JPH03218695A - Magnetic shielding device using superconductor - Google Patents

Abstract

PURPOSE:To easily obtain a low magnetic field at a low cost without elongating a shielding body in an axial direction by a method wherein a cylindrical ferromagnetic member is provided covering the opening end of a cylindrical shielding body. CONSTITUTION:A cylindrical ferromagnetic member 2 whose inner diameter is slightly larger than the outer diameter of a shielding body 1 is fitted into the end of the cylindrical shielding body 1 protruding outwards from the end of the shielding body 1 and overlapping the end of the body 1 by a certain length. A magnetic field adjacent to the ferromagnetic member 2 (a component H1 in an axial direction, a component H2 in a direction vertical to an axis) extends just as shown by lines of magnetic force in a figure. The ferromagnetic member 2 is magnetized by a surrounding magnetic field, and the magnetic field induced inside it attenuates an external magnetic field such as a geomagnetic field and the like a little in the axial direction of the body 1 but sharply attenuates the external magnetic field in the direction vertical to the axis of the body 1. By this setup, an inner magnetic field inside the shielding body 1 can be lessened in intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shielding device for realizing an extremely low magnetic field space that is magnetically shielded with a superconductor. [Prior Art] A magnetic shielding device using a conventionally known superconductor includes a cylindrical shield body made of a material exhibiting the Meissner effect (for example, an oxide superconductor), and a shield body that is heated to the critical temperature of the Meissner effect. [It is equipped with a cooling means for cooling down to below rc, and magnetic shielding of the space is performed by the following procedure.

(1) First, a cylindrical shield is placed so as to cover the space to be shielded. However, the temperature of the shield body at this point is higher than the critical temperature Tc. In other words, the shield body is in a normally conductive state. (2) Next, the shield body is cooled down to a critical temperature Tc or lower to transition to a superconducting state. In the superconducting state, the shield becomes a completely diamagnetic material, so magnetic flux cannot enter the space covered by the shield and is pushed outside (Meissner effect), resulting in the space inside the shield being magnetically shielded. It turns out. [Problem to be solved by the invention] By the way, in the conventional sealing device as described above,
The degree of the low magnetic field formed inside the sinilt body (the smallness of the internal magnetic field) is determined by the ratio of the length and diameter of the shield body.

As shown in FIG. 8, if the radius of the cylindrical shield body 81 is a, and the distance from the opening end face to the inside on the axis is Z, then the distance Z with respect to the external magnetic field strength H1 in the axial direction of the shield body 81 is: The internal magnetic field strength H + a at the position is H, a = H, exp (-3.83 z/a)...
- (1) Internal magnetic field strength H at a position at a distance Z from the external magnetic field strength Ht in the direction orthogonal to the axis of the shield body 81
it is H1t=Htexp(-1.84z/a) --・(
2) It is given as follows.

Therefore, inside the shield body 81, the influence of the external magnetic field strength Ht in the direction orthogonal to the axis becomes dominant, and the length of the shield body is determined so that the degree of low magnetic field required for the internal magnetic field strength }lit is satisfied. That will happen. For this reason, in the conventional magnetic shielding device, there was a problem in that in order to realize a low magnetic field, the length of the shield body in the axial direction had to be made large.

The present invention has been made in view of the above points, and an object of the present invention is to provide a magnetic shielding device that can easily and inexpensively realize a low magnetic field without making the axial length of the shield body particularly long. That is.

[Means for solving the problem] In the magnetic shielding device using a superconductor according to the present invention,
A cylindrical shield body made of a superconducting material that changes from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled to a temperature below a critical temperature; A magnetic shielding device using a superconductor having a cooling means for cooling the superconductor to transform it into a superconducting state, characterized in that a cylindrical ferromagnetic member covering an open end of the cylindrical shield body is provided. It is something.

Further, as the cylindrical seal body, one open at one end and one open at both ends are used. The shape of the cylindrical ferromagnetic member that covers the open end of the cylindrical seal body includes a sleeve shape, a shape with one end closed, and a shape with different opening areas at both ends.

