JP2764842B2 - Shield box for measuring variable magnetic field shield performance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield box for measuring variable magnetic field shielding performance, which can evaluate the shielding performance of various magnetic materials against a variable magnetic field from various angles.

[0002]

2. Description of the Related Art Recently, devices installed in intelligent buildings and precision factories are increasingly sensitive to magnetism. For example, in an electron microscope, a fluctuation component of magnetism is suppressed to 2 mG (milligauss) or less in order to increase sensitivity. In contrast, in today's everyday environment, various magnetic sources are present nearby.
For example, large magnetism is generated around trains, cars, or transmission lines, and when building a building near these,
A fluctuating magnetic field of about several tens mG exists. The precision equipment installed therein is exposed to a magnetically bad environment, and the performance of the equipment cannot be exhibited satisfactorily.

As a countermeasure for this, a permalloy, amorphous,
A method of installing a magnetically shielded room (box) that is surrounded by a ferromagnetic material such as a silicon steel plate and prevents intrusion of magnetism by absorbing an intruding magnetic field from the outside is adopted. The ferromagnetic material described above has excellent magnetic properties of 1 G (Gauss) or less, exhibits high magnetic permeability, and can efficiently shield magnetism even in a small magnetic field such as a fluctuating magnetic field.

[0004] However, such a ferromagnetic material has high magnetic shield performance inherent in the material, but has many problems when formed into a magnetic shield room. For example, a large area requires a seam and an opening such as a door or a window. A large leakage magnetic field is generated from such a place. Further, the magnetic shield performance greatly changes depending on the type and thickness of the material and the type (magnitude, frequency, direction, etc.) of the target magnetic field.

For this reason, in designing a magnetic shield room for a fluctuating magnetic field, various data on the magnetic shield are required. Computer simulation by magnetic field analysis is also performed to collect data, but it is often obtained through experiments. Shielding experiments for fluctuating magnetic fields include those that seek the original shielding performance of the material and those that seek the shielding performance in various shapes.

[0006] The inherent shielding performance of a material is obtained by a method in which a ring-shaped sample is prepared, a current is applied to a coil wound around the circumference, a magnetic field is applied in the circumferential direction, and the magnetic flux density is measured by a search coil. The sample has a diameter of about 45 mm, so that the experiment can be performed relatively easily. On the other hand, the shielding performance in various shapes is performed by a method of preparing models of the respective shapes and measuring the performance in a magnetic field generated by a coil. However, in this method, since much cost and labor are required for model creation, a cylinder (for example, Φ10 cm × length 3) is required.
(About 0 cm) in a magnetic field, and a simple method of measuring the internal magnetic field is often used. If a joint is provided in the cylinder, magnetic leakage from the joint can be confirmed.

[0007]

The above-mentioned prior art has the following problems. Creating models of various shapes requires a lot of cost and labor. Therefore, it is not possible to easily change the position of the opening or the position of the joint, etc.
Many types of data are not available. A smaller model requires less material costs, but requires as much effort and reduces measurement accuracy.

On the other hand, the simple method using a cylinder has a shape greatly different from that of an actual magnetically shielded room, and cannot incorporate elements of the shape, and cannot grasp the distribution of a magnetic field. In addition, magnetic wraparound also occurs, which is problematic in terms of accuracy. As described above, in the conventional model for measuring the varying magnetic field shielding performance, it is difficult to evaluate the shielding performance with respect to the varying magnetic field in a large number of times, and it is desired that the shielding performance can be measured easily and with high accuracy.

An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a shield box for measuring a variable magnetic field shield which can perform various shield experiments with one apparatus.

[0010]

Means for Solving the Problems (1) A hexahedral box is formed by firmly joining a plate material of a ferromagnetic material such as permalloy / amorphous / silicon steel without magnetic resistance so as not to leak a magnetic field from a joint. Then, an opening and a mounting (screw) hole for mounting test materials of various shapes are provided on one surface of the box. (2) On the other side of the box, a sensor installation opening that enables various operations inside the box is provided, which can be easily opened and closed. Install a door that can suppress magnetic field leakage. (3) The cable connecting the inside and the outside of the box is penetrated, and an opening for taking out the cable is provided to minimize leakage of the magnetic field.

[0011]

The plate material made of a ferromagnetic material such as permalloy, amorphous, silicon steel or the like constituting the shield box prevents an external fluctuating magnetic field from entering the box. By mounting test materials of various materials and shapes in the test material mounting openings provided on one surface of the shield box and replacing them, various shield performances against a fluctuating magnetic field can be measured.

