JP2003257751A - Magnetic shield apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that thickness of a magnetic body must be increased with a conventional technology to provide sufficient shield characteristics even if the magnetic body of a wall surface has double- or multiple-structure, because of insufficient spatial magnetic flux control that depends on a conventional magnetic shield basic structure. <P>SOLUTION: In a magnetic shield apparatus, a shield wall 1 of a soft magnetic material encloses a prescribed shield space. A conductor 5 is disposed near point of shield wall 1 parallel to external magnetic field direction Ho that represents maximum magnetic flux density caused by an external magnetic field. The conductor constitutes a closed coil 50. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield, and more particularly to a magnetic shield device having a hollow structure.

[0002]

2. Description of the Related Art A conventional magnetic shield has a rectangular cross section structure or a ring cross section structure, and has a structure in which the wall surface of a magnetic material constituting the shield is doubled or tripled according to the required shielding characteristics. Alternatively, it is common to deal with the structure in which the thickness of the magnetic material on the wall surface is changed.

[0003]

However, in the prior art, in order to obtain sufficient shield characteristics, even if the magnetic body on the wall surface has a double or more multi-layer structure, the magnetic body thickness is increased. I had to. The reason for this is that the magnetic flux control in space tends to be insufficient depending on the basic structure of the conventional magnetic shield. For example, as a general principle, at the interface between a high permeability magnetic material and vacuum (air), the magnetic flux density is continuous in the direction perpendicular to the direction of the magnetic flux in the vacuum, and is continuous in the direction parallel to the interface. The magnetic field becomes continuous. Where the relative permeability of the magnetic material is μ,
Since the magnetic field H is given by H = B / μ, where the magnetic flux density is B, the parallel component of the spatial magnetic field near the interface becomes smaller as the relative permeability μ increases.

When the magnetic flux density in the space increases, the magnetic field in the magnetic material also increases, and the magnetic material approaches saturation. At this time, the relative magnetic permeability of the magnetic material decreases, so that the shield characteristics deteriorate. In order to avoid this effect, it is necessary to increase the saturation magnetic flux density of the magnetic material or increase the thickness of the magnetic material to reduce the density. In the conventional technology, permalloy (NiF) having a large relative magnetic permeability is used to improve the shield rate.
e alloy) is often used. In the case of Permalloy,
Since the saturation magnetic flux density is relatively small, it was necessary to increase the thickness of the magnetic body. In addition, since the conventional technology does not have the technology to control the magnetic flux component in the direction perpendicular to the interface between the magnetic body and the vacuum, only increasing the refractive index at the interface of the magnetic flux lines is a method of shielding the magnetic flux of the vertical component. Met.
In this method, since the refractive index is proportional to the relative magnetic permeability, it was necessary to keep the thickness of the magnetic material sufficiently thick to avoid deterioration of the relative magnetic permeability.

As a technique for avoiding magnetic saturation of a magnetic material for shielding, a technique for forming a tapered shape in a bent portion as disclosed in Japanese Patent Laid-Open No. 57-8000, or a magnetic path having a tapered shape is doubled. There is a technique of providing a magnetic body for doing so. However, the conventional techniques disclosed therein are techniques for avoiding saturation of the magnetic flux collected for shielding, and the magnetic flux of the external magnetic field cannot be efficiently controlled with respect to the entire device that performs magnetic shielding. .

However, these prior arts have a problem that the shield wall constituting the magnetic shield device becomes heavy because the magnetic material needs to be thickened. If the volume of the space for the magnetic shield is small, this problem can be solved by weakening the structural strength of the wall surface and reducing the overall weight. But,
When the space to be shielded is large, the shield wall itself has a large area, and the structure supporting the shield wall is required to be large and have sufficient strength as the self-weight increases.
In this situation, it has been impossible to reduce the weight of the structure by reducing the proportion occupied by the magnetic material in the conventional shield structure.

The object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a magnetic shield device that can obtain high-performance shield characteristics without increasing the thickness of the magnetic material that forms the shield wall.