[Function] The function of the wooden invention will be explained with reference to FIG. 7, which shows an enlarged view of the end portion of the seal body according to the first embodiment of the present invention. In the figure, at the end of the cylindrical shield body 1, a cylindrical ferromagnetic member 2 having an inner diameter slightly larger than the outer diameter of the shield body 1 has an overlapping portion with the end of the shield body 1,
The shield body 1 is fitted so as to protrude from the end face of the shield body 1. In addition, the magnetic field near the ferromagnetic member 2 (axial component H
1. The component H2) in the direction perpendicular to the axis becomes like the lines of magnetic force shown in FIG.

The ferromagnetic member 2 is magnetized by the surrounding magnetic field, and the magnetic field generated inside it has a small amount of attenuating external magnetic fields such as the earth's magnetic field in the axial direction of the shield body, but in the direction orthogonal to the axis, it does not attenuate the external magnetic field. Significantly attenuates the magnetic field.

That is, since Ht in equation (2) giving the internal magnetic field strength Hit in the direction perpendicular to the axis of the shield body 1 described above is reduced, the internal magnetic field of the shield body 1 becomes smaller.

In addition, if the ferromagnetic material covering the opening of the cylindrical shield body is a cylindrical body with radius r and length Z closed at one end, both ends with radius r and length 2Z are open. It has the same shielding effect as a cylindrical body, and the entire device can be further miniaturized.

Furthermore, if the ferromagnetic member is a cylindrical body with different opening areas at both ends, the shielding effect will be improved compared to a cylindrical body with equal open opening areas at both ends, and the overall device will be further improved. Can be made smaller.

Here, the material constituting the ferromagnetic member covering the open end of the cylindrical shield used in the present invention is not particularly limited as long as it is ferromagnetic, but in order to achieve a lower magnetic field, The higher the magnetic permeability, the better, and the higher the magnetic permeability, the smaller the thickness of the ferromagnetic member can be. Specifically, those having a relative magnetic permeability of 300 or more are preferably used, such as permalloy. Amorphous iron. Examples include ferrite.

In the present invention, at least one side of the cylindrical shield body needs to be open in order to take in and take out the object to be measured.

[Example] Example = 1 Fig. 1 is a perspective view showing the configuration of a main part of a magnetic shielding device according to a first example of the present invention.

In the figure, a cylindrical shield body 1 is made of an oxide superconductor with an inner diameter of 10 cm, a thickness of 4 mm, and a length of 30 cm in circular cross section, and has a heat insulating layer (not shown) on the outer and inner surfaces for thermal insulation. is provided. The cylindrical shield body l is provided with a cleaning means (not shown) using, for example, liquid nitrogen.
It is designed to be cooled by The length of the cylindrical shield body 1 in the axial direction is set depending on the size of the space to be shielded and the target internal magnetic field, but generally the cylindrical shield body 1 is 2 to 20 of inner diameter
The degree is normal. Furthermore, both open ends of the cylindrical shield l have a relative magnetic permeability t
oooo permalloy (iron 20 zero, nickel 8096)
Inner diameter 11cm, thickness 10a+m, length 20c
m cylindrical ferromagnetic members 2a, 2b are attached.

Next, the results of measuring the magnetic flux density in the space to be sealed by the above-mentioned sealing device will be explained. The magnetic flux density was measured using a magnetic sensor (not shown) placed near the center of the shielded space. First, a cylindrical shield body 1 equipped with ferromagnetic members 2a and 2b is installed in an extremely low magnetic field space (io-' Gauss or less),
The cylindrical shield body 1 was cooled to a critical temperature Tc with liquid nitrogen in an extremely low magnetic field space.

Thereafter, the cylindrical shield body 1 was taken out of the extremely low magnetic field space, and the magnetic flux density near the center (measurement point m+) inside the cylindrical shield body 1 was measured under the earth's magnetic field (approximately 0.4 Gauss). As a result, the magnetic flux density was a very low value of 4.0x 10-' Gauss.

Comparative Example: 1 A cylindrical shield body similar to that of Example 1 was used and cooled to below the critical temperature TC in an extremely low magnetic field space without attaching a ferromagnetic member. After that, the cylindrical shield was taken out of the extremely low magnetic field space, and the magnetic flux density near the center of the cylindrical shield was measured under the earth's magnetic field. As a result, the magnetic flux density is 3
．． O x 10-3 Gauss and 3 from the case of the present invention example
The digits were also too large.

