JP2526601B2 - Superconducting magnetometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting magnetometer for measuring a weak magnetic field by utilizing a critical current of a superconducting material.

(B) Conventional technology RF-SQU is a conventional magnetometer using superconductivity.
There are ID and DC-SQUID. All of these have a Josephson junction (JJ) in the superconducting ring. An example of a Josephson junction element is shown in FIG. In the figure, a superconducting thin film (eg Nb) 12 is formed on an insulating substrate (eg SiO ₂ ) 11, and the superconducting thin film 12 constitutes a superconducting ring 13. Song Junction 14 is formed.

(C) Problems to be Solved by the Invention In the conventional superconducting magnetometer described above, it is necessary to set the critical current value of the Josephson junction to about several μA,
There are many problems in manufacturing, and the number of manufacturing processes is large.

The present invention focuses on the above problems and aims to provide a superconducting magnetometer which can simplify the structure of the magnetic sensor part and can be easily manufactured.

(D) Means and Actions for Solving Problems The superconducting magnetometer of the present invention has a superconducting material having an exciting terminal, an output terminal and a pickup coil connecting terminal, and a small critical current value, and the exciting terminal. And a pickup coil which is connected to the pickup coil and is excited at the critical current value or more, and a pickup coil whose both ends are connected to the pickup coil connecting terminal and which forms a superconducting loop with the superconducting material.

In this superconducting magnetometer, normally, the superconducting material is
It is over-excited by the excitation source, and the output voltage is derived to the superconducting material. Here, when a magnetic field enters the pickup coil, an induced current flows in the superconducting loop and is superimposed on the current from the excitation source. Therefore, this becomes a change in the output of the superconducting material, and the magnetic field is detected. In this superconducting magnetometer,
Since the superconducting material has a simple structure, it is easy to manufacture.

(E) Examples Hereinafter, the present invention will be described in more detail with reference to Examples.

FIG. 1 is a circuit connection diagram of a superconducting magnetometer showing an embodiment of the present invention. In the figure, a thin-film superconductor 2 such as niobium is characteristically provided.
Is a strip-shaped thin film, the pickup connection terminals 2a, 2a,
Furthermore, it is provided with 2b and 2b which are used as both the excitation terminal and the output terminal. The pickup coil 1 is connected to the pickup coil connecting terminals 2a, 2a of the superconductor 2 by superconducting connecting wires 4, 5. Further, the fundamental frequency current generating circuit 3 is connected to the excitation terminals 2b, 2b of the superconductor 2, and the alternating excitation current is of a predetermined frequency is input. On the other hand, the connection terminals 2b, 2b are connected to the AC amplifier 6 and the superconductor 2
The current that flows in the superconductor changes output depending on the superconducting state or normal state of the superconductor.
The output voltage e is amplified by the synchronous rectifier circuit 7 and periodically rectified by the synchronous rectifier circuit 7. The equivalent circuit diagram of the superconducting magnetometer of FIG. 1 is shown in FIG. 2. The current is flows in the superconductor by the alternating current of the input signal source a ₀ sin ωt, which is the excitation source, Normally, this current is configured so that an exciting current larger than the critical current ic flows as shown by the solid line in FIG. L is the inductance of the pickup coil, and when the magnetic flux φ of the surrounding magnetic field is linked to this L, the current ix flows. Thus, now showing the relationship between the input current and the output voltage of the superconductor 2, as shown in FIG. 3, for the input up to the critical current ic, the output is in the superconducting state. The output V is zero, but since it is in the overexcitation state after that, the superconductor 2 is in the normal state, the normal conductor,
That is, since it has a certain resistance value, a voltage is output at a predetermined resistance value. In this example superconducting magnetometer,
Since the amplitude of the current is input from the fundamental frequency current generation circuit 3 is set to be in the overexcitation state, that is, larger than the critical current, the output voltage, that is, the voltage output from the AC AMP6 is shown in FIG. As shown in the right part of FIG. That is, the output voltage shown by the solid line is obtained. On the other hand, when the magnetic flux φx due to the magnetic field is now input to the pickup coil 1, an induced current ix flows due to this, and this ix, that is, ix is superimposed on the alternating current is, and the input current is As shown by the broken line in the lower part of FIG. 3, the output voltage also changes as shown by the broken line in the right part, and the output voltage changes. By deriving this change as an output, the strength of the minute magnetic field can be known.

(F) Effect of the Invention According to the present invention, a plate-shaped superconducting thin film is used as a sensor, and a superconducting loop is formed between the superconducting thin film and the pickup coil. Since it is not a complicated structure such as the Josephson junction provided at the intersection of the superconducting rings like the skid magnetometer of, the manufacturing is simple and can be easily made. Further, since the sensor itself does not form a superconducting loop, there is an advantage that the area of the sensor portion is reduced and a large number of sensors can be arranged.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a superconducting magnetometer showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of the superconducting magnetometer, and FIG. 3 shows an operation of the superconducting magnetometer. FIG. 4 is a perspective view showing an example of a conventionally used Josephson junction element, which is a waveform characteristic diagram of input / output current and voltage. 1: Pickup coil, 2: Superconductor, 3: Fundamental frequency current generation circuit, 4,5: Superconducting connection line, 6: AC AMP, 7: Synchronous rectification circuit.

Claims (1)

(57) [Claims] 1. A superconducting material having an excitation terminal, an output terminal and a pickup coil connection terminal, having a small critical current value, an excitation source connected to the excitation terminal and exciting at a value of the critical current value or more, A superconducting magnetometer, comprising: a pickup coil having both ends connected to a pickup coil connecting terminal, the pickup coil forming a superconducting loop with the superconducting material.