JPH03291996A - Magnetic shielding device - Google Patents

Abstract

PURPOSE:To shield a magnetic flux leakage and to reduce a weight and a cost by adhering or winding a magnetic plate or stripe of the same or different type at the center of a magnetic material for forming a shielding device. CONSTITUTION:A cylindrical shielding vessel is formed of Permalloy PC plate having 0.5mm of thickness. Then, the center of the cylinder is wound by the same PC material. When the difference in thicknesses between the center and the end of the material is t0, the adhering or winding thickness (t) of the material at a distance x from the center to the end is determined by an equation t=t0(1 - (2x/L)<2>), where L is the length of the magnetic shielding device.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to devices such as shield containers for shielding magnetism used in connection with electrical equipment, electronic equipment, and the like.

(Conventional technology) With the improvement in performance and rapid expansion of use of electrical and electronic equipment,
As the magnetic fields used by these devices become larger, in order to protect operation rooms, test rooms, and human bodies from magnetic fields, and to prevent interference between electronic devices due to magnetic fields, active shielding is required to shield the magnetic fields emitted from the devices and prevent intrusion into the devices. Passive shielding is used to block the incoming magnetic fields, and magnetic shielding materials are used.

For example, in an imaging apparatus using nuclear magnetic resonance (NMR), a high magnetic field from a superconducting magnet or the like is required, resulting in a large leakage of magnetic flux outside the measurement area. Therefore, magnetic shielding is used to reduce the leakage of magnetic fields into the environment.

In order to avoid such magnetic interference, soft magnetic materials such as iron are used as shielding materials.

For example, magnetic shielding is performed using a thick iron plate using nuclear magnetic resonance (NMR). In addition, when shielding a room, magnetic ribbons such as electromagnetic steel sheets, permalloy, and amorphous have recently come to be used in response to demands for smaller size and lighter weight.

A material with high magnetic permeability is generally used for the magnetic shield. However, since the magnetic permeability actually changes depending on the strength of the magnetic field to be shielded, it is necessary to select an appropriate material. In addition, magnetic shielding collects the magnetic flux of the magnetic field to be shielded, so as the magnetic field increases, it becomes necessary to increase the cross-sectional area of the material or use materials with high magnetic flux density. .

(Problems to be Solved by the Invention) Materials used as materials with high magnetic flux density include pure iron-based electromagnetic thick plates and electromagnetic steel plates. However, even with such materials, as the magnetic field increases, the leakage magnetic field increases, and the cross-sectional area must be increased. In the case of shielding a high magnetic field from a superconducting magnet, the cross-sectional area becomes considerably large, the shielding device alone becomes quite heavy, and the material cost also increases.

Further, materials with high magnetic permeability such as permalloy and amorphous have a saturation magnetic flux density as low as about 1/2 to 1/3 of that of electrical steel sheets. Therefore, when the magnetic field to be shielded is large, if the cross-sectional area is increased by laminating layers, the weight and material cost will be enormous. Therefore, there may be problems with construction costs and construction.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a shielding device that has a small average cross-sectional area, is lightweight, and has a good shielding effect at low cost even when the shielding magnetic field is large.

(Means for Solving the Problems) The present invention provides for changing the cross-sectional shape of the magnetic material for magnetic shielding,
Provided is a shielding device that improves magnetic shielding characteristics and is lightweight and inexpensive.

When performing magnetic shielding, a material with high magnetic permeability is required when selecting a shielding material, but the saturation magnetic flux density of the materials currently available as magnetic materials is low when the magnetic permeability is high. Permalloy PC is a typical material with high magnetic permeability.
Although the maximum magnetic permeability is 100,000 or more, its saturation magnetic flux density is about 7 kG, which is considerably lower than the 20 kG of iron. Permalloy PB exhibits a maximum magnetic permeability of 30,000 or more, but a saturation magnetic flux density as low as 14 kG. When the shielding magnetic field is large, an iron-based material is used, but it has a high saturation magnetic flux density but a low magnetic permeability, so it is necessary to increase the plate thickness.

Therefore, when performing magnetic shielding, if the magnetic material is saturated and magnetic flux leaks in response to the magnetic field to be shielded, this is dealt with by increasing the thickness of the material. However, increasing the thickness of the board naturally increases the weight, and large shield devices are heavier and require more effort to install.In extreme cases, the floor weight installation standards of the building may be exceeded, making it impossible to even install the equipment. In some cases it may be possible. Furthermore, materials with high magnetic permeability are expensive, and shielding costs increase rapidly as the plate thickness increases.

Therefore, in the present invention, the cross-sectional area of the magnetic material is not uniformly increased, but only a portion of the cross-sectional area is increased, thereby providing a shielding device with excellent magnetic shielding properties and workability.

One way to increase the cross-sectional area is to use a magnetic material plate or strip.
Attach or wrap one or more sheets.

The attached magnetic material may be of the same type or may have different magnetic permeability or saturation magnetic flux density. In this way, materials with high magnetic permeability can be used effectively, making it possible to reduce weight, improve workability, and reduce shielding costs.

FIG. 1 is a diagram of magnetic flux leakage into a shielded container.

