JP2869776B2 - SQUID magnetometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a SQUID (Supercon
A SQUID magnetometer that measures a magnetic field using a ducting Quantum Interference Device (superconducting quantum interference device), and in particular, a SQUID that connects a plurality of SQUIDs
The present invention relates to a SQUID magnetometer using a D array. here,
SQUID is a liquid helium, liquid nitrogen, etc., kept in a low temperature state in an insulated container (cryostat, etc.)
A DC current is applied as a bias current to a SQUID loop, which is a superconducting loop including a Josephson junction, in the loop and driven. A magnetic flux from the outside through a pickup coil or an input coil or directly in the SQUID loop. When coupled and applied, a circulating current is induced in the SQUID loop, and as a transducer that converts a weak change in the applied external magnetic flux into a large change in the output voltage due to the quantum interference effect in the Josephson junction in the loop. An element that measures a small change in magnetic flux by utilizing its operation.

[0002]

2. Description of the Related Art Conventionally, d including two Josephson junctions
As a magnetometer using cSQUID, a dewar (or cryostat), which is an adiabatic containment container for storing liquid helium as a coolant for maintaining a low-temperature environment (cooling system), and a SQUID probe operating in liquid helium And an amplifier (amplifier) operating at room temperature and a controller, and a configuration is known in which the SQUID probe in liquid helium and the amplifier at room temperature are connected by a coaxial cable or a twist cable or the like. Such a SQUID magnetometer has a magnetic flux resolution of 10 ^-5.
φ. / Hz ^1/2 (φ: magnetic flux quantum) to 10 ⁻⁶ φ. / H
Very high sensitivity of z1 ^{/ 2,} and the response of SQUID is very fast, from several GHz (gigahertz) to several tens GH.
The feature is that it operates on z. However, the conventional SQ
The UID magnetometer has a drawback that it has a very high magnetic flux resolution and is susceptible to external noise and induction noise. Also, the SQUID is usually "FLL: Flux
A feedback circuit for linear operation called "Locked Loop (flux lock loop)" is provided and controlled so that the "zero order method" is established. The FLL is a method of amplifying the SQUID output and returning the SQUID output to the SQUID ring in the form of a magnetic flux in a loop circuit. According to this method, the magnetic flux in the SQUID ring is held at a specific value (magnetic flux lock), so that the magnetic flux in the SQUID ring is maintained at a specific value (operating point). The SQUID will generate a voltage. In this case, if a large amplitude or high-speed external magnetic noise that cannot be followed by the FLL circuit is added to the SQUID, or an electric pulse noise is added to the FLL circuit, the operating point of the FLL loop is deviated (referred to as “lost lock”). )), And the subsequent linear operation is hindered. In order to solve the above problem, as one method for canceling external noise, a pair of differential coils called a gradiometer is used, an input signal is picked up as an in-phase component, and a magnetic flux is applied to a SQUID ring by a superconducting transformer. It is widely practiced to remove the in-phase signal by transmitting.

However, when an external magnetic field is magnetically coupled to the SQUID ring using a pickup coil, the inductance of the pickup coil is usually much larger than the inductance of the SQUID, so that the magnetic flux transmission efficiency is several percent.
There is a problem that it becomes extremely low as follows. on the other hand,
When the external magnetic field is directly picked up by the SQUID ring, the sensitivity to the magnetic field increases, but there is a disadvantage that the inductance of the SQUID ring increases and noise increases. For this reason, a system in which a gradiometer is configured with a pair of SQUID rings has been devised. However, a gradiometer requires a longer baseline, and a longer baseline increases inductance.
It has been virtually impossible to take measures to cancel external noise by configuring a gradiometer with a SQUID ring. As a countermeasure for this, at present, a magnetic flux meter of the type that directly detects an external magnetic field with a SQUID ring is used.
The external noise is canceled in the same manner as in the above-described gradiometer by installing the two magnetometers separated by a base line length and calculating the difference between the electric signal outputs of the respective magnetometers. Hereinafter, this method is referred to as a “two magnetometer method”. A magnetometer is a SQUID that picks up an external magnetic field with a normal pickup coil without using a differential coil like a gradiometer.
It refers to a SQUID magnetometer of the type coupled to a ring.