This shield box is installed in a magnetic field space formed by coils, and the shield performance is evaluated by measuring the internal magnetic field. The difference between the measured values for each test material is the shielding performance of the test material.
As the test material, materials having various shapes are attached. For example, a material having a gap or an opening, or a material having a different thickness or a different type of material is also possible. By changing the magnitude, frequency, and distribution of the magnetic field generated from the coil and changing the angle of the shield box with respect to the magnetic field, it is possible to cope with any fluctuating magnetic field.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In the figure, 1 is permalloy, amorphous,
A plate made of a ferromagnetic material such as silicon steel (hereinafter referred to as a permalloy plate), 2 is an opening for mounting a test material, 3 is a mounting hole for a test material, 4 is an opening for installing a sensor, 5 is a door of an opening 4 for installing a sensor, 6 is an opening for taking out a cable, 7 is a test material, 8
Is a test material mounting hole provided in the outer peripheral portion of the test material 7, 9 is a second test material mounting opening provided in the test material 7, 11 is a test material mounting hole provided around the opening 9, and 12 is a second test sample mounting hole. Reference numeral 13 denotes a test material mounting hole provided on the outer peripheral portion of the second test material 12, and 10 denotes a shield box (entire). 14
Is a backing plate of the same material as the plate material 1, 15 is a backing plate of a non-magnetic plate material, 16 is a half permalloy plate, 17 is a cable hole provided in the half permalloy plate 16, 18 is a cable, 20 is 1
Pair of Helmholtz coils, 21 is computer, 22
Is an information line, 23 is a Gauss meter, 24 is a mount for the Helmholtz coil 20, 25 is a rotary table of the shield box 10, 26 is a mount on which the mount 24, the rotary table and the like are mounted, and 27 is a sensor.

FIG. 1 is an overall view of a shield box according to the present invention. The shape is a hexahedron, and has a test material mounting opening 2 on the front. In addition, a sensor installation opening 4, a door 5, and a cable takeout opening 6 are provided on the adjacent surface. A test material mounting hole 3 is provided on the four circumferences of the test material mounting opening 2, and the test material 7 and the shield box 10 are attached to each other with screws so as to be in close contact with each other without any gap between the contact surfaces.
It is effective that the pitch of the screw, that is, the interval between the test material mounting holes 3 is 50 mm or less and arranged in a staggered manner. Although the position of each opening may be a place where various operations are easy,
The arrangement as shown in the drawing is desirable because the degree of leakage of the magnetic field from the contact surface can be grasped in comparison with the flat plate on the opposite surface.

The material of the plate 1 constituting the shield box 10 may be any material having a high magnetic permeability such as permalloy, amorphous, silicon steel, etc. In this embodiment, PC permalloy having the most excellent magnetic shield characteristics is used. It will be described on the assumption. PC permalloy is an alloy containing about 78% nickel, has a very high magnetic permeability in a low magnetic field, and is optimal for shielding a fluctuating magnetic field.

Usually, the test material 7 is mounted in a size that covers the test material mounting opening 2. However, some materials cannot be manufactured in a large size. In this case, after the small second test material 12 is firmly attached to the slightly smaller opening 9 provided in the test material 7 with screws using the test material attachment holes 11 and 13, the test material attachment holes 3 and 3 are attached together with the test material 7.
Attach to the shield box with a screw by 8 FIG. 3 shows this state.

[0017] Permalloy, which is on the market due to the production equipment, has a width of only about 330 mm. Therefore, in order to make a board of about 1 m square, it is necessary to join several boards. In this case, it is necessary to take measures to suppress the leakage of the magnetic field from the joint. 4 to 6 show examples of a method of joining a permalloy plate. FIG. 4 shows a permalloy backing plate 14 extending over two permalloy plates 1 fixed with screws. The width of the backing plate 14 and the pitch of the screws vary depending on the thickness of the permalloy plate 1. If the thickness is 1.5 mm, the width is 100 mm and the pitch of the screws is about 50 mm.

FIG. 5 shows a permalloy patch 14 fixed by spot welding. In this case, it is necessary to perform magnetic annealing again in order to recover the deterioration of the magnetic characteristics due to welding. The width of the backing plate 14 and the pitch of the spot welding vary depending on the thickness of the permalloy plate 1, but the thickness is 1.5
mm, a width of 100 mm and a pitch of 30 to 50 mm are required.

FIG. 6 shows an example in which the parts are joined by butt fusion welding. In this case, it is necessary to remove the distortion by the leveler together with the magnetic annealing. Therefore, it is difficult with a large size. As shown in FIG. 7, the test material 7 is attached with screws to a nonmagnetic patch plate 15 having taps attached around the opening 2 of the permalloy plate 1 by argon welding. In order to suppress the leakage of the magnetic field from the contact surface, the contact width is set to about 50 mm, and the pitch of the screw is set to 50 mm.

