JP2000284032A - Squid flux meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To also apply to a high-temperature superconductive SQUID where spatially three-dimensional pickup coil cannot be formed easily by applying a feedback magnetic flux with a size that is proportional to the output of the drive circuit of one of at least three SQUIDs to at least one of the SQUIDs. SOLUTION: The SQUID flux meter is provided with at least three SQUIDs 11a-14a, drive circuits 11b-14b for independently driving each of the SQUIDs 11a-14a, and feedback coils 11c-14c for feeding back magnetic flux with a size being proportional to the output of the drive circuit being mounted to each of the SQUIDs. Then, feedback magnetic flux with a size that is proportional to the output of the drive circuit of one of the SQUIDs 11a-14a is applied to at least one of the SQUIDs via the feedback coils 11c-14c of the SQUID. Also, feedback magnetic flux with a size being proportional to the output of the drive circuit of the SQUID other than the SQUIDs is additively applied to one SQUID via a feedback coil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SQUID (Superconducting Quantum Interference Device).
Unantum Interference Device
e) SQUID using a highly sensitive magnetic sensor called
The present invention relates to a magnetometer, and more particularly to a SQUID magnetometer using a high-temperature superconducting SQUID as a SQUID and employing a gradiometer effective for removing extraneous magnetic noise. This SQUID magnetometer is suitable mainly for a biomagnetism measuring device.

[0002]

2. Description of the Related Art At present, multi-channel SQUID magnetometers using a large number of SQUIDs have been actively developed, and biomagnetic measurements such as magnetoencephalograms and magnetocardiograms using such magnetometers have been studied. This biomagnetic measurement has already been found to be effective for research on cerebral physiology and diagnosis of ischemic heart disease and arrhythmia.

[0003] Since the SQUID that operates at extremely low frequencies requires a large-scale cooling mechanism, there is a problem that the overall configuration of the biomagnetism measuring apparatus is large and the operating cost is high.

Under these circumstances, in recent years, SQUIDs using a high-temperature superconducting material are approaching practical use. High temperature superconducting S
The QUID can be cooled with liquid nitrogen, which is easy to handle. For this reason, by incorporating the high-temperature superconducting SQUID into the biomagnetism measuring device, it is expected that a particularly large-scale cooling mechanism is not required, and that the entire device can be prevented from being large-sized and the operating cost can be reduced. I have.

[0005] When measuring biomagnetism using a SQUID magnetometer, the magnetic field generated from a living body is extremely weak.
Unless this is called "environmental magnetic field"), effective measurement cannot be expected. For this reason, the technology for removing the environmental magnetic field has formed one of the main fields of biomagnetic measurement.

FIG. 13 shows some conventional methods for removing an environmental magnetic field. FIG. 1A is called a primary differential pickup (detection) coil for detecting magnetic flux used in a SQUID magnetometer. This pickup coil is a coil adopted mainly for a SQUID magnetometer operating at liquid helium temperature, and two loops are wound in opposite directions by a superconducting wire. This first-order differential pickup coil exhibits a highly sensitive detection characteristic for magnetic fields generated from the vicinity of the coil, such as the heart and the brain, but has two coils for environmental magnetic fields generated at a distance. Since magnetic fluxes of almost the same magnitude are linked, canceling is performed.

FIG. 1B shows a pickup coil in which two first-order differential pickup coils described above are connected in a state of being superimposed in the central axis direction in opposite directions. This pickup coil is called a second-order differential type pickup coil, and can exhibit a higher removing ability of the environmental magnetic field than the first-order differential type. A magnetometer provided with these differential pickup coils and measuring a gradient component of a magnetic field is called a “gradiometer”.

[0008] A technique for electrically or softwarely implementing the gradiometer is described in, for example, US Pat.
122,744, JP-A-4-264281, JP-A-5-232202 and JP-A-6-138197. These electrical or software methods can be applied to a SQUID magnetometer for cryogenic use, but it is difficult to form a big coil as shown in FIGS. 13 (a) and 13 (b). The present invention can be suitably applied to a SQUID magnetometer.

[0009] Among them, in particular, Japanese Patent Laid-Open No. 5-232202.
Japanese Patent Application Laid-Open No. H11-163,887 discloses an example of configuring a second-order derivative gradiometer by software, which is schematically shown in FIG. According to the figure, four magnetometers are used, a difference between outputs of two magnetmeters among them is calculated, an output of a first derivative is obtained, and a difference between the difference outputs is calculated again. By performing the calculation, the output of the second derivative is obtained. In addition, a reference magnet meter is prepared separately, and a current proportional to the measured value of the reference magnet meter is supplied to the other four magnet meters as a compensation current, so that the input is common to the four magnet meters. A spatially uniform environmental magnetic field having a large value is subtracted from each detected value in advance.

[0010] By configuring the second-order differential gradiometer in this way, the ability to remove the environmental magnetic field can be increased as compared with the first-order differential gradiometer. Naturally, the more a gradiometer having a higher differential order such as the third order or higher is configured, the more the environmental magnetic field can be removed up to the higher order components.

[0011]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open Publication No.
The secondary differential gradiometer described in No. 32202 calculates a difference after removing a uniform component of an environmental magnetic field having a large value in advance, so that even if the dynamic range of each magnetometer is small, one step is required. The primary differential output value, which is the output of the eye difference calculation, can provide a highly accurate measurement value.

However, in the second derivative gradiometer described in the publication, the environment magnetic field includes the same.
There is a problem that the ability to remove a first-order gradient component of a magnetic field having a large value is extremely low.

That is, most of the first-order gradient components are mixed in the two first-order differential outputs. Therefore, a small secondary gradient component included in a primary gradient component of a large environmental magnetic field must be extracted by the second-stage difference calculation. Therefore, in order to obtain the secondary differential output value with high accuracy, a large dynamic range and strict gain setting are required for the primary differential output value. In order to secure a large dynamic range and a strict gain setting for the primary differential output value, it is necessary to increase the dynamic range of each magnet meter. Therefore, SQUI
Strict gain settings for the D drive circuit and each amplifier are required.

For example, the peak value of the uniform component of the environmental magnetic field is about 10 nT, the beak value of the primary gradient component is about 100 p１００,
The beak value of the secondary gradient component is lpｌ, and the environmental magnetic field per unit frequency is 100 pT / √Hz for the uniform component, 1 pT / √Hz for the primary gradient component, and 10 fT / √Hz for the secondary gradient component.
Suppose that it is desired to measure with a minimum resolution of 10 fT / √Hz.