[0004]

SUMMARY OF THE INVENTION However, FLL
When a circuit is used, the open-loop gain decreases in inverse proportion to the frequency, so that the frequency characteristic of the rate at which the common mode signal of the gradiometer is removed decreases in the high frequency band. Therefore, in the two magnetometer system, the noise removal characteristic is low in an environment where a high-speed noise signal is included.
There was a disadvantage.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been developed to improve the dynamic characteristics of SQUIDs, in particular, the frequency characteristics and noise resistance of SQUIDs.
It is intended to provide a D magnetometer.

[0006]

In order to solve the above-mentioned problems, the SQUID magnetometer according to the first aspect of the present invention has the following features.
Alternatively, n (n: a natural number satisfying n ≧ 1) first magnetometers provided with an array-like SQUID and n second second magnetometers are arranged so that the directions of the magnetic field sensitivity are opposite to those of the first magnetometers.
It is characterized in that a magnetometer is arranged.

[0007] The SQUID according to the second aspect of the present invention.
2. The SQUID magnetometer according to claim 1, wherein the D magnetometer is a 1 or array negative feedback coil for performing a negative feedback directly from an output terminal of the SQUID to the SQUID, and a negative feedback for controlling an amount of the negative feedback. And a resistor.
Let Mn be the coupling capacity between the QUID and the negative feedback coil,
When the SQUID is one, the magnetic flux voltage conversion rate is dV /
When dφ and the negative feedback resistance value are Rn, the configuration is such that the following expression is satisfied: n × (dV / dφ) × (Mn / Rn) ≧ 1.

[0008] The SQUID according to the third aspect of the present invention.
The D magnetometer according to claim 1 or 2, wherein the SQUID is driven to adjust the sensitivity.
And a bias magnetic flux injection source for injecting a bias magnetic flux into the SQUID to perform phase adjustment and adjust the phase or sensitivity of the SQUID.

[0009] The SQUID according to the fourth aspect of the present invention.
D magnetometer, according to claim 2 or claim 3 SQUID magnetometer described more in reversing the sign of the negative feedback in the negative feedback coil, said first magnetometer first
It is characterized in that the direction of the magnetic field sensitivity of the two magnetometer is reversed.

[0010] The SQUID according to the fifth aspect of the present invention.
5. The SQUID magnetometer according to claim 3 , wherein the first magnetometer and the second magnetometer are D magnetometers.
Each bias current source of the meter can be independently turned on or off.

[0011]

SUMMARY OF] According to the onset bright having the above structure, since the arrangement the same number of the magnetometer with a magnetic field sensitivity of the opposite directions, can be operated as a gradiometer.
This SQUID magnetometer can be configured by providing a negative feedback coil and a negative feedback resistor. In addition, a bias current source and a bias magnetic flux injection source are provided to adjust the phase or sensitivity of the SQUID. Also, the direction of the magnetic field sensitivity can be reversed by reversing the sign of the negative feedback of the negative feedback coil. In addition, the bias current source is turned on independently.
Alternatively, by turning it off, it can be operated as a primary differential gradiometer, a secondary differential gradiometer, or simply a magnetometer .

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration near the SQUID of the SQUID magnetometer according to the first embodiment of the present invention. As shown in the figure, the SQUID magnetometer 101 shows a connection relationship near a SQUID of a first-order differential magnetometer in which a series SQUID array directly connected to a negative feedback circuit is connected in series with a superconducting or normal conductor. , N connected in series (N:
SQUID array Aa composed of dcSQUIDs Sa1 to SaN (N is a natural number satisfying 1) and N ds connected in series
SQUID array Aa consisting of cSQUIDSb1 to SbN
And a SQUID array Ab connected to one end of the
Negative feedback circuit Na connected in parallel to both ends of D array Aa
And a negative feedback circuit Nb connected in parallel to both ends of the SQUID array Ab. Also, SQUID
One end of the array Aa is connected to the terminal Ta, and the other end of the SQUID array Aa and one end of the SQUID array Ab are connected to the terminal Tb.
Connected to The other end of the SQUID array Ab is connected to a terminal Tc. Each of the above SQUID arrays A
a and the negative feedback circuit Na are connected to the first magnetometer by SQUI
The D array Ab and the negative feedback circuit Nb constitute a second magnetometer, respectively.

