JPH0555782A - Divided element of oxide superconducting magnetic shield - Google Patents

Abstract

PURPOSE:To provide an oxide magnetic shield divided element in which an L/D is large and a magnetically shielding effect is 1000 times or more by combining a cylindrical or rectangular parallelepiped vessel having about 1 of LAD of an oxide high temperature superconducting shield. CONSTITUTION:A plurality of both end-opened or one end-closed/one end-opened cylindrical or rectangular parallelepiped oxide superconductor vessels 1 are axially opposed, and a similar oxide superconductor vessel 2 having a diameter slightly larger than that of the superconductor is engaged with the outer peripheries of the opposed parts of the superconductors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield division body utilizing a superconducting phenomenon (excluding magnetic flux), and particularly L /
The present invention relates to a magnetic shield division body in which D can be increased and the magnetic shield effect can be increased 1000 times or more.

[0002]

2. Description of the Related Art Recently, studies have been conducted to apply an oxide superconductor to a magnetic shield container by utilizing the superconducting phenomenon of eliminating its magnetic flux. In this case, the superconducting shield does not take an external magnetic field into the superconductor and eliminates it toward the outside so that the magnetic field does not penetrate into the internal space, and the magnetic shield effect is orders of magnitude greater than that of a ferromagnetic material. That is, the ferromagnetic shield has a limit due to the presence of residual magnetization, and the magnetic shield in a region exceeding this limit must wait for the superconducting magnetic shield. However, for example, in Nb-based metal superconductors, liquid helium needs to be used as a coolant, so there is a cost barrier in the magnetic shield construction, and superconducting shields have been put into practical use except for a small part. The reality is that there is none.

Recently, studies have been activated to measure the magnetic field emitted from the brain to elucidate the mechanism of the brain, elucidate headache, and examine the brain. Conventionally, MRI and positron C
Although the search for the inside of the brain such as T is practiced clinically,
There are restrictions on the resolution and the radiation used, and the strength of the brain wave is an extremely weak magnetic field of 10 −9 Gauss, and the earth's magnetism is 0.3 Gauss. It is in the area beyond the limit in.
In this case, a magnetic flux sensor called SQUID (superconducting quantum interference device) and a superconducting magnetic shield are essential.

The present inventors have previously clarified that a magnetic shield using an oxide high-temperature superconductor has an order of magnitude better shielding effect than a conventional ferromagnetic material (Japanese Patent Application No. 254711). This magnetic shield container has an essential requirement that the depth / caliber (L / D) ratio be 1 or more. Now, when measuring a brain magnetic field, the innermost caliber that the target patient does not have fear of and can be clinically adopted needs to be at least 50 to 100 cm. When a superconducting container is placed outside this inner container, and a cooling container and a container for insulating the cooling container are placed, the diameter of the superconductor reaches 1 m. When L / D is 1 or more, preferably 2-3, the depth of the container is 2-3 m. Even if it is technically possible to make such a large container integrally,
It is extremely difficult and almost impossible to manufacture from a practical point of view considering cost.

According to the present invention, an oxide high temperature superconducting shield is combined with a cylindrical or rectangular container having an L / D of about 1 so that the L / D can be increased and the magnetic shield effect can be 1000 times or more. It is intended to provide a magnetic shield split body.

[0006]

According to the present invention, a plurality of both-end opening or one-end closed / one-end opening cylindrical or rectangular-shaped oxide superconductors are butted in the axial direction, and the oxide superconductors The problem is solved by fitting a similar oxide superconductor having a diameter slightly larger than that of the superconductor on the outer periphery of the abutting portion. In the present invention, the superconductor may be formed by forming a thick oxide superconductor film on the surface of a metal container made of nickel, inconel, hastelloy or the like with an intermediate layer made of zirconia, silver or the like.

[0007] In such a divided body, by combining and stacking containers having L / D of about 1
A large magnetic shield space that is difficult to obtain with one body is obtained,
The magnetic shield effect defined by the ratio of the external magnetic field / internal magnetic field can be made 1000 times or more. Here, the magnetic shield effect S is represented by the ratio of the magnetic field strength inside the superconductor at the liquid nitrogen temperature (77) K, and can be written as S = external magnetic field / internal magnetic field.

In FIG. 1, two cylindrical or rectangular-shaped oxide superconductor containers 1 with both ends open or one end closed / one end open are butted in the axial direction as shown in FIG. It is obtained by fitting the same oxide superconductor container 2 having a diameter slightly larger than that of the body 1 so as to be overlapped with each other as shown in (b). Here, for example, by using three containers with L / D = 1, it became possible to greatly expand the region having a magnetic shield effect of 1000 times or more in the longitudinal direction of the container. Further, as shown in FIG. 1 (c), by using three containers with L / D = 1 and two containers with L / D = 0.6 as containers to be stacked on top of them, the size that a human body can enter The magnetic shield space can be obtained, and the magnetic shield effect is 1000 times to 100,000 times, and the S / N ratio sufficient for the brain magnetic field measurement can be achieved. The L / D of the container 2 superposed on the abutting portion is at least 0.5, and preferably 1 or more. in this case,
The gap between the container 1 and the container 2 is preferably as narrow as possible, and in general, the gap is preferably 1 to 2% or less of the diameter.

