JPH05343883A - Removing device for electromagnetic wave in electromagnetic shielding room - Google Patents

Abstract

PURPOSE:To obtain a simple electromagnetic wave removing device having a large damping effect for an electromagnetic shielding room by providing a signal generating means capable of applying currents having antiphase to currents in a shielding material, in which electromagnetic waves are generated, to the shielding material. CONSTITUTION:A coaxial line 15 is stretched near a metal plate 5, currents generated in the metal plate 5 are extracted by the coaxial line 15, and the currents are input to a spectrum analyzer 13. Consequently, a graph reradiated near 300 MHz from the spectrum analyzer 13 is acquired. As a result, the output terminal of a signal generator is connected to a section, where currents are generated largely in the metal plate 5, and currents having the same current value as currents in peak frequency and antiphase are applied to the metal plate 5 from the signal generator. Accordingly, currents generated by arrival radio waves in the metal plate 5 are cancelled by a signal supplied from the signal generator, thus preventing the reradiation of electromagnetic waves from the metal plate 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave removing device for an electromagnetically shielded room.

[0002]

2. Description of the Related Art An electromagnetically shielded room is constructed by blocking incoming electromagnetic waves on walls surrounding the room.
It is provided for the purpose of obtaining a space free from electromagnetic interference. FIG. 5: is explanatory drawing which shows the conventional electromagnetic shield room.
In FIG. 5, the electromagnetically shielded room 101 has, for example, a ceiling, a wall, and a floor covered with a radio wave absorber 103, and the inside is finished with a metal plate 105 having a thickness of 0.6 to 1.6 [mm]. The joint portion of 105 is soldered, and the metal plate 105 is connected to the ground 107 by an electric wire 109.

In such an electromagnetically shielded room 101, the electric current Ia generated in the metal plate 105 by the incoming radio wave 121 escapes to the earth 107 via the electric wire 109, and the electromagnetic wave 123 is re-radiated into the room by the electric current Ia. To prevent. Also, the metal plate 10 as a shield material
As No. 5, an iron plate or a copper foil having a small electric resistance was used.

[0004]

However, in the electromagnetically shielded room having the above-described structure, it takes a lot of time and labor to construct the electromagnetically shielded room, and the metal plate is solder-bonded. There was a drawback that was required. Further, the electromagnetic shield room could not enhance the shielding effect for a specific frequency.

Furthermore, if an electromagnetic shield room having a damping effect of 80 [dB] or more is to be obtained, the equipment becomes expensive, and an electromagnetic shielding room having a damping effect of 120 [dB] or more cannot be obtained. It was The present invention is
In view of the above-mentioned drawbacks, it is an object of the present invention to provide an electromagnetic wave removing device for an electromagnetically shielded room that is simple and has a large damping effect.

[0006]

In order to achieve the above object, an electromagnetic wave removing device for an electromagnetically shielded room according to the present invention comprises:
In the electromagnetic shield room where the floor, ceiling, and walls are covered with the shield material, when electromagnetic waves re-radiating from the shield material in the electromagnetic shield room to the electromagnetic shield room are generated,
The present invention is characterized in that a signal generating means for applying a current having a phase opposite to that of a current in the shield material for generating the electromagnetic wave to the shield material is provided.

[0007]

The electromagnetic wave coming from the outside is absorbed by the shield material, but is changed into an electric current in the shield material, and a part of the electromagnetic wave is re-radiated to the inside of the electromagnetic shield room. Therefore, by supplying a current having a phase opposite to that of the current from the signal generator to the shield material to cancel the current in the shield material, re-radiation of electromagnetic waves is eliminated.

[0008]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is an explanatory diagram showing an embodiment of an electromagnetic wave removing device for an electromagnetically shielded room according to the present invention. In FIG.
The electromagnetically shielded room 1 covers, for example, the ceiling, walls, and floor with the radio wave absorber 3, and has a thickness of 0.6 to 1.6 [m] on the indoor side.
m], the joint portion of the metal plate 5 is adhered so as to be electrically conductive, and the metal plate 5 is connected to the ground 7 by an electric wire 9.

External radio waves are absorbed by the radio wave absorber 3 in the electromagnetically shielded room 1, but a part of them reaches the metal plate 5. The radio wave is absorbed by the metal plate 5, changes into a current in the metal plate 5, and a part of it becomes an electromagnetic wave again to be re-radiated into the electromagnetic shield room 1. As a simple electromagnetic shield room 1, for example, a ceiling, a wall,
The floor may be made of reinforced concrete or the like, and the entire indoor side thereof may be configured by attaching a metal plate 5 having a thickness of 0.6 to 1.6 [mm].

