JPH08186394A - Electromagnetic wave screening breathing hole - Google Patents

Abstract

PURPOSE: To provide an electromagnetic wave screening breathing hole used for an electric dark room and an electromagnetic screening room for screening electromagnetic waves within a wide band from a low frequency to a mm-wave region. CONSTITUTION: In an electromagnetic wave screening breathing hole, a honeycomb screening material is provided in the entrance of the breathing hole and a pyramid or wedge-shaped electric wave absorbing material is fitted to the inner wall of the breathing hole. In the electric wave absorber, the view up to an exit is closed since the section entire region of the breathing hole is hidden by either absorbing body when viewed from the entrance surface of the breathing hole, and the installation position of the electric wave absorber is shifted in the depth direction of the breathing hole to secure the circulation of air. A length L of the breathing hole for fitting the electric wave absorbing body should be 2-3 wavelengths or longer. With this structure, an improved screening property can be achieved within a wide frequency range from a low frequency region to a mm-wave region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave shielding vent hole, and more particularly to electromagnetic wave shielding of a vent hole in an electromagnetic wave shielding room, an anechoic chamber or the like.

[0002]

2. Description of the Related Art In an electromagnetically shielded room or an anechoic chamber, all walls including a floor and a ceiling are surrounded by metal plates for shielding electromagnetic waves, but there are some places that cannot be surrounded by metal walls.
One of them is a vent, and this part must ensure the circulation of air and at the same time shield it from electromagnetic waves. Conventionally, a honeycomb shielding material as shown in FIG. 8 is used for the ventilation holes of this type of electromagnetic shielding room or anechoic chamber, and an electromagnetic wave absorber (d) is provided on the inner wall of the ventilation hole as shown in FIG. It is known that the device is constructed of a mounted wall, and is bent so as not to have a straight line of sight as a passage to prevent electromagnetic waves from leaking and shield electromagnetic waves.

[0003]

The above-mentioned prior art has the following problems. As shown in the enlarged view, the shielding material of the honeycomb filter shown in FIG. 8 is a collection of small metal waveguides, and these waveguides block electromagnetic wave propagation. The electromagnetic wave can be shielded in the frequency range in which the waveguide of the honeycomb shielding material blocks electromagnetic wave propagation. Regarding this, when considering a waveguide having a quadrangular cross section, for example, when the cross section is a quadrangle (a> b) having a width a and a height b, the free space wavelength λ becomes 2a <λ. In the frequency range, the waveguide blocks electromagnetic waves. Therefore, if the frequency at which 2a = λ is fo, the cutoff occurs in the frequency range lower than fo.

The honeycomb cross section of the honeycomb shown in FIG. 8 is hexagonal. By analogy with the example of consideration of the above-mentioned waveguide having a square cross section, if the diameter of the honeycomb waveguide cross section is a. It may be considered that the cut-off waveguide is formed in the frequency range where 2a << λ. Normally, a> 3 mm in a honeycomb used as a ventilation hole shielding material. This size is used because the ventilation is insufficient with a diameter a smaller than this. Here, the upper limit frequency at which the honeycomb having a diameter a of 3 mm acts as a shield will be estimated. If the free space wavelength λ requires about 20 mm, the frequency is 1
The frequency is 5 GHz, and at a frequency higher than this, there is a problem that the honeycomb does not shield electromagnetic waves.

As shown in FIG. 9, the inner wall of the ventilation hole is formed of a wall on which a radio wave absorber (d) is mounted, and the space of the ventilation hole is bent so that it cannot be seen straight.
In what is intended to be used as a substantial shield, the frequency band is limited by the frequency characteristics of the radio wave absorber. The electromagnetic wave absorber (d) used here should have a wide frequency band as much as possible, so a pyramid-shaped or wedge-shaped electromagnetic wave absorber is used, but the height of both electromagnetic wave absorbers is about the wavelength. The amount of electromagnetic wave absorption is large only at frequencies above the same level as

