital FLL circuit 20 includes an amplifier 31, an AD (Analog-to-Digital) converter 32, a digital integrator 33, a DA (Digital-to-Analog) converter 34, and a voltage-current converter 35. In the digital FLL circuit 20, the amplifier 31 and the voltage-current converter 35 are included in the front-stage circuit unit 21, and the AD converter 32, the digital integrator 33, and the DA converter 34 are included in the rear-stage circuit unit 22. Although the feedback coil 36 arranged close to the SQUID 10 is physically separated from the digital FLL circuit 20, it may be included in the functional block of the digital FLL circuit 20.

The front-stage circuit unit 21 and the rear-stage circuit unit 22 are connected to each other by a plurality of electric cables FLC such as a power cable 37 and a control signal line (amplifier output line 38, voltage line 39). A plurality of electric cables SQC are wired between the SQUID 10 and the feedback coil 36 and the pre-stage circuit unit 21. Hereinafter, the electric cables SQC and FLC are also simply referred to as cables SQC and FLC.

In this embodiment, the pre-stage circuit unit 21 that does not include a digital circuit is installed in the magnetic shield room MSR together with the SQUID 10 and the feedback coil 36. The subsequent circuit unit 22 including the digital circuit is installed outside the magnetic shield room MSR. Therefore, for example, it is possible to prevent the radiated magnetic field noise generated by the operation of the digital circuit that operates in synchronization with the clock from being transmitted in the magnetic shield room MSR. This makes it possible to prevent the SQUID 10 from detecting the radiated magnetic field noise generated from the digital circuit.

Further, since the pre-stage circuit unit 21 includes only a minimum number of circuits, the volume of the pre-stage circuit unit 21 occupied in the magnetic shield room MSR can be minimized, and the magnetic shield room MSR can be effectively used. ..

In the specification of the present application, the "magnetic shield room" is a space constructed by using a magnetic material or a material having high electrical conductivity alone or in combination as a shield material (wall material), and the influence of environmental magnetic field noise on the inside is exerted. Refers to what is reduced.

Since the magnetic field generated from the living body is as weak as 10 minus 10 to the 14th power, it is required that urban noise (environmental magnetic field noise) can be attenuated and acquired in order to acquire it accurately with SQUID 10. Therefore, as the performance of the magnetic shield room, it is required to reduce the environmental magnetic field noise by about 60 dB. Hereinafter, an example of the magnetic shield room will be described, but the present invention is not limited to this.

The magnetic shield room MSR is formed by covering the circumference of the internal space SIN in which the SQUID 10 is arranged with a shielding member (indicated by a thick alternate long and short dash line) that shields magnetism. The shielding member corresponds to a shielding material (wall material) that separates the inside and the outside of the magnetic shield room MSR. As a result, the internal space SIN inside the magnetic shield room MSR where the SQUID 10 is arranged and the external space SOUT outside the magnetic shield room MSR are magnetically shielded. By arranging the SQUID 10 in the magnetic shield room MSR, it is possible to make it less susceptible to the influence of environmental magnetic fields such as geomagnetism.

The amplifier 31 amplifies the output voltage generated in the SQUID 10 from the magnetic flux penetrating the SQUID 10, and outputs the amplified output voltage to the AD converter 32 via the amplifier output line 38. The AD converter 32 converts the analog signal from the amplifier 31 into a digital signal (voltage value) by sampling at a predetermined sampling frequency, and outputs the analog signal to the digital integrator 33.

The digital integrator 33 integrates the change in the voltage of SQUID 10 (to be exact, the amplified voltage output from the amplifier 31) from the lock point, which is the starting point of each period of the φ-V characteristic, and integrates the voltage value. Is output to the DA converter 34.

Further, the digital integrator 33 outputs the integrated voltage value to a data processing device 70 such as a computer. The data processing device 70 obtains the value of the biomagnetic field signal, which is the magnetic flux generated from the living body (brain, heart, nerve, etc.) to be measured, based on the voltage value from the digital integrator 33.

The DA converter 34 converts the voltage value (digital signal) integrated by the digital integrator 33 into a voltage, and outputs the converted voltage to the voltage-current converter 35 via the voltage line 39. The voltage-current converter 35 converts the voltage received from the DA converter 34 into a current, and outputs the converted current to the feedback coil 36.

The feedback coil 36 generates a magnetic flux by the current received from the voltage-current converter 35, and feeds back the generated magnetic flux to the SQUID 10 as a feedback magnetic flux. As a result, the voltage generated by the SQUID 10 can be maintained near the lock point (linear region) of the Φ-V characteristic, and the biomagnetic field signal can be obtained accurately.

The configuration shown in FIG. 1 shows one channel of the magnetic field measuring device 100A. One channel includes one SQUAD 10 and a digital FLL circuit 20 connected to the SQUID 10. Hereinafter, the magnetic field measuring device 100A will be described as having 128 channels. The magnetic field measuring device 100A may have 200 channels or more.