In this case, since a signal of 100 pT is output to the output of each magnet meter and the primary differential output at the peak, the minimum resolution of the primary differential output is 100 pT while maintaining at least 10 fT / √Hz or less. It must be designed so that it does not run off at the peak value of. The signal value of the primary differential output is 1 pT / √Hz per unit frequency, and since it is necessary to extract a signal of 10 fT / √Hz from this, the gain setting accuracy of each magnetometer, amplifier, and difference calculator is required. In addition, the in-phase signal rejection ratio of the first-stage difference operation and the second-stage difference operation needs to be at least 40 dΒ or more. Further, since it is necessary to take out a first-order differential output having a minimum resolution of 10 fT / √Hz from a difference including a uniform component of the environmental magnetic field of 100 pT / √Hz, the uniform component of the magnetic field is obtained by a reference magnetometer. The amount of compensation given to each magnetometer to eliminate it must be matched with an accuracy of 80 dB.

In the case of the conventional example described in this publication, a compensation current adjusting circuit (variable resistor) is provided so as to match the amount of compensation given to each magnet meter with an accuracy of 80 dB. Is corrected.

However, it is troublesome to manually adjust the variation of all magnet meters. In addition, even after the adjustment is completed, the resistance value fluctuates with time due to a temperature change of the adjustment resistance or the wiring resistance, so that there is a problem that such adjustment must be performed frequently. Was.

In addition to the four magnet meters, there is another problem that a magnet meter must be separately added for reference.

The present invention relates to the above-mentioned JP-A-5-23220.
The high-temperature superconducting SQUID, which is made in consideration of the conventional problem seen in the second-order differential gradiometer described in No. 2 and is difficult to form a spatially three-dimensional big-up coil
SQUID as a high-order differential gradiometer that does not require a magnet magnet for reference, does not require frequent adjustment of a compensation current, and can realize a high removal rate of an environmental magnetic field. It is an object to provide a magnetometer.

[0020]

In order to achieve the above object, according to the SQUID magnetometer according to the present invention, three or more SQUIDs and a drive circuit for independently driving each of the three or more SQUIDs are provided. , A feedback coil attached to each of the three or more SQUIDs and for feeding back a magnetic flux having a magnitude proportional to the output of each of the drive circuits. And the three or more SQs
Means for applying to the at least one SUID of the UIDs a feedback magnetic flux having a magnitude proportional to the output of the drive circuit of the other SQUID via the feedback coil of the SQUID; Means for applying a feedback magnetic flux having a magnitude proportional to the output of the SQUID driving circuit to the at least one SQUID through a feedback coil of the SQUID. Thus, a secondary or higher order gradiometer is configured.

Further, by providing a fine adjustment circuit of the feedback gain in each drive circuit of the gradiometer configured as described above, it is possible to prevent a deterioration in output accuracy due to a minute variation of each SQUID.

According to another aspect of the present invention, a plurality of SQUIDs, a drive circuit for independently driving each of the plurality of SQUIDs, and a feedback coil attached to each of the plurality of SQUIDs are provided. SKU provided
In the ID magnetometer, means for applying a feedback magnetic flux of a magnitude proportional to the output of the drive circuit of the SQUID to each of the plurality of SQUIDs via the feedback coil of the SQUID; and a plurality of the plurality of SQUIDs. Means for additively applying a feedback current supplied to another one of the SQUIDs to each feedback coil, and at least one SQUID among a plurality of SQUIDs to which the feedback current is additively applied; Means for further applying a feedback current of a magnitude proportional to the output voltage of the drive circuit of the other SQUID of the plurality of SQUIDs to the feedback coil, and a conversion coefficient from the output voltage to the current. And a changeable means.

As described above, according to the present invention, a SQUID magnetometer having a secondary or higher order electric differential gradiometer is constituted. In summary of one embodiment of this configuration, two electric primary differential gradiometers are respectively constituted by magnetometers, and the feedback current of one primary differential gradiometer is added to the other primary differential gradiometer. In this configuration, the voltage is applied. With this configuration, it is not necessary to provide an extra magnetometer for removing a uniform magnetic field, and a high-order differential gradiometer having a wide dynamic range and excellent characteristics can be easily configured.

Further, according to another aspect of the present invention, in a SQUID magnetometer including a plurality of SQUIDs and a plurality of drive circuits for individually driving the plurality of SQUIDs, each of the plurality of SQUIDs is positive or negative. Means for providing at least one of an alternating bias current and a positive / negative modulation magnetic flux, and a modulation signal and a bias signal generated by a common oscillator for at least two of the plurality of driving circuits. Means for supplying at least one of the above, wherein the at least two drive circuits have means for demodulating the output of the SQUID using a reference signal based on the oscillation output of the common oscillator. .

For example, while feedback coils of at least two of the plurality of SQUIDs are connected in series with each other, a modulation current based on the oscillation output of the common oscillator is shared by the feedback coils connected in series. Means for supplying to the

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) A SQUID magnetometer according to a first embodiment will be described with reference to FIG. This embodiment shows a basic configuration for implementing the present invention.

This SQUID magnetometer is configured as an electric second derivative gradiometer using a magnetometer. SQUID built into each magnet meter
Is formed of a high-temperature superconducting material.

As shown in FIG. 2, the secondary differential gradiometer 1 has first to fourth four magnetometers 11 to 11.
14. Each magnet meter 11 (~ 1
4) a SQUID (superconducting ring) 11a (（14a) formed of a high-temperature superconducting material, a FLL (flux locked loop) circuit 11b (〜14b) for driving this SQUID, and a feedback coil for feeding back magnetic flux to the SQUID 11c (〜14c) and a feedback amplifier 11d (〜14c) inserted in a feedback loop connected to the feedback coil.
d). Gain of the feedback amplifier 11d~14d is β ₁ ~β ₄ respectively.

Of the four magnet meters, the second and fourth magnet meters 12 and 14 are provided with an adder circuit 15.
And 16 respectively. Each of the adders 15 and 16 is inserted between the feedback coil 12b (14b) and the amplifier 12d (14d) in the feedback loop. The addition circuits 15 and 16 receive the input from another magnet meter in addition to having the original feedback loop as one input, and apply their combined input to the SQ.
Feedback is provided to the UID.

Addition circuit 1 of second magnetometer 12
5 includes a FLL circuit 11 of the first magnetometer 11.
A branch path branched from the output end of the switch c is connected. Gain beta _'1 of the amplifier 17 is inserted in the branch path.