As shown in FIG. 8, the contact surface between the permalloy plate constituting the door 5 of the sensor installation opening 4 and the permalloy plate constituting the shield box 10 main body is overlapped in order to suppress the leakage of the magnetic field from the contact surface. Take about 50mm width,
When the door 5 is closed, it is mechanically pressed to bring both into close contact. For mechanical pressing, a method using several fasteners provided in the periphery can be considered.

The structure near the cable outlet 6 will be described with reference to FIGS. 9 and 10. FIG. The end of the cable is a connector (not shown), which is larger than the diameter of the cable 18. Therefore, the cable extraction opening 6 enough to allow the connector to pass through the shield box 10
And a cable hole 17 of about the diameter of the cable 18 is made of a half permalloy plate 16. The half permalloy plate 16 is attached to the non-magnetic backing plate 15 having a tap attached around the opening 6 by argon welding.
Installed with screws.

The above-described shield box 10
The portions other than the flat plate portion of permalloy that directly expects a shielding effect and the backing plate that prevents leakage of a magnetic field from a gap need to be made of a nonmagnetic material such as stainless steel in order to eliminate the influence of magnetism. In consideration of the eddy current effect caused by the fluctuating magnetic field, a non-conductive material such as bakelite or FRP is desirable. As a result, a pure shielding effect can be grasped.

Next, the shield box 10 according to the present invention will be described.
2 will be described with reference to FIG. The shield box 10 is installed in the magnetic field space created by the Helmholtz coil 20 via the turntable 25 and the installation table 26. The installation table 26 prevents the magnetic field from being disturbed by the reinforcing steel on the floor, and lifts the entire apparatus upward. The turntable 25 adjusts the direction and height of the shield box with respect to the Helmholtz coil 20.

The size of the shield box 10 is 1/1 / the outer diameter of the Helmholtz coil 20 due to the uniformity of the magnetic field.
If the outer diameter of the Helmholtz coil is 2 m, the size is 1 m or less. The sensor 27 of the Gauss meter 23 installed in the shield box 10 measures the internal magnetic field, and sends data to the computer 21 through the information line 22.

[0025]

The shield box for measuring the variable magnetic field shield performance according to the present invention is provided on one surface of a hexahedron made of a plate material of a ferromagnetic material such as permalloy, amorphous, silicon steel, etc. And a door for covering the sensor installation opening, a cover for covering the same opening, and a cable take-out opening are provided on the other surface of the hexahedron.

As a basic model, only one hexahedral shield box is required, and the cost and labor required for the experiment can be greatly reduced. Further, by changing the size of the gap, the shape of various joints, the size and position of the opening, etc. in the shape of the test material attached to one surface, the fluctuating magnetic field shielding characteristics for various elements of the shield room can be grasped from all angles. Differences due to differences in material and thickness can also be easily determined.

Also, since the internal magnetic field distribution can be measured with a size about 1/10 of the actual size, very high-precision information can be obtained as compared with the conventional apparatus. By feeding this result back to the computer simulation, it becomes possible to accurately simulate the shield characteristics in the entire shape of the magnetic shield room.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment of a shield box of the present invention.

FIG. 2 is a configuration diagram showing a method for measuring a fluctuating magnetic field shield performance using a shield box according to the present invention.

FIG. 3 is a front view of a test material to which a second test material is attached.

FIG. 4 is a cross-sectional view showing a permalloy plate joined by screws.

FIG. 5 is a cross-sectional view showing a joining state of a permalloy plate by spot welding.

FIG. 6 is a cross-sectional view showing a joined state of a permalloy plate by butt fusion welding.

FIG. 7 is a cross-sectional view of a test material attachment portion.

FIG. 8 is a cross-sectional view showing a contact state between a door of a sensor installation opening and a peripheral portion.

FIG. 9 is a front view of a half-permalloy plate that covers a cable outlet.

FIG. 10 is a sectional view taken along the line AA of FIG. 9;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 permalloy plate 2 opening for mounting test material 3 mounting hole for test material 4 opening for installing sensor 5 door 6 opening for taking out cable 10 shield box

Claims (1)

(57) [Claims] 1. A surface of a hexahedron made of a plate material of a ferromagnetic material such as permalloy, amorphous, silicon steel or the like is provided with an opening for mounting a test material and a mounting hole for a test material arranged around the opening. A shield box for measuring variable magnetic field shielding performance, wherein an opening for sensor installation, a door covering the opening, and an opening for cable extraction are provided on the other surface of the hexahedron.