Further, in the following, for example, eight cable SQCs are connected for each channel between the SQUID 10 and the feedback coil 36 and the front circuit unit 21, and between the front circuit unit 21 and the rear circuit unit 22 for each channel. It will be described as assuming that eight cable FLCs are connected to the cable FLC. That is, the magnetic field measuring device 100A having 128 channels has 1024 cable SQC and 1024 cable FLC. The cables SQC and FLC include a control cable in addition to the cable shown in FIG. Further, the power cable of the cable FLC may be shared by a predetermined number of channels.

FIG. 2 is a layout diagram showing an example of installation of the magnetic field measuring device 100A of FIG. For example, the magnetic field measuring device 100A shown in FIG. 2 is a magnetoencephalograph, and has a bed 12 on which the subject lies and a depression 13 in which the head of the subject lying on the bed is placed in the center of the magnetic shield room MSR. Cooling container) and is arranged. The Duwa 13 is a container that uses liquid helium to maintain an extremely low temperature environment, and a plurality of sets of SQUAD 10s for magnetoencephalography measurement and a feedback coil 36 are arranged inside the recesses of the Duwa 13.

In the magnetic shield room MSR, the shield material 90 (wall material) that separates the internal space SIN and the external space SOUT is, for example, a plate material made of permalloy or the like, which is a high magnetic permeability material, and a plate material made of a conductor such as copper or aluminum. Is formed by laminating and. As shown in FIG. 1, the magnetic shield room MSR generally has a rectangular parallelepiped shape, and the shield material 90 is provided on each of the four wall portions, the ceiling portion, and the floor portion. The magnetic shield room MSR has a door that allows various devices to be transported and people to enter and exit, but the description of the door is omitted in FIGS. 2 and the following.

For example, the front-stage circuit unit 21 is installed on a shelf 80 attached to the upper part of the inner wall (inner surface) of the shield material 90 of the magnetic shield room MSR diagonally above the dewar 13. That is, the front-stage circuit unit 21 is installed at a position higher than the upper surface of the dewar 13 in the upper part of the inner wall of the magnetic shield room MSR.

By installing the pre-stage circuit unit 21 on the shelf, the internal space SIN of the magnetic shield room MSR can be effectively used. Further, by installing the front stage circuit unit 21 at a position higher than the upper surface of the duwa 13, the cable SQC can be guided to the cable insertion port of the duwa 13 according to gravity, and the influence of the load of the cable SQC applied to the cable insertion port can be exerted. It can be mitigated.

Then, the front-stage circuit unit 21 and the SQUID 10 and the feedback coil 36 (not shown) arranged inside the duwa 13 are connected via a plurality of cables SQC. For example, the cable SQC is inserted into the duwa 13 through a cable insertion port provided on the upper part of the duwa 13.

Further, the front-stage circuit unit 21 and the rear-stage circuit unit 22 installed in the external space SOUT of the magnetic shield room MSR are connected via a cable FLC passed through a through hole provided in the wall portion of the magnetic shield room MSR. Will be done. The pre-stage circuit unit 21 may be placed on the floor surface at a position in contact with or close to the inner wall of the magnetic shield room MSR. However, in order to prevent the cable FLC from being exposed to the internal space SIN and to prevent the radiated magnetic field noise generated from the cable FLC from being radiated to the internal space SIN, the pre-stage circuit unit 21 is installed in contact with the inner wall. It is preferable to be performed (Fig. 2).

Here, in the cable FLC connecting the front-stage circuit unit 21 and the rear-stage circuit unit 22, the length of the cable FLC from the front-stage circuit unit 21 to the inner surface of the shield material 90 is determined by the SQUID 10, the feedback coil 36, and the front-stage circuit unit 21. It is relatively short compared to the length of the cable SQC to be connected. That is, the length of the cable FLC from the front-stage circuit portion 21 to the inner surface of the shield material 90 is relatively short compared to the length of the cable SQC from the duwa 13 to the front-stage circuit portion 21.

As the cables SQC and FLC, for example, a 136-core type cord assembly type cable is used. Hereinafter, a cord assembly type cable in which 136 cables SQC (or FLC) are bundled is also referred to as a cable SQC (or FLC). In each of the 1024 cable SQC and the 1024 cable FLC, the number of cord collective cables SQC and FLC routed to the internal space SIN and the external space SOUT is eight, respectively.

The cord assembly type cables SQC and FLC are thicker and have higher flexural rigidity than the separate cables SQC and FLC. Therefore, for example, it is preferable that the front-stage circuit unit 21 is installed at a position where bending of the cable SQC is minimized and the load of the cable SQC is not concentrated on the cable insertion port of the duwa 13. In this respect, the front-stage circuit unit 21 is preferably installed diagonally above the dewar 13.

For example, the front-stage circuit unit 21 is composed of at least one printed circuit board housed in a housing shown in a rectangular parallelepiped shape in FIG. In this case, the housing is preferably made of a material capable of shielding the radiated magnetic field noise generated from the power supply wiring on the printed circuit board. The front-stage circuit unit 21 may include a housing shown in a rectangular parallelepiped shape in FIG. 2 and at least one printed circuit board housed in the housing. Hereinafter, the term “pre-stage circuit unit 21” will be referred to as including a housing in which the pre-stage circuit unit 21 is housed.