The adder circuit 16 of the fourth magnet meter 14 includes the second and third magnet meters 11
Are connected from the output ends of the FLL circuits 12c and 13c. These branches have a gain β ′ ₂
And β ′ ₃ amplifiers 18 and 19 are inserted respectively.

First to fourth magnet meters 11 to 14
A bias current is supplied to each of the SQUIDs 11a to 14a by a bias current supply circuit (not shown). Further, a modulation magnetic flux is applied to the SQUIDs 11 to 14 from a modulation circuit (not shown) in the FLL circuits 11c to 14c. The outputs of the SQUIDs 11a to 14a are amplified by amplifiers in the FLL circuits 11c to 14c, detected and demodulated by a detection circuit, integrated by an integrator, and further amplified as necessary, and output voltage V
1 (an amplifier, a detection circuit, an integrator, etc. are not shown).

[0034] In the first SQUID 11, the feedback circuit (loop) outputs "β" which is proportional to the output voltage V1.
A feedback magnetic flux having a magnitude of “ ₁ · V ₁ ” is applied to the SQUID 11a via the feedback coil 11b. FLL circuit 11c from that operate as externally applied SQUID11a, that is, magnetic flux [Phi ₁ and the feedback magnetic flux β ₁ · _{V 1} detected from the living body becomes equal,

[Number 1] Φ ₁ = β ₁ · _{V I,} and the output voltage _{V I} is

V ₁ = Φ ₁ / β ₁ That is, the first magnet meter 11 outputs an output voltage V _I proportional to the magnetic flux [Phi ₁ input.

The SQ of the second magnetometer 12
The UID 12a has its output voltage V ₂Is proportional to₂
・ V₂And the first magnetic flux.
Output voltage V of gnet meter 11₁“Β ′₁
・ V₁Flux with the feedback flux of the magnitude
Is applied. That is,

Φ ₂ = β ′ ₁ V ₁ + β ₂ V ₂ and the output voltage V ₂ is

V ₂ = (Φ ₂ − (β ′ ₁ / β ₁ ) Φ ₁ ) / β ₂ Accordingly, if the gains β ′ ₁ and β ₁ match, the second magnet meter 12 detects the magnetic flux Φ ₁ detected by the first magnet meter 11 and the magnetic flux Φ ₁ detected by the second magnet meter 12. the difference between [Phi _2, i.e. the magnetic flux 1
Voltage V ₂ (= (Φ ₂ −Φ ₁ ) /
β ₂ ) is output.

SQUID of third magnetometer 13
13a has “β ₃ ·· which is proportional to the output voltage V _3.
A feedback magnetic flux having a magnitude of “V ₃ ” is applied.
That is,

Φ ₃ = β ₃ V ₃ and the output voltage V ₃ is

V ₃ = Φ ₃ / β ₃ Therefore, the third magnetometer 13 outputs a voltage V ₃ which is proportional to the magnetic flux [Phi ₃ for its detection.

The SQUID of the fourth magnet meter 14
14a, the output voltage V of the second magnet meter 12
A feedback magnetic flux of a magnitude β ′ ₂ V ₂ proportional to ₂ and a feedback magnetic flux of a magnitude β ′ ₃ V ₃ proportional to the output voltage V ₃ of the third magnetometer 13;
A magnetic flux that is the sum of a feedback magnetic flux having a magnitude of β ₄ V ₄ proportional to the output voltage V ₄ of the fourth magnet meter 14 is applied. That is,

Φ ₄ = β ′ ₂ V ₂ + β ′ ₃ V ₃ + β ₄ V ₄ , and the output voltage V ₄ is

(Equation 8) Becomes Therefore, gains β ′ ₁ and β ₁ , β ′ ₂ and β ₂ ,
If β ′ ₃ is equal to β ₃ , the fourth magnetometer 14 determines the difference between the magnetic fluxes Φ1 and Φ2 detected by the _first and _second magnetometers 11 and 12, and the third and third magnetometers. Fourth magnet meters 13 and 14
And outputs a voltage V ₄ proportional to the difference between the magnetic fluxes Φ ₃ and Φ ₄ , that is, the second-order difference value of the magnetic flux.

As described above, the first to fourth magnetometers 11 to 14 are used, and the output value V ₁ of the first magnet meter 11 is multiplied by a gain to obtain a feedback signal of the second magnet meter 12. Add
The output value V ₃ of the magnet meter 13 is multiplied by a gain and added to the feedback signal of the fourth magnet meter 14. Further, the first-order difference output V ₂ of the second magnet meter 12 is multiplied by a gain and further added to the feedback signal of the fourth magnet meter 14. As a result, the fourth
Voltage V ₄ that is from the magnetometer 14 second-order difference is obtained.

The second-order differential gradiometer of the present embodiment is
Since it does not require a three-dimensional pickup coil, it can be applied to high-temperature superconducting SQUIDs. In addition, it is not necessary to adopt a configuration that requires a separate magnet meter for reference, so that manufacturing costs can be reduced. Become.

(Second Embodiment) In the first embodiment, the environmental magnetic field component included in the output detected by the second-order differential gradiometer 1 is detected by each of the magnetometers 11 to 14. Of the uniform component of the applied magnetic field is approximately “1- (2) ^1/2 β ′ / β” times, or “1-β ′ ₂ / β ₂ ” times the primary gradient component of the environmental magnetic field, whichever is larger. Of about. Here, “β ′ / β” is
Typical values of “β ′ ₁ / β ₁ ” and “β ′ ₃ / β ₃ ”. For example, the magnitude of the uniform component of the magnetic field is about 100 p
Assuming that T / √Ηz and the required magnetic field resolution are 10 fT / 、 １z, 1-2β ′ / β needs to be about 10 ⁻⁴ or less. That is, each gain of the pair of beta ₁ and beta ₃ must be the same for about half of ^10-4 errors. Also, the magnitude of the primary gradient component of the environmental magnetic field is set to about 1 pT
/ √Hz, 1−β ′ ₂ / β ₂ needs to be about 10 ⁻² or less, and the gain of β ₂ is 1
0 must be matched ^-2 order of accuracy.

A specific embodiment for realizing this will be described as a second embodiment with reference to FIG. In the following embodiments, the same reference numerals are given to the same or equivalent components as those of the SQUID magnetometer of the embodiments described above, and the description thereof will be omitted or simplified.

The SQUID magnetometer shown in FIG. 2 has four magnetometers 11 to 11 as in the first embodiment.
The second derivative gradiometer 1 as a SQUID magnetometer is configured by electrically connecting the 14.

