JP3156396B2 - Differential SQUID magnetometer and biomagnetic field measurement device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called SQUID magnetometer using a SQUID. Especially thin film type SQUI
D-type magnetometer (hereinafter, also simply referred to as "SQUID magnetometer") and a differential SQUID magnetometer suitable for a biomagnetometer for performing biomagnetic measurement using multiple channels using the same, and a SQUID magnetic flux using the same Meter system.

[0002]

2. Description of the Related Art As an example of a conventional SQUID magnetometer, an example of a so-called magnetometer in which a detection coil does not have a differential configuration is shown in FIG. The magnetic flux detected by the detection coil 30 is transmitted to the SQUID 20 through the input coil 11. The SQUID is a superconducting ring having two weakly-coupling portions (indicated by x in the figure) as schematically shown in FIG.
The SQUID outputs this magnetic flux in the form of a voltage by driving using a known feedback circuit called FLL.
Here, the modulation magnetic flux is input to the SQUID via the modulation coil 12. The feedback magnetic flux is input to the detection coil via the feedback coil 13. In a magnetometer, the detection coil detects noise flux as well as signal flux. Since the noise magnetic flux is generally five orders of magnitude greater than the brain magnetic field, when measuring the brain magnetic field using a magnetometer, a magnetically shielded room having a shielding rate of 4 to 5 digits against an external magnetic field is required. Examples of SQUIDs for magnetometers include Biomagnetism '87, (1988), 446th to 4th.
49 (Biomagnetism '87 (1988), pp. 446-449). When a brain magnetic field is measured in a simple shielded room having a shielding rate of about two to three digits, a gradiometer having a differential detection coil is generally used (see FIG. 8 for a conventional gradiometer). Is shown.) Gradiometers have better performance as the upper and lower coils have equal areas and are parallel. Japanese Patent Application Laid-Open No. Sho 61-122585 discloses an example in which a coil is made of a thin film instead of a wire such as an Nb-Ti wire in order to realize a high-performance gradiometer. Biomagnetism '89, (1989), 6th
69-672 (Biomagnetism '89 (1989), pp. 669-67)
As described in 2), the sensor of the magnetoencephalograph has a structure in which 30 to 40 such gradiometers are arranged in parallel.

[0003]

As shown in the above-mentioned known example of the gradiometer, it is practical that the coil portion requiring a large area and the SQUID requiring high processing accuracy are formed on separate substrates. In this case, the coil and SQUID
Superconducting joints between them are needed. Superconducting joints are required to have sufficiently high reliability against thermal cycling between room temperature and helium temperature and aging. In addition, it is not possible to prevent the inductance from being parasitic at this junction, and there is a possibility that external electromagnetic noise may enter. An object of the present invention is to realize a thin-film SQUID magnetometer that operates in a simple magnetically shielded room and does not require a superconducting junction, and a SQUID magnetometer system using a plurality of such SQUID magnetometers.

[0004]

SUMMARY OF THE INVENTION At least two magnetometers using a SQUID that has a detection coil, an input coil, a feedback coil, a modulation coil, and a SQUID and operates in a flux locked loop (FLL) are provided. Then, the signal generated by at least one magnetometer is magnetically applied to at least one other magnetometer. Differential SQUI
In the D magnetometer, a signal line for magnetically applying a signal generated by at least one magnetometer to at least one other magnetometer is set to a normal conduction at an operating temperature of the magnetometer, and the generation of the at least one magnetometer is performed. To the detection coil of at least one other magnetometer, the signal generated by the at least one magnetometer is used as the return magnetic flux of the magnetometer, and the return magnetic flux of the at least one magnetometer is used as the magnetometer. To the detection coil. In the differential SQUID magnetometer,
A detection coil, an input coil, a feedback coil, a modulation coil, and a coil for magnetically applying a signal from another magnetometer are formed on one substrate for each magnetometer. The sensitivity, which is the output voltage per detected magnetic flux of the cancellation magnetometer, which is a magnetometer that gives signals to other magnetometers, is the same as the detected magnetic flux of the sensing magnetometer, which is a magnetometer that can receive signals from other magnetometers. Higher than the output voltage of the sensitivity. Further, a SQUID magnetometer system is configured by using a plurality of sets of differential SQUID magnetometers each including one sensing magnetometer connected to one of the cancellation magnetometers. Also, a plurality of sensing magnetometers are connected to one of the cancellation magnetometers to constitute a differential SQUID magnetometer that enables selection of which cancellation magnetometer operates. SQUID using multiple sets of differential SQUID magnetometers
Construct a magnetometer system. In these SQUID magnetometer systems, the number of sensing magnetometers is larger than that of cancellation magnetometers, and the modulation frequency is different at least between adjacent differential SQUID magnetometers. To summarize briefly, a set of SQUID magnetometers for sensing and cancellation are used, and the return magnetic flux of the magnetometer for cancellation is detected not only by the detection coil of the magnetometer for cancellation but also by the detection coil of the magnetometer for sensing. Also magnetically coupled. The sensitivity of the magnetometer, which is defined as the output voltage per detected magnetic flux, is set to be higher in the sensing magnetometer than in the cancellation magnetometer. Further, when a plurality of the magnetometers are used to form a magnetometer system, at least adjacent magnetometers are set to have different modulation frequencies. A detection coil, an input coil, a feedback coil, a modulation coil, and a coil for magnetically applying a signal from another magnetometer are formed on one substrate for each magnetometer.