In the following description, the position where the front-stage circuit unit 21 contacts the inner wall or the like or the position close to the inner wall or the like means that the portion of the front-stage circuit unit 21 facing the inner wall or the like comes into contact with or is close to the inner wall or the like. For example, when the front-stage circuit unit 21 includes a rectangular parallelepiped housing, it indicates that the side surface, the upper surface, or the bottom surface of the housing facing the inner wall or the like is in contact with or close to the inner wall or the like.

The subsequent circuit unit 22 is composed of at least one printed circuit board housed in a housing such as a rack shown in a rectangular parallelepiped shape in FIG. Hereinafter, the term “post-stage circuit unit 22” will be referred to including a housing in which the rear-stage circuit unit 22 is housed.

In this embodiment, since the pre-stage circuit unit 21 is installed along the inner wall of the shield material 90 of the magnetic shield room MSR, the cable FLC including the power cable 37 (FIG. 1) is wired in the magnetic shield room MSR. Can be prevented. Therefore, it is possible to prevent the SQUID 10 arranged in the Duwa 13 from detecting the radiated magnetic field noise generated from the power cable 37, and it is possible to improve the measurement accuracy of the biomagnetic field signal by the SQUID 10.

The front-stage circuit unit 21 may be directly attached to the inner wall of the magnetic shield room MSR above the dewar 13, or may be attached to the inner wall via an attachment panel or the like. Further, as shown by the broken line frame (A), the front stage circuit unit 21 may be placed on the floor surface at a position in contact with or close to the inner wall of the magnetic shield room MSR. However, as described above, it is preferable that the front-stage circuit unit 21 is installed in contact with the inner wall. By placing the pre-stage circuit portion 21 on the floor surface, a part of the load of the cable SQC can be received on the floor, and the influence of the load of the cable SQC applied to the cable insertion port of the Duwa 13 can be reduced.

FIG. 3 is a layout diagram showing another example of the installation of the magnetic field measuring device 100A of FIG. The same elements as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

For example, the magnetic field measuring device 100A shown in FIG. 3 is a spinometer. Almost in the center of the magnetic shield room MSR, a bed 12 divided into two, in which the subject lies in the supine position, and a storage container 15 of the SQUID 10 installed at a position corresponding to the waist of the subject lying on the bed 12 are installed. There is. The SQUID 10 and the feedback coil 36 shown in FIG. 1 are arranged in the storage container 15.

Similar to FIG. 2, the front-stage circuit unit 21 is set on the shelf 80 attached to the inner wall of the shield material 90 of the magnetic shield room MSR diagonally above the dewar 14. That is, the front-stage circuit unit 21 is installed at a position higher than the upper surface of the dewar 13 in the upper part of the inner wall of the magnetic shield room MSR. Thereby, as in FIG. 2, the internal space SIN of the magnetic shield room MSR can be effectively used. Further, the cable SQC can be guided to the cable insertion port of the Duwa 13 according to gravity, and the influence of the load of the cable SQC applied to the cable insertion port can be reduced.

The front-stage circuit unit 21 may be directly attached to the inner wall of the magnetic shield room MSR above the duwa 14, or may be attached to the inner wall via an attachment panel or the like. Further, as in FIG. 2, as shown by the broken line frame (A), the front-stage circuit unit 21 may be placed on the floor surface at a position in contact with or close to the inner wall of the magnetic shield room MSR.

Further, in the cable FLC connecting the front stage circuit unit 21 and the rear stage circuit unit 22, the length of the cable FLC from the front stage circuit unit 21 to the inner surface of the shield material 90 is such that the SQUID 10 and the feedback coil 36 are connected to the front stage circuit unit 21. It is relatively short compared to the length of the cable SQC. That is, the length of the cable FLC from the front-stage circuit portion 21 to the inner surface of the shield material 90 is relatively short compared to the length of the cable SQC from the duwa 14 to the front-stage circuit portion 21.

(Second embodiment)
FIG. 4 is a block diagram showing an example of the magnetic field measuring device according to the second embodiment of the present invention. The same elements as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The magnetic field measuring device 100B shown in FIG. 2 is the same as the magnetic field measuring device 100A shown in FIG. 1 except that the pre-stage circuit unit 21 is installed outside the magnetic shield room MSR.

That is, in the magnetic field measuring device 100B, the cable SQC is routed through a through hole in the wall portion of the magnetic shield room MSR. For example, the magnetic field measuring device 100B adopts a digital FLL method, and can be applied to a magnetoencephalograph, a spinograph, a magnetocardiograph, a myomagnetometer, or the like.

FIG. 5 is a layout diagram showing an example of installation of the magnetic field measuring device 100B of FIG. The same elements as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. The magnetic field measuring device 100B shown in FIG. 5 is a magnetoencephalograph as in FIG. 2, and a bed 12 and a dewar 13 are arranged substantially in the center of the magnetic shield room MSR.