As shown in FIG.
As feedback amplifiers 14, resistance elements R _{1 to} R ₄
Are used respectively. Further, the SQUIDs 12a and 14 of the second and fourth magnet meters 12 and 14
a is provided with two feedback coils 12b 'and 12b "and 14b' and 14b", respectively.

After the resistance element R1 of the feedback loop of the _first magnetometer 11 is connected to its own feedback coil 11b, the coil 11b is connected to the second feedback coil 11b.
Are connected in series to one of the two feedback coils 12b ′ of the magnetometer 12.
The resistance element R ₂ of the feedback loop of the second magnet meter 12 is connected to the other feedback coil 12.
b "to being connected. In the same manner, after the resistance element R ₃ in the feedback loop of the third magnetometer 11 is connected to the feedback coil 13b of the own
The coil 13b is connected in series to one of the two feedback coils 14b 'of the fourth magnetometer 14. Resistance element R ₄ in the feedback loop of the fourth magnetometer 14 is connected to the other of the feedback coil 14b ".

This second-order differential gradiometer 1 has a second
And by providing a fourth two feedback coils magnetometer 12 and 14, the feedback gain beta ₁ and beta _'1, and, beta ₃ and beta' can be increased each degree of coincidence _3. Hereinafter, the degree of coincidence of the feedback gain and the accuracy of the output signal according to the present embodiment will be described.

The feedback gains β ₁ and β ′ ₁ are respectively

Β ₁ = ９ ₁ / R ₁ , β ′ ₁ = Μ ₂ / R ₁ Micromax ₁ is a mutual inductance between the feedback coil 11b and SQUID11a in the first magnetometer meter 11, _{'the second} feedback coil 12b of the second magnetometer 12' Micromax ₂ and M the SQUID12a with and 12b " When the SQUID and the coil are formed of a thin film, they can be formed with an accuracy higher than 10 ⁻⁴ .

The third and fourth magnet meters 13 and
The same applies to and. Μ ₃Is the third magnet
Feedback coil 13 in tomometer 13
b and the SQUID 13a.
Μ₄And M '₄Is the fourth magnet meter 14
Feedback coils 14b 'and 14b "
With each mutual inductance with SQUID14a
is there. Therefore, “1-2^1/2β '/ β ”is 10⁴degree
It can be set to the following sizes.

The feedback gains β ₂ and β ′ ₂ are respectively

(Equation 10)And Μ ′₂And Μ ′₄Is 10^-2With higher accuracy than
Easily formed, R₂And R '₂Also 10^-2With higher accuracy
Since they can be matched, "1-β '₂/ Β ₂To
About 10^-2Set to a size less than
Can be.

The difference value detecting function of the second-order differential gradiometer 1 is the same as that of the first embodiment. That is, the output voltage V ₄ of the second derivative output from the fourth magnet meter 14 is

[Equation 11] It is.

In this embodiment, a second-order differential gradiometer is constructed without the need for a difference calculator as in the conventional example. Therefore, the accuracy of the second-order differential output is not limited by the difference in gain between the two magnet meters and the in-phase signal removal ratio of the difference calculator as in the conventional example, and the environmental magnetic field is removed with high accuracy. can do. In addition, since the required high-precision ability to remove the environmental magnetic field can be obtained without an adjusting resistor for adjusting the compensation current, it is not necessary to frequently adjust the compensation current.

(Third Embodiment) A third embodiment is shown in FIG.
And 4.

The SQUID magnetometer of this embodiment is also configured as an electric secondary differential gradiometer 1 using four magnetometers 11 to 14.

In each feedback loop of the magnet meters 11 to 14, constant current circuits 11e to 14e (gains α _{1 to} α ₄ ) are provided as circuits for supplying a feedback current.
Are adopted respectively. In the figure, M1 to M4 are mutual inductances between each SQUID and the feedback coil, respectively.

The field of the first magnetometer 11 is
Feedback coil 11b and second magnetometer 12
Is connected in series with the feedback coil 12b of
The feedback coil of the third magnetometer 13
Of the magnet 13b and the fourth magnet meter 14
And the cocole 14b are connected in series, whereby the second
As described in the embodiment, the feedback gain β
₁And β ′₁, And β ₃And β ′₃Improve the match of
ing.

Further, the output voltage V ₂ of the second magnet meter 12 is applied to the feedback coil 14 b of the fourth magnet meter 14 via another constant current circuit 21 (gain α ′ ₂ ).

The constant current circuit 11 used in the present embodiment
One example of e to 14e is shown in FIG. This constant current circuit is configured as a voltage-current conversion circuit. In this circuit, each of the illustrated resistance elements has a value that maintains the following relationship.

[0057]

Equation 12] _{R f / R s = (R} 2 + R 3) / R 1 Thus, the output current _{I L} of the constant current circuit, as represented by the following formula, a value which is proportional to the input voltage _{V s} Becomes

[0058]

## EQU13 ## I _L = (R _f / (R _s R ₃ )) V _s The difference value detection function as the second-order differential gradiometer 1 in the present embodiment is the same as that in the first embodiment. That is, the output voltage V ₄ of the second derivative output from the fourth magnet meter 14 is

[Equation 14] It is.

As described above, a second-order differential gradiometer is configured without using a difference calculator as in the first embodiment. Unlike the conventional example, the accuracy of the second-order differential output is not limited by the in-phase signal rejection ratio of the difference calculator,
A second-order differential gradiometer capable of removing an environmental magnetic field with high accuracy can be provided. Furthermore, since the required accuracy can be obtained without an adjustment resistor for adjusting the compensation current, it is possible to provide a second-order differential gradiometer that does not require frequent adjustment of the compensation current. Furthermore, since it is not necessary to provide two feedback coils in each of the second and fourth magnet meters as shown in the first embodiment, the configuration is simplified and the crosstalk between the coils is reduced. Is also eliminated.

(Fourth Embodiment) FIG.
It will be described based on. The SQUID magnetometer of this embodiment is also configured as an electric second-order differential gradiometer 1 using four magnetometers 11 to 14.

This second-order differential gradiometer 1 has a third
As in the first embodiment, constant current circuits 11e to 14e are used in each magnet meter as a circuit for supplying a feedback current. On the other hand, the feedback coil 11b of the first magnet meter 11 and the feedback coil 12b of the second magnet meter 12 are connected in series, and similarly, the feedback coil 13b of the third magnet meter 13 and the fourth magnet The feedback coil 14b of the meter 14 is connected in series, whereby the feedback gains β ₁ and β ′ ₁ and β ₃
And β ′ ₃ are improved.

