JPH0526544Y2 - - Google Patents

Description

[Detailed description of the invention] "Industrial application field" This invention consists of an inner tank containing a SQUID and filled with a cryogenic liquid such as liquid helium, the outer circumference of which is surrounded by a radiation shielding member. The present invention relates to a magnetic field detection device that detects an external magnetic field using the SQUID at an extremely low temperature.

"Conventional technology" First, the above SQUID is
Superconducting Quantum Interference
Devices is an abbreviation for a sensor that operates in a superconducting state, and utilizes the property of a substance such as Nb to transform into a superconducting state at extremely low temperatures.

By the way, FIG. 5 is a schematic diagram showing a known magnetic field detection device 1 using the above-mentioned SQUID 2. According to this, the SQUID 2 is made of metal such as Cu or Al to prevent radiant heat from entering from the outside. It is surrounded by a hollow cylindrical radiation shield member 3 made of material.

Therefore, when trying to detect a change in the external magnetic field with the magnetic field detection device 1, part of the magnetic field is generated by the eddy current A in the circumferential direction on the upper surface 3a of the radiation shield member 3, or the eddy current A in the circumferential direction on the outer peripheral surface 3b. It is converted into longitudinal vortex currents B and C, and as a result, the strength of the magnetic field is
This is attenuated, making it difficult to measure the magnetic field and reducing accuracy, or even making it impossible to measure a particularly small magnetic field.

That is, for example, normally 1V in a 100Hz magnetic field at room temperature.
However, due to the generation of the eddy current described above, only a measured value of 0.6V (60%) can be obtained.
Furthermore, if the temperature becomes extremely low at this time, the radiation shield member 3
As the resistance of .

"Problems to be Solved by the Invention" The present invention has been made in order to eliminate the drawbacks of the prior art described above. By arranging the strips in the circumferential direction at a predetermined distance from each other and fixing them to form a hollow cylindrical cage shape, when measuring an external magnetic field,
The eddy current generated in the radiation shield member becomes almost non-existent, thereby reducing the attenuation of the magnetic field as much as possible, making it possible to accurately measure even the smallest magnetic field. That is its purpose.

``Embodiment'' The present invention will be explained below with reference to an embodiment shown in the drawings. As clearly shown in FIG. 4, the magnetic field detection device 11
As is known, it includes an outer tank 12, an inner tank 13, and a radiation shield member 14.

The outer tank 12 is formed of a synthetic resin material into a cylindrical shape with an open top, and the opening is closed by fixing a lid member 16 made of a synthetic resin material.
A cylindrical tube 16a projects from the center of the outer tank 12 into the outer tank 12, and the upper end opening of the through hole 16b of the cylindrical tube 16a is located on the upper surface of the lid member 16, and the O-ring 1
8 and is closed by a plug member 20 fixed with a set screw 21 so as to be sealed.

The inner tank 13 is a container filled with a cryogenic liquid 22 made of liquefied gas such as liquid helium, that is, a dewar, and is made of reinforced plastic (FRP) and is formed in a hollow cylindrical shape. The lower end of the pipe 16a is fixed so as to communicate with the lower end of the pipe 16a,
A cryogenic liquid 22 is supplied and stored in the inner tank 13 through the through hole 16b of the cylindrical tube 16a.

In the center of the lower surface of the inner tank 13, a cylindrical storage recess 13a that protrudes downward is formed as is also known, and the storage recess 13a has a lid made of synthetic resin that houses the SQUID 2. A cylindrical hollow container body 23 is housed therein, and a liquid level gauge 24 is installed in the inner tank 13 to electrically measure the liquid level of the cryogenic liquid 22.
is attached, and the liquid level gauge 24 is connected to an external connector 2 fixed to the top surface of the lid member 16 by wiring 25.
6, and a predetermined measuring device is connected to this.

The radiation shield member 14 is shown in FIG.
It is formed of a metal material such as Cu, Al, etc., and the width of the opposing upper and lower horizontal pieces 28a, 28a' gradually becomes narrower toward the axis of the vertical mounting, that is, toward the inner tip, so that the overall shape is U-shaped. A plurality of strips 2 formed in the shape of
It is formed by a set of 8.