Therefore, for example, if the current generated in the metal plate 5 of the electromagnetic shield room 1 is the current Ia as shown in FIG. 2 (a), the metal plate 5 will have the current Ia as shown in FIG. 2 (b). The signal generator 11 is caused to generate a current Ib having a phase opposite to that of the generated current. The current Ib generated by the signal generator 11 is supplied to the relevant portion of the metal plate 5. As a result, the current Ia generated by the incoming radio wave in the metal plate 5 is canceled by the current Ib supplied from the signal generator 11 (state of zero current for each time as shown in FIG. 2C). Therefore, the re-radiation of electromagnetic waves from the metal plate 5 is eliminated. The signal generator 11 is a device that can generate a high frequency signal from a low frequency to a high frequency, and can also output by adjusting the strength and phase of the high frequency signal, and a commercially available one may be used. ..

To detect that an electric current is generated in the metal plate 5, as shown in FIG. 3, for example, a portable spectrum analyzer 13 is used to measure the incoming radio wave outside the electromagnetic shield room 1. .. The spectrum analyzer 13 is a device that can obtain a graph in which the horizontal axis represents frequency and the vertical axis represents electric field strength, and a commercially available device may be used. As a result, FIG.
As shown in, 1 scale 100 [MHz], 1 scale 10
A specific frequency (for example, 300 [M
There are large peaks near [Hz] and 450 [MHz], and there is a graph in which radio waves are evenly distributed.

Next, as shown in FIG. 4, a coaxial line 15 is stretched around the metal plate 5, the current generated in the metal plate 5 is taken out through the coaxial line 15, and this is input to the spectrum analyzer 13. Then, spectrum analyzer 1
From FIG. 3, a graph in which re-radiation is performed around 300 [MHz] as shown in FIG. 5B is obtained. Therefore, in FIG.
As shown in FIG. 2, the output terminal of the signal generator 11 is connected to the portion of the metal plate 5 where the current generation is large, and a current having the same current value as the current of the peak frequency but opposite phase is output from the signal generator 11. It is applied to the metal plate 5. Thereby, the metal plate 5
The electric current generated by the incoming radio wave is canceled by the signal supplied from the signal generator 11, so that the electromagnetic wave is not re-radiated from the metal plate 5.

When the re-radiation from the metal plate 5 is not completely eliminated, the output terminal of the signal generator 11 is connected to a predetermined section of the metal plate 5 as described above, and the interior of the electromagnetic shield room 1 is closed. Install a receiving antenna in, connect the antenna to the spectrum analyzer 13, for example,
By adjusting the potential and phase of the output signal of the signal generator 11 to the best one so that the spectrum analyzer 13 does not receive the re-radiated radio wave, re-radiation can be surely eliminated.

[0014]

As described above, according to the electromagnetic wave removing device of the electromagnetic shield room of the present invention, the current in the shield material due to the re-radiated electromagnetic waves is erased by applying the opposite phase current to the shield material. Therefore, it is possible to obtain an electromagnetic shield room having a high electromagnetic shield effect.

Further, according to the electromagnetic wave removing device for an electromagnetically shielded room of the present invention, it is possible to selectively remove only the frequency that is considered unnecessary from the external electromagnetic waves. Further, according to the electromagnetic wave removing device for an electromagnetically shielded room of the present invention, the shield effect can be enhanced in a wide range of frequencies by using a signal generator capable of supplying a wide range of signals, and the frequency to be shielded can be used for that purpose. It can be arbitrarily selected according to.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an electromagnetic wave removing device for an electromagnetically shielded room according to the present invention.

FIG. 2 is an explanatory diagram for explaining that a current due to an incoming radio wave is canceled according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a measurement example in the case of measuring a tendency of an external radio wave in the example.

FIG. 4 is an explanatory diagram showing an example of measurement of an electromagnetic wave of re-radiation in the electromagnetically shielded room of the same embodiment.

FIG. 5 is a graph showing the measurement results of FIGS. 3 and 4 above.

FIG. 6 is an explanatory diagram showing a configuration of a conventional electromagnetic shield room.

[Explanation of symbols]

 1 Electromagnetic Shield Room 3 Electromagnetic Wave Absorber 5 Metal Plate (Shield Material) 7 Earth 9 Electric Wire 11 Signal Generator 13 Spectrum Analyzer

Claims (1)

[Claims] 1. An electromagnetic shield room in which a floor, a ceiling and a wall are covered with a shield material, and when the electromagnetic wave re-radiated from the shield material in the electromagnetic shield room to the electromagnetic shield room room, the electromagnetic wave is generated. An electromagnetic wave removing device for an electromagnetically shielded room, which is provided with a signal generating means capable of applying a current having a phase opposite to that of the current inside the shield material.