In particular, the difference from the gradiometer of the third embodiment is that the first and third magnetometers 11 are different.
And 13 are provided with circuits for supplying currents proportional to the output voltages to the second and fourth magnet meters 12 and 14 by a newly added constant current circuit. That is, the output voltage V ₁ of the first magnet meter 11 is applied to the feed coil 12 b of the second magnet meter 12 via the constant current circuit 22 (gain γ ₁ ). Voltage V ₃
Is supplied to the feed coil 14b of the fourth magnet meter 14 via the constant current circuit 23 (gain γ ₃ ).

The difference value detecting function of the second-order differential gradiometer 1 in the present embodiment is the same as that of the first embodiment. That is, the fourth magnet meter 14
The output voltage V ₄ of the second derivative output from,

(Equation 15) It is.

The above-described newly added constant current circuit 2
In the third embodiment, when the values of the mutual inductances _{１ 1} and Μ ₂ and the values of M ₃ and M ₄ are slightly different in the third embodiment, β ₁ and β ′ ₁ , and β ₃ and β ′ _This is for improving the point that the high degree of coincidence required for No. ₃ cannot be secured. Specifically, the first and second (and third and fourth) magnet meters 11 and 12 (and 13, 14)
Feedback coils 11b, 12b (and 13b,
14b) to be compared with the current supplied Ι ₁ = α ₁ V ₁ (and Ι ₃ = α ₃ V ₃₎ in common, small current I _'2 = γ ₁ V
By supplying ₁ (and Ι ′ ₄ = γ ₃ V ₃ ) to the feedback coil 12 b of the second magnetometer 12 (and the feedback coil 14 b of the fourth magnetometer 14), the mutual inductances M ₁ and Μ ₂ ( And the slight difference in the values of M ₃ and M ₄ ).

The newly added constant current circuits 22 and 2
No. 3 has a variable gain. For this reason, when a uniform magnetic field is applied to each magnet meter, the second and fourth
Are adjusted so that the outputs of the magnet meters 12 and 14 are minimized. The gain adjustment of the constant current circuits 22 and 23, for example, be achieved by adjusting the value of the resistor R ₃ of Figure 4 described above. The gain when ideally adjusted is

Γ ₁ = α ₁ (M ₁ / M ₂ −1) and

Equation 17] gamma ₃ = alpha a value of _{3 (M 3 / M 4 -1} ). These gains are α ₁ and α ₁ if the mutual inductances M ₁ and M ₂ match each other with high precision.
_Since these values are considerably smaller than ₃ , these values have little effect on the accuracy of the output value, and adjustment is easier than in the conventional method.

The mutual inductances M ₁ , Μ ₂ , Μ
_3, the variation of Micromax ₄ has been made to occur mainly during manufacture, since when Q change is very small, after once performing adjustment, need not be adjusted over a long period of time.

According to the present embodiment, in addition to the same effects as in the second embodiment, the output of the second-order differential gradiometer due to a slight variation in the mutual inductance between the feedback coil of the SQUID and the superconducting ring. Deterioration in accuracy can be compensated for by a constant current circuit whose gain can be adjusted. Therefore, the output accuracy of the second derivative can be further improved. Further, there is an advantage that it is not necessary to frequently perform the adjustment work for that.

(Fifth Embodiment) FIG.
A description will be given based on FIGS. The SQUID magnetometer of this embodiment is also configured as an electric second-order differential gradiometer 1 using four magnetometers 11 to 14.

This second-order differential gradiometer 1 has a third
As in the first embodiment, constant current circuits 11e to 14e are employed as circuits for supplying a feedback current. Feedback coil 11 of first magnetometer 11
b and the feedback coil 12b of the second magnetometer 12 are connected in series, and the feedback coil 13b of the third magnetometer 13 and the feedback coil 14b of the fourth magnetometer 14 are connected in series. Feedback gain β ₁
And β ′ ₁ , and β ₃ and β ′ ₃ .

In addition to the configuration of the third embodiment, the output voltage V ₂ of the second magnet meter 12 is
2 (gain γ ₂ ) and the fourth
Is added to the output of the magnet meter 34.

Further, a voltage proportional to the output voltage V ₁ of the _first magnetometer 11 is newly added to the amplifier circuit 3.
0 (gain γ ₁ ), and this voltage is
1, a configuration for adding to the output voltage of the second magnetometer 12 is newly provided. A voltage proportional to the output voltage V ₃ of the third magnet meter 13 is generated by the newly added amplifier circuit 34 (gain γ ₃ ), and this voltage is added to the output voltage of the fourth magnet meter 14 by the addition circuit 35. A configuration for adding is newly provided.

The function of detecting the difference value as the second-order differential gradiometer 1 in this embodiment is the same as in the above-described embodiment. That is, the output voltage V ₄ of the second derivative output from the fourth magnet meter 14 is

(Equation 18) It is.

The newly added amplifier circuits 30 and 34
And the adders 31 and 35 are provided in the third embodiment as mutual inductances M ₁ , M ₂ , _{３ 3} , M ₄ and α ₂
When α and α ′ ₂ are slightly different from each other, it is possible to improve a problem that a uniform component or a first-order gradient component is mixed in an output value to output only a second-order differential component.

The amplification circuits 30, 32, and 34 are configured so that their gains can be changed. When a uniform magnetic field is applied to each magnet meter, the differential outputs of the second and fourth magnet meters become zero. And adjust the gains γ ₁ and γ ₃
Γ ₂ is adjusted so that the output of the fourth magnet meter becomes 0 when a uniform gradient magnetic field is applied to each magnet meter.

FIG. 7 shows a specific circuit configuration for adjusting the gain. Gain control section 41 in computer 40
Is output as a digital signal, the gain value is converted by the D / Α conversion circuit 44 into a corresponding analog voltage. An output voltage (input signal 1) output from each magnet meter and a gain signal converted into an analog voltage are input to a multiplication circuit 45, and a product signal of the two is calculated. This product signal is added by the adding circuit 46 to the output voltage (input signal 2) from the FLL circuit of another magnet meter. This addition signal is supplied to the signal processing circuit 47.
After signal processing such as gain adjustment and filter processing is performed, the signal is sent to the signal collection unit 43 of the computer 40. The signal is converted into a digital signal by the signal collecting unit 43 and is provided for gain control in the gain control unit 41. The computer 40 includes a magnetic field generating coil control unit 42, which can control the generation of a magnetic field from a reference magnetic field generating coil 48 installed near the SQUID sensor. According to this configuration, the gains of the amplifier circuits 30, 32, and 34 can be arbitrarily changed according to a command from the computer 40.