In FIG. 5, the front-stage circuit unit 21 is attached to, for example, the outer wall (outer surface) of the shield material 90 of the magnetic shield room MSR, which is located diagonally above the dewar 13. That is, the front-stage circuit unit 21 is installed in contact with the outer wall of the shield material 90 in the external space SOUT. By installing the pre-stage circuit unit 21 outside the magnetic shield room MSR, the internal space SIN of the magnetic shield room MSR can be effectively used. Further, similarly to FIG. 2, the cable SQC can be guided to the cable insertion port of the Duwa 13 according to gravity, and the influence of the load of the cable SQC applied to the cable insertion port can be reduced.

The cable SQC extending from the duwa 13 is connected to the front-stage circuit portion 21 through a through hole provided in the wall portion diagonally above the duwa 13. The cable FLC connecting the front-stage circuit unit 21 and the rear-stage circuit unit 22 is wired in the external space SOUT outside the magnetic shield room MSR.

Here, in the cable SQC that connects the SQUID 10 and the feedback coil 36 to the front circuit unit 21, the length of the cable SQC from the front circuit unit 21 to the outer surface of the shield material 90 is the length of the cable SQC from the SQUID 10 and the feedback coil 36 to the shield material 90. It is relatively short compared to the length of the cable SQC to the inner surface. That is, the length of the cable SQC from the pre-stage circuit portion 21 to the outer surface of the shield material 90 is relatively short compared to the length of the cable SQC from the duwa 13 to the inner surface of the shield material 90.

The front-stage circuit unit 21 may be installed on the shelf 80 attached to the outer wall of the magnetic shield room MSR, as in FIG. In this case, the external space SOUT around the magnetic shield room MSR can be effectively used. Further, as in FIG. 2, as shown by the broken line frame (A), the front-stage circuit unit 21 may be placed on the floor surface at a position in contact with or close to the outer wall.

Even when the front-stage circuit unit 21 and the rear-stage circuit unit 22 are installed outside the magnetic shield room MSR, the front-stage circuit unit 21 and the rear-stage circuit unit 22 are housed in different housings. This makes it possible to increase the degree of freedom in installing the front-stage circuit unit 21 and the rear-stage circuit unit 22 in the external space SOUT.

Further, for example, the front-stage circuit unit 21 can be installed in contact with or close to the outer wall of the shield material 90 regardless of the position where the rear-stage circuit unit 22 is installed. When the pre-stage circuit unit 21 is installed in contact with or close to the outer wall, the length of the cable SQC can be minimized. Further, when the front stage circuit portion 21 is installed in contact with the outer wall, the cable SQC is not exposed to the external space SOUT. As a result, it is possible to prevent the minute signal output from the SQUID 10 and transmitted to the cable SQC from being affected by the radiation noise flying in the external space SOUT outside the magnetic shield room MSR.

FIG. 6 is a layout diagram showing another example of the installation of the magnetic field measuring device 100B of FIG. The same elements as those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. For example, the magnetic field measuring device 100B shown in FIG. 6 is a spinometer as in FIG. 3, and is installed at a position corresponding to the waist of the subject and the bed 12 divided into two in the substantially center of the magnetic shield room MSR. The storage container 15 of the SQUID 10 to be used is installed.

In FIG. 6, the front-stage circuit unit 21 is attached to an outer wall located diagonally above the dewar 14 in, for example, the shield material 90 of the magnetic shield room MSR, as in FIG. Then, the cable SQC extending from the duwa 14 is connected to the front-stage circuit portion 21 through a through hole provided in the wall portion diagonally above the duwa 14. The cable FLC connecting the front-stage circuit unit 21 and the rear-stage circuit unit 22 is wired in the external space SOUT outside the magnetic shield room MSR.

As a result, the internal space SIN of the magnetic shield room MSR can be effectively used as in FIGS. 2 and 5. Further, the cable SQC can be guided to the cable insertion port of the Duwa 13 according to gravity, and the influence of the load of the cable SQC applied to the cable insertion port can be reduced.

Here, in the cable SQC that connects the SQUID 10 and the feedback coil 36 to the front circuit unit 21, the length of the cable SQC from the front circuit unit 21 to the outer surface of the shield material 90 is the length of the cable SQC from the SQUID 10 and the feedback coil 36 to the shield material 90. It is relatively short compared to the length of the cable SQC to the inner surface. That is, the length of the cable SQC from the front circuit portion 21 to the outer surface of the shield material 90 is relatively short compared to the length of the cable SQC from the dewa 14 to the inner surface of the shield material 90.

As in FIG. 3, as shown by the broken line frame (A), the front-stage circuit unit 21 may be placed on the floor surface at a position in contact with or close to the outer wall. Further, similarly to FIG. 5, when the front stage circuit unit 21 and the rear stage circuit unit 22 are installed outside the magnetic shield room MSR, the front stage circuit unit 21 and the rear stage circuit unit 22 are housed in separate housings. Will be done. This makes it possible to increase the degree of freedom in installing the front-stage circuit unit 21 and the rear-stage circuit unit 22 in the external space SOUT.