For example, if the cross section of the vent hole is about 300 mm on a side and the radio wave absorber is a pyramid shape with a height of 50 mm, the frequency is 6 GHz (the wavelength is 50 m).
Below m), the amount of absorption is not large, and as a result, sufficient shielding cannot be expected. As described above, when the absorber is attached to the inner wall of the ventilation hole, there is a problem that the absorber cannot be shielded on the low frequency side due to the performance of the absorber. Recently, the frequency of electronic devices has spread to the high-frequency millimeter wave region, and as a result, shielding is required in a wide frequency range from the low frequency (1 GHz or less) that has hitherto been reached to the millimeter wave region in anechoic chambers and electromagnetic shield rooms. However, the above-mentioned conventional technique has a problem that it cannot be dealt with.

[0007]

According to the present invention, there is provided a ventilation hole made of a metal plate, wherein a pyramid-shaped electromagnetic wave absorber or a wedge-shaped electromagnetic wave absorber is attached to an inner wall surface of the ventilation hole, and an inlet of the ventilation hole, or The electromagnetic wave shielding vent hole is characterized in that at least one of the cross sections of the outlet is covered with a honeycomb shielding material. Further, the present invention is the electromagnetic wave shielding vent hole described above, wherein the vent hole is a vent hole that is bent so that a straight line cannot be seen from the inlet to the outlet.

Further, according to the present invention, when a plurality of ventilation holes made of a metal plate are used, the pyramid-shaped radio wave absorber or the wedge-shaped radio wave absorber having a bottom surface smaller than the cross section of the vent hole is used and viewed from the vent hole entrance surface. The entire cross-sectional area is hidden by one of the absorbers so that it cannot be seen through to the outlet, and the air absorber is installed in the depth direction of the ventilation hole to ensure air circulation, and the inlet or outlet of the ventilation hole is also secured. The electromagnetic wave shielding vent hole is characterized in that at least one of the cross sections is covered with a honeycomb shielding material. In addition, in the present invention, the inlet and outlet of the vent hole are the entrance on the side of the anechoic chamber or the electromagnetic shield room of the vent hole, and the exit side is the outside of the vent hole. As shown in FIG. 1, the side of the ventilation hole (b) provided in the anechoic chamber or the electromagnetically shielded room (a) is the entrance,
The side of the air arrow is the exit.

[0009]

The function of the present invention will be described. In the present invention, the electromagnetic wave shielding ventilation hole is a ventilation hole made of a metal plate, the inner wall surface of which is fitted with a pyramidal radio wave absorber or a wedge radio wave absorber, and at least an inlet or an outlet of the vent hole. The cross section of either one is covered with a honeycomb shielding material. When the radio wave absorber is relatively small, this vent has a structure that is bent so that the entrance to the exit of the vent cannot be seen in a straight line. When multiple radio wave absorbers or wedge-shaped radio wave absorbers are used, the entire cross-section area is hidden by one of the absorbers when viewed from the entrance surface of the vent hole, and the radio wave is not visible in the depth direction of the vent hole. A structure is adopted in which the installation position of the absorber is shifted to ensure air circulation, and at least one of the inlet and outlet of the ventilation hole is covered with a honeycomb shielding material.

With such a structure, good shielding can be obtained in a wide frequency range from low frequencies to the millimeter wave region. However, in order to achieve good shielding, the honeycomb shielding material and the electromagnetic wave absorber must be combined in consideration of the frequency characteristics. That is, in the present invention, the ventilation hole (b) provided in the anechoic chamber or the electromagnetic shielding room (a) as shown in FIG. 1 extends from the low frequency (1 GHz or less) to the millimeter wave region. It shields electromagnetic waves in a wide frequency range. This is because the honeycomb shielding material contributes to electromagnetic wave shielding in the low frequency region, and the electromagnetic wave absorber contributes to shielding in the high frequency region.The electromagnetic wave shielding is performed in a wide band by both the electromagnetic wave absorber and the honeycomb shielding material. It is something.