[0005]

[Function] The cancelation magnetometer mainly relates to measurement of noise magnetic flux. As is apparent from the operation of the FLL, this feedback magnetic flux is approximately equal to the amount of noise magnetic flux. This is also input to the detection coil of the sensing magnetometer to cancel out the noise magnetic flux, so that only the signal magnetic flux is input to the detection coil of the sensing magnetometer. When the sensing magnetometer detects this, one set of magnetometers operates similarly to the gradiometer. A signal line connecting the cancellation magnetometer and the sensing magnetometer may be a normal conductor. Since the magnetometer has high sensitivity per magnetic flux density, the area of the detection coil may be smaller than that of the gradiometer. Therefore, as shown in the known example, all of the detection coil, SQUID, feedback coil, and modulation coil can be formed in a thin film on the same substrate, and a superconducting junction is unnecessary. Here, in the simple shielded room, since the noise magnetic flux is about three orders of magnitude larger than the signal magnetic flux, it is effective to set the sensitivity of the cancellation magnetometer lower than that of the sensing magnetometer. Still further, the SQUID according to the present invention
When a magnetoencephalography measurement device is configured using a plurality of magnetometers, interference between sensors does not occur because the modulation frequency is different between magnetometers that may be spatially magnetically coupled.

[0006]

FIG. 1 shows a differential type S according to a first embodiment of the present invention.
It is a figure showing composition of a QUID magnetometer. Using two SQUID magnetometers similar to the magnetometer of FIG.
One set of differential SQ with one as a magnetometer for cancellation and the other as a magnetometer for sensing
Construct a UID magnetometer. The sensing magnetometer is provided with a noise canceling coil 34, which is connected in series with the feedback coil 13a of the cancellation magnetometer. M1 is a detection coil 10 and a feedback coil 13
M2 is a mutual inductance between the detection coil 30 and the noise canceling coil 34, and M1 is
= M2. The detection coil 10 of the cancellation magnetometer and the detection coil 30 of the sensing magnetometer are formed on the same axis and have the same area. That is, the structure is similar to that of the conventional gradiometer of FIG.
Although omitted in the figure, the whole is 3
It is placed in a magnetic shield room of about an order of magnitude, and the sensitivity of the cancellation magnetometer is set to about two orders of magnitude lower than that for sensing. In this configuration, the coil area does not necessarily have to be equal for cancellation and for sensing. When the coil area for cancellation is S1 and the coil area for sensing is S2, M1: M2 = S1: S2. I just need. Next, the operation of each magnetometer will be described. The canceling magnetometer uses the magnetic flux passing through the detection coil 10 as FL.
It operates so as to be canceled by the magnetic flux of the feedback coil 13a from L25a. The current flowing through the feedback coil 13a also flows through the noise canceling coil 34 of the sensing magnetometer, and simultaneously cancels the magnetic flux passing through the sensing coil 30 of the sensing magnetometer. The magnetic flux detected by the detection coil 10 of the cancellation magnetometer includes a signal magnetic flux and a noise magnetic flux.
1000 times larger. Therefore, the magnetic flux that the feedback coil 13a and the noise canceling coil 34 of the cancellation magnetometer give to the detection coil is exclusively a noise magnetic flux. As a result, the detection coil 30 of the sensing magnetometer exclusively detects the signal magnetic flux. Therefore,
The output of the sensing magnetometer may be considered as the difference output between the coil 10 and the coil 30.