The above-mentioned negative feedback circuit Na is constituted by connecting a negative feedback resistor Rn for limiting current and coils La1 to LaN for negative feedback in series. The negative feedback circuit Nb includes a current limiting negative feedback resistor Rn and negative feedback coils Lb1 to Lb1.
LbNs are connected in series. J is each dcSQ
This is a Josephson junction provided in the UID. Although not shown, each dcSQUID is shunted by a shunt resistor. The magnetic flux to be detected is transmitted directly to the SQUID ring or transmitted by a pickup coil (not shown) and a superconducting transformer (not shown).

Here, a coupling coefficient for coupling one dc SQUID and one negative feedback coil is Mn, and one d
Assuming that the magnetic flux voltage conversion rate of the cSQUID is dV / dφ and the negative feedback resistance value is Rn, the following equation is satisfied: N × (dV / dφ) × (Mn / Rn) ≧ 1 (1) A constant value of each circuit element is determined.

FIG. 2 is a diagram showing the spatial arrangement of elements including the direction of the sensitivity surface of the SQUID array of the first embodiment. The SQUID arrays Aa and Ab are formed as thin films on a rectangular substrate. I have. In the example shown in FIG. 2A, the arrow indicates the direction of the sensitive surface, and the direction of the sensitive surface is determined by the substrates Pa and Pb.
Are opposite to each other, and are arranged so as to face each other with an appropriate baseline interval D1.

Next, each SQUID array Aa,
The overall circuit configuration of the magnetometer for driving Ab and amplifying the signal from the SQUID will be described with reference to FIG. As shown in FIG. 5, this SQUID magnetometer 101
Is an independent magnetometer, SQUID array A
a negative feedback circuit Na, another independent magnetometer, a SQUID array Ab and a negative feedback circuit Nb connected to the SQUID array Aa at a terminal Tb, and a bias current source 3 for driving these SQUID arrays Aa and Ab. And differential amplifiers 4 and 5 for amplifying the outputs from the terminals Ta and Tc of the SQUID arrays Aa and Ab, and variable current sources 7 and 8 for setting the operating point of each SQUID array Aa and Ab. Each SQUID array A
a, Ab are provided with magnetic flux injection coil arrays 9 and 10 for injecting a bias magnetic flux. In the above description, the variable current sources 7 and 8 and the magnetic flux injection coil arrays 9 and 10 constitute a bias magnetic flux injection source.

A voltage source 6 for offset adjustment is connected to the differential amplifier 5. This offset voltage is set to Vb. The mutual inductance of the magnetic flux injection coils constituting the magnetic flux injection coil arrays 9 and 10 is Mb. The bias current source 3
Is ib, and the current values of the variable current sources 7 and 8 are imb1 and imb2, respectively.

Next, the operation of the SQUID magnetometer 101 will be described. Looking at one of the magnetometers (for example, a magnetometer composed of the SQUID array Aa and the negative feedback circuit Na) of the SQUID magnetometer 101, if negative feedback is applied so that the above equation (1) holds, FIG. The effective magnetic flux-to-voltage conversion rate dV / dφeff at the operating point on the magnetic flux-voltage curve of SQUID is expressed by the following equation: dV / dφeff = N × dV / dφ / ｛1+ (dV / dφ) × (Mn / Rn) ｝ ……… (2)

When negative feedback is performed, the linear operation area of the SQUID is 1φ from φ1 to φ2 in FIG.
(Φ: magnetic flux quantum), and at the same time, nonlinear distortion is reduced. In FIG. 8, the characteristic shown by the thin line shows the case where the negative feedback is zero, and the characteristic shown by the thick line shows the case where the negative feedback is present. When a bias magnetic flux is applied to the dc-SQUID so that the center of the operating point is located at the center of the slope on the curve in FIG. 8, depending on the input magnetic flux, between the terminal Ta and the terminal Tb in FIG. An output voltage appears between the terminal and the terminal Tc.

