JPH0697696A - Superconductive magnetic shielding body - Google Patents

Abstract

PURPOSE:To make weak magnetic signal measurement possible such as a biological magnetic signal and various high precision magnetic measurement by using a shielding body, which comprises an open-ended tubular superconductor and a plate-like superconductor arranged inside both ends of the tubular superconductor. CONSTITUTION:A plate-like superconductor 2 is arranged at a distance (z) inward from each of the open ends of a tubular superconductor 1. Since the combination of the tubular superconductor 1 and the plate-like superconductors 2 stops external magnetic fields from leaking through the ends of the tubular superconductor 1, a ratio L/D of a length L to an opening diameter D which is necessary for high magnetic shield characteristic can be made small. Therefore, a low magnetic field space can be acquired readily and various high precision magnetic measurement including weak magnetic signal measurement such as a biological magnetic signal becomes possible without being affected by earth magnetism, noises, magnetic field, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnetic shield.

[0002]

2. Description of the Related Art Conventionally, as a magnetic shield material, many materials having a high magnetic permeability such as permalloy alloy have been used, but these materials have a poor shield efficiency in an AC magnetic field of low frequency (several Hz or less). Further, in order to obtain a high attenuation factor, a plurality of laminated layers are required, and there is a drawback in that the weight of the shield material made of these metals or alloys becomes remarkably large when practically used.

As another magnetic shield material, a magnetic shield body utilizing the Meissner effect of a tubular superconductor has been proposed, but in this case, due to the effect of a leakage magnetic field that wraps around the inside of the openings at both ends of the tubular body. , Good shield efficiency (attenuation rate) cannot be obtained. As a countermeasure against this, a tubular superconductor having a length at least three times the opening diameter of the tubular superconductor is required.

[0004]

DISCLOSURE OF THE INVENTION The present invention can easily obtain a low magnetic field space that cannot be obtained by a conventional high magnetic permeability material, and can detect a weak magnetic field such as a biomagnetic signal without being affected by a geomagnetic field or a noise magnetic field. An object of the present invention is to provide a superconducting magnetic shield body which enables various highly accurate magnetic measurements including signal measurement, and is lightweight and low cost.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a superconducting magnetic shield comprising a tubular superconductor with both ends open and plate-shaped superconductors disposed inside both ends of the tubular superconductor. is there.

The tubular superconductor and the plate-shaped superconductor are not limited to oxide superconductors, but are preferably oxide superconductors, and the oxide superconductors are sintered bulks and thick It is preferably made of either a film or a thin film. Further, the tubular superconductor may have a tubular integral structure or a structure in which a plurality of tubular superconductors are combined. In the superconducting magnetic shield according to the present invention, it is important to dispose the plate-shaped superconductor slightly inside the open ends of both ends of the cylindrical superconductor.

FIG. 1 is a sectional view of a superconducting magnetic shield according to the present invention. Reference numeral 1 is a cylindrical superconductor, 2 is a plate-shaped superconductor, and the plate-shaped superconductor 2 is a cylindrical superconductor 1. It is arranged slightly inside from the openings at both ends. In this case, the magnetic shield efficiency is significantly affected by the position of the plate-shaped superconductor. That is, when the plate-shaped superconductor 2 is arranged outside the openings at both ends of the cylindrical superconductor 1, when the plate-shaped superconductor 2 is arranged at only one end, or the plate-shaped superconductor 2 is not arranged. In the case where both end openings are open, the attenuation rate is remarkably lowered as shown in the comparative example, and the intended purpose cannot be achieved.

