JPH07193390A - Formation of magnetic shield space - Google Patents

Abstract

PURPOSE:To enable formation of a magnetic shield space of high magnetic shield effect by a relatively simple structure. CONSTITUTION:First superconductive members 5,... wherein a shield surface comprised of a superconductive thick film is formed are attached to the outer surface of an inner frame body 6, second to sixth superconductive members 11 to 14 are laminated in an outer surface of the first superconductive member 5 one by one to form a shield wall, a magnetic shield box 17 is formed by fixing it by an outer frame body 15 from an outside of the shield wall and magnetic flux is prevented from entering a shield space 7 from an outside of the magnetic shield box 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a magnetic shield space which prevents external noise such as geomagnetism from entering.

[0002]

2. Description of the Related Art Conventionally, a magnetic shield space such as a magnetic shield box or a magnetic shield room has been used for weak magnetic measurement in order to shield external noise (earth magnetism etc.). Such a magnetic shield space forms a shield space with a wall body using a high magnetic permeability material such as permalloy, and captures an external magnetic flux with the wall body made of the high magnetic permeability material,
A method of preventing an external magnetic flux from penetrating into the inside has been generally used.

[0003]

However, in the magnetic shield space using the wall body made of a high magnetic permeability material, the shield effect is low against a low frequency magnetic field (weak magnetic field of about 10 Hz or less), and biomagnetic properties are low. There is a problem that a sufficient shield effect cannot be expected in order to measure very low frequency weak magnetism. Further, the high permeability materials forming the wall body are required to be in good contact with each other, which makes the design and manufacturing very complicated.

The magnetic shield using a superconductor is
Since it does not depend on frequency, it can be used for measurement of low-frequency magnetic field. It is known that inside the cylinder of the superconductor, the magnetic field exponentially decreases from the opening end toward the center, and a low magnetic field space is obtained, which is H (z) = H
It is known by the logical expression of _e exp (-KZ / D). Incidentally, H (z) is the magnetic field at distances z point from the open end on the center axis size, H _e is the external magnetic field magnitude, if K is a proportional constant (external magnetic field in the radial direction 3.6 , 7.6) in the axial direction, and D is the diameter of the cylinder.

However, in order to obtain a low magnetic field space in a superconductor cylinder, the axial length with respect to the diameter of the cylinder is required, and the actual low magnetic field space is near the center. It will be limited. In addition, in order to manufacture an integrated container of a superconductor, it is necessary to heat treat the whole container uniformly, and the size that can be manufactured is limited by the size of the heat treatment furnace. Therefore, it is practically difficult to secure a relatively large magnetic shield space by the cylinder of the superconductor.

Therefore, an object of the present invention is to provide a method of forming a magnetic shield space which can realize a magnetic shield space having a high magnetic shield effect even with a low frequency magnetic field with an extremely simple structure.

[0007]

In order to achieve the above object, a method of forming a magnetic shield space according to the present invention is a superconducting member (eg, a superconducting member of any shape) having a shield surface (4) made of a superconducting material. A shield space (7) is formed by using a plurality of first superconducting members 5, second to sixth superconducting members 16 to 14), and an edge portion of the shield surface of each superconducting member forming the shield space is By forming another shield wall having a multilayer structure by laminating other superconducting members so as to cover it, and placing the shield wall in an environment below the critical temperature of the superconducting substance, the shield surface of each superconducting member is formed. To a superconducting state, which prevents the magnetic flux from entering the shield surface by the Meissner effect, and the magnetic flux that has entered the shield wall from the edge of the shield surface in the outermost layer of the shield wall is To reach the shielded space And to attenuate to a predetermined level below in.

[0008]

[Function] The magnetic flux that has entered the shield wall from the edge of the shield surface in the superconducting state cannot enter the inner layer without passing through the edge of the shield surface in each layer. Was forced to proceed along
It is appropriately attenuated before reaching the shielded space through the innermost layer.
Further, the amount of attenuation of the invading magnetic flux while passing through the shield wall can be appropriately changed depending on the moving distance when passing through the shield wall and the like.

[0009]

EXAMPLE An example of forming a magnetic shield box will now be described as an example of a method of forming a magnetic shield space according to the present invention with reference to the accompanying drawings.