7 and 8 are explanatory views showing an example of a wiring path of the magnetic field measuring device 100A of FIG. The present inventors wired the cables SQC and FLC connecting the duwa 13, the front circuit unit 21, and the rear circuit unit 22 with seven wiring routes, and investigated the influence of noise on the SQUID 10 due to the difference in the wiring routes.

In case 1, the front-stage circuit unit 21 is placed on the upper surface of the duwa 13, and the cable SQC is connected from the front-stage circuit unit 21 to the inside of the duwa 13. The cable FLC is lowered from the front circuit portion 21 to the floor surface along the side surface of the duwa 13, and then routed around the bed 12. Then, the cable FLC is connected to the subsequent circuit portion 22 installed in the external space SOUT through a through hole provided on the floor side of the wall portion of the magnetic shield room MSR. In case 1, the length of the cable SQC can be minimized, but the length of the cable FLC routed in the magnetic shield room MSR becomes long.

In the case 2, the case 3 and the case 4, the front stage circuit unit 21 is placed on the floor surface at a position in contact with or close to the inner wall of the magnetic shield room MSR (Note that FIG. 7 shows the front stage circuit unit 21 in the magnetic shield room). An example of contacting the inner wall of the MSR is shown). In the case 2, the case 3, and the case 4, the cable SQC is pulled upward from the front circuit unit 21 along the inner wall of the magnetic shield room MSR, and then connected to the inside (SQUID) of the duwa 13. The length of the cable SQC in the case 2, the case 3 and the case 4 is longer than that in the case 1. Although not particularly limited, for example, in Cases 2 to 4, the length of the cable SQC is 10 m.

In the case 2, the cable FLC is routed around the bed 12 after crossing the bed 12 at a position facing the front surface of the duwa 13 from the front circuit unit 21. Then, the cable FLC is connected to the subsequent circuit portion 22 installed in the external space SOUT through a through hole provided on the floor side of the wall portion of the magnetic shield room MSR. In case 2, the length of the cable FLC is as long as in case 1.

In the case 3, the cable FLC was pulled upward from the front circuit section 21 along the inner wall of the magnetic shield room MSR, then lowered to the through hole along the inner wall, and installed in the external space SOUT through the through hole. It is connected to the subsequent circuit unit 22. In the case 3, the cable FLC is as long as the cases 1 and 2, but is routed at a position away from the dewar 13.

In the case 4, the cable FLC is wired on the floor surface from the front stage circuit portion 21 to the through hole, and is connected to the rear stage circuit portion 22 installed in the external space SOUT through the through hole. In case 4, the length of the cable FLC can be minimized. For example, the length of the cable FLC of the case 3 is 8 m, and the length of the cable FLC of the case 4 is 1 m. For example, the size of the magnetic shield room MSR is that the wall surface with the through hole has a height of 2 m and a width of 3.6 m, and the depth is 2.3 m.

In FIG. 8, in the case 5 and the case 6, the front-stage circuit unit 21 is placed on the floor surface at a position in contact with or close to the outer wall of the magnetic shield room MSR. In the case 5 and the case 6, the cable SQC is drawn into the magnetic shield chamber MSR through a through hole in the wall portion of the magnetic shield chamber MSR facing the front circuit portion 21. After being wired to the floor surface along the inner wall, the cable SQC is pulled upward along the inner wall of the magnetic shield room MSR and connected from the upper part of the duwa 13 to the inside of the duwa 13.

In the case 5, the cable FLC is drawn into the internal space SIN from the pre-stage circuit portion 21 through a through hole provided on the floor side of the wall portion of the magnetic shield room MSR. The cable FLC drawn into the internal space SIN is wired around the bed 12 and is connected to the subsequent circuit unit 22 installed in the external space SOUT through the through hole again. In the case 5, as in the case 2 of FIG. 7, the cable FLC crosses the bed 12 at a position facing the front surface of the dewar 13. The length of the cable FLC in the case 5 is longer than that in the other cases. In the case 6, the cable FLC is not routed in the magnetic shield room MSR, is wired only in the external space SOUT, and is connected to the subsequent circuit unit 22.

In the case 7, the front-stage circuit unit 21 is installed on the shelf 80 attached to the inner wall of the magnetic shield room MSR diagonally above the dewar 13 as in FIG. 2. In the case 7, the cable SQC is lowered from the pre-stage circuit unit 21 toward the duwa 13 and connected to the inside of the duwa 13. Therefore, in the case 7, the length of the cable SQC is longer than that of the case 1, but shorter than that of the other cases 2 to 6 (for example, the length of the cable SQC of the case 7 is 2.2 m). ). In the case 7, the cable FLC is not routed in the magnetic shield room MSR, is wired only to the external space SOUT through the through hole provided in the wall portion, and is connected to the subsequent circuit portion 22.

9 to 12 are waveform diagrams showing the measurement results of the magnetic field noise in each of the cases shown in FIGS. 7 and 8. FIG. 9 shows the measurement results of the magnetic field noise in Case 1 and Case 2 shown in FIG. FIG. 10 shows the measurement results of the magnetic field noise in Cases 3 and 4 shown in FIG. FIG. 11 shows the measurement results of the magnetic field noise in the cases 5 and 6 shown in FIG. FIG. 12 shows the measurement result of the magnetic field noise in the case 7 shown in FIG.

