JPS5814053B2 - How to demagnetize a magnetic shield room - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for demagnetizing a magnetically shielded room made of a high magnetic permeability material such as permalloy.

Generally, permalloy, which is a high magnetic permeability material, is used as the material for magnetically shielded rooms, but the magnetic permeability of this type of material decreases due to mechanical distortion during assembly or subsequent external factors such as the earth's magnetism. It is unavoidable that the shielding effect will decrease.

That is, in this type of constituent material, when a large magnetic field acts even temporarily, the magnetic hysteresis curve approaches the saturation region and the magnetic permeability μ decreases from the highest point as the magnetic field H increases.

Therefore, in a magnetically shielded room, residual magnetism must be demagnetized on the shield wall as necessary.

A common example of a demagnetizing treatment method for this type of material is the AC demagnetization method, in which a coil is wound to supply AC power and the current is gradually reduced in the case of small-sized permalloy iron cores used in various transformers. Then, a thermal demagnetization method is used in which the iron core is heated to a temperature above its single point.

In the case of a magnetically shielded room, since it has a cubic or polyhedral structure with a side of approximately 2 m or more, thermal demagnetization is virtually impossible, and AC demagnetization is suitable.

Conventional AC demagnetization methods for magnetically shielded rooms include: ■ winding a degaussing coil around the magnetically shielded room for each degaussing process, and ■ winding a demagnetizing coil around the magnetically shielded room in advance and installing it permanently. There are times when you leave it.

However, in the former method, the coil winding work is troublesome and inefficient, and in the latter method, deterioration of the shielding effect can be avoided because many through holes must be provided in the shield wall and the coil must be wound. Furthermore, there is a drawback that the permanently installed coil acts as an antenna and introduces noise into the shielded room.

The present invention has been made in view of these drawbacks, and an object of the present invention is to provide a method for demagnetizing a magnetically shielded room, which is simple in degaussing processing work, and has a high demagnetizing effect.

As a degaussing means for a magnetically shielded room, the present invention is provided with multi-pole connectors for interconnection at both ends of a cable made by bundling a plurality of electric wires, so that when the connectors are interconnected, each electric wire is connected in series to form a coil. According to this degaussing method, a through hole may be provided in each magnetically shielded room at opposing positions in the shield walls facing each other.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 respectively show the schematic shape of a magnetically shielded room in a partial longitudinal cross-sectional view and a cross-sectional view.

This magnetically shielded room 1 consists of a shield wall made of permalloy in three layers, 2 is an outer door, 3 is an inner door, and 4 is a lower stand.

According to the present invention, the through-holes 5 used for winding the demagnetizing coil around the shield wall may be provided one at a time at opposing positions on the facing shield walls.

FIG. 3 shows a degaussing cable for forming a small amount of coils used in the present invention, with some parts omitted.

This degaussing cable 10 is made by bundling a predetermined number of electric wires of a predetermined length and applying a sheath, and a male connector 11 and a female connector 12 each having a number of poles corresponding to the number of wires are connected to both ends of the cable. By interconnecting them, a coil having the number of turns equal to the number of wires can be formed.

13 and 14 are lead wires for connecting an AC power source.

FIG. 4 schematically shows an exploded view of the cable of FIG. Wire connection between the terminals is made by shifting the terminal by one terminal, for example, connecting terminal P1 of the connector 11 and the corresponding terminal P2' of the connector 12, which is shifted by one terminal from the terminal P'1. The cable 10 is designed to have a coiled shape when connected to the connector 12.

Also, the terminal P55 which should be the starting end or the ending end of the coil
Lead wires 13 and 14 for power supply connection are connected to pP1'.

FIGS. 5 and 6 are schematic diagrams showing the case where a magnetically shielded room is demagnetized according to the present invention.

The degaussing cable 10 has a length such that when it is inserted into the through hole 5 provided in the facing shield wall of the magnetically shielded room 1, the connectors 11 and 12 can be connected outside the shielded room 1. A cable 10 is installed so as to wrap around the shield wall, and power is supplied from lead wires 13 and 14.

The through hole 5 is provided approximately at the center of the shield wall, so that the cable 10 can freely rotate outside the shield wall as shown by the arrow in the figure, centering on the area between the through holes 5 on both sides. As a result, the entire shielded room 1 can be demagnetized using only the cable 10.

Of course, the magnitude of the generated magnetic field can also be changed by changing the applied current.

For reference, Table 1 shows the measurement results of the internal magnetic field before and after demagnetization when a three-layer magnetically shielded room is demagnetized according to the present invention.

The measurement points inside the shield room are shown in Figure I, a and b.

As is clear from Table 1, it can be seen that if the shield wall is demagnetized by the demagnetization method according to the present invention, the internal magnetic field in the shield room can be significantly reduced.

Of course, the shape of the magnetically shielded room, the number of shielding layers, etc. are not limited to those in the embodiment, and the through holes 5 are not only provided at one position facing the shielding wall facing the magnetically shielded room 1, but also in the opposite positions of the shielding walls of the shielded room 1. Depending on the shape, one or more locations may be provided so that the entire area can be demagnetized, and two or more demagnetizing cables may be used to perform demagnetizing work.
The through hole after the cable is removed after the degaussing operation is completed can be shielded with a shield cap made of the same high magnetic permeability material.

As explained above, according to the present invention, demagnetization work on a magnetically shielded room can be easily and efficiently performed in a short time, and the magnetic shielding function can be improved. It has great practical effects because various experimental measurements in medical or physical fields can be carried out with high precision.

[Brief explanation of drawings]

Fig. 1 shows a schematic structure of a magnetically shielded room in a partial vertical cross-sectional view, Fig. 2 is a cross-sectional view thereof, Fig. 3 shows a degaussing cable used in the present invention with a part omitted, and Fig. Figure 4 schematically shows its exploded view, and Figures 5 and 6 respectively.
FIGS. 7A and 7B are diagrams showing a magnetically shielded room from the side and back for explaining the degaussing method according to the present invention, and FIGS. 7A and 7B are diagrams showing magnetic field measurement points in the magnetically shielded room, respectively. In the diagram, 1 is a magnetically shielded room, 2 is an outer door, 3 is an inner door,
4 is a lower stand, 5 is a through hole, 10 is a degaussing cable, 11 is a male connector, 12 is a female connector, 13 and 14 are power supply connection lead wires.

Claims (1)

[Claims] 1. In a magnetically shielded room made of a high magnetic permeability material such as permalloy, through holes are provided at opposing positions in the facing shield walls, and each through hole has a cable connected to both ends of a bundle of multiple electric wires. When the connectors are interconnected, each wire is connected in series to form a coil.The cable is inserted so as to be wound around the shield wall, and power is applied to the coil. A method for demagnetizing a magnetically shielded room, characterized by demagnetizing a shield wall by applying an electric current.