FIG. 1 shows, for example, a flat quadrangular superconducting member 1. The superconducting member 1 has a thickness of a superconducting material on one surface of a substrate 2 (for example, a 0.5 mm ^t Ag substrate). By forming a superconducting thick film 3 made of a film (for example, a 0.1 mm ^t Bi-based superconducting thick film), one surface is shielded by
It is designed to be When forming the superconducting thick film 3, for example, a superconducting paste is applied to the substrate 2 by a screen printing method with good uniformity, and then 850 ° C.
By firing at a high temperature of 900 ° C., the superconducting thick film 3 having a uniform film thickness and excellent strength is obtained. The superconducting member 1 only needs to have a shield surface 4 made of a superconducting material,
For example, a plate material may have a structure in which a superconducting substance is sandwiched from both sides, or a bulk may be fired into a plate shape. The superconducting material used for the superconducting thick film may be a metal-based compound superconductor that exhibits superconducting properties in the liquid helium temperature range, but a high-temperature superconductor that exhibits superconducting properties in the liquid nitrogen temperature range (mainly An oxide-based superconducting material) is suitable.

The superconducting member 1 as described above is used, for example, 200
6 mm of the first superconducting member 5 formed into a square plate of mm × 200 mm
The first step of applying the FRP resin to the six faces of the cubical inner frame 6 using, for example, a single sheet is performed (see FIG. 2). One surface (for example, the upper surface) of the inner frame body 6 is open, and the inner frame body 6 is
Although a measuring instrument, a sample, and the like can be taken in and out of the shielded space 7 formed inside, the open surface of the inner frame body 6 may be shielded by a lid member or the like. In the embodiment shown in the drawings, the fluxgate magnetometer 8 is housed in the shielded space 7, and the fluxgate magnetometer 8 is fixed to the substantially central portion of the shielded space 7 by a fixing means (not shown). I can do it.

The wiring cord 9 of the fluxgate magnetometer 8 uses an extremely thin lead wire and is pulled out from the gap formed between the edge portions of the two adjacent first superconducting members 5 and 5. . The first superconducting members 5 need not be brought into close contact with the respective surfaces of the inner frame body 6, and therefore voids for wiring cords may be formed in advance.

Next, a second step of covering the six corners 5a of the cube covered with the first superconducting members 5 with the six second superconducting members 10 is performed (see FIG. 3). This second superconducting member 1
0 is composed of three superconducting plates which are orthogonal to each other, and the corners 5a formed by the three first superconducting members 5, 5, 5 are covered with the second superconducting members 10 ... The side portions 5b adjacent to the superconducting members 5 can be substantially covered. The wiring cord 9 is the second superconducting member 10 ...
It is intended to be pulled out from the gap between them. In addition, the second
As a method of forming the superconducting member 10, the superconducting thick film 3 may be formed integrally with the mold frame or the like, or may be formed by bending a flat plate material and welding it.

Then, a third step of covering four parallel side portions 10a of the cube covered with the second superconducting members 10 with four third superconducting members 11 is performed (see FIG. 4). . The third superconducting member 11 is an angle member having an L-shaped cross section and composed of two superconducting plates that are orthogonal to each other, and can cover the gap between the second superconducting members 10 ... On the four continuous side surfaces. . When the third superconducting member 11 ... Is formed, if the superconducting thick film 3 is bent while being formed on the substrate 2, the superconducting thick film 3 will be cracked and the characteristics will be deteriorated. Therefore, after bending the plate material, a paste of a superconducting substance may be attached with a brush or a spray so as to fill the crack, and the paste may be fired again. The wiring cord 9 is pulled out from the gap between the third superconducting members 11 ...

Thereafter, the third superconducting member 1 is similarly processed.
The fourth step (see FIG. 5) of further stacking the fourth superconducting member 12 having the same structure as that of No. 1, the third and fourth superconducting members 1 described above.
The fifth step (see FIG. 6) of further stacking the fifth superconducting member 13 having the same configuration as that of Nos. 1 and 12 is sequentially performed, and the sixth superconducting member 14 having the same configuration as that of the first superconducting member 5 ... The sixth step (see FIG. 7) is carried out in which each of the three is attached to the six sides of the cube.

In the shield wall obtained by laminating the second to sixth superconducting members 10 to 14 on the outer surface of the first superconducting member 5 as described above, the shield in the sixth superconducting member 14 which is the outermost layer. The distance from the edge of the surface 4 to the edge of the shield surface 4 in the innermost first superconducting member 5 becomes long.

In order to hold the shield wall obtained as described above, for example, the first to sixth FRP resin products are used.
The outer frame bodies 15a to 15f are attached to the respective surfaces of the sixth superconducting member 14 (see FIGS. 8 and 9), and the first to sixth outer frame bodies 15a to 15f are further tightened by the frame holding material 16. By wearing the magnetic shield box 17, the magnetic shield box 17 is obtained (see FIG. 10). Thus, if the shield wall having the shield surfaces 4 ... Stacked is formed between the inner frame body 6 and the outer frame body 15, the reinforcing effect of the shield wall can be expected. In addition, since the magnetic shield box 17 does not require any special fastening means or the like, it is extremely easy to assemble and disassemble, and a sample and a measuring instrument can be easily taken in and out without providing a special opening / closing lid. It is possible.