FIG. 2 shows a differential type S according to a second embodiment of the present invention.
It is a figure showing composition of a QUID magnetometer. FIG. 2 shows an embodiment in which the feedback coil 13 of the cancellation magnetometer is connected to the feedback coil 13b of the sensing magnetometer. Here, in the canceling magnetometer and the sensing magnetometer, the mutual inductance between the feedback coil and the detecting coil is equal, and M1 = M
2. According to this configuration, there is an effect that the noise canceling coil becomes unnecessary. FIG. 3 is a diagram showing a configuration of a differential SQUID magnetometer according to a third embodiment of the present invention. FIG. 3 shows an embodiment in which the feedback output of the cancellation magnetometer is divided into the feedback coil 13a of the cancellation magnetometer and the noise canceling coil 34 of the sensing magnetometer. Each is provided with means for adjusting the amount of current (variable resistors 32 and 35 in this embodiment). According to the present embodiment, the amount of magnetic flux input to each of the detection coils 10 and 30 can be finely adjusted. In particular, even when M1 and M2 are different, there is an effect that the noise cancellation rate does not decrease. In the present invention, the SQUID is used after being exposed to an external magnetic field. S
In order to reduce the influence of an external magnetic field on the QUID, a known differential SQUID is useful. FIG. 5 is a schematic diagram showing an embodiment of the differential SQUID according to the present invention. The SQUIDs shown in FIGS. 5A, 5B and 5C are SQUIDs.
Since the ID itself forms a gradiometer and does not detect noise, there is an effect that the SQUID does not malfunction.
On the other hand, in order to increase the amount of magnetic flux to be detected, for example, IEE Transactions on Magnetics Vol. 27, No. 2, (1991) pp. 3001 to 3004 (I
EEE Transactions on Magnetics, vol. 27, no. 2, 1991, pp.
A directly coupled magnetometer as known from 3001 to 3004) is useful. FIG. 9 shows an equivalent circuit diagram of the detection coil and the SQUID.

In FIGS. 1 to 4, the inside of the dotted line is formed on one substrate. FIG. 6 shows an embodiment of this substrate. The substrate 5 is silicon. Each of the detection coils 10 and 30, the feedback coil 13, and the noise canceling coil 34 is formed of a thin niobium wire. Reference numeral 20 denotes a known Ketjen-type SQUID or differential SQUID, and a signal terminal, a bias current terminal 21, and a modulation coil terminal 22 are formed from the SQUID. FIG. 7 shows another embodiment of the substrate. Coil 1
The configuration is such that the area of 0, 30 is maximized on the substrate. According to this configuration, the effective area of the coil becomes large, especially when it is mounted on a multi-channel biomagnetometer,
/ N is improved. FIG. 10 shows a first embodiment of a 37-channel biomagnetism measuring apparatus constituted by using the 74 substrates shown in FIG. 110 is a FLL unit, 100 is a liquid helium dewar, and only the lower part shows the internal structure. The upper plate 120 is provided with a cancellation magnetometer, and the lower plate 130 is provided with 37 sensing magnetometers. Here, when interference between channels becomes a problem, the modulation frequency is configured to be different at least between adjacent channels. Reference numeral 140 denotes a flexible board on which signal lines are mounted, which is connected to the upper FLL. The subject places the measurement site directly below the Dewar. The device and the subject are placed in a simple magnetically shielded room. In this embodiment, the magnetometers corresponding to the upper and lower phases are connected one-to-one, but another embodiment relating to the configuration of the magnetometer is shown in FIGS. FIG. 11 is a diagram showing a configuration of a differential SQUID magnetometer according to a fourth embodiment of the present invention.
FIG. 11 shows an embodiment in which three cancellation magnetometers are connected to one sensing magnetometer. The operation of the magnetometer of this configuration is the same as that of the configuration of FIG. 1, but which of the three cancellation magnetometers is used for measurement can be selected by the selection circuit 36 and the control input. . This configuration has an effect that the distance between the magnetometer for sensing and the magnetometer for cancellation (so-called baseline) can be selected depending on the depth of the measurement target. Here, there is no need to use a superconducting switch when selecting a baseline, and the reliability is high. It is needless to say that a 37-channel biomagnetic measurement device with a variable baseline can be configured by using 37 sets of these, for example. FIG. 12 shows a 37-channel biomagnetic measurement apparatus according to a second embodiment in which four cancellation magnetometers are provided for one set of sensing magnetometers. Nine or ten sensing magnetometers are connected to one cancellation magnetometer. In this configuration, although the noise cancellation rate is lower than in the embodiment of FIG. 10, the number of cancellation magnetometers can be reduced and the system configuration can be simplified.