The measurement results of Example 1 and Comparative Example 1 above demonstrate that the magnetic shielding device of the present invention can achieve a lower level of magnetic field than conventional ones.

Embodiment 2 FIG. 2 is a perspective view showing the main parts of a magnetic shielding device according to a second embodiment of the present invention.

In this embodiment, a cylindrical shield body 21 with an inner diameter of 10 cm, a thickness of 4 mm, and a length of 15c+a (the length of 172 in embodiment 1) is closed at one end (the bottom surface is shown with diagonal lines).
was used. This cylindrical shield body 21 is made of an oxide superconductor with a heat insulating layer provided on the inner and outer surfaces as in Example 1, and has a cylindrical reinforcing layer made of permalloy similar to Example 1 at its open end. Magnetic member 22 (inner diameter 11cm, thickness 101Il)
m, length 2ocm) is attached. Using such a shield device, the magnetic flux density at the center of the bottom surface of the cylindrical shield body 21 (measurement point mz) was measured in the same manner as in Example 1. As in Example 1, the magnetic flux density was 4. The value was very low, OX 10-' Gauss.

Embodiment 3 FIG. 3 is a perspective view showing essential parts of a magnetic shielding device according to a third embodiment of the present invention.

In this example, the inner diameter is 10 cm and the thickness is 4 nm.
, and is made of an oxide superconductor with a length of 30 cm, and a heat insulating layer (not shown) for thermal insulation is provided on the outer and inner surfaces. The cylindrical shield body 31 is cooled by a cooling means (not shown) using liquid nitrogen, for example. Further, both opening ends of the shield body 3l have a relative magnetic permeability of 100.
00 permalloy (iron 2096, nickel 8H'), inner diameter 11cm, thickness 10mm. length locn+
Cylindrical ferromagnetic members 32a and 32b with one end closed are attached.

Thereafter, this shield body 31 was taken out of the extremely low magnetic field space, and the magnetic flux density near the center of the silt body 31 (measurement point m+) was measured under the earth's magnetic field (about 0.4 Gauss). As a result, the magnetic flux density was a very low value of 2.5x10-6 cous.

Embodiment 4 FIG. 4 is a perspective view showing the main parts of a magnetic shielding device according to a fourth embodiment of the present invention.

In this example, a cylindrical shield body 41 with an inner diameter of 10 cm, a thickness of 4 mm, and a length of 15 cm (the length of 172 in Example 1) closed at one end (the bottom surface is shown with diagonal lines) was used. Similar to the third embodiment, this shield body 41 has an inner
It is made of an oxide superconductor with a heat insulating layer on its outer surface, and at its open end is a cylindrical ferromagnetic member 42 (inner diameter 11 cm, thickness romn) made of permalloy and closed at one end, similar to that in Example 3.
+, length l Octa) is attached.

Using such a shield device, the magnetic flux density at the center of the bottom surface of the shield body 4l (measurement point m2) was measured in the same manner as in Example 3, and the magnetic flux density was the same as in Example 3.2.
It was a very low value of 5×10 −6 Gauss.

Embodiment 5 FIG. 5 is a perspective view showing the main parts of a magnetic shielding device according to a fifth embodiment of the present invention. In this example, the inner diameter is 10 cm, the thickness is 4 mm,
It is made of an oxide superconductor with a length of 30c+n, and a heat insulating layer (not shown) for heat insulation is provided on the outer and inner surfaces. The cylindrical shield body 51 is cooled by cooling means (not shown) using liquid nitrogen, for example.

In addition, permalloy (iron 20*, nickel 80 zero) with a relative magnetic permeability of ioooo is placed at both open ends of the cylindrical shield body 51.
A large cylinder with an inner diameter of 11 cm and a length of 10 cm, and an inner diameter of 2
2 cm and a small cylinder with a length of 2 cm, and cylindrical ferromagnetic members 52a and 52b with different opening areas at both ends are attached.

After that, take out the shield body 5l from the extremely low magnetic field space,
The magnetic flux density at a measurement point mt near the center of the shield body 5l was measured under the earth's magnetic field (approximately 0.4 Gauss). As a result, the magnetic flux density was a very low value of 4 x 10-' Gauss.