FIG. 2 is a (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting magnetic shield produced in Example 1 and Comparative Example 2 described later, and the high magnetic permeability material shown in Comparative Example 1. It is a graph which showed the magnetic shield characteristic of the magnetic shield body made from. In FIG. 2, the vertical axis represents the attenuation rate (Htr / He
x), the horizontal axis represents Z / D (Z: distance from the opening, D: opening diameter). A is a graph showing the magnetic shield characteristics with respect to the ratio Z / D of the distance Z from the opening end to the opening diameter D of the tubular oxide superconducting magnetic shield body shown in Example 1 according to the present invention, and B is a comparative example. The distance Z from the opening end with respect to the opening diameter D of the tubular oxide superconducting magnetic shield shown in FIG.
3 is a graph showing the magnetic shield characteristics with respect to the ratio Z / D of (in the case where both ends are open without a plate-shaped superconductor). Further, C is a graph showing the magnetic shield characteristics with respect to the ratio Z / D of the distance Z from the opening end to the opening diameter D in the high magnetic permeability material permalloy cylinder shown in Comparative Example 1. From FIG. 2, it can be seen how the superconducting magnetic shield of the present invention has excellent shield characteristics.

The superconducting magnetic shield according to the present invention can reduce the magnetic field inside the shield due to the Meissner effect of the superconductor and block the fluctuation of the external magnetic field to easily obtain a low magnetic field space. It is possible to obtain an ideal environment space for measuring a very weak magnetic signal using a high-accuracy magnetic sensor such as SQUID including magnetic measurement.

Further, the superconducting magnetic shield according to the present invention can shield the leakage magnetic field leaking from the openings at both ends of the tubular superconductor by combining the tubular superconductor and the plate superconductor. It is possible to reduce the ratio L / D of the length L to the opening diameter D required for high magnetic shield characteristics, and thus it is possible to obtain effective magnetic shield characteristics at a low weight and at low cost. Next, examples of the present invention will be described.

[0011]

[Examples] Example 1 (Bi, Pb) ₂ molded and sintered into a cylindrical shape and a disk shape.
A superconducting magnetic shield manufactured by using an Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting bulk will be described.

Bi: Pb: Sr: Ca: Cu = 2: 0.
Oxides and carbonates (Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , Cu mixed in a ratio of 4: 2: 2: 3).
O) is calcined in the air at 850 ° C. for 100 hours and then slowly cooled to obtain (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy.
An oxide superconducting powder was produced.

This powder has an outer diameter of 160 mm and an inner diameter of 150 m.
m, 400 mm long cylinder and 2 disks with a diameter of 145 mmφ and a thickness of 5 mm are formed and sintered to form (Bi, P
b) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting cylinder and disk (Tc = 105K, Jc = 1000A / cm ² ).
Was produced.

At both ends of the oxide superconducting bulk cylinder, a disk-shaped superconducting bulk was arranged at a position within 10 mm from the open end, perpendicular to the center axis of the cylinder. After cooling them with liquid nitrogen (77K), a magnetic field was applied from the outside in the directions parallel and perpendicular to the central axis of the cylinder, and the magnetic shield characteristics were measured. A magnetic shield space having an attenuation rate of 10 ⁻⁵ or more was obtained as a whole (see A in FIG. 2).

Example 2 (Bi, Pb) ₂ Sr ₂ on MgO cylinders and discs
A superconducting magnetic shield manufactured by depositing a Ca ₂ Cu ₃ Oy oxide superconducting thick film will be described.

Bi: Pb: Sr: Ca: Cu = 2: 0.
Oxides and carbonates (Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , Cu mixed in a ratio of 4: 2: 2: 3).
O) is calcined in the air at 850 ° C. for 100 hours and then slowly cooled to obtain (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy.
An oxide superconducting powder was produced.

This powder and terpineol in which 10 wt% of polyisobutylmethacrylate were dissolved were mixed at a weight ratio of 3: 1 to form a paste.

Outer diameter 160 mm, inner diameter 150 mm, length 4
The paste was applied to a surface of a cylinder of 00 mm and two disc-shaped MgO polycrystalline sintered bodies having a diameter of 145 mm and a thickness of 1 mm to a film thickness of 200 μm, followed by firing in air at 850 ° C. for 100 hours and gradual cooling. By doing so, on the MgO cylinder and the disk surface, (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting thick film (Tc = 105K, Jc = 1000A /
cm ² ) was deposited.

