JPH01197679A - Superconducting magnetometer - Google Patents

Abstract

PURPOSE:To make induction by an external magnetic field difficult by providing a photoelectric converter, an optical fiber of necessary length, a nonmagnetic photoelectric converter, etc. CONSTITUTION:This magnetometer is equipped with the photoelectric converter 12 which converts the current signal from a phase detector 7 which is passed through a feedback resistance 9 and the high frequency current signal from an RF oscillator 8 at the same time, the optical fiber 13 which transmits the output light of this converter 12 by necessary length, and the nonmagnetic photoelectric converter 14 which converts the output light from the fiber 13 into a current signal. Then the converter 14 is arranged nearby a feedback modulating coil 3 within the range wherein an extremely small magnetic noise exerts no adverse influence, and the output light from the fiber 13 is converted into the current signal, which is sent to a coil 3. Thus, the feedback modulated current signal transmitted by the system of the converter 12, fiber 13, and converter 14 is not induced by the external electromagnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting magnetometer that is mounted on an aircraft or the like and measures a weak magnetic field similar to that of earth's magnetism with high sensitivity.

[Conventional technology]

Figure 2 is a configuration diagram showing an example of a conventional superconducting magnetometer, in which (1) is a Josephson junction, (2) is a superconducting ring,
(3) is a feedback modulation coil, (4) is a battery, (5) is a variable resistor, (6) is an amplifier, C7) is a phase detector, (8) is an RF oscillator, (9)\ is a feedback resistor, αG is from 8Q, U ('5uper QUa-mt um engineering interfe
(111 is a feedback modulation signal transmission line. Components not related to this invention are omitted. The superconducting ring (2) is 2 here.
A high-temperature superconductor with two tunnel-type Josephson junctions (1), for example, an oxide-based Y-Ba-cu-o, whose shape is a square of about 200 μm x 200 μm, and its ring width is It is a flat type with a thickness of about 20 μm and a thickness of about 10 μm. The feedback modulation coil (3) is made of the same material as the superconducting ring (2) and has the same shape as the superconducting ring (2). feedback current and RF oscillator (8)
The modulated current from the superconducting ring (2) is transmitted to the superconducting ring (2) via the feedback modulated signal transmission line U by transformer coupling. A battery (4) and a variable resistor (5) set the operating point of the superconducting ring (2). The amplifier (6) is a low noise amplifier and amplifies the output of the jth superconducting ring (2) while maintaining a required signal-to-noise ratio. A phase detector (71) detects the phase of the output of the amplifier (6) using the output signal of the 100 KHz RF oscillator (8) as a reference signal. ) and the feedback modulation coil (3) from the SQU to the sensor section α.
I will call it 1.

The superconducting magnetometer described above is called an eLa sQ, DID magnetometer, and an outline of its operating principle will be described below.

Figure 3 is an explanatory diagram of the magnetic flux detection method using da 8QU, and the fourth figure is an explanatory diagram of the modulation method in (10SQ, UID).As is well known, in a superconductor, electrons form pairs (Cooper pairs). Therefore, a coherent current with zero electrical resistance is flowing.In the Josephson junction, a phase difference occurs in the electron waves, and the current flow is expressed by the following equation.

■=ICsinθ (11 here e
Ic: Superconducting critical current 02 phase difference.

In addition, in a superconducting ring, the magnetic flux inside the ring is Φ, and the magnetic flux quantum is Φ0 (107X1 G -10Wb).

Φ=nΦo (n: integer) (2) holds true. The superconducting critical current of two Josephson junctions is calculated by setting the phase difference of IC1 electron waves to 01. If θ2 is the basic equation of the Josephson effect, it can be expressed as H sin θ1 + IC sin σ2 (3), and from the quantization of fluxoids in the superconducting ring.

Φ 01-02: 2π (-10n) (n: integer) (4) Φ0. The phase difference that occurs on both sides of the Josephson element is determined by the magnetic flux Φ that passes through the ring. From equations (3) and (4), the case when n=0 can be obtained.

From dcsQ, U, depending on whether the magnetic flux in the ring is nΦ0 or (n+-)Φ0, the tune fi! in Fig. 3 is generated. Since the knee V characteristics change as shown in jIA and curve B, if a current slightly larger than the superconducting critical current C is applied as shown in Figure 2, the voltage V has an amplitude of ΔV and Φ. The value becomes a periodic function. Here, the operating point of the superconducting ring (2) is set at point D in Figure 4, and the RF oscillator (7)
When the AC magnetic flux of KH2 is added, the output is only the p 200 KH2 component, which is twice the modulation frequency, but when the external magnetic flux Φ is added thereto, a 100 KHz component is generated. When this signal is processed by the phase detector (7) and fed back to the output 't-feedback modulation coil (3), the feedback current f indicates the value of the external magnetic flux, and from this value the external magnetic field is You can know the strength.

In FIG. 2, the value of the current flowing through the feedback modulation signal transmission line (11) is very small, at a maximum of approximately ±5 mA, when measuring a weak magnetic field on the order of geomagnetism with this system.