[0008]

The first invention of the present application is a magnetic shield device in which a predetermined shield space is surrounded by a shield wall provided with a soft magnetic material, wherein the shield wall is parallel to the external magnetic field direction. The magnetic shield device is characterized in that a conductor is installed in the vicinity of a portion exhibiting the maximum magnetic flux density by an external magnetic field, and the conductor forms a closed coil. In order to further exert the effect of suppressing the magnetic saturation of the shield wall, it is preferable that the inner peripheral shape of the closed coil and the outer peripheral shape of the magnetic shield device match as much as possible.

A second invention of the present application is a magnetic shield device in which a predetermined shield space is surrounded by a shield wall provided with a soft magnetic material, wherein the shield wall parallel to the external magnetic field direction has a central portion in the external magnetic field direction. A magnetic shield device is characterized in that a conductor is installed in the vicinity of, and the conductor forms a closed coil.

In the case where the shield wall is provided with a window or an opening for drawing the wiring or piping into the magnetic shield device, the magnetic flux easily enters the shield space through the opening.
The opening here is a portion where the magnetic material does not exist or is magnetically discontinuous with the magnetic material of the shield wall even if the magnetic material exists.

A third invention of the present application is a magnetic shield device in which a predetermined shield space is surrounded by a shield wall provided with a soft magnetic material, the shield wall having an opening,
The magnetic shield device is characterized in that a conductor surrounding the opening is installed on the shield wall, and the conductor forms a closed coil.

In each of the above inventions, a shield wall made of a sheet-like material obtained by laminating a soft magnetic thin body containing FeSi alloy microcrystals with a non-magnetic resin can be preferably used.

The magnetic shield reduces the magnetic flux density in a desired space by collecting magnetic flux from the space around the shield body to perform magnetic sealing. For this reason, when the volume of the space for shielding increases or the magnetic flux density in the space around the shield increases, the magnetic flux flowing into the soft magnetic material forming the shield increases, and the magnetic flux density in the soft magnetic material increases. To rise. The maximum amount of magnetic flux that can exist in the soft magnetic body is determined by the saturation magnetic flux density, but the relative magnetic permeability generally deteriorates as the magnetic flux density in the soft magnetic body approaches the saturated magnetic flux density. The magnetic permeability of the soft magnetic material that constitutes the magnetic shield device is an important factor that determines the shield rate, and if the magnetic permeability decreases, the shield rate also decreases. The present invention provides a magnetic shield room that is lightweight and excellent in workability by forming a foil body made of a microcrystalline magnetic body into a sheet shape, but is large because the magnetic body thickness of the shield room wall surface is thin. In order to perform shield in a shielded space having a volume or in a strong magnetic field, it is necessary to design so as to avoid magnetic saturation of the soft magnetic material. Although it can be dealt with simply by increasing the thickness of the magnetic body, this may increase the weight of the magnetic body and impair the characteristics of the shield device of the present invention. Therefore,
A means for applying a magnetic field to the wall of the magnetic shield room where magnetic saturation is likely to occur is provided in advance, and by applying a magnetic field in the direction opposite to the magnetization of the shield wall, the magnetic flux density of the shield wall is reduced and the relative permeability is reduced. It prevents deterioration of magnetic susceptibility.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a magnetic flux density distribution of a shield wall provided with a soft magnetic material that constitutes a magnetic shield room. The shield space 2 is a space on the far side in FIG. 1 and is surrounded by the shield wall 1 and another shield wall (not shown). The external magnetic field is applied in the direction of the arrow Ho, and the magnetic flux 3 passes through the shield wall 1 in the same direction. The direction of magnetization of the soft magnetic material forming the shield wall 1 is the same as the direction of the magnetic flux 3 passing through the shield wall 1. The magnetic flux density increases from white to gray and black. The portion with the highest magnetic flux density is mainly the central portion of the shield wall 1 in the direction of the external magnetic field, and this portion is most likely to cause magnetic saturation. This is because the magnetic flux 3 enters the shield wall 1 not only from the end of the shield wall 1 but also from a part in the longitudinal direction of the shield wall 1, and is emitted into the space not only from the other end but also from the part in the middle. is there.