A disk-shaped superconducting thick film was disposed at a position within 10 mm from the opening end on both ends of the oxide superconducting thick film cylinder perpendicularly to the central axis of the cylinder. After cooling these with liquid nitrogen (77K), applying a magnetic field from the outside in the direction parallel and perpendicular to the central axis of the cylinder, and measuring the magnetic shield characteristics,
With respect to an external magnetic field of 10 G or less, a magnetic shield space having an attenuation rate of 10 ⁻⁵ or more was obtained almost entirely inside the magnetic shield body.

Example 3 A superconducting magnetic shield manufactured by depositing a YBa ₂ Cu ₃ Ox oxide superconducting thick film on a Ni cylinder and a disk will be described.

Oxides and carbonates (Y ₂ O ₃ , BaCO ₃ , Cu) mixed in a ratio of Y: Ba: Cu = 1: 2: 3.
O) was calcined in the air at 950 ° C. for 50 hours and gradually cooled to prepare a YBa ₂ Cu ₃ Ox oxide superconducting powder.

This powder was mixed with terhineol containing 5% by weight of ethyl cellulose dissolved in a weight ratio of 3: 1 to form a paste.

Outer diameter 160 mm, inner diameter 150 mm, length 4
After applying the above-mentioned paste in a thickness of 200 μm on the surface of a cylinder of 00 mm and two disc-shaped Ni surfaces of 145 mm in diameter and 1 mm in thickness, the Ni cylinder was baked at 975 ° C. for 60 minutes in an oxygen stream and then slowly cooled. And YB on the Ni disk surface
a ₂ Cu ₃ Ox oxide superconducting thick film (Tc = 90K, Jc
= 1000 A / cm ² ) was formed.

A disk-shaped oxide superconducting thick film was arranged at both ends of the cylinder of the oxide superconducting thick film perpendicularly to the center axis of the cylinder at a position within 10 mm from the open end. Liquid nitrogen (77K)
In After cooling, cylinder center by applying a magnetic field from outside to the parallel and perpendicular direction to the axis, results of measurement of the magnetic shielding characteristics, a magnetic to following external magnetic field 10G shield body portion of the substantially overall attenuation rate 10 ^- A magnetic shield space of ⁵ times or more was obtained.

[0025]

COMPARATIVE EXAMPLE Comparative Example 1 An external magnetic field was applied to a high magnetic permeability permalloy cylinder weak magnetic shield body having a diameter of 50 mm and a length of 150 mm, and the magnetic shield characteristics were measured. As a result, only a magnetic shield characteristic with an attenuation rate of 10 ⁻² was obtained. I couldn't do it. (Shown as C in FIG. 2)

Comparative Example 2 An open-ended superconducting magnetic shield will be described. B
i: Pb: Sr: Ca: Cu = 2: 0.4: 2: 2: 3
Oxides and carbonates (Bi ₂ O ₃ , P
bO, SrCO ₃ , CaCO ₃ , CuO) is calcined in the air at 850 ° C. for 100 hours and then slowly cooled (B
i, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting powder was prepared.

This powder has an outer diameter of 160 mm and an inner diameter of 150 m.
m, molded and sintered into a cylinder with a length of 400 mm, (Bi, P
b) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting cylinder (Tc
= 105 K, Jc = 1000 A / cm ² ) was produced.

The disk-shaped oxide superconductor was not placed at both ends of the oxide superconducting bulk cylinder but was left open, and after being cooled with liquid nitrogen (77 K), it was parallel to the central axis of the cylinder. A magnetic field was applied from the outside in the vertical direction and the magnetic characteristics were measured. As a result, a decrease in the attenuation rate was observed near both openings due to the leakage magnetic field from both openings of the cylinder. (Shown as B in FIG. 2)

Comparative Example 3 A superconducting magnetic shield in which a plate-shaped oxide superconductor is provided only on one end will be described.

