JP3131609B2 - Radio wave absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber.
More specifically, the present invention relates to an improvement in radio wave absorption characteristics of a radio wave absorber made of a wood-based material or a carbon-based material suitable for use as a building interior material.

[0002]

2. Description of the Related Art Conventionally, as a radio wave absorbing material, for example, a material described in Japanese Patent Application Laid-Open No. Hei 3-151698 is known.

[0003] The conventional radio wave absorbing material is obtained by mixing carbon powder and carbon fiber with a wood chip together with a binder.

[0004]

The above-mentioned conventional radio wave absorbing material solves the problem of low shape preservation of the prior radio wave absorbing material obtained by mixing carbon, ferrite, etc. with styrene foam resin, urethane resin or the like. It is used as an interior material for buildings. However, it is effective in absorbing radio waves in the short wave (HF wave) band and ultra-high frequency (VHF wave) band having a frequency of 10 MHz to 50 MHz, but is effective in absorbing the millimeter wave (EHF wave) band having a frequency of about 60 GHz. There is a problem that it is not very effective.

In recent offices, factories, etc., high-speed wireless LAN equipment for transmitting data information and image information using millimeter-wave band radio waves has been used, and millimeter-wave bands from indoor walls and ceilings have been used. It has been recognized that there is a need to prevent the deterioration of transmission quality due to multiple reflections of radio waves. For this reason, in this technical field, there is a demand for the development of an interior material that can effectively absorb radio waves in the millimeter wave band.

The present invention has been made in consideration of such problems and demands, and is capable of effectively absorbing radio waves in the millimeter wave band, and is suitable for use as a building interior material. The task is to provide

[0007]

Means for Solving the Problems To solve the above-mentioned problems, the radio wave absorbing material according to the present invention employs the following means.

That is, according to the first aspect, in a radio wave absorbing material obtained by mixing a wood-based material and a carbon-based material, three layers having different mixing ratios are provided in the plate thickness direction and formed into a plate shape. Mixing the carbon-based material of the inner layer with respect to 1 l of the wood-based material in the range of 0 to 10 g of the carbon-based material with respect to 1 liter of the wood-based material without containing the carbon-based material in the layer located thereon It is characterized by increasing the ratio.

[0009]

According to the above-described means, in the first aspect, the function of absorbing radio waves up to an incident angle of 40 degrees in the millimeter wave band was confirmed. In particular, the most effective absorption function was confirmed for millimeter-wave radio waves having a frequency of about 60 GHz.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the radio wave absorbing material according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment which is formed in a thin plate shape having three layers in the plate thickness direction.

The first absorbing layer 1 of this embodiment constitutes a layer located on the outermost side of the building structure W farthest from the building structure W among the three layers. This first absorption layer 1 has a thickness a of 2 m.
m is the mixing ratio of 3 g of the carbon-based material to 1 l of the wood-based material. The dielectric constant of the first absorption layer 1 is 1.93−
0.72j.

Further, the second absorption layer 2 constitutes a layer located in the middle of the three layers. This second absorption layer 2
Is a ratio of a mixture of 0 g of a carbon-based material (that is, no carbon-based material is contained) per 1 l of a wood-based material having a thickness b of 2 mm. The dielectric constant of the second absorption layer 2 is 2.2
5-0.13j.

The third absorbing layer 3 constitutes a layer located on the inner side closest to the structure W of the building among the three layers. The third absorption layer 3 has a thickness c of 2 mm and is made of a mixture of 10 g of the carbon-based material with respect to 1 l of the wood-based material. The dielectric constant of the third absorbing layer 3 is 2.25-0.3.
2j.

The woody material of this embodiment includes wood chips. Wood chips crush various kinds of wood,
It is preferable to pulverize and cut to obtain a powder having a particle size of about 10 to 100 mesh.

Further, as the carbon-based material of this embodiment,
Examples thereof include finely pulverized graphite, coke, and the like, carbon powder such as carbon black, and polyacrylonitrile-based, rayon-based, and pitch-based carbon fibers. In addition, the thing made into the chop of about 1-3 mm is preferable for carbon fiber.

These wood-based materials and carbon-based materials are mixed in the above-mentioned ratio, and are mixed with resin-based binders such as vinyl acetate-ethylene, vinyl acetate-ethylene-acryl, and styrene-vinyl chloride. It is preferable to mix a carbon-based material and a wood-based material.

[0018] The mixed wood-based material and carbon-based material are mixed into a first absorbent layer 1, a second absorbent layer 2, and a third absorbent layer by molding or the like.
The absorption layer 3 is individually formed into a plate shape. Then, the first absorption layer 1, the second absorption layer 2, and the third absorption layer 3 are bonded and laminated. Note that a wood-based material and a carbon-based material in a mixing ratio of the first absorption layer 1, the second absorption layer 2, and the third absorption layer 3 are deposited and laminated inside the molding die. The second absorbing layer 2 and the third absorbing layer 3 can be integrally laminated.