The computer 40 can also be used as a device for receiving the detection output (at least the output voltage V ₄ of the fourth magnet meter) of the second-order differential gradiometer 1 and analyzing the magnetic field source and the like. .

Next, the procedure of gain adjustment will be described. The gain control unit 41 sets the gains of all the amplifier circuits 30, 32, and 34 to zero once. Next, the magnetic field generating coil control unit 42 generates a magnetic field of a predetermined pattern in the plurality of magnetic field generating coils 48 installed near the SQUID sensor. The signal collecting unit 43 collects the output of each magnetometer at that time and stores it in a memory in the computer. Next, an arithmetic unit (not shown), for example, disclosed in
The gain of each amplifier circuit is determined using the method described in Japanese Patent No. 06626, and the gain control unit 41 controls the gain of each amplifier circuit based on the determined gain value.

According to the present embodiment, Μ ₁ , Μ ₂ , Μ ₃ ,
It is possible to prevent the output accuracy of the deterioration due to the variation of M _4. Variations in the mutual inductances Μ ₁ , M ₂ , M ₃ , and M ₄ mainly occur during manufacturing, and the temporal changes are extremely small. Therefore, once the adjustment is performed, the adjustment is performed again for a long time thereafter. This is almost never necessary.

According to the present embodiment, in addition to the same effects as those of the third embodiment, due to the slight variation in the mutual inductance between the feedback coil of the SQUID and the superconducting ring, the second-order differential gradiometer can be used. Even in the case where the output accuracy is deteriorated, the gain can be compensated by the gain-adjustable amplifier circuit and the adder circuit. Therefore, the output accuracy of the second derivative can be further increased, and there is a characteristic that it is not necessary to frequently perform the adjustment work for that.

Although the present embodiment has exemplified the case where the newly added amplifier circuit and adder circuit are electrically configured, the invention is not necessarily limited to this.
As another configuration example, the configuration may be based on software processing. When amplification and addition are performed by software processing, gain adjustment for amplification can be easily performed by software processing, so that a special gain adjustment means as shown in FIG. 7 is not required, and the circuit configuration is greatly simplified. There is an effect that can be.

(Sixth Embodiment) A sixth embodiment will be described with reference to FIG.
It will be described based on. The SQUID magnetometer of this embodiment is configured as an electric second-order differential gradiometer 1 using three magnetometers. This gradiometer is another basic configuration of the second derivative gradiometer according to the present invention.

The secondary differential gradiometer 1 is composed of three magnetometers 11 to 13, each of which is composed of three SQUIDs 11a (to 13c) and a FLL circuit 11c (to 13c) as a driving circuit. In each magnet meter, the gain β ₁ (~
The current proportional to the output voltage is returned to each feedback coil 11b (ｂ13b) by the feedback amplifier 11c (〜13c) of β ₃ ).

In addition to this, the first magnet meter 1
1 is amplified by the feedback amplifier 51 having the gain β ′ ₁ and the second output voltage V ₁ is supplied to the second magnet meter 12.
Is applied to the adder 52 inserted in the feedback loop. Further, the output voltage V _{3 of} the third magnet meter 13 is amplified by the feedback amplifier 53 having the gain β ′ ₃ and applied to the addition circuit 52. Adder 52
The output voltages of the first to third magnet meters added in the above are supplied to the feedback coil 12b of the second magnet meter 12.

As a result, the first and third magnet meters 11 and 13 operate as ordinary magnet meters, while their output voltages V ₁ and V ₃ are changed to β ₁ and β, respectively.
_The tripled magnetic flux is applied to the SQUID 12a of the second magnet meter 12 together with a magnetic flux proportional to the output of the second magnet meter itself. For this reason, the output voltage V ₂ of the _second magnetometer 12 is

[Equation 19] It is represented as

Therefore, an output corresponding to the second derivative can be obtained by reducing β ′ ₁ / β ₁ and β ′ ₃ / β ₃ to _１ ／. In the case of this circuit configuration, in order to obtain the output of the primary differentiation, it is necessary to perform a difference operation between the output voltages of the first and third magnetometers. Since only three sets of drive circuits are required, there is an advantage that the configuration is greatly simplified and facilitated.

FIG. 9 shows an example in which the above-mentioned principle of the second derivative gradiometer 1 shown in FIG. This configuration can use the same method as in each of the above-described embodiments, and can provide the same effects as those described above, except that the primary differential output cannot be directly obtained.

Specifically, the magnet meters 11 to 13
Constant current circuits 11e to 13e
(Gains α _{1 to} α ₃ ) are respectively inserted. In each of the magnet meters 11 to 13, the SQUID
The feedback coil for 11a (~ 13a) is 2
It is provided individually.

The feedback coils 11 b ′ and 11 ″ (the mutual inductances are M ₁ and M ′ ₁ ) of the _first magnetometer 11 are connected in series with each other, receive the feedback current of their own output, and coil is connected to a further two feedback coils 12b 'and 12 "(mutual inductance _M 2, M' ₂₎ one 12b of the second magnetometer 12 '. Similarly, the feedback coils 13b ′ and 13 ″ (the mutual inductances are M ₃ and M ′ ₃ ) of the _third magnetometer 13 are connected in series with each other, receive the feedback current of their own output, and The coil is further connected to one feedback coil 12b 'of the second magnetometer 12.
In the magnet meter 12, a current proportional to its own detection output is fed back to the other feedback coil 12b ″.

The output of the gradiometer 1 is given from the second magnetometer 12 and its value is

(Equation 20) It is represented by When two feedback coils provided for one SQUID are configured to have the same mutual inductance M to the superconducting ring, an output corresponding to the second derivative can be obtained.

As in the second embodiment, since a subtraction circuit or the like is not used to obtain the secondary differential output, it is possible to measure the secondary gradient component of the magnetic field with high accuracy.

(Seventh Embodiment) A seventh embodiment is shown in FIG.
0 will be described. The SQUID magnetometer of this embodiment is configured as an electric third-order differential gradiometer as a third- or higher-order gradiometer.