Bi: Pb: Sr: Ca: Cu = 2: 0.
Oxides and carbonates (Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , Cu mixed in a ratio of 4: 2: 2: 3).
O) was calcined in air at 850 ° C. for 100 hours and gradually cooled to prepare (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting powder.

This powder has an outer diameter of 160 mm and an inner diameter of 150 m.
m, 400 mm long cylinder and one disk with a diameter of 145 mm and a thickness of 5 mm are formed and sintered to form (Bi, P
b) ₂ Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting cylinder and disk (Tc = 105K, Jc = 1000A / cm ² ).
Was produced.

1 from the open end of one end of this superconducting bulk cylinder
A disk-shaped superconductor was placed at a position of 0 mm inside perpendicular to the central axis of the cylinder, cooled with liquid nitrogen (77 K), and then a magnetic field was applied from the outside in the directions parallel and perpendicular to the central axis of the cylinder. As a result of measuring the magnetic shield characteristics, a decrease in the attenuation rate due to a leakage magnetic field leaking from the opening was found at one end where the disc-shaped superconductor was not arranged.

Comparative Example 4 An oxide superconducting magnetic shield in which a plate-shaped oxide superconductor is provided outside the openings at both ends of a cylindrical oxide superconductor will be described.

Bi: Pb: Sr: Ca: Cu = 2: 0.
Oxides and carbonates (Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , Cu mixed in a ratio of 4: 2: 2: 3).
O) is calcined in the air at 850 ° C. for 100 hours and then slowly cooled to obtain (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ Oy.
An oxide superconducting powder was produced.

This powder has an outer diameter of 160 mm and an inner diameter of 150 m.
m, length 400 mm cylinder and diameter 145 mm, thickness 5
Formed and sintered into 2 mm discs (Bi, Pb)
_{A 2} Sr ₂ Ca ₂ Cu ₃ Oy oxide superconducting cylinder and a disk (Tc = 105K, Jc = 1000A / cm ² ) were produced.

From the open end to both ends of this superconducting bulk cylinder,
As a result of applying a magnetic field from the outside in a direction parallel and perpendicular to the central axis of the cylinder at an external position separated by 0 mm and measuring the magnetic shield characteristics, as in the case where the disc-shaped superconductor is not arranged, A decrease in the attenuation factor was observed near both openings due to the leakage magnetic field from the openings.

[0037]

According to the superconducting magnetic shield of the present invention, it is possible to easily obtain a low magnetic field space that cannot be obtained with a conventional high permeability material such as permalloy, without being affected by the earth magnetism or noise magnetic field. Various highly accurate magnetic measurements including weak magnetic signal measurements such as biomagnetic signals can be performed.
Further, since the superconducting magnetic shield of the present invention is only a combination of a tubular superconductor and a plate-shaped superconductor, it is possible to obtain an effective magnetic shield effect at a low weight and at a low cost.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view of a superconducting magnetic shield according to the present invention.

FIG. 2 is a graph showing magnetic shield characteristics of superconducting magnetic shields of the present invention and a comparative example (conventional example).

[Explanation of symbols]

1-Cylindrical Superconductor 2-Plate-shaped Superconductor A-Magnetic Shielding Characteristic Curve of a Cylindrical Oxide Superconducting Magnetic Shield Body According to the Present Invention B-Magnetic Shielding Characteristic Curve C- of a Conventional Cylindrical Oxide Superconducting Magnetic Shield Body C- Magnetic shield characteristic curve of conventional high permeability material Permalloy

Claims (3)

[Claims] 1. A superconducting magnetic shield comprising a tubular superconductor with both ends open and plate-shaped superconductors disposed inside both ends of the tubular superconductor. 2. The superconductor according to claim 1, wherein the tubular superconductor and the plate-shaped superconductor are oxide superconductors made of sintered bulk, thick film or thin film. Magnetic shield body. 3. The tubular superconductor has a tubular integral structure or a structure in which a plurality of tubular superconductors are combined.
Alternatively, the superconducting magnetic shield according to item 2.