On the other hand, as shown in FIG. 2, when the closed coil 4 is used to apply a magnetic field in the direction Hc opposite to the magnetization of the shield wall, the magnetic flux density inside the soft magnetic material forming the shield wall 1 decreases, It is possible to improve the relative magnetic permeability. In the example of FIG. 2, a plurality of closed coils 4 are arranged along the location where the magnetic flux density of the shield wall 1 is the largest and the axial direction thereof is aligned with the above-mentioned magnetization direction. According to the law of electromagnetic induction, the magnitude of a magnetic field around a conductor changes with time, so that an electromotive force is generated in the conductor. Therefore, when the conductor forms a closed circuit, an induced current flows in the circuit due to this electromotive force. In this case, the current direction is the direction in which the magnetic field intersecting the closed circuit is eliminated. Therefore, when the closed coil is placed in the external magnetic field, the magnetic field created by the induced current by the closed coil opposes the external magnetic field. The external magnetic field will be reduced by the magnetic field created by the closed coil. Therefore, the shield wall 1
Magnetic flux density is reduced, and it becomes difficult for magnetic saturation to occur.

The efficiency of the magnetic shield is higher as the magnetic resistance of the shield portion is lower than that of the magnetic circuit including the surrounding space. Therefore, the reduction of the magnetic resistance caused by the improvement of the relative permeability is caused by the magnetic shield. Will improve the performance of. Here, the magnetic field applying means in FIG. 2 may be a permanent magnet or the like.

The actual external magnetic field is often composed of components in three directions that are orthogonal to each other. Even in this case, by applying the present invention to each of the components in each direction, it is possible to prevent magnetic saturation from occurring without increasing the thickness of the magnetic body forming each shield wall in the triaxial direction.

FIG. 3 shows an embodiment of the present invention when the unidirectional component Ho of the external magnetic field is applied to the magnetic shield device. The magnetic shield device 10 of the present invention includes a shield wall 1 forming six surfaces and a closed coil 5 provided on the wall surface of the shield wall 1.
It is composed of four conductors 5 forming 0. The external magnetic field is an alternating magnetic field, and the magnetic flux densities in the four shield walls parallel to the one-way component Ho thereof become maximum at almost the central portion in the Ho direction. The conductor 5 is installed there. When the external magnetic field component Ho is applied, a current is generated in the closed coil 50 in a direction in which a magnetic field in a direction canceling it is generated. Since the resulting magnetic flux density is maximum at the position of the conductor 5, it acts on the maximum magnetic flux density in the shield wall, greatly reducing it, and preventing deterioration of the relative permeability of the shield wall. Since the magnetic flux density in the shield wall is less likely to be saturated, the magnetic flux density in the space increases, and it is not necessary to thicken the shield wall even when the space to be shielded is large. Therefore, it is possible to reduce the amount of magnetic material used, reduce the overall weight, and improve workability. The conductor 5 may be a metal band or electric wire having a low electric resistance such as copper or aluminum. Although the closed coil 50 has one turn in the embodiment shown in FIG. 3, the number of turns can be increased. In that case, the effect of lowering the magnetic flux density of the shield wall becomes larger, but the effect per turn becomes lower.

Next, an embodiment in which an opening is provided in the magnetic shield device will be described with reference to FIG. An opening 6 was provided in a shield wall perpendicular to the one-way component Ho of the external magnetic field, and a door 7 was attached so as to close the opening. Four conductors 5 were provided on the wall surface of the shield wall 1 so as to surround the opening 6, and they were joined to form the closed coil 50. The conductor 5 is a metal strip and is perpendicular to the shield wall 1. The external magnetic field Ho tries to enter from the door 7, but is blocked by the electromagnetic induction action of the closed coil 50.

According to the present invention, in each of the magnetic shield magnetic bodies described above, the magnetic body used as a material has a sheet shape, and the thickness of one sheet is 10 μm or more and 200 μm or less. And Since the magnetic flux in the space can be collected efficiently in the configuration using the sheet-shaped magnetic body, it is possible to use a magnetic body having a smaller thickness than the conventional magnetic shield. The advantage of using a thin magnetic material is that the structural weight of the magnetic shield can be reduced, and the assembly and workability of the shield device can be improved. For example, in a shield using a rolled thin plate (thickness 0.5 to 1 mm) such as soft iron or NiFe alloy, 350 × 350 mm to 500 for a weight of 1 kg.
The limit is to make a shield wall of x500 mm. However, with a sheet of 200 μm, it is possible to make a shield wall of 2 × 2 m, and the number of parts of the shield wall can be greatly reduced. The characteristics of the shield are Ni
The shield ratio of one Fe plate is about 20 dB, and in the present invention, the shield ratio is 10 to 15 dB even under the condition of 10 μm sheet, and by setting this to 200 μm, the shield ratio of 20 dB or more can be obtained.