FIG. 9 is a diagram showing the above relationship. FIG.
As shown in (A), the sensitivity planes are opposed to each other and are arranged at a baseline interval D1.
A UID array Aa is formed, and a SQUID is
An array Ab is formed. In this way, voltages having opposite signs are output from the SQUID arrays Aa and Ab. When the phases of the outputs in the opposite directions are matched by the variable current sources 7 and 8 in FIG. 5, the magnetic flux voltage conversion characteristics of each dc-SQUID array are as follows.
As shown in FIG. 9, the sign of the slope of the characteristic curve is reversed in the operation region, and a voltage output obtained by adding these is obtained between the terminals Ta to Tc. At this time, each dc-S
Since the output voltages of the QUID array have opposite signs, if the absolute values of the slopes of the characteristic curves are equal, the output voltages are canceled to zero. That is, each SQUID array Aa, A
When an external magnetic flux having the same phase and the same magnitude enters b, each SQ
The output value of the UID array becomes zero, and functions as a "primary differential gradiometer" as a whole.

FIG. 2B shows another configuration example 101a of the first-order differential gradiometer as described above, in which a substrate Pa whose sensitivity planes are opposite to each other.
And Pb are juxtaposed on the same plane with an appropriate baseline interval D2. In this case, the direction of the sensitivity surface of the substrate Pa is a direction from the back of the drawing to the front, and the direction of the sensitivity surface of the substrate Pb is a direction from the front to the back of the drawing. Even with such a configuration, the same operation as that in the case of FIG. 2A can be performed.

Next, a second embodiment of the present invention will be described. SQ of a SQUID magnetometer according to a second embodiment of the present invention
FIG. 3 shows the configuration near the UID. As shown in the figure, this SQUID magnetometer 102 is a SQID magnetometer of the first embodiment described above.
In the UID magnetometer 101, a magnetometer including an SQUID array Ac is connected in series between a magnetometer including an SQUID array Aa and a magnetometer including an SQUID array Ab. SQ
The UID array Ac is composed of 2N dcSQs connected in series.
UIDs Sc1 to Sc, 2N. The SQUID array Ac has a current limiting negative feedback resistor (resistance value: Rn
/ 2) and 2N negative feedback coils Lc1 to Lc,
A negative feedback circuit Nc having 2N connected in series is connected in parallel. In the second embodiment, as in the first embodiment, the magnetic flux to be detected is transmitted directly to the SQUID ring, or is picked up by a pickup coil (not shown) and a superconducting transformer (not shown). Is transmitted.

FIG. 4 is a view showing the spatial arrangement of elements including the direction of the sensitivity surface of the SQUID array of the second embodiment.
The QUID arrays Aa, Ab, Ac are formed as thin films on a rectangular substrate. In the example shown in FIG. 4A, the arrow indicates the direction of the sensitive surface, and the direction of the sensitive surface is determined by the substrates Pa and Pc.
, Substrates Pc and Pb are opposite to each other, and are disposed so as to face each other with an appropriate baseline interval D3. Here, the SQUID on the substrates Pa and Pb
The magnetometer including the arrays Aa and Ab constitutes a first magnetometer, and the magnetometer including the SQUID array Ac on the substrate Pc constitutes a second magnetometer.