This shielding magnetic material may be any magnetic material, and can be applied to a shielding device composed of permalloy, amorphous, etc. with high magnetic permeability, electromagnetic steel plate, electromagnetic thick plate, etc. with high magnetic flux density.

In the case of magnetic shielding, if the shielding magnetic field is small and the soft magnetic material is not saturated, the shielding performance is best at the center of the shielding device - the center of the magnetic material, as shown in Figure 1a.

However, it has been found that when the shielding magnetic field is large and the magnetic material is saturated and magnetic flux leaks, magnetic flux leaks from the center as shown in FIG. 1, and the shielding performance deteriorates.

Therefore, when the shielding magnetic field is large, there is no need to increase the thickness of the plate, and it is possible to effectively shield by changing the cross-sectional area of the material.

The cross-sectional area of the magnetic material is changed by making the center part larger and the end parts smaller along the magnetization direction of the material, that is, the direction of the shielding magnetic field. This difference in cross-sectional area can be determined experimentally using the following formula.

Now, assuming that the difference in cross-sectional area between the end of the shield member and the material is ΔS, ΔS is replaced by the plate thickness difference Δt since the material width is constant. When the length of the material is L, Δt is expressed as a function of to is the difference in thickness of the laminate at the center of the material, and x-
L/2, 1-0.

10 is a value determined by the shield length L and the shield magnetic field strength if the materials are the same.

However, when actually designing a shield container, since the value of t according to equation (1) is continuous, it is used instead of t as an integral multiple of the plate thickness of the magnetic material used.

In normal cases, it is sufficient to attach or wrap it by a distance of 1/3 to 1/2 of L.

(Example 1) A cylindrical shield container with an inner diameter of 1100a and a length of 5 (10m) was manufactured using Permalloy PC with a thickness of 0.5+++m.Next, the center of the cylinder was wrapped with the same PC material to a length of 200mm to form a cylinder and subjected to a magnetic shielding test. provided.

For comparison, we also produced a cylinder in which no PC material was attached to the center (Comparison 1), and a cylinder in which the PC material was wrapped around the entire length to form two layers (Comparison 2).

The shielding property was measured by installing the cylinder in a parallel DC magnetic field so that the length direction was parallel to the magnetic field, and measuring the magnetic field at the center inside the cylinder while changing the DC magnetic field strength.

Table 1 shows the measurement results.

The shield container 1 according to the present invention exhibited shielding performance equivalent to that of the comparative container 2 in which the PC material was wrapped around the entire length. On the other hand, in the case of Comparison 1, as the shielding magnetic field increased, the shielding performance at the center deteriorated.

Table 1 Table 2 Shield magnetic field 20 3G 5G IOG invention 10001000103 5.3 Comparison 1 1000
1000 4.3 1.0 comparison 2 10001000
985.1 Invention 6.2 Comparison 16.0 Comparison 2 1.1 So book - Shield magnetic field Hex / Post-shield magnetic field H1 (Example 2) 0.5 m plate thickness laminated on plate center part 150 mm, plate thickness 1 m The same 3% St steel plate was assembled into a rectangular tube of 100+*m square and 500 mm long, and the same experiment as in Example 1 was conducted.

For comparison, rectangular tubes were manufactured with lamination (Comparison 1) and no lamination (Comparison 2) with a thickness of 1 mm over the entire length.

Table 2 shows the results.

It can be seen that the shield body of the present invention exhibits shielding characteristics equivalent to the square tube of Comparison 1 with 1+am lamination.

(Example 3) Two layers of 25 part thick Co-based amorphous ribbon, 60 + am angle, 300
I made a shield body that was as long as the neck. Next, two layers of a 25-thick Fe-based ribbon were attached to the center of the shield body, each having a length of about 100 mm.

For comparison, a shield body having a total length of 300 mm with Fe-based ribbons was made, and the same experiment as in Example 1 was conducted.

The results are shown in Table 3.

It can be seen that the shield body according to the present invention effectively shields the shield magnetic field even in the case of such a thin magnetic material, and achieves the same effect as the comparative material.

Table 3 Present invention 81 1.0 Comparison 83 1.5 (Effects of the invention) The present invention provides a method of magnetic shielding using magnetic materials, in which a magnetic plate of the same or different type is placed in the center of the magnetic material constituting the shielding device. Or attach or wrap a belt,
By increasing the cross-sectional area of the central portion, it is possible to shield magnetic flux leakage, making it possible to reduce weight and cost.

[Brief explanation of drawings]

FIG. 1 is a diagram of magnetic flux leakage into a shielded container. Representative Patent Attorney Tatsuo Chanoki×

Claims (2)

[Claims] 1. 1. A magnetic shielding device characterized in that a magnetic material plate or band of the same or different kind is attached or wrapped around the center of a magnetic material constituting the magnetic shielding device. 2. When the difference in thickness between the center and the end of the magnetic material is t_0, the thickness t of attaching or wrapping the magnetic material at the distance x from the center to the end is t=t_0(1-(2x/
The magnetic shielding device according to claim 1, characterized in that L)^2). Here, L: length of the magnetic shielding device