JPS62175681A - Cryostatic container for skid magnetometer - Google Patents

Abstract

PURPOSE:To enable the safe and accurate measurement of minute magnetism by providing a nonmagnetic thin metal sheet together with a nonmagnetic FRP (fiber glass reinforced plastics) plate forming a cryostatic container. CONSTITUTION:A cryostatic container 1 is formed in a dual structure composed of an inner layer 2 and an outer layer 3 and a vacuum space 4 is formed be tween the layers 2 and 3. The inner layer 2 is filled with such a freezing mix ture 5 as helium or the like. The outer layer 3 is constituted by a small diame ter cylinder portion 10 and a main cylinder portion 11 in correspondence with the inner layer 2 and the outer layer 3 has shielding thin aluminum sheets 13 (13a-13e) buried in an FRP 12. Even when broadcast waves or radio waves for a civil communication reach the cryostatic container 1, the container 1 is shielded by the thin aluminum sheets 13 provided in the outer layer 3 and the waves do not reach a pickup coil 6 and a skid element 8. Therefore the skid element 8 is not affected by any external wave, enabling a stable measure ment to be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a cryogenic container for a SQUID magnetometer that is effective for detecting, for example, magnetism emitted by living organisms.

(b) Conventional technology In general, the magnetic field emitted from the heart, lungs, brain, etc. of a living body is extremely small, on the order of 10-10 to i0-''T.
Therefore, biomagnetism can be measured using a skid magnetometer in a multi-layered shielded room made of permalloy, or alternatively, the shape of the pick-up coil of a skid magnetometer can be shaped differentially without using a shielded room. However, external magnetic noise is canceled using a second-order differential method.

On the other hand, the detection part of the skid magnetometer, that is, the pickup coil, skid element, etc., is housed in a cryogenic container filled with a cryogen such as helium, and this cryogenic container is made of nonmagnetic FRP (glass fiber reinforced plastic). plastic).

(c) Problems to be Solved by the Invention When measuring biomagnetism, it is desirable to conduct the measurement in a completely shielded room as described above, but creating a shielded room using permalloy is expensive and impractical. Therefore, a skid magnetometer that uses the second-order differential method will be used. Although this skid magnetometer can cancel external magnetic noise to some extent, radio wave noise caused by broadcast waves and private communication radio waves becomes a problem. In order to eliminate the influence of this radio wave noise, it is conceivable to connect a shunt resistor to the input terminal of the skid element, or to electromagnetically shield the area around the pickup coil with a PB, brass pipe, or the like.

However, if the shunt effect is made too strong, thermal noise due to the resistance becomes a problem, and if a metal pipe is provided around the pink-up coil, noise is generated due to the secondary magnetic field in response to the external magnetic field, so it is not a perfect countermeasure.

In view of the above, an object of the present invention is to provide a cryogenic container for a skid magnetometer that can measure minute magnetism without a shield room and without being affected by broadcast waves, private communication radio waves, etc.

(d) Means and operation for solving the problems The cryogenic container of the skid magnetometer of the present invention has a peripheral wall, a bottom, and a ceiling made of FRP, is injected with a cryogen such as liquid helium, and has a pickup coil. In the case where the skid element is housed, a thin metal plate for shielding is installed inside the FRP. This thin metal plate prevents external broadcast waves and private communication radio waves from penetrating the skid element and pickup coil.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a sectional view of a cryogenic container 1 of a skid magnetometer showing an embodiment of the present invention. This cryogenic container 1 is formed in a double structure of an inner layer 2 and an outer layer 3, and a vacuum section 4 is formed between both layers 2.3.

The inner layer 2 is filled with a cryogen 5 such as helium, and is composed of a narrow cylindrical part 7 that accommodates a pickup coil 6 at the lower part and a main cylindrical part 9 in which the skid element 8 at the upper part is immersed. As is well known, the skid element 8 is composed of a JJ element, an input coil, etc. (not shown).

The outer layer 3 also has a narrow cylindrical portion 10 and a main cylindrical portion 11 corresponding to the inner layer 2.
It consists of These inner layer 2 and outer layer 3 are made of FRP as in the conventional case.