Next, each of the above SQUID arrays Aa,
The overall circuit configuration of the magnetometer for driving Ab and Ac and amplifying the signal from the SQUID will be described with reference to FIG. As shown in FIG. 6, this SQUID magnetometer 1
Numeral 02 denotes an SQUID array Aa and a negative feedback circuit Na, which are independent magnetometers, and an SQUID array Ac1 and a negative feedback circuit N, which are other independent magnetometers and are connected to one output terminal of the SQUID array Aa.
c1 and other independent magnetometers and SQ
SQUI connected to one output terminal of UID array Ac1
D array Ac2 and negative feedback circuit Nc2, SQUID array Ab and negative feedback circuit Nb which are other independent magnetometers and are connected to one output terminal of SQUID array Ac2, and SQUID arrays Aa, Ac1 and Ac
2 and Ab, which are individually connected to and can individually drive these bias current sources 13, 14, 15, 16;
Differential amplifiers 17 and 18 for amplifying the output from the output terminals of the QUID arrays Aa, Ac1, Ac2 and Ab, and each SQ
Variable current sources 21, 22, 23, and 24 for individually setting the operating points of the UID arrays Aa, Ac1, Ac2, and Ab, and magnetic flux injection for injecting a bias magnetic flux into each of the SQUID arrays Aa, Ac1, Ac2, and Ab. Coil array 25, 2
6, 27 and 28 are provided. The SQUID array Ac1 is composed of N dcSQUIDSc1 connected in series.
ＳScN, and the SQUID array Ac2 has N dcSQUIDSc, N + 1 Sc, 2N connected in series. Further, the negative feedback circuits 26 and 27 have N magnetic flux injection coils connected in series. In the above,
Variable current sources 21 to 24 and magnetic flux injection coil arrays 25 to 2
Reference numeral 8 denotes a bias magnetic flux injection source.

The differential amplifier 18 is connected to a voltage source 19 for offset adjustment. This offset voltage is set to Vb. The mutual inductance of each of the magnetic flux injection coils constituting the magnetic flux injection coil arrays 25 to 28 is Mb. The current value of the bias current source 13 is ib1, the current value of the bias current source 14 is ib2, the current value of the bias current source 15 is ib3, the current value of the bias current source 16 is ib4, and the current values of the variable current sources 21 to 24 are The values are respectively imb3 to imb6.

The SQUID magnetometer 1 of the second embodiment described above
In FIG. 2A, as shown in FIG. 4A, the directions of the sensitivity planes are opposed to each other and arranged with a baseline interval D3. For example, an SQUID array Aa is formed on the substrate Pa, and an SQUID array is formed on the substrate Pb. Ab is formed, and a SQUID array Ac is formed on the substrate Pc. In this case, the number of SQUIDs in the SQUID arrays Aa and Ab is N and the number of SQUIDs in the SQUID array Ac is 2N. Therefore, the magnetic field sensitivity of the substrate Pa: the magnetic field sensitivity of the substrate Pc: the magnetic field sensitivity of the substrate Pb = 1: 2: 1. In this way, each SQ
Voltages corresponding to the respective magnetic field sensitivity directions are output from the UID array, and this output is output to the variable current sources 21 to 24 shown in FIG.
Dc-SQUI
As shown in FIG. 9, in the magnetic flux voltage conversion characteristics of the D array, the signs of the slopes of the characteristic curves are reversed in the operation region, and a voltage output is obtained between the terminals Ta to Tc. At this time, if the absolute values of the slopes of the characteristic curves are equal, the output voltages of the respective dc-SQUID arrays are canceled and become zero. That is, the SQUID magnetometer 102 functions as a “second-order differential gradiometer” as a whole.

FIG. 4B shows another configuration example 102a of the second-order differential gradiometer as described above, in which the direction of the sensitivity plane is from the front to the back of the figure. And a substrate Pc in which the direction of the sensitivity plane is from the back of the figure to the front, and a substrate Pb in which the direction of the sensitivity plane is from the front to the back of the figure, separated by an appropriate baseline interval D4. They are juxtaposed on the same plane. Even with such a configuration, the same operation as in the case of FIG. 4A can be performed. Further, in FIG. 4A or FIG. 4B, the ratio of the number of SQUID arrays on each substrate is 1: 2: 1. This means that the ratio of the effective area of the SQUID is 1: 2: 1. It doesn't matter. If this idea is developed, a gradiometer of any order can be realized by operating multiple magnetometers as a combination gradiometer and making the direction and value of the magnetic field sensitivity of each magnetometer total zero. be able to.

