JPS588475B2 - Magnetic flux detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for detecting magnetic flux, commonly called a SQUID.

SQUID takes advantage of the property of superconducting materials such as Nb to transition to a superconducting state at extremely low temperatures, and creates a weak bond in a part of a ring made of superconducting materials to keep this superconducting ring at extremely low temperatures. This device detects a change in the external magnetic flux by detecting a change in the state of the ring coupling portion caused by crossing the ring with a magnetic flux corresponding to the external magnetic flux to be measured.

FIG. 1 is an explanatory diagram of the principle of SQUID. In the figure, a ring 1 made of a superconducting material (hereinafter referred to as a superconducting ring) has a weak bonding portion, for example, a point contact portion 11 in a part.

The coil 2 together with the capacitor 3 forms a tank circuit 4 which is inductively coupled to the superconducting ring 1 .

The tank circuit 4 is an LC resonant circuit that receives weak high frequency power from the high frequency power supply 6 and resonates at high frequencies.

The coil 5 is connected to a search coil (not shown) for searching for external magnetic flux to form a closed circuit with this.

This coil 5 is also arranged to be inductively coupled to the superconducting ring 1.

The superconducting ring 1, the high frequency resonant circuit 4, and the coil 5 are placed in a cryostat of liquid helium, indicated by the dotted line B, and maintained at helium temperature.

A high frequency voltage generated in the resonant circuit 4 by high frequency power from the high frequency power source 6 is amplified by an amplifier AMP and rectified by a rectifier, and then becomes an output signal.

Now, if the external magnetic flux crossing the search coil connected to the coil 5 changes and the magnetic flux crossing the superconducting ring 1 changes, the weakly coupled portion 11 of the superconducting ring changes to a superconducting state in response to this magnetic flux change. ←Repeat the switching operation in normal conduction state.

As a result, the output signal repeatedly oscillates as the external magnetic flux increases, forming a waveform characteristic curve as shown in FIG.

The maximum value of the output appears every time the external magnetic flux increases by one flux quantum (1.).

By counting the number of oscillations that appear in this output, it is possible to measure the change value, that is, the integral value, of the magnetic flux that intersects with the search coil.

In such devices, recent advances in thin film manufacturing technology have made it possible to construct weak coupling portions with thin film bridges.

FIG. 3 is a block diagram showing an example of such a thin film SQUID.

In this thin film SQUID, a thin film 13 is formed by depositing a superconducting material such as Nb on a sapphire substrate 12 to a thickness of 700 Å to 1000 Å,
Two holes 14 and 15 are provided in this thin film, and a thin film bridge corresponding to a weak connection portion is provided in the middle of narrow grooves 16 and 17 connecting these holes 14 and 15.

A device in which the weak connection portion is formed by a thin film bridge has various advantages, such as stable operation over a long period of time, compared to a structure in which the weak connection portion is formed by a point contact type.

Here, the present invention aims to provide a magnetic flux detection device that includes the above-mentioned thin film SQUID and a coil efficiently coupled to the SQUID, and that is compact and lightweight as a whole and is suitable for mass production.

FIGS. 4 and 5 are configuration diagrams showing an example of a coil used in the device according to the present invention.

In the embodiment shown in FIG. 4, spiral coils 22 are arranged at different positions on both planes of a substrate (for example, glass epoxy) 21.
．． 23 is formed, and these spiral coils 22 and 23 are electrically connected through a through hole 24 to form an approximately figure-eight-shaped coil as a whole.

25 and 26 are lead wires of the coil. In the embodiment shown in FIG. 5, a plurality of through-holes are provided in the substrate 21, and the conductive wire is wound through these through-holes so as to span both planes of the substrate 21 so as to form an approximately figure-eight shape as a whole. two coils 22
．． 23.

FIG. 6 shows the arrangement relationship between the thin film SQUID 1 and the coil 2. The centers of the coils 22 and 23 forming a substantially figure 8 shape are the centers of the holes 14 and 15 provided in the thin film of the thin film SQUID 1. Both are arranged parallel to each other so as to be substantially opposite to each other.

In this way, the coil 2 is arranged in parallel with the thin film SQUID 1, and a high frequency signal is transmitted to the coil 22 through the lead wires 25 and 26.
．． 23, the resulting magnetic lines of force are as shown in FIG.

That is, if we consider the half cycle in which the lead wire 25 side is + and the lead wire 26 side is +, then the coil 22.
As shown in the direction of the arrow in FIG. 6, the current flowing through the conductor 23 flows in the same direction through two or four conductors that are close to each other.

Therefore, magnetic lines of force are generated by combining these two or four conductors as shown by the arrows in FIG. 1, and efficiently intersect the thin film SQUID 1.

Note that here, the coil 2 to which the high frequency signal is applied is the fourth coil.
Although the structure shown in FIG. 5 and FIG. 5 is shown in which this and the thin film SQUID are arranged, the coil 5 in FIG. It may be arranged on the opposite side.

Further, although the coils shown in FIGS. 4 and 5 are shown with two turns on the left and right, a total of four turns, a different number of turns may be used.

According to the device constructed in this way, the thin film SQUID and coil can be assembled in a thin shape, the coupling between the SQUID and the coil can be improved, and the mechanical alignment between them is easy, making mass production possible. A magnetic flux detection device can be realized.

FIG. 8 is an assembly diagram showing another embodiment of the device according to the present invention.

In this figure, 7 is a superconducting ring block made of white metal, for example, and has a groove 71 in which the thin film SQUID 1 is accommodated, cylindrical small holes 72 and 13 that penetrate the block and are arranged in parallel, and these holes. A void 14 communicating with the small holes 72 and 73 is provided.

8 is a spacer with a thickness of about 1 mm interposed between the thin film SQUID 1 and the coil 2, and 9 is a coaxial cable.

8L82 is a holding screw, and after storing the thin film SQUID 1 in the groove 11, stack the spacer 8 and coil 2 and tighten these screws 8.
1 and 82, the superconducting ring block 7, thin film SQUID 1, spacer 8 and coil 2 are assembled together.

In the device of this embodiment, a small cylindrical hole 72. is provided in the superconducting ring block 7. A coil 5 for applying a measurement magnetic field is inserted into 73.

Note that this coil 5 is made of a cylindrical bobbin wound with a conducting wire.

When the thin film SQUID is held by a superconducting ring block as in this example device, the superconducting block 7 and the thin film SQUID are combined, and the whole forms one SQUID sharing a weak bonding part. This has the advantage that the inductance is reduced and the detection sensitivity is increased.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. A thin film SQUID, which is constructed by providing two holes in a thin film of superconducting material adhered to an insulating substrate and a weak bonding part in the middle of a thin groove connecting the two holes, and a flat plate substrate. The coil is divided into both planes and formed into a generally figure-eight shape, and the thin film SQUID and the coil are connected to the two holes provided in the thin film and the center of the coil forming the figure-eight, respectively. Magnetic flux detection device arranged to correspond. 2. The magnetic flux detection device according to claim 1, wherein the thin film SQUID is held by a superconducting ring block having two cylindrical small holes arranged in parallel with each other and a gap communicating with these small holes. .