[0011]

Embodiments of the present invention will be described with reference to the drawings. [Embodiment 1] An embodiment of the present invention is shown in FIGS. FIG. 2 is a configuration diagram of an electromagnetic wave shielding vent hole showing an embodiment of the present invention. A honeycomb shielding material (c) is provided at the entrance of the vent hole, and a pyramid-shaped or wedge-shaped radio wave absorber (d) is attached to the inner wall of the vent hole. As shown in FIG. 2, the radio wave absorber (d) is such that when viewed from the inlet surface of the vent hole (b), the entire cross-sectional area of the vent hole is hidden by one of the absorbers and the outlet cannot be seen through. In addition, the installation position of the electromagnetic wave absorber (d) is shifted in the depth direction of the ventilation hole to ensure air circulation.

The length L of the ventilation hole for mounting the radio wave absorber is
Although it depends on how much shielding is required, it is empirically said that two or more wavelengths are required. Now
When the upper limit frequency at which the honeycomb shielding material is effective is fs and the free space wavelength at that time is λs, the radio wave absorber contributes to shielding in a high frequency region where the honeycomb is not effective, and therefore the length L of the vent hole is , 2-3 λs or more is required. The honeycomb shielding material is provided so as to cover the cross section of at least one of the inlet and the outlet of the ventilation hole. In the configuration of the electromagnetic wave shielding ventilation hole shown in FIG. Since it is provided on the outlet side of the pores, the shielding effect is the same as in FIG.

[Embodiment 2] A second embodiment of the present invention is shown in FIG.
Shown in FIG. 4 is a configuration example of the electromagnetic wave shielding ventilation hole of the second embodiment, in which the ventilation hole (b) having the electromagnetic wave absorber (d) attached to the inner wall cannot be seen straight from the entrance to the exit of the ventilation hole. So that the honeycomb shielding material at the entrance (c)
It is an electromagnetic wave shielding vent having a structure provided with. The length (L1 + L2) of the ventilation hole is 2 to 3 λs, as in the case of the first embodiment.
The above is necessary. When the radio wave absorber (d) is attached to the inner wall of the ventilation hole (b), the pyramid-shaped or wedge-shaped attachment of the radio wave absorber may be provided only on two opposite surfaces of the ventilation hole inner wall, or the inner wall of It may be attached to all surfaces.

[Embodiment 3] A third embodiment of the present invention will be described with reference to FIGS. 5, 6 and 7. FIG. 5 and FIG. 6 are configuration examples of the electromagnetic wave shielding vent hole of the third embodiment, and FIG. 7 is a diagram for explaining a method of combining the honeycomb shielding material and the radio wave absorber. In FIG. 5, a radio wave absorber (d) is provided in the ventilation hole, and the radio wave absorber (d) is a pyramid-shaped radio wave absorber or a wedge-shaped radio wave absorber. This radio wave absorber (d) is supported by a thin rod, for example, a plastic thin rod, in the vent hole. The pyramid-shaped radio wave absorber (d) has its apex on the lower (entrance) side, and the wedge-shaped one has its tip on the lower (entrance) side. A honeycomb shielding material (c) is provided at the inlet of the ventilation hole.

In FIG. 5, the ventilation hole (b) is considered to be a waveguide, and a plurality of electromagnetic wave absorbers (d) are provided in the waveguide so as to attenuate the electromagnetic wave propagating in the waveguide, and the ventilation hole entrance. Is provided with a honeycomb shielding material (C). Further, the plurality of radio wave absorbers (d) are provided so that the positions from the entrance to the exit of the ventilation hole cannot be seen in a straight line. The plurality of radio wave absorbers (d) provided in this waveguide are also designed to ensure ventilation, and from that point as well, a plurality of radio wave absorbers should be installed from the inlet to the outlet of the ventilation hole. The position should be staggered so that the line of sight cannot be seen.

Similar to FIG. 5, FIG. 6 shows the ventilation hole in which the electromagnetic wave absorber (d) is supported by a thin rod, for example, a thin plastic rod, and the honeycomb shielding material (c) is provided in the ventilation hole. It is provided on the back side (outlet of the vent). In this way, the entrance of the vent hole can maintain the radio wave absorption property at least in a high frequency band, and is therefore suitable as a vent hole of an anechoic chamber. The length L of the ventilation hole to which the radio wave absorber is attached needs to be 2 to 3 λs or more for the same reason as in the first and second embodiments.