Further, after forming into a plate shape, a non-combustible material and a coloring pigment are applied and impregnated as necessary in order to provide characteristics as an interior material.

The present inventors have shown in FIG.
An experiment to confirm the effect was performed using the experimental equipment shown in FIG.

The experimental equipment comprises a transmitter 5, a receiver 6, and a network analyzer (not shown) which are set at positions of regular reflection with respect to a measurement sample and sweep a radio wave R in a 1 GHz band of 57-58 GHz. . The radio wave absorbing material according to the present invention, which is a measurement sample, has a third structure instead of the building structure W.
A metal plate 4 is attached to the back of the absorption layer 3.

In an experiment using this experimental facility, first, the reflection level of radio waves R was measured using the radio wave absorbing material according to the present invention as a measurement sample, and then the reflection level of radio waves R was measured using only the metal plate 4 as a measurement sample. Was measured. And from both measurements,
The return loss of the radio wave absorber according to the present invention was determined. In addition,
This measurement was performed with two types of linearly polarized waves, that is, vertical polarization perpendicular to the incident surface of the measurement sample and horizontal polarization parallel to the incident surface. The incident angle θ of the radio wave R with respect to the measurement sample is 7 degrees to 7 degrees.
Performed within 5 degrees.

Further, for comparison with the radio wave absorbing material according to the present invention, the same measurement was performed on a concrete plate of the same quality as a concrete wall surface of a general building.

The experimental data is shown in FIG.

As is clear from the experimental data shown in FIG. 3, when the incident angle θ is up to 40 degrees, the radio wave absorbing material according to the present invention has a return loss of 13 dB or more, whereas concrete has a return loss of 10 dB or less. Of the return loss.
When the incident angle θ is up to 20 degrees, the radio wave absorbing material according to the present invention has a maximum return loss of 30 dB. Therefore, it is understood that the radio wave absorbing material according to the present invention absorbs a large amount of radio waves as compared with a concrete wall surface of a general building. In addition, in the case of concrete, the horizontal polarization near the incident angle θ of 70 degrees has a return loss of 30 dB or more, but it is based on the Brewster angle.

This embodiment can be applied to a ceiling, a wall, etc. by an ordinary method as an interior material. In addition, because it is thin, it can be laminated to the interior material that has already been constructed,
It is also possible to use it as a part of a member such as furniture.

As described above, in addition to the illustrated embodiment, an embodiment having a configuration of a plurality of layers composed of four or more layers is also possible.
In addition, it is also possible to change the thickness of each of the plurality of layers and stack them.

Further, an embodiment in which the mixing ratio of the wood-based material and the carbon-based material in each layer is changed is also possible.

[0029]

As described above, the radio wave absorbing material according to the present invention has an effect of remarkably absorbing radio waves up to an incident angle of 40 degrees and remarkable absorption of millimeter wave bands having a frequency of about 60 GHz. is there.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a radio wave absorbing material according to the present invention.

FIG. 2 is a plan view showing an experimental facility for confirming the effect of FIG.

FIG. 3 is a graph showing experimental data obtained by the experimental equipment shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st absorption layer 2 2nd absorption layer 3 3rd absorption layer R electric wave W Building structure

────────────────────────────────────────────────── ─── Continuing on the front page (51) Int.Cl. ⁷ Identification code FI E04F 13/10 E04F 13/10 A (72) Inventor Toshio Ihara 4-2-1 Nukaikitamachi, Koganei-shi, Tokyo Inside the research institute (72) Shuichi Takasaka Inventor Kashima Construction 2-9-1-1, Tobita-shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. Inside the Technical Research Institute Co., Ltd. (72) Kiyoshi Horikoshi 2-9-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. (72) Katsori Yamaki 2-1-1, Tobita-Shiita, Chofu-shi, Tokyo deer Island construction Co., Ltd. intra-technology research Institute (56) reference Patent Sho 64-58502 (JP, a) JP Akira 59-176035 (JP, a) (58 ) investigated the field (Int.Cl. ^7, D Name) E04B 1/92 E04F 13/08 - 13/18 H05K 9/00 B32B 1/00 - 35/00

Claims (1)

(57) [Claims] 1. An electromagnetic wave absorbing material comprising a mixture of a wood-based material and a carbon-based material, wherein three layers having different mixing ratios are provided in the plate thickness direction to form a plate shape, and a carbon layer is provided in the middle layer. Made of wood-based material only, without wood-based material, and wood-based material 1
1. A radio wave absorber, wherein the mixing ratio of the carbon-based material in the inner layer is higher than that in the outer layer within the range of 0 to 10 g of the carbon-based material.