In addition, in Fig. 2, a battery (41), a variable resistor (5
).

The electronic circuits and electronic components of the amplifier (6), two-phase detector (71), and RF oscillator (8) ensure that the magnetic noise they generate does not have a more detrimental effect on the magnetometer than the ac 8QU.

, 8Q is usually installed at a distance of about 5 m or more from the DID sensor section αG.

[Problem to be solved by the invention]

Although the above-mentioned DC 8QU magnetometer theoretically has an altitude of 10-5 gamma (1 ga/ma = IQ, 6), the feedback modulation current is as small as about ±5 mA at maximum.

In addition, this signal must be transmitted to the feedback modulation coil located approximately 5 meters or more away, so even if the feedback modulation signal transmission line is shielded, the operation of the system may become unstable due to the induction of external electromagnetic fields. There was a problem that could easily arise. In particular, when this dcsQ, DID magnetometer is mounted on an aircraft to measure the earth's atmosphere, etc., it is strongly guided by electromagnetic field signals generated by other onboard electronic equipment, which stabilizes the system. The problem was that it was extremely difficult to operate the system.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a superconducting magnetometer whose operation is stable even when subjected to external electromagnetic field induction.

[Means to solve the problem]

The superconducting magnetometer according to the present invention requires a photoelectric converter that simultaneously converts a current signal from a two-phase detector via a feedback resistor and a high-frequency current signal from a Ry oscillator into an optical signal, and an output light of this photoelectric converter. an optical fiber that transmits a length of
It is equipped with a nonmagnetic photoelectric converter that converts the output light from this optical fiber into a current signal.

[Effect]

The feedback modulation current signal transmission system of the photoelectric converter, the optical fiber of a required length, and the nonmagnetic photoelectric converter in this invention makes it less susceptible to external electromagnetic field induction.

〔Example〕

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

(Lz is a photoelectric converter, Q3 is an optical fiber, and α is a non-destructive photoelectric converter. In the figure, components not related to this invention are omitted. The photoelectric converter α2 is AICk aA Q A light emitting diode of /G aA @ semiconductor element has a peak of its emission spectrum at 860 μm, and simultaneously emits the current signal from the two-phase detector (7) via the feedback resistor and the high-frequency current signal from the RF oscillator. The optical fiber 03 that converts into signals is an 81-series optical fiber with a core diameter of about 50μ and an outer circumference with a thickness of about 0.1μ.
Covered with MS nylon.

The total length is approximately 5.3 m, and the output light from the photoelectric converter (2) is transmitted with low loss. The non-magnetic photoelectric converter α fathom is GaA.

All mechanical parts of the system, except for the semiconductor element part that receives light from the solar cell, are made of non-magnetic material 2 such as P/RP (FlberRei
Constructed of nforced plastic. This non-magnetic photoelectric converter I is installed in the vicinity of the feedback modulation coil (3) within a range where its ultra-minute magnetic noise does not have an adverse effect, and converts the output light from the optical fiber 〇 into a current signal. and sends it to the feedback modulation coil (3). The functions of the other components are the same as those described in FIG. The feedback modulated current signal transmitted through the system of photoelectric converter C12° optical fiber α31 and nonmagnetic photoelectric converter No. 6 is not induced by an external electromagnetic field.

〔Effect of the invention〕

As described above, according to the present invention, a minute current signal transmitted to a feedback modulation coil is converted into an optical signal by a photoelectric converter,
After transmitting this optical signal over the required distance using optical fiber,
Since the signal is converted into a current signal using a non-magnetic photoelectric converter, it is possible to obtain a superconducting output meter with stable operation despite the induction of an external electromagnetic field.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional embodiment, Fig. 3 is an explanatory diagram of a magnetic flux detection method using dQ 8QU, and Fig. 4 is a dcsQT] It is an explanatory diagram of a modulation method in . In the figure, (1) is a Josephson junction, (2) is a superconducting ring, (3) is a feedback modulation coil, (4) is a battery, (
5) is a variable resistor, (6) is an amplifier, (71 is a phase detector, (8) is a Ry oscillator, <9) is a ul'Nl resistor,
(IIU SQ, TlID sensor i. all is feedback modulation signal transmission line, (12 is photoelectric converter,
α3 is an optical fiber, and αhiro is a nonmagnetic photoelectric converter. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] a superconducting ring having two Josephson junctions, a feedback modulation coil transformer coupled to the superconducting ring, means for setting an operating point of the superconducting ring, and an amplifier for amplifying the output of the superconducting ring; A phase detector that detects the phase of the output from the amplifier using a predetermined high frequency signal from the RF oscillator as a reference signal, a current output from the output from the phase detector via a feedback resistor, and a high frequency current output from the RF oscillator. an optical fiber that transmits the optical signal from the photoelectric converter over a required distance; and an optical fiber that converts the optical signal from the optical fiber into a current signal and transmits the current signal to the feedback modulation coil. A superconducting magnetometer characterized by comprising a non-magnetic photoelectric converter that sends a signal to a non-magnetic photoelectric converter.