To describe this in more detail, ears 28b bent perpendicularly are formed at the inner tips of the horizontal pieces 28a of the strip 28, and the ears 28b of the upper horizontal piece 28a are formed at the inner ends of the horizontal pieces 28a. , a metal connecting member 30 attached to the cylindrical tube 16a,
The ears 28b of the lower horizontal piece 28a are each fixed to a disk-shaped concentrator 32 made of synthetic resin by adhesive or other means, whereby the plurality of strips 28 are arranged in a circle as described above. It is composed of a hollow cylindrical cage shape so as to surround the inner tank 13 with a predetermined distance 〓g in the circumferential direction.

Here, the reason why metal is used for the connecting member 30 is to transmit the evaporation cold heat of the cryogenic liquid 22 to the radiation shield member 14 for cooling, and at this time, the eddy current due to the member 30 is small. However, this has no real impact.

Here, if it is necessary to reinforce the strength of the strip 28, on the inner surface of the upright piece 28c of each strip 28,
A ring-shaped reinforcing plate 34 made of synthetic resin is preferably bonded, and the ears 28b of the upper horizontal piece 28a may be directly fixed to the outer peripheral surface of the cylindrical tube 16a by adhesive or the like.

In addition, in the illustrated example, the outer tank 12 and the radiation shield member 1
A heat insulating material 40 is placed in the space 36 formed between the
38 is a stopper provided on the lid member 16, and the space 36 is evacuated through the opening.

When an external magnetic field is measured using the device configured as described above, the strip 28 will move for a short period of time.
Since it has a segmented composition with g, neither the circumferential vortex flows A and B nor the longitudinal vortex flow as explained in the conventional example lose their flow paths and are not generated. Almost no eddy current is generated, the attenuation rate of the magnetic field is extremely small, and since the inner tank 13 is surrounded by a radiation shield member 14 that is shielded from the outside by a heat insulating material 40 housed in a vacuum, only a small amount of eddy current is generated. Although 〓g exists during this period, it effectively blocks the radiant heat from the outside
The cryogenic liquid 22 inside can always maintain an extremely low temperature, and the magnetic field measurement function of the SQUID 2 is always maintained in a good condition.

"Means for Solving the Problems" In summary, the present invention has an inner tank 13 that contains the SQUID 2 and is filled with a cryogenic liquid 22 such as liquid helium, and that radiant heat from the outside does not enter the inner tank 13. A radiation shield member 14 formed of a metal material so as to surround the inner tank 13 is provided. A large number of strips 28 are formed in a U-shape by a horizontal strip 28a and an upright strip 28c, and these strips 28 are spaced apart from each other by a predetermined distance in the circumferential direction to form a hollow cylindrical cage shape. None, the inner tips of the upper and lower horizontal pieces are each made of a metal connecting member,
It is characterized by being fixed to a non-conductive member.

"Effect of the invention" With the above configuration, when measuring an external magnetic field,
Since almost no eddy current is generated in the radiation shield member 14, the attenuation of the magnetic field is minimal, and therefore even minute magnetic fields can be measured accurately, and the original requirement of blocking radiant heat is fully satisfied. It is possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a radiation shield member which is a main part of the magnetic field detection device according to the present invention, FIG. 2 is a perspective view showing a portion of the same member, FIG. 3 is a plan view of the detection device, and FIG. The figure is a vertical sectional front view of the same, and FIG. 5 is a schematic perspective view of a magnetic field detection device using a vertical SQUID. 2...SQUID, 11...Magnetic field detection device using SQUID, 13...Inner tank, 14...Radiation shield member, 22...Cryogenic liquid, 28...Strip piece, 2
8a...Horizontal piece, 28c...Upright piece.

Claims (1)

[Scope of utility model registration request] Equipped with an inner tank containing a SQUID and filled with cryogenic liquid, and a radiation shield member formed of a metal material to surround the inner tank to prevent radiant heat from entering the inner tank from outside. In this case, the radiation shielding member has a large number of strips formed in a U-shape by upper and lower horizontal pieces and upright pieces whose width gradually becomes narrower toward the inner tip. The radiation of the SQUID cooling device is formed into a hollow cylindrical cage shape with a predetermined distance in the circumferential direction, and the inner tips of the upper and lower horizontal pieces are fixed to a metal connecting member and a non-conductive member, respectively. shield device.