Next, a third embodiment of the present invention will be described. The configuration of the entire circuit of the SQUID magnetometer 103 of the third embodiment is the same as that of the above-described second embodiment.
The third embodiment differs from the second embodiment in the spatial arrangement of the substrates. FIG. 7A shows a spatial arrangement configuration of the substrate of the SQUID magnetometer according to the third embodiment of the present invention. As shown in the figure, the direction of the sensitivity surface is oriented in the direction of the arrow, and each is arranged at a baseline interval D5.
A QUID array Aa is formed, and a SQUID
A D array Ab is formed, a SQUID array Ac1 is formed on the substrate Pc1, and a SQUID array Ac2 is formed on the substrate Pc2.
Is formed. In this case, the number of SQUIDs in the SQUID array Aa, Ab, Ac1, Ac2 is N
And the magnetic field sensitivity is the same. Therefore,
The magnetic field sensitivity of the substrate Pa: the magnetic field sensitivity of the substrate Pc1: the magnetic field sensitivity of the substrate Pc2: the magnetic field sensitivity of the substrate Pb = 1: 1: 1: 1.

Each of the SQUID arrays Aa, Ab,
The overall circuit configuration of the magnetometer for driving Ac1 and Ac2 and amplifying the signal from the SQUID is the same as in FIG.
The bias current sources 13, 14, 15, 16 can be turned on or off independently. Here, when all the bias current sources 13 to 16 are turned on, all the S
The QUID arrays Aa, Ab, Ac1, Ac2 are turned ON. Therefore, in FIG. 7A, all the substrates Pa, P
b, Pc1 and Pc2 are turned ON. This corresponds to FIG.
The configuration is substantially the same as that of the case (A). Therefore, in this case, it operates as a second-order differential gradiometer. When only the bias current sources 13 and 14 are turned on and the bias current sources 15 and 16 are turned off, the SQUID
Only the arrays Aa and Ac1 are turned on, and the SQUID arrays Ac1 and Ab are turned off. Therefore, in FIG.
Only the substrates Pa and Pc1 are turned on, and the other substrates are turned off. This is substantially the same configuration as the case of FIG. 2A described above. Therefore, in this case, it operates as a first-order differential gradiometer. When only one of the bias current sources is turned on, only one corresponding SQUID array is turned on. Therefore, FIG.
In (A), only one of the substrates is turned on. In this case, it operates as a magnetometer. As described above, if the configurations shown in FIGS. 7A and 6 are employed, the magnetometer, the primary and secondary differential gradiometers can be realized simultaneously by one circuit.

FIG. 7B shows another configuration example 103a of the SQUID magnetometer as described above, in which the direction of the sensitivity surface is from the front to the back of the drawing.
The substrates Pc1 and Pc2 whose sensitivity planes are directed from the back to the front of the figure and the substrate Pb whose sensitivity planes are directed from the front to the back of the figure are separated by an appropriate baseline interval D6. Are arranged side by side on the same plane. Even with such a configuration, the same operation as that in the case of FIG. 7A can be performed. Similarly, by increasing the distance D between the substrates, the number of substrates, the sensitivity, and the sensitivity surface, a gradiometer having a variable differential length can be configured.

Next, a fourth embodiment of the present invention will be described. The configuration of the entire circuit of the SQUID magnetometer 104 of the fourth embodiment is the same as that of the first embodiment.
The fourth embodiment differs from the first embodiment in that the directions of the sensitivity planes are matched, but the coupling coefficients of the negative feedback circuit are reversed from each other as shown by Mn and (-Mn) in FIG. It is in. That is, as shown in FIG. 11, when the negative feedback is zero, the magnetic flux voltage conversion characteristic becomes as shown in FIG.
By setting the sign of the negative feedback magnetic flux to be opposite between the SQUID arrays Aa and Ab, taking the same amount of negative feedback and adjusting the phase by the bias magnetic flux, the respective characteristics are shown in FIGS. 11 (C). With this configuration, the same operation as that of the first-order differential gradiometer shown in FIG. 1 can be realized. Further, similarly to the above embodiments, the same operation as that of FIG. 10B can be realized even if they are arranged on the same plane as shown in FIG.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same function and effect can be realized by the present invention. It is included in the technical scope of the invention.