In the waveforms of FIGS. 9 to 12, the magnetic field noise of 180 Hz is constantly observed as the third harmonic noise of the power supply noise of 60 Hz. Further, in Case 1, Case 2, Case 3 and Case 5, magnetic field noise unrelated to power supply noise is observed around 168 Hz. The magnetic field noise around 168 Hz in which the magnetic field noise was observed seems to be peculiar to the length of the cable FLC and the pre-stage circuit unit 21, but the noise source is unknown.

In Case 1, Case 2 and Case 5 where the cable FLC is routed near the Dewa 13, magnetic field noise of 168 Hz is clearly observed. Further, even in the case 3 in which the cable FLC is routed for a long time in the magnetic shield room MSR, a very small magnetic field noise of 168 Hz is observed.

On the other hand, in case 4 where the cable FLC is routed in the magnetic shield room MSR is short, and in case 6 and case 7 where the cable FLC is not routed in the magnetic shield room MSR, magnetic field noise of 168 Hz is not observed.

From the above, it can be seen that the closer the cable FLC is arranged to the Duwa 13, and the longer the cable FLC wiring is in the magnetic shield room MSR, the easier it is for the SQUID 10 to detect magnetic field noise. That is, it can be seen that there is a correlation between the positional relationship between the cable FLC and the Duwa 13 and the magnetic field noise detected by the SQUID 10. Further, it can be seen that there is a correlation between the length of the cable FLC in the magnetic shield room MSR and the magnetic field noise detected by the SQUID 10.

For example, if the front-stage circuit unit 21 is placed on the upper surface of the duwa 13 as in case 1, the installation area of the front-stage circuit unit 21 can be overlapped with the installation area of the duwa 13, and the inside of the magnetic shield room MSR can be overlapped. It can be used efficiently. However, when the cable FLC is routed near the duwa 13 by installing the pre-stage circuit unit 21 at a position close to the duwa 13, unnecessary magnetic field noise is generated. Alternatively, when the dewar 13 is installed away from the cable FLC in order to avoid the influence of magnetic field noise, the installation position of the dewa 13 is limited.

On the other hand, the minute signal output from the SQUID 10 to the cable SQC is less likely to be a source of noise because the change in amplitude is gentler than that of the digital signal. On the contrary, since the minute signal transmitted to the cable SQC is easily affected by radiation noise and the like, it is preferable that the length of the cable SQC is as short as possible.

Therefore, in order to suppress the magnetic field noise generated by the magnetic field measuring devices 100A and 100B, the cable FLC should not be routed in the magnetic shield room MSR, and the length of the cable SQC should be as short as possible. Is preferable. In order not to route the cable FLC into the magnetic shield room MSR, it is preferable that the front circuit unit 21 is installed in close proximity to or in contact with the inner wall or outer wall of the magnetic shield room MSR.

Further, when the pre-stage circuit unit 21 is installed in the magnetic shield room MSR, it is preferable that the pre-stage circuit unit 21 is in contact with the inner wall of the magnetic shield room MSR so that the cable FLC is not exposed in the magnetic shield room MSR. Further, when the front stage circuit unit 21 is installed outside the magnetic shield room MSR, it is preferable that the front stage circuit unit 21 is in contact with the outer wall of the magnetic shield room MSR so that the cable SQC is not exposed to the external space SOUT.

For example, a magnetic field measuring device that minimizes the magnetic field noise detected by the SQUID 10 can be configured by determining the installation position of the pre-stage circuit unit 21 according to the cases 4 and 7 that satisfy such conditions. .. From the examples of the case 4 and the case 7, the cable FLC (0 m, 1 m) from the front circuit portion 21 to the inner wall (or through hole) of the magnetic shield room MSR is relative to the length (10 m) of the cable SQC. As a result, the pre-stage circuit unit 21 is installed near the wall surface of the shield room.

Thereby, the measurement accuracy of the biomagnetic field signal by SQUID 10 can be improved. For example, by installing the pre-stage circuit unit 21 at the positions shown in FIGS. 2, 3, 5, and 6, the magnetic field noise detected by the SQUID 10 can be minimized.

(Third Embodiment)
FIG. 13 is a block diagram showing an example of the magnetic field measuring device according to the third embodiment of the present invention. The same elements as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The magnetic field measuring device 100C shown in FIG. 13 adopts an analog FLL method, and can be applied to a magnetoencephalograph, a spinograph, a magnetocardiograph, a myomagnetometer, or the like.

The magnetic field measuring device 100C has a SQUID 10, an analog FLL circuit 40, and a feedback coil 36. The analog FLL circuit 40 includes an amplifier 31, an integrator 43, an AD converter 44, and a voltage-current converter 35. The feedback coil 36 arranged close to the SQUID 10 may be included in the analog FLL circuit 40.

In the analog FLL circuit 40, the amplifier 31 and the voltage-current converter 35 are included in the pre-stage circuit unit 21 as in FIG. Further, in the analog FLL circuit 40, the integrator 43 and the AD converter 44 are included in the subsequent circuit unit 42.