The present invention also provides any one of the above magnetic shield magnetic bodies, wherein the sheet-shaped magnetic body has a sheet thickness of 10 μm or more and 30 μm or less.
It is characterized by being constituted by a laminated body of one or more sheets. In the sheet-shaped magnetic body, magnetic anisotropy may occur depending on the direction of the sheet surface depending on the manufacturing method.
In the present invention, by using two or more of the sheet-shaped magnetic bodies in a stacked manner, the effect of magnetic anisotropy is canceled out, and a shield characteristic independent of the direction of the spatial magnetic field for shielding can be obtained. For example, the magnetic properties of the shield wall surface can be improved isotropically by stacking two sheet-shaped magnetic bodies having magnetic anisotropy so that the easy magnetization directions are perpendicular to each other. Further, since the stacking effect increases the volume of the magnetic body used for the shield, it brings about the effect of keeping the magnetic permeability of the entire magnetic body high. Therefore, the efficiency of the magnetic shield can be improved.

The present invention also provides any one of the magnetic shield magnetic bodies described above, which has a particle size of 500 containing iron as a main component.
It is characterized in that it is made of an alloy material in which fine crystal grains of nm or less occupy at least 50% or more of the structure and has a sheet or tape shape. The fine crystalline material (also referred to as nanocrystalline material) of the iron alloy (Fe alloy) can be obtained by heat-treating an amorphous material at a desired temperature as disclosed in Japanese Patent No. 2625485. Since the magnetic flux in the space can be collected efficiently in the configuration of this patent, it is possible to use a magnetic material having a smaller thickness than the conventional magnetic shield. In order to obtain a thin magnetic material, for example, there are foils produced by rolling or ultra-quenching, but soft iron or NiFe alloys that can be easily rolled, or amorphous foils obtained by ultra-quenching are deformed by sheet material due to the reverse strain effect. Since the characteristics are likely to deteriorate, there is a possibility that problems such as difficulty in handling the shield wall may occur. Further, particularly in NiFe alloys, the hardness of the material becomes insufficient, and the crystal defects caused by the deformation of the sheet due to the weight of the shield wall significantly deteriorate the magnetic characteristics. On the other hand, in the magnetic sheet obtained by heat-treating a foil body formed by superquenching a high-permeability Fe-based alloy, the hardness of the obtained Fe-based alloy is sufficient and the inverse magnetostriction effect is caused. Since it is difficult, it is possible to obtain a magnetic sheet of sufficient thickness. Further, as described in Japanese Patent Application Laid-Open No. 6-112031, it is possible to make the material less likely to be destroyed by mechanical deformation and significantly reduce the geometrical constraint on the processing. In the magnetic shield of the present invention using this magnetic sheet, the shield wall can be made lighter and the influence of stress can be eliminated as much as possible, so that the material can be handled easily during construction. As described above, according to the present invention, it is possible to provide a magnetic shield that is lightweight and has excellent workability.

The iron alloy (Fe
Alloy) is preferably Fe-Cu-Nb.
A soft magnetic material having a fine crystal structure (or fine crystal grains) of —Si—B type bccFe is used. More preferably, a material in which the average crystal grain size of the fine crystal grains is 100 nm or less is used.

[0024]

(Experimental Example 1) In this experimental example, an experiment was conducted to find out how much the magnetic shield device of the present invention shown in FIG. 3 has a shield ratio (dB) superior to that of the conventional magnetic shield device shown in FIG. Shown in data. Table 1 shows the specifications of the magnetic shield device of the present invention and the conventional magnetic shield device.