FIG. 10 shows a third-order differential gradiometer 1
Is shown below. This gradiometer 1
Is provided with eight magnetometers 11 to 14 and 61 to 64. Of these, the four magnetometers 11 to 14 shown on the left side of the drawing have the same configuration as that of the first embodiment described above. The remaining four magnet meters 61 to 64 shown on the right side of the drawing have the same configuration as the four magnet meters 11 to 14 on the left side. Further, the detection output V _{4 of} the fourth magnet meter 14 is supplied to the feedback loop of the eighth magnet meter 64 via the feedback amplifier 70.

[0093] Therefore, first, third, magnetometer output _V 1 in magnetometer 11,13,61 and 63 of the fifth and _7, V 3, _{V 5} and _{V 7,} the second and sixth
The primary differential outputs V ₂ and V _{6 are} output to the magnet meters 12 and 62, and the secondary differential output V is output to the fourth magnet meter 14.
_4, and the magnetometer 64 of the eighth can be obtained cubic differential output _{V 8.}

(Eighth Embodiment) An eighth embodiment is shown in FIG.
1 will be described. The SQUID magnetometer of this embodiment is also configured as an electric third-order differential gradiometer as a third- or higher-order gradiometer.

FIG. 11 shows a third-order differential gradiometer 1
3 shows another basic configuration. This gradiometer 1
It has four magnetometers 11 to 14. The basic circuit of the magnet meters 11 to 14 including the SQUID, the feedback coil, the FLL circuit, and the feedback amplifier is the same as that described above.

In addition to this, the third magnet meter 1
3 The feedback loop, the adder circuit 71 is inserted, this adder circuit 71 in addition to its own detection output V _3, the detection output V ₂ of the feedback amplifier 72 (gain of the second magnetometer 12 beta ′ ₂ )
Also so that the detection output V ₄ of the fourth magnetometer 14 is added via a feedback amplifier 73 (gain beta _'4). Further, the fourth magnet meter 1
In the feedback loop of No. ₄ , another adding circuit 75 is inserted, and the current obtained by multiplying the own detection output V4 by a gain and the first
It adapted to provide a feedback coil 14b with the detection output V ₁ of the feedback amplifier of magnetometer 11 (gain beta _'1) by adding the gain-multiplied current.

Therefore, regarding the gain, β ′₁/ Β
₁And β ′₂/ Β₂To 1, β '₄/ Β ₄To 1/2 or 1/3
By setting a certain constant such as
Third derivative output V from data 13₃But

(Equation 21) Is obtained. In this way, a tertiary differential output can be obtained with only four magnetometers.

Similarly, a fourth or higher order differential gradiometer according to the present invention can be constructed.

(Ninth Embodiment) A ninth embodiment is shown in FIG.
2 will be described. The SQUID magnetometer of this embodiment relates to the improvement of the feedback circuit.

SQUID using high-temperature superconducting SQUID
In many cases, the magnetometer employs a configuration in which an AC bias circuit is adopted and a modulation signal added to a feedback current is input to a feedback coil with the intention of reducing low-frequency noise. A configuration example of such a circuit is disclosed in
8103 is described in detail.

FIG. 12 shows a SQUI using such a circuit configuration.
1 shows a preferred embodiment of an ID magnetometer. The SQUID magnetometer 1 has a plurality of magnetometers 91, 92,...
2a), a feedback coil 91b (92b), a drive circuit 91c (92c), and a constant current circuit 91d (92d) for voltage / current conversion inserted into the feedback system. Driving circuits 91c and 92c each include an amplifier D
a, a demodulator Db, and an integrator Dc in this order from the input side. The feedback coils 91b, 92b of the superconducting rings 91a, 92a are connected in series to each other while being connected in series to their own feedback loops.

A plurality of magnet meters 91, 92,... Are provided with a common AC bias circuit 93. The AC bias circuit 93 includes a transmitter 94, a frequency divider 95, an exclusive OR circuit 96, and a constant current circuit 97.

This AC bias circuit 93 is provided with only one oscillator 94 for generating a modulation signal for a plurality of magnet meters 91, 92,... Connected in series with feedback coils 91b, 92b,. The modulation signal is voltage-current converted by the constant current circuit 97, and the converted current is supplied to the serially connected feedback coils 91b, 92b,. Further, the driving circuit 91
Each of c and 92c is characterized in that after the output voltage of each of the SQUIDs 91a, 92a,. This circuit configuration is based on the first
Applying to each of the eighth to eighth embodiments, the feedback current is generated in the manner described in each of the first to eighth embodiments.

According to the present embodiment, the high-temperature superconducting SQUI
Since low-frequency noise remarkable in D can be effectively suppressed, it can be suitably applied to a high-temperature superconducting SQUID. Furthermore, since a modulation signal generated by a common oscillator is supplied to each drive circuit and demodulated by a reference signal based on the common oscillator, a distortion occurs in an output voltage due to an unintended interaction between channels. However, since the distortion always acts constantly between the channels, this interaction appears as a distortion similar to the variation of each channel. Therefore, measurement and correction can be performed by the method described in the fifth embodiment. Therefore, by implementing the present embodiment in combination with the fifth embodiment, the effect of the interaction between the channels can be eliminated, and the magnetic field gradient can be measured with higher accuracy.

In the above-described embodiment, the gradiometer using an electric circuit has been described as an example. However, the main constituent elements of the present invention can be executed by software. The same effect as that obtained is obtained.

[0106]

As described above, the SQUID of the present invention is
According to the D magnetometer, it is not necessary to provide an extra magnet meter for reference, and a secondary or higher order gradiometer can be configured electrically or by software. Therefore, it is not necessary to frequently adjust the compensation current using a high-temperature superconducting SQUID in which a spatially three-dimensional pickup coil is difficult to configure, and a high-order differential gradiometer that realizes a high removal rate of an environmental magnetic field. Can be provided. Therefore, it is possible to provide an inexpensive and easy-to-operate biomagnetic measurement device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an SKU according to a first embodiment of the present invention.
The block diagram which shows the outline of the 2nd derivative gradiometer as an ID magnetometer.

FIG. 2 is a diagram illustrating an SKU according to a second embodiment of the present invention.
The block diagram which shows the outline of the 2nd derivative gradiometer as an ID magnetometer.

FIG. 3 is a diagram showing an SKU according to a third embodiment of the present invention.
The block diagram which shows the outline of the 2nd derivative gradiometer as an ID magnetometer.

FIG. 4 is a circuit diagram of a constant current circuit used for a feedback circuit.