For example, the front-stage circuit unit 21 is arranged together with the SQUID 10 in the magnetic shield room MSR, and the rear-stage circuit unit 42 is arranged outside the magnetic shield room MSR. As in FIG. 4, the front-stage circuit unit 21 may be installed outside the magnetic shield room MSR together with the rear-stage circuit unit 42.

The integrator 43 is an analog circuit and has the same function as the digital integrator 33 of FIG. As a result, the integrator 43 can integrate the change in the voltage of SQUID 10 (to be exact, the amplified voltage output from the amplifier 31) from the lock point of the Φ-V characteristic, and the integrated voltage (signal). Voltage) can be output to the voltage-current converter 35 and the AD converter 44. The AD converter 44 converts the voltage from the integrator 43 into a digital value and outputs it to the data processing device 70.

In the magnetic field measuring device 100C, the installation example of the front-stage circuit unit 21 and the rear-stage circuit unit 42 is the same as in FIGS. 2, 3, 5, and 6 described above. That is, the front-stage circuit unit 21 is arranged at a position in contact with or close to the inner wall or outer wall of the shield material 90 of the magnetic shield room MSR. The subsequent circuit unit 42 is installed in the external space SOUT, which is outside the magnetic shield room MSR.

As a result, the magnetic field measuring device 100C of this embodiment can reduce the magnetic field noise generated in the magnetic shield room MSR in the same manner as the magnetic field measuring devices 100A and 100B described above, and the SQUID 10 detects the magnetic field noise. Can be prevented. As a result, the measurement accuracy of the biomagnetic field signal by SQUID 10 can be improved.

In the above embodiment, the example in which the front stage circuit unit 21 is installed on the inner wall (inner surface) or the outer wall (outer surface) of the shield material 90 of the magnetic shield room MSR has been described, but the front stage circuit unit 21 is the shield of the magnetic shield room MSR. It may be installed on the ceiling of the material 90. At this time, the pre-stage circuit unit 21 may be installed either inside the magnetic shield room MSR (that is, the inner surface of the shield material 90) or outside (that is, the outer surface of the shield material 90).

Further, the pre-stage circuit unit 21 may be installed under the floor (that is, the outer surface of the shield material 90) when there is a space under the floor of the shield material 90 of the magnetic shield room MSR.

(Comparative Example 1)
FIG. 14 is a layout diagram showing an example (comparative example) of installation of another magnetic field measuring device. The same elements as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. The magnetic field measuring device 110A shown in FIG. 14 is a magnetoencephalograph, but may be a magnetoencephalograph, a magnetocardiograph, a myomagnetic meter, or the like. In the magnetic field measuring device 110A, the FLL circuit 50 is installed inside the magnetic shield room MSR.

For example, the FLL circuit 50 is a digital FLL circuit, and includes a front-stage circuit unit 21 and a rear-stage circuit unit 22 shown in FIG. Alternatively, the FLL circuit 50 is an analog FLL circuit, and includes a front-stage circuit unit 21 and a rear-stage circuit unit 42 shown in FIG.

The FLL circuit 50 is connected to the duwa 13 via a cable SQC. Further, the FLL circuit 50 is connected to the power supply device 60 and the data processing device 70 installed outside the magnetic shield room MSR via a plurality of electric cable PCCs including a signal cable and a power supply cable. Hereinafter, the electric cable PCC is also simply referred to as a cable PCC.

In the configuration shown in FIG. 14, since the FLL circuit 50 is installed in the internal space SIN of the magnetic shield room MSR, the SQUID 10 (not shown) arranged in the dewar 13 is the FLL circuit 50 (particularly, the subsequent circuit units 22 and 42). There is a risk of detecting the radiated magnetic field noise generated in. Further, since the cable PCC including the power cable for supplying power to the FLL circuit 50 is wired in the magnetic shield room MSR, the SQUID 10 may detect the radiated magnetic field noise generated from the cable PCC.

On the other hand, the cable SQC connecting the SQUID 10 and the amplifier 31 of the FLL circuit 50 can have the same length as the cable SQC shown in FIGS. 2 and 3. Therefore, the influence of noise on the minute signal transmitted to the cable SQC can be reduced.

Further, when the FLL circuit 50 is installed in the magnetic shield room MSR, the available space in the internal space SIN becomes narrow. As a result, when it is necessary to increase the magnetic shield room MSR, the cost of the magnetic field measurement system including the magnetic field measuring device 110A and the magnetic shield room MSR increases.

(Comparative Example 2)
FIG. 15 is a layout diagram showing another example (comparative example) of installation of another magnetic field measuring device. The same elements as those in FIGS. 2 and 14 are designated by the same reference numerals, and detailed description thereof will be omitted. The magnetic field measuring device 110B shown in FIG. 15 is a magnetoencephalograph, but may be a magnetoencephalograph, a magnetocardiograph, a myomagnetic meter, or the like. In the magnetic field measuring device 110B, the FLL circuit 50 is installed outside the magnetic shield room MSR.