[0009]

According to the present invention, a differential SQUID magnetometer which does not require a superconducting junction operates in a simple magnetic shield room having a shielding rate of about 2 to 3 digits for an external magnetic field. effective. In addition, since the detection coil having a three-dimensional structure can be formed of a thin film, there is an effect that at least a four-digit cancellation rate can be obtained. Further, according to the present invention, when a magnetoencephalography measurement device is configured using a plurality of the SQUID magnetometers, there is an effect that interference between the magnetometers does not occur due to interference of a modulated signal carrying a signal. . No superconducting joint is needed between the magnetometers,
High reliability.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a differential SQUID according to a first embodiment of the present invention;
The figure which shows the structure of a magnetometer.

FIG. 2 is a diagram showing a differential SQUID according to a second embodiment of the present invention;
The figure which shows the structure of a magnetometer.

FIG. 3 is a diagram showing a differential SQUID according to a third embodiment of the present invention;
The figure which shows the structure of a magnetometer.

FIG. 4 is a conventional example of a magnetometer which is an example of a SQUID magnetometer.

FIG. 5 is a schematic diagram showing an embodiment of a differential SQUID according to the present invention.

FIG. 6 is a first embodiment of a SQUID substrate according to the present invention.

FIG. 7 shows a second embodiment of the SQUID substrate according to the present invention.

FIG. 8 is a schematic diagram showing a conventional gradiometer.

FIG. 9 is an equivalent circuit diagram of a detection coil and a SQUID.

FIG. 10 is a first embodiment of a biomagnetic measurement apparatus using a SQUID substrate according to the present invention.

FIG. 11 is a diagram illustrating a differential SQUID according to a fourth embodiment of the present invention;
The figure which shows the structure of a D magnetometer.

FIG. 12 is a second embodiment of the biomagnetic measurement apparatus using the SQUID substrate according to the present invention.

[Explanation of symbols]

5, 5A, 5B, 5C, 7 ... SQUID element substrate, 10
... Detection coils (for cancellation), 11, 11
a, 11b: input coil, 12, 12a, 12b: modulation coil, 13, 13a, 13b: feedback coil, 20, 2
0a, 20b SQUID, 21 bias current, signal voltage terminal, 22 modulation coil terminal, 25a, 25b F
LL, 30: detection coil (for sensing), 34: noise canceling coil, 36: selection circuit, 100: liquid helium dewar, 110: FLL part, 120: magnetometer board for cancellation, 130: magnetometer board for sensing, 140: Signal line substrate.

Continuing on the front page (72) Inventor Akihiko Kamtori 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. References JP-A-63-32384 (JP, A) JP-A-4-134878 (JP, A) JP-A-2-96677 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name ) G01R 33/00-33/18

Claims (8)

(57) [Claims] 1. A cancellation for detecting noise magnetic flux
For SQUID magnetometer and sensing to detect signal magnetic flux
Having a SQUID magnetometer for the cancellation
The signal generated by the SQUID magnetometer is sent to the sensing S
A differential type SQUID magnetometer characterized by applying a voltage to a detection coil of a QUID magnetometer . 2. A differential SQUID magnetometer according to claim 1, wherein said cancellation SQUID magnetometer is generated.
The signal to be transmitted is the SQUID magnetic flux for cancellation.
Differential SQUID characterized by the feedback magnetic flux of the meter
Magnetometer. 3. A differential SQUID magnetometer according to claim 1, wherein said cancellation SQUID magnetometer is generated.
Signal to the sensing SQUID magnetometer
A differential SQUID magnetometer characterized in that a signal line applied to the SQUID is a normal conductor . 4. The differential type SQUID magnetometer according to claim 1, wherein said canceling SQUID magnetometer has a sensitivity.
Is lower than the sensitivity of the SQUID magnetometer for sensing.
A differential type SQUID magnetometer characterized in that it is set to a high value. 5. The differential type SQUID magnetometer according to claim 1, wherein a plurality of said sensing SQUID magnetometers are provided.
SQUID magnetometer for cancellation is connected
The cancellation SQUID magnet to be operated
A differential type S having means for selecting a bundle meter
QUID magnetometer. 6. The differential SQUID magnetometer of claim 1, wherein the number of said sensing SQUID magnetometers is
Larger than the number of SQUID magnetometers for
SQUID magnetometer, characterized in that that. 7. The differential type S according to claim 5 or claim 6.
Using a plurality of QUID magnetometer differential adjacent at least
Different modulation frequencies between SQUID magnetometers
Characteristic biomagnetic field measurement device. 8. For cancellation for detecting noise magnetic flux.
For SQUID magnetometer and sensing to detect signal magnetic flux
Use with a set of SQUID magnetometer and cancel
The return magnetic flux of the SQUID magnetometer for
Detection coil of the SQUID magnetometer for
Magnetically coupled to the detection coil of the SQUID magnetometer
Differential SQUID magnetometer, characterized in that that.