[0033]

As described in the foregoing, according to this onset bright having the above structure, linearized with negative feedback, by the magnitude of the magnetic flux-voltage conversion rate equal polarities combine opposite the magnetometer, easily A gradiometer can be configured. Since the operating frequency of the SQUID is extremely high, the frequency characteristic of common-mode noise removal is superior to the case where a circuit has a differential configuration. On the other hand, since the respective magnetometers are connected in series, various differential characteristics can be realized with the same configuration by turning on and off with a bias current. Also, the vector magnetometer can be received by one circuit, and the circuit can be simplified .

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration near a SQUID loop of a first embodiment of a SQUID magnetometer according to the present invention.

FIG. 2 is a diagram showing a spatial arrangement of substrates of the SQUID magnetometer shown in FIG.

FIG. 3 is a circuit diagram showing a configuration near a SQUID loop of a second embodiment of the SQUID magnetometer according to the present invention.

FIG. 4 is a diagram showing a spatial arrangement of substrates of the SQUID magnetometer shown in FIG. 3;

FIG. 5 is a diagram showing an overall configuration of the SQUID magnetometer shown in FIG. 1;

FIG. 6 is a diagram showing an entire configuration of the SQUID magnetometer shown in FIG. 3;

FIG. 7 is a view showing a spatial arrangement of substrates in a third embodiment of the SQUID magnetometer according to the present invention.

FIG. 8 is a diagram (1) for explaining the operation of the SQUID shown in FIG. 1;

FIG. 9 is a diagram (2) illustrating an operation of the SQUID shown in FIG. 1;

FIG. 10 is a diagram showing the configuration of a fourth embodiment of the SQUID magnetometer according to the present invention.

11 is a diagram illustrating the operation of the SQUID magnetometer shown in FIG.

[Explanation of symbols]

 Reference Signs List 3 bias current source 4,5 differential amplifier 6 offset voltage source 7,8 variable current source 9,10 magnetic flux injection coil array 13-16 bias current source 17,18 differential amplifier 19 offset voltage source 21-24 variable current source 25 -28 Magnetic flux injection coil array Aa, Ab, Ac SQUID array D1-D6 Baseline interval ib Bias current imb Current for bias magnetic flux J Josephson junction La1-LaN, Lb1-LbN, Lc1-LcN Negative feedback coil Mb, Mn Coupling coefficient Rn Negative feedback resistor Sa1-SaN, Sb1-SbN, Sc1-ScN SQUID 101-104 SQUID magnetometer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-264281 (JP, A) JP-A-3-42587 (JP, A) JP-A-5-232202 (JP, A) JP-A-7- 260911 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01R 33/035 ZAA G01R 33/02 H01L 39/22 ZAA

Claims (5)

(57) [Claims] 1. n with one or an array of SQUIDs
(N: a natural number satisfying n ≧ 1) first magnetometers;
SQUID magnetometer wherein n second magnetometers are arranged so that the direction of the magnetic field sensitivity is opposite to that of the first magnetometer. 2. The SQUID magnetometer according to claim 1, wherein one or an array of negative feedback coils for performing negative feedback directly from an output terminal of the SQUID to the SQUID, and a negative feedback for controlling an amount of the negative feedback. A coupling capacitance between the SQUID and the negative feedback coil is Mn.
When the magnetic flux voltage conversion rate when the SQUID is one is dV / dφ and the negative feedback resistance value is Rn,
SQUI is characterized in that it is configured to satisfy the following expression: nx (dV / dφ) × (Mn / Rn) ≧ 1.
D magnetometer. 3. The SQUID according to claim 1 or claim 2.
In the magnetometer, a bias current source for driving the SQUID to perform sensitivity adjustment, and injecting a bias magnetic flux into the SQUID.
A SQUID magnetometer having a bias magnetic flux injection source for performing phase adjustment and adjusting the phase or sensitivity of the SQUID. 4. The SQUID according to claim 2 or claim 3.
In fluxmeter, more reversing the sign of the negative feedback in the negative feedback coil, said first magnetometer and a second Magunetome
Characterized by reversing the direction of magnetic field sensitivity of the data
UID magnetometer. 5. The SQUID according to claim 3 or claim 4.
A SQUID magnetometer wherein each of the bias current sources of the first magnetometer and the second magnetometer can be independently turned ON or OFF.