The cable SQC connected to the SQUID 10 (not shown) in the Duwa 13 is connected to the FLL circuit 50 through a through hole provided in the wall portion of the magnetic shield room MSR. The FLL circuit 50 is connected to the power supply device 60 and the data processing device 70 installed outside the magnetic shield room MSR via a plurality of cable PCCs including a signal cable and a power supply cable.

In the configuration shown in FIG. 15, since the FLL circuit 50 is installed outside the magnetic shield room MSR, there is no possibility that the SQUID 10 will detect the radiated magnetic field noise generated from the FLL circuit 50 or the cable PCC. On the other hand, since the cable SQC is wired up to the FLL circuit 50 installed outside the magnetic shield room MSR, the minute signal transmitted to the cable SQC may be affected by noise. Since the FLL circuit 50 is installed outside the magnetic shield room MSR, the internal space SIN of the magnetic shield room MSR can be effectively used.

Although the present invention has been described above based on each embodiment, the present invention is not limited to the requirements shown in the above embodiments. With respect to these points, the gist of the present invention can be changed without impairing the gist of the present invention, and can be appropriately determined according to the application form thereof.

10 SQUID
12 Bed 13, 14 Dewa 15 Storage container 20 Digital FLL circuit 21 Front circuit section 22 Rear circuit section 31 Amplifier 32 AD converter 33 Digital integrator 34 DA converter 35 Voltage current converter 36 Feedback coil 37 Power cable 38 Amplifier output line 39 Voltage line 40 Analog FLL circuit 42 Later circuit part 43 Integrator 44 AD converter 50 FLL circuit 60 Power supply device 70 Data processing device 80 Shelf 90 Shielding material 100A, 100B, 100C Magnetic field measuring device 110A, 110B Magnetic field measuring device FLC electric cable MSR Magnetic Shield Room PCC Electrical Cable SIN Internal Space SOUT External Space SQC Electrical Cable

Japanese Unexamined Patent Publication No. 11-118893

Claims (12)

Superconducting quantum interference device and
It has a front-stage circuit unit including an amplifier connected to the output of the superconducting quantum interference element, and a magnetic flux lock loop circuit including a rear-stage circuit unit connected to the front-stage circuit unit.
The pre-stage circuit portion is installed along the inner surface or the outer surface of the shield material that separates the inside and the outside of the magnetic shield room in which the superconducting quantum interference element is installed.
The subsequent circuit unit is a magnetic field measuring device characterized in that it is installed outside the magnetic shield room. The magnetic flux lock loop circuit includes an analog circuit and a digital circuit.
The pre-stage circuit unit includes only the analog circuit.
The magnetic field measuring device according to claim 1, wherein the digital circuit is included in the subsequent circuit section. According to claim 1 or 2, the cable length from the pre-stage circuit portion to the shield material is relatively shorter than the cable length between the superconducting quantum interference element and the pre-stage circuit portion. The magnetic field measuring device described. The magnetic field measuring device according to any one of claims 1 to 3, wherein the front-stage circuit unit is installed in contact with the inner surface or the outer surface of the shield material. The magnetic field measuring device according to claim 4, wherein the front-stage circuit unit is attached to the inner surface or the outer surface of the shield material. The magnetic field measuring device according to any one of claims 1 to 4, wherein the front-stage circuit unit is installed on a shelf provided on the inner surface or the outer surface of the shield material. The magnetic field measuring device according to any one of claims 1 to 4, wherein the front-stage circuit unit is installed on a floor surface inside or outside the magnetic shield room. Further having a cooling container in which the superconducting quantum interference element is housed,
The magnetic field according to any one of claims 1 to 6, wherein the pre-stage circuit portion is installed at a position higher than the upper surface of the cooling container on the inner surface or the outer surface of the shield material. Measuring device. The magnetic field measurement according to any one of claims 1 to 8, wherein the cable connecting the front-stage circuit unit and the rear-stage circuit unit is wired except for the inside of the magnetic shield chamber. apparatus. Claims 1 to 9 are characterized in that, when the front-stage circuit portion is arranged along the outer surface of the shield material, the front-stage circuit portion and the rear-stage circuit portion are housed in different housings from each other. The magnetic field measuring device according to any one of the above. The latter-stage circuit unit
An AD converter that converts the signal amplified by the amplifier into a digital value,
An integrator that integrates the digital values converted by the AD converter, and
It has a DA converter that converts the integrated value integrated by the integrator into a voltage.
The pre-stage circuit section further
A voltage-current converter comprising a voltage-current converter that converts a voltage converted by the DA converter into a current and supplies the converted current to a coil installed in the vicinity of the superconducting quantum interference element. The magnetic field measuring device according to any one of claim 10. The latter-stage circuit unit
An integrator that integrates the signal amplified by the amplifier, and
It has an AD converter that converts the signal integrated by the integrator into a digital value, and
The pre-stage circuit section further
A voltage-current converter comprising a voltage-current converter that converts a signal voltage integrated by the integrator into a current and supplies the converted current to a coil installed in the vicinity of the superconducting quantum interfering element. The magnetic field measuring device according to any one of claim 10.

Images