FIG. 11 virtually shows a schematic cross section of the magnetic shield box 17 having the above-described structure. The edge portion of the shield surface 4 (that is, the edge portion of each superconducting member). It will be understood that even if the wiring cord 9 is derived through the wiring so as to have the shortest distance, this distance is required.

If the magnetic shield box 17 is placed in an environment below the critical temperature so that the shield surface 4 exhibits superconducting characteristics, magnetic flux cannot enter from the shield surface 4 ... Since the Meissner effect does not occur in the gap formed between the edge portions of No. 4, the magnetic flux enters from the gap. However, by adopting the above-mentioned laminated structure of the superconducting member, the other shield surface 4 is positioned so as to cover the edge portion of each shield surface 4, so that at least the above-mentioned wiring path of the wiring cord 9 is provided. The shielded space 7 cannot be reached unless the distance is the same.

When the above principle is schematically shown in FIG. 12, the magnetic flux (shown by a wavy line in the figure) that has entered from the outside through the gap is the outermost first shield plate 18a and second shield plate 18b. Penetrates into the inner layer through the gap between
Because of the bent third shield plate 18c, the invading magnetic flux is forced to travel between the first shield plate 18a and the third shield plate 18b or between the second shield plate 18b and the third shield plate 18c. It The penetrating magnetic flux that has traveled between the first shield plate 18a and the third shield plate 18b enters the innermost layer through the gap between the third shield plate 18c and the fourth shield plate 18d. Due to the shield plate 18e, the invading magnetic flux is forced to travel between the third shield plate 18c and the fifth shield plate 18e or between the fourth shield plate 18d and the fifth shield plate 18e. Thus, the third shield plate 18c
The magnetic flux penetrating between the fifth shield plate 18e and the fifth shield plate 18e reaches the inner side of the innermost layer (in the shielded space) from the gap between the fifth shield plate 18e and the sixth shield plate 18f. In the meantime, the invading magnetic flux is attenuated because it has to move a considerable distance while being sandwiched between the shield surfaces 4.

FIG. 13 shows a coil 19 for applying an external magnetic field.
5 mm from the center of the surface of the magnetic shield box 17
FIG. 14 shows an example of the configuration of an experiment performed by fixing the fluxgate magnetometer 8 at a fixed position apart from the inner wall of the shield box 17 by a distance a [mm].
It is shown in. The magnetic shield box 17 used in this experimental example has a magnetic shield space of 200 mm × 200 mm × 200 mm. First, in the characteristic curve a showing the state measured without providing the superconducting plate, the fluxgate magnetometer 8 detected a magnetic field of about 9 × 10 ⁻⁶ [T] even at a distance of 100 mm. On the other hand, in the characteristic curve b measured by disposing the superconducting member so as to obtain a single-layer shield surface, 10 ⁻⁸ [T]
Improved before and after. Further, when measured using the magnetic shield box 17 having the laminated structure as in the above-mentioned embodiment, the shield effect is increased to 10 ⁻⁹ [T] or less.

In the above embodiment, the relatively small magnetic shield box 17 is formed. However, according to the magnetic shield space forming method of the present invention, a relatively large magnetic shield space can be formed. Can also be applied to.

As shown in FIG. 15, the single-plane superconducting members 19 ... Are attached to the outer wall of the structural inner frame body in a tile shape, and the outer surfaces of the three-sided superconducting members 20 and the two-sided superconducting members 21. By laminating the single-sided superconducting members 19 and the like, it is possible to embody a laminated structure of the shield surface 4 which is similar to the above-mentioned shield box 17, so that a relatively large magnetic shield room can be constructed. However, the superconducting members 19 to 21 having an appropriate size may be used, and it is not necessary to use a particularly large superconducting member.

A case of forming an opening / closing door on the shield wall of the magnetic shield room having such a structure will be described with reference to FIG. The shield wall 22 is similar to each of the above embodiments,
A shield layer 22c is provided between the inner frame body 22a and the outer frame body 22b, and the shield surface 4 is laminated by a superconducting thick film. The opening of the shield wall 22 is, for example, an opening end 22d in which an end edge of the shield surface is formed in a stepwise manner that spreads from the inside to the outside of the shield wall 22 (see FIG. 16A). . Further, the opening / closing door 23 is also provided with a shield layer 23c between the inner frame body 23a and the outer frame body 23b, and at the outer edge of the opening / closing door 23, a staircase that narrows inward from the outside of the opening / closing door 23. It is a closed end edge portion 23d in which an edge portion of the shield surface is formed in a shape.

