JPH0654347B2 - Magnetometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a highly sensitive magnetometer using a Josephson device.

[Background of the Invention]

Magnetometers using Josephson devices are known in the art and are known as SQUID magnetometers. Prior art magnetometers are DC-SQUID magnetometers, AC-
It is represented by the SQUID magnetometer. The DC-SQUID magnetometer is a device for observing a magnetic flux interlinking with a superconducting loop composed of two Josephson junctions and an inductor as a change in the maximum superconducting current flowing in the superconducting loop at a direct current. r
The f-SQUID magnetometer is a device for observing the magnetic flux interlinking with a superconducting loop composed of one Josephson junction and an inductor, as a change in the maximum superconducting current flowing in the superconducting loop. In any of the conventional SQUID magnetometers, the essential SQUID is a passive element that detects the magnetic flux interlinking with the superconducting loop, and the SQUID using the Josephson junction is immersed in liquid helium and the output signal is wired. It is configured to be sent to a measurement circuit and a data processing circuit at room temperature via a cable. The SQIUD measures a very weak magnetic flux, and the output signal of the Josephson element is also a weak signal itself. Therefore S
The signal sent from the QUID to the measurement circuit at room temperature is an extremely weak signal of, for example, about 1 μV. Therefore, the sensitivity of the conventional SQUID magnetic flux system is limited by the thermal noise at room temperature.

Direct current magnetic flux parametron (DC Flux Parametron: DCF)
The circuit (referred to as P) is an active switching device that operates in liquid helium and provides high circuit gain. This D
The CFP circuit is described in detail in RIKEN Symposium Proceedings 1984, pp. 1-3 and pp. 48-78, and RIKEN Symposium Proposal 1984, pp. 1-13. Since this DCFP circuit has high sensitivity to magnetic flux and operates at an extremely low temperature (liquid helium temperature), thermal noise is extremely small. However, since the DCFP circuit is a switching circuit, a binary (ON-OFF) servo mechanism is required for use in analog measurement such as a magnetic flux system.

[Object of the Invention]

An object of the present invention is to provide a highly sensitive magnetic flux meter that uses a DCFP circuit and is strong against external noise.

[Outline of Invention]

In order to achieve this object, the present invention uses a DCFP circuit as a high sensitivity magnetic flux comparison circuit, and this DCFP circuit is used to compare the input magnetic flux with a reference signal of a reference signal generation circuit provided elsewhere. A circuit control method that uses a signal as an output signal is adopted.