FIG. 5 is a diagram illustrating an SKU according to a fourth embodiment of the present invention.
The block diagram which shows the outline of the 2nd derivative gradiometer as an ID magnetometer.

FIG. 6 is a diagram illustrating an SKU according to a fifth embodiment of the present invention.
The block diagram which shows the outline of the 2nd derivative gradiometer as an ID magnetometer.

FIG. 7 is a circuit diagram illustrating a gain adjustment method.

FIG. 8 is a diagram illustrating an SKU according to a sixth embodiment of the present invention.
The block diagram which shows another basic form of the 2nd-order differential gradiometer as an ID magnetometer.

FIG. 9 is a configuration diagram showing a specific example of the second-order differential gradiometer of FIG. 8;

FIG. 10 is a block diagram showing a configuration of an S according to a seventh embodiment of the present invention.
FIG. 2 is a configuration diagram showing an example of a third-order differential gradiometer as a QUID magnetometer.

FIG. 11 is a block diagram showing a configuration of an S according to an eighth embodiment of the present invention.
The block diagram which shows another example of the 3rd-order differentiation type gradiometer as a QUID magnetometer.

FIG. 12 is a block diagram showing a configuration of a ninth embodiment of the present invention;
FIG. 2 is a block diagram showing a schematic configuration of a QUID magnetometer.

FIG. 13 is a configuration diagram of a pickup coil and a gradiometer used for explaining a conventional technique.

[Explanation of symbols]

1 Secondary differential gradiometer (SQUID magnetometer) 11-14 Magnet meter 11a-14a SQUID (superconducting ring) 11b-14b Feedback coil 11c-14c FLL circuit 11d-14d Feedback amplifier 11e-14e Constant current circuit 11'b , 11 "b, 12'b, 12" b, 14'b, 1
4 "b Feedback coil 17 to 19 Feedback amplifier 21 Constant current circuit 22, 23 Constant current circuit 30, 32, 34 Amplification circuit 31, 33, 35 Addition circuit 40 Computer 44 D / A conversion circuit 45 Multiplication circuit 46 Addition circuit 47 Signal Processing circuit 48 Magnetic field generating coil 51, 53 Feedback amplifier 52 Addition circuit 61-64 Magnet meter 71, 75 Addition circuit 72, 73, 74 Feedback amplifier 91, 92 Magnet meter 91a, 92b High-temperature superconducting ring 91a, 92b Feedback circuit 93 AC Bias circuit

Claims (11)

[Claims] An SQUID having three or more SQUIDs, a drive circuit for independently driving each of the three or more SQUIDs, and a drive circuit attached to each of the three or more SQUIDs and being proportional to an output of each of the drive circuits. Provided with a feedback coil for feeding back a magnetic flux having a predetermined size
In the ID magnetometer, at least one SQ of the three or more SQUIDs
A means for applying a feedback magnetic flux having a magnitude proportional to the output of another drive circuit of one SQUID to the UID via the feedback coil of the SQUID, and applying a feedback magnetic flux to the output of the drive circuit of another SQUID other than these SQUIDs. Means for additively applying a feedback magnetic flux having a proportional magnitude to the at least one SQUID via a feedback coil of the SQUID. 2. The SQUID magnetometer according to claim 1, further comprising a plurality of feedback coils for said at least one SQUID, wherein at least one feedback coil is in series with a feedback coil of said another SQUID. SQUID characterized by being connected to
Magnetometer. 3. The SQUID magnetometer according to claim 1, wherein an output terminal of each drive circuit of the SQUID is connected to each of the three or more SQUID feedback coils via a constant current circuit. Of the feedback coils of one, a specific feedback coil is
One of the SQUID feedback coils is connected in series, and the other end of the drive circuit connected to one SQUID of the other series-connected feedback coil pair is connected to another constant current circuit at this connection point. A SQUID magnetometer characterized by being connected via a wire. 4. The SQUID magnetometer according to claim 3, wherein said another constant current circuit connected to said connection point is a circuit for supplying a current proportional to an output voltage of said drive circuit. Magnetometer. 5. The SQUID magnetometer according to claim 3, wherein a feedback coil of another SQUID is connected to the connection point. 6. The SQUID magnetometer according to claim 1, wherein a signal having a magnitude proportional to an output value of a plurality of driving circuits is output to an output of one of the plurality of driving circuits. An SQUID magnetometer comprising an addition arithmetic unit, wherein the conversion coefficients can be individually changed. 7. The SQUID magnetometer according to claim 1, wherein means for converting output signals of the plurality of drive circuits into digital values, and weighted addition of the output signals of the respective drive circuits converted into digital values. SQUID magnetometer characterized by comprising an arithmetic means for performing the calculation, the weight coefficient of which can be changed. 8. The plurality of SQUIDs and the plurality of SQUIDs
A driving circuit for independently driving each of the IDs;
In the SQUID magnetometer having a feedback coil attached to each of the SQUIDs, a feedback magnetic flux having a magnitude proportional to the output of the drive circuit of the SQUID is given to each of the plurality of SQUIDs.
Means for applying a feedback current supplied to another one of the plurality of SQUIDs to each of the plurality of SQUIDs of the plurality of SQUIDs; The feedback coil of at least one SQUID of the plurality of SQUIDs to which the feedback current is applied additively has a magnitude proportional to the output voltage of the drive circuit of the other SQUID of the plurality of SQUIDs. Means for applying the feedback current further additively;
Means for changing a conversion coefficient from the output voltage to the current. A SQUID magnetometer. 9. S according to any one of claims 6 to 8,
A SQUID magnetometer comprising: a magnetic field generating coil; and means for determining the changeable conversion coefficient based on a measured value of a magnetic field generated by the magnetic field generating coil. 10. A plurality of SQUIDs and a plurality of SQIDs
SQ having a plurality of drive circuits for individually driving UIDs
A means for supplying at least one of a bias current alternating between positive and negative and a modulation magnetic flux alternating between positive and negative to each of the plurality of SQUIDs; and at least two of the plurality of drive circuits.
Means for supplying at least one of a modulation signal and a bias signal generated by a common oscillator, wherein the at least two drive circuits each include a reference signal based on an oscillation output of the common oscillator. Using the SQ
A SQUID magnetometer comprising means for demodulating the output of a UID. 11. The SQUID magnetometer according to claim 10, wherein at least two of the plurality of SQUIDs are SQUIDs.
A SQUID magnetometer comprising: means for connecting the feedback coils of D in series with each other, and supplying a modulation current based on the oscillation output of the common oscillator to the feedback coils connected in series.