JP3002586B2 - Cryogenic container for skid sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic container for a skid (SQUID) sensor for detecting weak magnetism.

[0002]

2. Description of the Related Art For example, a magnetic field generated from a living body is very small and is about 10 ^-10 to 10 ^-13 T, and a highly sensitive sensor such as a skid is required to detect such a weak magnetic field. Indispensable. However, since the skid sensor is also a microwave sensor, it is susceptible to electromagnetic interference, and must be used in an environment in which not only external magnetic noise but also radio wave noise due to broadcast waves and communication radio waves is shielded.

As a technique for shielding the radio noise, as disclosed in Japanese Patent Application Laid-Open No. 62-175681, a technique of embedding a non-magnetic metal thin plate in the outer layer FRP (fiber reinforced plastic) of a cryogenic container, There is a technique in which a mylar film on which aluminum is deposited, which is used as a heat insulating material, is used between outer layer walls.

[0004]

As described above, in the prior art, a technique of embedding a non-magnetic metal thin plate in the outer layer FRP portion or using a heat insulating material has been proposed. Notches are formed in the metal sheet and the heat insulating material in order to prevent the occurrence of cracks, so that a closed loop structure is not taken. However, due to the presence of the notch, problems such as generation of noise due to static electricity and invasion of an external radio wave from the notch have arisen. Some thermal insulation materials are short-circuited at the notch end and grounded as a countermeasure against static electricity.However, on the contrary, eddy currents are generated, and magnetic noise is generated by this. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a skid sensor capable of suppressing magnetic noise induced by the generation of eddy current and preventing the intrusion of external radio noise. The purpose is to obtain a cryogenic container for use.

[0006]

Means for Solving the Problems] skid sensor for cryogenic container of the invention, the outer layer wall portion forming a container with a non-magnetic, conductivity ^{4.4 × 10 3 ~4.9 × 10 4} Ω - ¹ ・ m ^-1
The conductive FRP of non-magnetic and non-conductive FRP
FR formed of RP and constituting the outer layer wall portion
P has a multilayer structure in which the orientation directions of the fibers cross each other, and the crossing angle is 60 ° to 150 °.

[0007]

[0008]

In the cryogenic container for a skid sensor according to the present invention, the outer wall of the container has a multilayer structure in which the orientation directions of the fibers cross each other, and the crossing angle is 60 ° to 150 °.
° and a conductivity of 4.4 × 10 ^{3 to} 4.9 × 10 ^4.
The use of a conductive FRP of Ω ^-1 · m ^-1 prevents the invasion of extraneous radio waves, and generates very small eddy currents. And is very weak, so there is no problem due to eddy current.

Further, the electric conductivity of the FRP on the outer layer wall is constituted.
The cutoff frequency of the external radio wave can be arbitrarily selected by controlling the crossing angle of the fiber .

[0010]

【Example】

Embodiment 1 FIG. FIG. 1 is a longitudinal sectional view showing a cryogenic container for a skid sensor according to an embodiment of the present invention. The cryogenic container 1 has a double structure including an outer layer 2 and an inner layer 3, and a vacuum section 4 for thermal insulation is provided between both layers. The inner layer 3 is filled with a cryogen such as liquid helium, in which a skid sensor 6 is housed. Since the inner layer 3 is close to the skid sensor 6 and greatly affected by the eddy current, the non-magnetic and non-conductive F
RP, for example F reinforced with glass or alumina fibers
RP is used. The wall of the outer layer 2 is made of non-magnetic and conductive FRP, for example, FRP reinforced with carbon fiber (CFRP).
Abbreviated).

FIG. 2 is a schematic cross-sectional view showing the outer layer 2 with a cutaway wall. As shown in the figure, CFRP carbon fibers 7 are oriented at an arbitrary angle α _i . FRP used for inner and outer layers
Is formed by a filament winding method of winding fibers or a sheet winding method of laminating prepreg sheets.

[0012]

[Table 1]

Table 1 shows the CFR when the fiber orientation of CFRP used for the outer layer wall material of the cryogenic vessel 1 shown in FIG. 1 was changed.
It is the result of obtaining the magnetic noise induced by the conductivity of P, the cutoff frequency of the external radio wave, and the generated eddy current. In the table, the values of the aluminum material, which is a non-magnetic and conductive metal, are also shown for comparison. Σ _C and f in the table are calculated by the following equations.

[0014]

(Equation 1)

Here, σ _：: conductivity in the fiber direction of the unidirectional CFRP material (Ω ^-1 · m ^-1 ) σ _：: conductivity in the direction perpendicular to the fiber of the unidirectional CFRP material (Ω
⁻¹ · m ⁻¹ ) α _i : fiber orientation angle of the i-th layer N: number of layers μ ₀ : 4π × 10 −7 δ: skin depth (set to 2 mm in thickness of CFRP material)

From the above results, the cutoff frequency can be designed in a wide frequency band by changing the orientation angle of the fiber of the CFRP material, and the magnetic noise induced by the eddy current is much weaker than that of aluminum, which is a problem. It turns out there is no. That is, since the cryogenic container of the present invention uses CFRP for the outer layer wall, the magnetic noise induced by the generation of the eddy current can be suppressed to a very small value, and the invasion of the external radio noise can be prevented. is there. Further, there is an effect that the cutoff frequency can be arbitrarily designed by controlling the conductivity of CFRP.

In the above embodiment, the case where the cutoff frequency is arbitrarily changed by changing the orientation angle of the fiber of the CFRP material has been described. However, the volume content of the fiber may be changed or different types of FRP may be used. It is also possible to arbitrarily design the cutoff frequency by changing σ _{層 間} by hybridizing between the layers of the outer layer wall or within the layer.
For example, when the outer layer wall is made of graphite, the volume content of the graphitized carbon fiber is set to about 100%, which is comparable to the case where the GFRP (glass fiber reinforced plastic) cryogenic container is covered with a CFRP cylinder. Is comparable to interlayer hybridization at the outer layer wall.

[0018]

As described above, the cryogenic container for a skid sensor according to the present invention has a non-magnetic material having a conductivity of 4.4 × 10 ^{3 to} 4.9 × 10 ⁴ Ω ^{-1 on} the outer wall of the container. ・ Using m- ¹ conductive FRP, non-magnetic and non-conductive FRP on inner layer wall
And the FRP constituting the outer layer wall portion is:
A multi-layered structure in which the orientation directions of the fibers cross each other, and the crossing angle is set to 60 ° to 150 °, so that magnetic noise induced by eddy current can be minimized and external high-frequency noise can be shielded. There is.

[0019]

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a cryogenic container for a skid sensor according to an embodiment of the present invention.

FIG. 2 is a schematic cutaway cross-sectional view of the outer layer wall of the cryogenic container for a skid sensor according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cryogenic container for skid sensors 2 Outer layer 3 Inner layer 5 Refrigerant 6 Skid sensor

Continuation of the front page (56) References JP-A-62-175681 (JP, A) JP-A-58-163878 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33 / 035 H01L 39/04

Claims (1)

(57) [Claims] 1. A cryogenic container for a skid sensor, comprising an inner layer and an outer layer formed by FRP, wherein a cryogen is injected into the inner layer, and a skid sensor is housed. The rate is 4.4 × 10
^{3 to} 4.9 × 10 ⁴ Ω ⁻¹ · m ⁻¹ is formed of a conductive FRP, and the inner layer wall is formed of a non-magnetic and non-conductive FRP, and the FRP constituting the outer layer wall is formed. Is a cryogenic container for a skid sensor, wherein a fiber has a multilayer structure in which orientation directions cross each other, and the crossing angle is 60 ° to 150 °.