The honeycomb shielding material and the electromagnetic wave absorber must be combined so that shielding can be obtained in a wider band by both. FIG. 7 shows the principle of combination, where the left vertical axis is the shielding amount S of the honeycomb shielding material and the right vertical axis is the shielding amount T of the radio wave absorber. When the diameter of the waveguide of the honeycomb shielding material is about the same as the wavelength, the shielding is rapidly deteriorated. Now, the shielding amount at a sufficiently low frequency is 9
The shielding amount of 0% is So, and the frequency at that time is fs. Further, the shielding amount of the wedge-shaped or pyramidal-shaped radio wave absorber depends on the ratio h / λ of the height h of the absorber and the wavelength λ, and the larger the ratio, the larger the shielding amount. Therefore, the shielding amount of the radio wave absorber increases as the frequency increases.

Now, let us say that the same value as So is To and the frequency at that time is fT. In order to maintain the shielding over a wide frequency band, it is necessary to combine them so that fs ≧ fT. If this relationship cannot be maintained, fs and f
During T, the shielding becomes poor. In addition, since it is desirable that the height of the radio wave absorber is as low as possible economically and in terms of space occupancy, fT does not need to be set extremely lower than fs. The relationship between fs and fT holds similarly in the first and second embodiments.

[0019]

By using the electromagnetic wave shielding vent hole of the present invention, the vent hole can be shielded in a wide band.
That is, the present invention has an effect that the shielding can be performed in a wide frequency range from a low frequency (1 GHz or less) to a high frequency millimeter wave region.

[Brief description of drawings]

FIG. 1 is a diagram showing ventilation holes provided in an anechoic chamber and an electromagnetically shielded room.

FIG. 2 is a structural example of an electromagnetic wave shielding vent hole according to the first embodiment of the present invention.

FIG. 3 is a configuration example of an electromagnetic wave shielding vent hole according to the first embodiment of the present invention.

FIG. 4 is a structural example of an electromagnetic wave shielding vent hole according to a second embodiment of the present invention.

FIG. 5 is a structural example of an electromagnetic wave shielding vent hole according to a third embodiment of the present invention.

FIG. 6 is a structural example of an electromagnetic wave shielding vent hole according to a third embodiment of the present invention.

FIG. 7 is a diagram for explaining a method of combining the honeycomb shielding material and the radio wave absorber.

FIG. 8 is a diagram of a conventional honeycomb shielding material.

FIG. 9 is a view of a ventilation hole in which a radio wave absorber of a conventional example is attached.

[Explanation of symbols]

 B: An anechoic chamber or an electromagnetic shield room. B: Vent hole. C: Honeycomb shielding material. D: Radio wave absorber. L, L1, L2: Length of the electromagnetic wave absorber mounting part

Claims (3)

[Claims] 1. A vent hole formed of a metal plate, wherein a pyramidal radio wave absorber or a wedge radio wave absorber is mounted on an inner wall surface of the vent hole, and a cross section of at least one of an entrance and an exit of the vent hole. An electromagnetic wave shielding ventilation hole characterized by covering the above with a honeycomb shielding material. 2. The electromagnetic wave shielding vent hole according to claim 1, wherein the vent hole is a vent hole that is bent so that a straight line cannot be seen from the entrance to the exit. 3. A ventilation hole made of a metal plate, and when a plurality of pyramid-shaped electromagnetic wave absorbers or wedge-shaped electromagnetic wave absorbers having a bottom surface smaller than the cross section of the ventilation hole are used and the entire cross-sectional area is viewed from the entrance surface of the ventilation hole One of the inlets and / or the outlets of the ventilation holes is hidden by one of the absorbers and cannot be seen through to the outlet, and the air absorber is displaced in the depth direction of the ventilation hole to ensure air circulation. An electromagnetic wave shielding ventilation hole, characterized in that one section is covered with a honeycomb shielding material.