However, the outer layer 3 is not simply formed of FRP, but a thin aluminum plate 13 for shielding is embedded in the FRP 12. That is, F of the bottom part 10a of the narrow cylindrical part 10
The aluminum thin plate 13a is attached to the RP12a, and the thin cylindrical portion 1
An aluminum thin plate 13b is buried in the bottom part 11C of the main cylinder part 11, and an aluminum thin plate 13c is buried in the FRP 12C of the bottom part 11C of the main cylinder part 11, and an aluminum thin plate 13d is buried in the narrow cylinder part lid.
However, thin aluminum plates 13e are also buried in the ceiling portion 11, respectively.

Among the above, the aluminum thin plate 13a of the bottom part 10a of the narrow cylindrical part 10 has a roughly circular shape as shown in FIG. 2 to match the shape of the bottom part. A notch 14 is provided up to the vicinity of the periphery.

Further, as shown in FIG. 3(al(b)), for example, the thin aluminum plate 13c of the narrow cylinder part 11c of the main cylinder part 11 is not completely cylindrical, but has a vertical notch 15 in a part of the cylinder. The cross-sectional shape is made not to form a closed loop.This is to prevent eddy currents from flowing through the thin aluminum plate.

Moreover, the aluminum thin plates 13c and 13e have a donut shape in terms of structure.

In the cryogenic container 1 of this embodiment, even if broadcast waves or radio waves for private communications arrive, they are shielded by the thin aluminum plates 13a, . . . , 13e provided on the outer layer 3, and the pickup coil 6 and skid Do not enter 8.

Therefore, the skid element 8 can perform stable measurements without being affected by external radio waves.

In the above embodiments, the external shape of the cryogenic container l is cylindrical, consisting of a narrow cylindrical part and a main cylindrical part, but the present invention can be applied without being limited to the external shape of the cryogenic container.

Further, in the above embodiments, an aluminum plate is used as the thin metal plate for shielding, but other nonmagnetic thin metal plates may be used.

Further, in the above embodiment, a case was shown in which a thin aluminum plate was embedded in FRP, but the thin aluminum plate may be sandwiched between FRP plates.

(f) Effects of the invention According to this invention, since the aluminum thin plate is provided in parallel to the FRP plate forming the cryogenic container, high frequency noise from the outside such as broadcast waves and private broadcast radio waves is completely blocked. Since these high-frequency noises do not become a noise source for the skid, safe and highly accurate micromagnetic measurements can be performed without providing a shield room. Therefore, it is extremely effective for biomagnetic measurement.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a cryogenic container of a skid magnetometer showing an embodiment of the present invention, FIG. 2 is a plan view showing the shape of a thin aluminum plate placed at the bottom of the same cryogenic container, and FIG.
The figures are diagrams for explaining the aluminum thin plate of the narrow cylindrical part of the same cryogenic container, and FIG.
b) is a cross-sectional view of the same. 1: Cryogenic container, 5: Cryogen, 6: Vinokur asop coil, 8 Niskit element, 12.1
2a.=-12e: FRP. 13・13a...13e Nialuminum thin plate,
14/15; Notch. Patent applicant: Shimadzu Corporation Agent
Patent Attorney Shigeru Nakamura Nobuzane 1 Figure 14.15: t777 evil Figure 2 Figure 3
figure

Claims (2)

[Claims] (1) In a cryogenic container for a skid magnetometer in which the peripheral wall, bottom, and ceiling are formed of FRP, a cryogen such as liquid helium is injected, and a pickup coil and skid element are housed, a shield is placed in the FRP. A cryogenic container for a skid magnetometer, which is characterized by being made of overlapping thin metal plates. (2) The thin metal plate of the peripheral wall portion is formed such that a notch is provided in the longitudinal direction of the cylinder portion, and the cross-sectional shape is a non-closed loop, and the thin metal plate of the bottom portion is formed such that the thin metal plate of the bottom portion passes through the center portion from the edge to the other side. 2. A cryogenic container for a skid magnetometer according to claim 1, wherein a band-shaped notch is provided up to the vicinity of an edge of the cryogenic container for a skid magnetometer.