[0009]

The mechanism of the magnetic shield by the oxide high temperature superconducting magnetic shield split body of the present invention constructed as described above will be explained for better understanding of the present invention. Therefore, the following description does not limit the scope of the invention.

Even if the both ends of the superconducting magnetic shield of one body are open, if a magnetic field tries to enter the opening,
A shield current flows in the circumferential direction of the cylinder to prevent the magnetic field from entering. In this case, the path of the current through which the superconducting current flows can be easily formed in the circumferential direction, but when the container is divided in the circumferential direction, the flow of the superconducting current is blocked, so the shielding effect is significantly reduced. From such a viewpoint, in the present invention,
A container that is not divided in the circumferential direction is used. As shown in FIG. 1A, when two such containers are arranged with their end faces abutted, the magnetic field in the longitudinal direction of the cylinder hardly penetrates through the gap between the containers.

Further, since the magnetic field in the direction perpendicular to the axis of the cylinder penetrates through this gap, as shown in FIGS. 1B and 1C, by stacking a container on this gap, the magnetic field in the direction perpendicular to the axis is increased. The magnetic field of can also be prevented. According to the present invention, a larger shielded space can be created by thus combining and superposing containers. The method of the present invention can be applied to a container manufactured by any method such as a bulk sintered body, a thick film, or a thin film.

[0012]

According to the present invention as described above, the following effects can be obtained. (B) It is possible to obtain a large magnetic shield space which is difficult for an integrated body. (B) Magnetic shield effect It is possible to greatly expand the shield space of 1000 times or more in the longitudinal direction of the cylinder or tubular body.

[0013]

Example 1 Bi: Pb: Sr: Ca: Cu = 0.8:
Using oxide superconductor powder having a composition of 0.2: 0.8: 1: 1.4, inner diameter 12 mm, length 38 mm, thickness 1 mm
The both-end-opened cylinder was molded by cold isostatic pressing and fired to prepare a bulk sample. Similarly, inner diameter 15m
A double-sided open cylindrical container having m, a length of 15 mm, and a thickness of 1 mm was also produced. These containers are arranged as shown in FIGS. 2 (A), (B), and (C), and the fluxgate type magnetic field sensor 3
The magnetic field inside the container was measured using (measurement sensitivity, 1 milligauss). The gap between the containers was 1 mm or less. In this case, an external magnetic field of 10 Gauss was applied in the axial direction of the cylinder. The external magnetic field was a DC magnetic field and an alternating magnetic field of 1 to 100 Hz.

The results of this measurement are shown in FIG. The magnetic shield effect S defined by the ratio of the external magnetic field to the internal magnetic field is about 10 ^{3 in} the case of (A) and about 2 × 10 ^{4 in} the cases of (B) and (C).
Met. As is clear from this result, it is understood that the shield effect does not decrease even if there is a gap between the containers.

Next, as shown in FIG. 4, a DC magnetic field was applied in the direction perpendicular to the cylinder axis to measure the internal magnetic field. as a result,
In the cases of (A), (B), and (C), the shield effect S was about 100, 2, 2 × 10 ³ or more, respectively. From this, only in the case of (C), the magnetic shield effect exceeding 1000 times was shown. As is clear from this, the superposition of the external magnetic field 10
It could be attenuated to less than 1/00.

[0016]

Example 2 A Bi-based superconducting thick film having the same composition as in Example 1 was formed on the surface of a silver container having almost the same size as in Example 1 by the dip coating method. The Bi-based superconducting powder was dispersed using ethanol, and a silver cylinder was immersed therein, pulled up, dried, and heat-treated. The thick film thus formed had a thickness of about 0.1 mm. This cylindrical container was subjected to the same test as in Example 1. The applied external magnetic field was less than 1 gauss. As a result, when an external magnetic field parallel to the cylinder axis is applied, it is 500 in (A) and about 10 ^{3 in} (B) and (C).
Met. Further, when an external magnetic field in the vertical direction is applied to the cylindrical axis, (A), (B), and (C) are about 70, 1.
It was 5, 10 ³ . From this, only in the case of (C) is 1
The magnetic shield effect was more than 000 times.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a combination example of a superconducting magnetic shield container.

FIG. 2 is an explanatory diagram showing a combination of a superconducting magnetic shield container and a measurement system, where (A) shows one container, (B) shows two containers arranged side by side, and (C) shows (B). The case where the containers are stacked on the outer periphery of the abutting portion is shown.

FIG. 3 is a relationship diagram showing frequency dependence of a magnetic shield effect S.

FIG. 4 is an explanatory diagram showing an example of measurement when a magnetic field is applied in the direction perpendicular to the cylinder axis.

[Explanation of symbols]

 1 Magnetic shield container 2 Magnetic shield container 3 Fluxgate type magnetic field sensor

Claims (2)

[Claims] 1. A plurality of cylinder-shaped or rectangular-shaped oxide superconductors having both open ends or one closed end / one open end are butted in an axial direction thereof, and the superconductor is provided on the outer periphery of the butted part of these oxide superconductors. An oxide superconducting magnetic shield split body formed by fitting similar oxide superconductors having a slightly larger diameter. 2. The oxide superconducting magnetic shield division body according to claim 1, wherein the oxide superconductor has a thick oxide superconductor film formed on the surface of a metal container.