Example of Invention

The present invention will be described below with reference to examples. FIG. 1 is a circuit diagram of a DCFP circuit used in the present invention. This DCFP
The circuit is a superconducting loop 1 consisting of two Josephson junctions 101 and 102 and two exciting inductors 103 and 104.
It is composed of 08. Input signal current is input line 107
Is injected into the superconducting loop 108 via. This input current is amplified by the exciting current flowing through the exciting wire 106 and becomes an output current, which flows through the load inductor 105. In this case, the flow direction of the output current is determined by the direction of the input current, and flows in the positive direction or the negative direction. That is, this DCFP circuit performs an operation of amplifying the input signal by the excitation current (excitation power) using the positive or negative polarity of the input signal as the seed signal, but the polarity of the output current is amplified depending on the seed signal. It is something. FIG. 2 shows a method of using the DCFP circuit as a comparison circuit. The comparison circuit shown in FIG. 2 has a configuration in which a reference signal transformer 110 and an input signal transformer 112 are connected in series to the input line 107 of the DCFP circuit shown in FIG. The input magnetic flux input via the input signal line 113 and the reference magnetic flux input via the reference signal line 111 are added to become the input magnetic flux of the DCFP circuit, and this magnetic flux becomes a seed signal and is amplified by the excitation current. Figure 3 shows DCF
Another method of using the P circuit as a comparison circuit is shown. The circuit shown in FIG. 3 has a DCFP circuit shown in FIG. 1 and a reference signal transformer 110 and an input signal transformer 112 connected in parallel to the input line 107.
a, 107b. FIG. 4 is a block diagram of a magnetometer according to the present invention. Magnetometer is DC
It is composed of a comparison circuit 201 composed of an FP circuit and a reference signal generation circuit 202. An input magnetic flux and a reference signal are applied to the comparison circuit 201 via the input signal line 113 and the reference signal line 111, respectively. The comparison circuit 201 uses the D
It is composed of a comparison circuit using a CFP circuit, and the difference between the input signal and the reference signal is amplified by excitation and input to the reference signal generation circuit 202 via the wiring 203 as an output signal. The reference signal generation circuit 202 outputs a signal obtained by amplifying the input signal as an output signal to the outside through the output signal line 204. Next, the configuration of the magnetometer according to the present invention will be described more specifically. FIG. 5 is a configuration example of the comparison circuit 201. The circuit shown in FIG. 5 is similar to the DCFP circuit shown in FIG.
07a, the magnetic flux antenna 5 via the input signal transformer 112
The input magnetic flux sensed at 01 is input. Input signal transformer 1
A calibration line 503 for calibrating the magnetic flux sensitivity is installed at 12. The input magnetic flux introduced into the DCFP circuit is compared with the reference signal input from the input line 107b, and the difference between the input signal and the reference signal is amplified. A current detection circuit including a magnetic flux coupling type quantum interference device 506 and a bias line 507 is installed in the load of the DCFP circuit. The magnetic flux coupling type quantum interference device 506 and the DCFP circuit are coupled via a wiring 505. A gate current is supplied to the magnetic flux coupling type quantum interference device 506 via a wiring 508. DC here
Part of the load inductor of the FP circuit is the wiring 50 of the detection circuit.
It has 5 inductors. The operating principle of this circuit is described in detail in Japanese Patent Application No. 58-222110. FIG. 6 shows a first embodiment of the control system of the magnetometer using the comparison circuit shown in FIG. This system is a typical example of a feedback loop. In the embodiment shown in FIG. 6, the reference signal generation circuit 202 includes a register 301 that indicates the value of the reference signal, a register control circuit 302 that increases or decreases the value of the register 301, and a D / A that converts the digital signal of the register into an analog signal. Conversion circuit 303, attenuator 3
It is composed of 04. In the magnetic flux system shown in FIG. 6, the reference current generating circuit and the comparison circuit shown in FIG. 5 form a feedback loop. That is, the reference signal value of the register is updated by the output signal of the comparison circuit 201, and the value is fed back to the comparison circuit 201 via the D / A conversion circuit 303 and the attenuator 304. FIG. 7 is a time chart of the operation of the magnetic flux system shown in FIG. DCFP
The circuit is excited periodically as shown by waveform 600. The output of comparator circuit 201 is shown in waveform 601. In this waveform, if the input signal is larger than the reference signal, the positive polarity is output, and if it is smaller, the negative polarity is output. The register control circuit 302 uses the polarity of the output signal of the comparison circuit 201 to register 3
The value of 01 is updated at the timing shown by the waveform 602. Here, for example, when the output waveform of the comparison circuit 201 has a positive polarity, the value of the register 301 is increased (counted up).
However, in the case of negative polarity, if the value of the register 301 is decreased (counted down), in the configuration shown in FIG. 7, a stable state is achieved when the input signal and the reference signal input to the comparison circuit are equal. it is obvious. If the attenuation factor of the attenuator is increased in this control system, the ratio of the output signal to the input signal, that is, the circuit gain can be increased, but on the other hand, the gain of the feedback loop is small and the response of the circuit becomes slow. FIG. 8 shows a second embodiment of the control system of the magnetometer using the comparison circuit shown in FIG. This system is a typical example of a feedforward system. Reference signal generation circuit 2
Reference numeral 02 designates a signal sweep circuit 401 and a D / A conversion circuit 30.
3, an attenuator 304, and a hold circuit 404. FIG. 9 is a time chart of the operation of the magnetometer shown in FIG. The output signal of the signal sweep circuit 401 indicates the value of the reference signal, and the value increases by one unit for each cycle. Since the D / A conversion circuit 303 uses the output signal of the signal sweep circuit 401 as an input signal, the output signal has a stepwise sweep waveform shown by a waveform 701. This stepwise sweep waveform is input as a reference signal to the comparison circuit 201 via the attenuator 304. Comparison circuit 201
The DCFP circuit of is excited in synchronization with the cycle of the signal sweep circuit 401 as shown by the waveform 700. Comparison circuit 201
The output waveform of is shown in waveform 702. In this waveform, if the input signal is larger than the reference signal, the positive polarity is output, and if it is smaller, the negative polarity is output. The reference signal value when the polarity of the output waveform of the comparison circuit 201 switches from positive to negative is equal to the input signal. Therefore, at this time, the hold circuit 404 outputs the waveform 7
A hold signal indicated by 03 is generated to hold the value of the reference signal. If the attenuation rate of the attenuator 304 is increased in this control system, the ratio of the output signal to the input signal, that is, the circuit gain can be increased, but on the other hand, the measurement accuracy decreases. In the above two control systems, the source of the reference signal was a digital signal source, but it is clear that it can be configured by an analog signal source.