Embodiment = 6 FIG. 6 is a perspective view showing the main parts of a magnetic shielding device according to a sixth embodiment of the present invention.

In this example, the inner diameter is 10cm+ and the thickness is 4cm.
A cylindrical shield body 61 with a length of 15 cm (half the length of Example 1 of solid b color) with one end closed (the bottom surface is shown with diagonal lines) was used. This cylindrical shield body 61 is made of an oxide superconductor with a heat insulating layer provided on the inner and outer surfaces as in Example 5, and has openings at both ends made of permalloy similar to Example 5. Cylindrical ferromagnetic member 62 with different surface lines
(Large cylinder: inner diameter 11cm, thickness 1.0IIm. length 1
0cm, small diameter: inner diameter 2cm, length 2c++) is attached. Using such a shield device, the magnetic flux density above the center of the bottom surface of the shield body 61 (measurement point m2) was measured in the same manner as in Example 5. As in Example 5, the magnetic flux density was 4
It was a very low value of 10-6 Gauss.

In this example and example 5, a ferromagnetic member with an inner diameter of 11 cm was used to cover the open end of the cylindrical shield.
．． Large tube with length locm, radius 2ctn, length 2cm
Although a combination of a small cylinder and a truncated cone is shown, the same effect can be obtained even if the inner diameter gradually decreases, such as a truncated cone. In addition, a dog cylinder with inner diameter rl + length Zl + and inner diameter r2 + length Z2
When combined with a small cylinder, r +/z l−r
If it is determined as 2/Z 2, it will have the same effect.

[Effects of the Invention] As explained above, the magnetic shielding device using a superconductor according to the present invention has a simple configuration in which a ferromagnetic member is attached to the open end of a cylindrical shield body. By attenuating the external magnetic field in the direction orthogonal to the axis of the shield body near the open end of the shield body, the magnetic field strength inside the shield body can be reduced. In addition, if the ferromagnetic member is a cylinder with one end closed, the shielding effect is higher than that of a cylinder with both ends open, and the entire device can be further miniaturized. When the body member is a cylinder with different opening areas at both ends, the sealing effect is improved compared to a cylinder where the opening areas at both ends are equally open, and the entire device can be further miniaturized.

That is, according to each of the present inventions, a low magnetic field space can be easily and inexpensively realized without making the axial length of the cylindrical shield body particularly long, and the magnetic shield device can be miniaturized. is also possible.

The magnetic shielding device of the present invention is effective, for example, for magnetic shielding of a measurement space using a SQUID (superconducting quantum interference device) that is susceptible to the influence of surrounding magnetic fields, and is useful for chemical technology and medical purposes. It has many useful uses for observing magnetic phenomena, and has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a main part of a sealing device according to a first embodiment of the present invention, FIG. 2 is a perspective view of a main part of a sealing device according to a second embodiment of the present invention, and FIG. 3 is a perspective view of a main part of a sealing device according to a second embodiment of the present invention. FIG. 4 is a perspective view showing essential parts of a magnetic shielding device according to a fourth embodiment of the present invention, and FIG. 5 is a perspective view showing essential parts of a magnetic shielding device according to a fifth embodiment of the present invention. FIG. 6 is a perspective view showing the main parts of a magnetic shielding device according to a sixth embodiment of the present invention, and FIG. 7 is a cylindrical shield body for explaining the operation of the present invention. A perspective view of an end portion, and FIG. 8 is a partial perspective view of a shield body for explaining a conventional example. [Description of symbols of main parts] 1, 21, 31, 41, 51, 61. 81 is a cylindrical shield body, 2, 2a, 2b, 22, 32a 32b, 42,
52a, 52b, and 62 are ferromagnetic members, and ml and m2 are measurement points.

Claims (1)

[Claims] (1) A cylindrical shield body made of a superconducting material that transitions from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled below a critical temperature, and a cylindrical shield body made of a superconducting material that transitions from a normal conductive state to a critical temperature for the Meissner effect. A magnetic shielding device using a superconductor having a cooling means for cooling the superconductor to a superconducting state by cooling it to a temperature below, characterized by comprising a cylindrical ferromagnetic member covering an open end of the cylindrical shield body. A magnetic shielding device using superconductors.