[0025]

[Table 1]

[Production of Shield Wall] Fe-Cu-Nb-S
The melt of i-B type alloy is quenched by the single roll method and the width is 50m.
An amorphous alloy ribbon having a thickness of m and a thickness of 20 μm was produced. Next, this alloy ribbon was held in a nitrogen gas atmosphere at 570 ° C. for 60 minutes and air-cooled. The obtained ribbon was a soft magnetic alloy mainly composed of crystals having a fine bccFe crystal structure and the majority of the structure consisting of crystal grains having a grain size of 50 nm or less. The thin strips were partially overlapped and joined in the width direction to produce a 600 mm × 600 mm sheet, and 10 sheets of this sheet were laminated to produce a shield wall. The easy magnetization direction (longitudinal direction of the ribbon) of each ribbon and each sheet is aligned, and it is set to the external magnetic field direction Ho.
Matched.

[Measurement conditions] A magnetic field of 18.5 μT (50 Hz, 100 Hz, 200 Hz) is generated at the center of the coil by a pair of Helmholtz coils having a diameter of 1800 mm, and a shield device composed of a cube having a side length of 600 mm therein. Was placed, the magnetic flux density was measured at the center point, and the shield ratio (dB) was calculated.

The results are shown in FIG. The thicker the closed coil, the greater the shielding effect, and the higher the frequency, the greater the shielding effect.

(Experimental Example 2) In this experimental example, it is shown that the closed coil is effective for enhancing the shielding effect of the magnetic shield device by using the magnetic shield devices shown in FIGS. The experiment used five magnetic shield devices. The specifications are summarized in Table 2.

[0030]

[Table 2]

The measurement conditions are the same as in Experimental Example 1, but the generated magnetic field is 19.4 μm by changing the current of the Helmholtz coil.
It was T to 124.3 μT. The frequency of the magnetic field was fixed at 200 Hz.

The results are shown in FIG. From the graph of, it can be seen that the shield effect of only the closed coil is up to about 6 dB. It can be seen from the difference between the graphs of and and the difference between the graphs of and when combined with the shield wall, the shield effect of the closed coil is expanded to about 9 dB. This is because the magnetic flux density of the shield wall has decreased
It is thought that this is due to the move to the larger one.

[0033]

By using the structure of the present invention, it is possible to provide a magnetic shield device which is hard to cause magnetic saturation without increasing the thickness of the magnetic material constituting the shield wall, is lightweight, and has high-performance shield characteristics. Can be provided. It is also possible to suppress the amount of expensive soft magnetic material used.

[Brief description of drawings]

FIG. 1 shows a state in which the magnetic flux density of a shield wall of a conventional magnetic shield device is high.

FIG. 2 is a state in which the magnetic flux density of the shield wall of the magnetic shield device of the present invention is low.

FIG. 3 is a diagram showing an embodiment of a magnetic shield device of the first invention of the present application.

FIG. 4 is a diagram showing an embodiment of a magnetic shield device of the third invention of the present application.

FIG. 5 is a diagram showing an embodiment of a magnetic shield device having a conventional structure.

FIG. 6 is a perspective view of a closed coil used in the present invention.

FIG. 7 is experimental data of shield ratios of the magnetic shield apparatus of the present invention shown in FIG. 3 and the conventional magnetic shield apparatus shown in FIG.

FIG. 8 is experimental data showing that a closed coil is effective for enhancing the shielding effect of the magnetic shield device using each of the magnetic shield devices shown in FIGS.

[Explanation of symbols]

1 shield wall 2 shield space 3 magnetic flux 4 closed coil 5 conductor 6 openings 7 doors 10 Magnetic shield device 50 closed coil Ho External magnetic field direction

Claims (3)

[Claims] 1. A magnetic shield device in which a predetermined shield space is surrounded by a shield wall provided with a soft magnetic material, the shield wall being parallel to the direction of the external magnetic field, in the vicinity of a portion showing the maximum magnetic flux density by the external magnetic field. A magnetic shield device, wherein a conductor is installed, and the conductor forms a closed coil. 2. A magnetic shield device in which a predetermined shield space is surrounded by a shield wall provided with a soft magnetic material, wherein a conductor is provided in the shield wall parallel to the external magnetic field direction in the vicinity of the central portion in the external magnetic field direction. A magnetic shield device, which is installed and constitutes a closed coil with the conductor. 3. A magnetic shield device in which a predetermined shield space is surrounded by a shield wall including a soft magnetic material, the shield wall having an opening, and a conductor surrounding the opening is installed in the shield wall. The magnetic shield device comprises a closed coil made of the conductor.