FIG. 10 shows a third embodiment according to the present invention. The comparison circuit 800 shown in FIG. 10 is shown in FIG. It is equivalent to the comparison circuit using the DCFP circuit, but the DCF is used to increase the amplification factor.
It has a configuration in which P circuits are connected in series. That is, DCF
The amplifier by the P circuit is a DCFP circuit 801a, DCFP
The circuit 801b and the DCFP circuit 801c have three stages connected in series by inductors 802a and 802b. Here, for example, the maximum superconducting current of the Josephson junction of the DCFP circuit 801a is 10 μA, and the DCFP circuit 801
The maximum superconducting current of the Josephson junction of b is 100 μA,
If the maximum superconducting current of the Josephson junction of the DCFP circuit 801c is set to 1000 μA, even a weak signal current due to an input magnetic flux of about 1 μA can obtain a large output current of 1000 times as an output. Here, the DCFP circuit is driven by three layers of excitation current so that the signal is propagated to only one side. That is, the DCFP circuit 801a has the excitation line 106a, the DCFP circuit 801b has the excitation line 106b,
The DCFP circuit 801c is driven by an exciting current whose phase is shifted by 120 degrees via an exciting line 106c. Although the example of FIG. 10 shows the example of the amplifier circuit in which the DCFP circuits are connected in three stages, it is clear that the amplifier circuit can be configured by connecting the DCFP circuits in series by any number of stages. Fig. 11 shows 10
It is an example of the magnetometer using the comparison circuit shown in the figure. In this circuit, the comparison circuit 800 shown in FIG. 10, the up / down counter circuit 810, and the D / A conversion circuit 303 form a closed loop. The up / down counter circuit 810 is updated by the control device 820. Here, it is obvious that the data can be updated in the same manner as in the embodiment shown in FIG.

〔The invention's effect〕

According to the present invention, a weak input magnetic flux signal can be taken out to a measuring machine and a processing device at room temperature in a form amplified in liquid helium. Therefore, the present invention is effective in constructing a magnetic flux meter having high resistance to thermal noise and high sensitivity. Use of this magnetometer is useful for measuring weak magnetic fields, such as magnetic fields generated by the human body.

[Brief description of drawings]

FIG. 1 is a block diagram of a DCFP circuit used in the present invention, and FIG.
FIGS. 3, 3, 5 and 10 are DCs used in the present invention.
FIG. 4 is a diagram showing a comparison circuit using an FP circuit, FIG. 4 is a block diagram showing a magnetometer according to the present invention, FIG. 6 is a diagram showing an embodiment of the magnetometer of the present invention, and FIG. 7 is a magnetic flux shown in FIG. 8 shows an operation time chart of the magnetometer, FIGS. 8 and 11 show another embodiment of the magnetometer of the present invention, and FIG. 9 shows an operation time chart of the magnetometer of FIG. . 101, 102 ... Josephson junction, 103, 104 ...
Excitation inductor, 105 ... Load inductor, 106 ... Excitation line, 107 ... Input line, 108 ... Superconducting loop, 110
Reference signal transformer, 112 ... Input signal transformer, 201 ...
Comparing circuit, 202 ... Reference signal generating circuit, 113 ... Input signal line, 204 ... Input signal line, 501 ... Flux antenna, 5
03 ... Calibration line, 506 ... Magnetic flux coupling type quantum interference device, 50
7 ... Bias line, 301 ... Register, 302 ... Register control circuit, 303 ... A / D conversion circuit, 304 ... Attenuator,
401 ... Signal sweep circuit, 404 ... Hold circuit, 8
00 ... Comparison circuit, 801 ... DCFP circuit, 802 ... Inductor, 810 ... Up-down counter circuit, 820 ...
Control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ushio Kawabe 1-280 Higashi Koigakubo, Kokubunji, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd. (72) Nobuo Miyamoto 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (56) Bibliographical Reference 59-15973 (JP, U) Proceedings of RIKEN Symposium 1984 Proc. 1-3, PP. 48-78 RIKEN Symposium Proceedings 1994 P.P. 1-13

Claims (6)

[Claims] 1. Use of means for inputting the magnetic flux to be detected as an input signal, means for generating a reference signal, and a DCFP circuit for amplifying the difference between the input signal and the reference signal by excitation and outputting it as an output signal. A magnetic flux meter characterized by comprising a comparison circuit that has been used. 2. A magnetometer according to claim 1, wherein increase or decrease of the reference signal is controlled by an output signal of the comparison circuit. 3. The reference signal according to claim 1, wherein the reference signal independently sweeps its value, all or part of the reference signal is introduced into the DCFP circuit, and the reference signal is output by the DCFP circuit. A magnetometer, wherein a case where the input signal and the magnetic flux of the reference signal match is found, and the value of the magnetic flux of the reference signal at that time is output. 4. A magnetometer according to claim 1, wherein two or more DCFP circuits of said comparison circuit are connected in series. 5. A magnetometer according to claim 1, wherein the means for inputting the magnetic flux to be detected as an input signal is a magnetic flux antenna. 6. The magnetometer according to claim 5, wherein the magnetic flux antenna is connected to the comparison circuit via a transformer.