Thus, the opening edge 22 of the shield wall 22
d and the closed end edge portion 23d of the opening / closing door 23 are fitted to each other, and when the opening / closing door 23 closes the opening of the shield wall 22, the shield layer 22c of the shield wall 22 is shielded. The pitch width of the surface and the pitch width of the shield surface in the shield layer 23c of the opening / closing door 23 become continuous. As a result, even in the gap portion formed between the opening / closing door 23 and the shield wall 22 of the magnetic shield room, the invading magnetic flux must advance to the inner layer in a stepwise manner along the shield surface. Be effective. That is, the opening / closing door can be provided in the magnetic shield room without adopting a complicated opening / closing structure.

Although not shown in each of the above-mentioned embodiments, a cooling means for bringing the shield surface into a superconducting state, a heat insulating means for keeping the cooling state, or the like may be appropriately added.
It is necessary to place it in the cryostat. For these means, any known existing technology may be used.

[0027]

As described above, according to the magnetic shield space forming method of the present invention, a shield wall is formed by laminating superconducting members having a shield surface made of a superconducting material. Since each shield surface was placed in an environment where each shield surface is in a superconducting state, the external magnetic flux could not enter from the shield surface due to the Meissner effect and entered the shield wall from the edge of the shield surface. Since the magnetic flux cannot enter the inner layer without passing through the edge of the shield surface in each layer, the invading magnetic flux is forced to proceed along the shield surface in each layer until it reaches the shielded space via the innermost layer. To be appropriately attenuated.

Therefore, unlike the conventional magnetically shielded space using a high magnetic permeability material, a complicated joining structure such as making good contact of each high magnetic permeability material is not required, so that the magnetically shielded space has a very simple structure. Can be formed. Moreover, since the shield surface made of a superconducting material is used in a superconducting state, the magnetic shield effect is enhanced even for a low frequency magnetic field. Further, in the method for forming the magnetic shield space according to the present invention, since the laminated structure of the superconducting member may be appropriately changed according to the required magnetic shield ability, the degree of freedom in design is high and It is also suitable when forming a large magnetically shielded room.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a superconducting plate.

FIG. 2 is a perspective view showing a first step in assembling the superconducting box.

FIG. 3 is a perspective view showing a second step in assembling the superconducting box.

FIG. 4 is a perspective view showing a third step in assembling the superconducting box.

FIG. 5 is a perspective view showing a fourth step in assembling the superconducting box.

FIG. 6 is a perspective view showing a fifth step in assembling the superconducting box.

FIG. 7 is a perspective view showing a sixth step in assembling the superconducting box.

FIG. 8 is a perspective view showing a seventh step in assembling the superconducting box.

FIG. 9 is a perspective view of the superconducting box with an outer frame attached.

FIG. 10 is a perspective view of the superconducting box with the outer frame fixed.

FIG. 11 is a schematic cross-sectional view of a superconducting box.

FIG. 12 is an explanatory diagram showing an external magnetic flux penetration path in a shield wall having a three-layer structure.

FIG. 13 is a schematic configuration diagram showing a configuration of an experiment in which an external magnetic field is applied to the superconducting box.

FIG. 14 is a characteristic curve diagram showing experimental results of the configuration shown in FIG.

FIG. 15 is a perspective view showing a schematic process for forming a relatively large magnetic shield room.

16A and 16B show the structure of the door of the magnetically shielded room, wherein FIG. 16A is a schematic cross-sectional view with the door open, and FIG. 16B is a schematic cross-sectional view with the door closed.

[Explanation of symbols]

 3 Superconducting thick film 4 Shield surface 5 1st superconducting member 7 Shielding space 10-14 2nd-6th superconducting member

Claims (1)

[Claims] 1. A shielded space is formed by using a plurality of arbitrary-shaped superconducting members having a shield surface made of a superconducting material.
By stacking other superconducting members so as to cover the edge of the shield surface of each superconducting member forming the shielded space, a shield wall having a multi-layer structure is formed. By placing in an environment below the critical temperature, the shield surface of each superconducting member is put into a superconducting state, magnetic flux intrusion into the shield surface is blocked by the Meissner effect, and the edge portion of the shield surface in the outermost layer of the shield wall. A method of forming a magnetic shield space, characterized in that the magnetic flux penetrating into the shield wall from is attenuated to a predetermined level or less before reaching the shield space through the edges of the shield surface of each layer.