JPH0797715B2 - Method of manufacturing 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 an electromagnetic wave absorber and a method of manufacturing the same, more specifically, it can be used on an outer wall of a building and can prevent generation of a ghost due to a reflected wave of television broadcasting. The present invention relates to a method for manufacturing a radio wave absorber.

[0002]

2. Description of the Related Art One proposed technique is to mix a main component as an outer wall of a building, such as concrete, with carbon fiber which is a conductive material, and to match the characteristic impedance of the radio wave in the air to obtain the radio wave. The absorption is good, and a conductive reflector is arranged in the outer wall or on the back surface of the outer wall, and the distance between the front surface of the outer wall and the conductive reflector is 1/4 of the internal wavelength λ in the outer wall of the electromagnetic wave. In this way, the incident wave and the reflected wave of the electromagnetic wave in the outer wall are canceled to prevent reflection of the electromagnetic wave to the outside of the outer wall.

[0003]

In such prior art, the thickness of the outer wall actually needs to be 4 to 20 cm. According to the experiments conducted by the inventors of the present invention, the orientation direction of the carbon fibers is important for improving the absorption performance of electromagnetic waves, and the fact that the carbon fibers extend parallel to the horizontal electric field of television broadcasting shows that It was found that this is preferable in improving the absorption performance of. At present, it is impossible to manufacture the outer wall containing the carbon fiber having such a preferred orientation by extrusion molding which is excellent in productivity.

An object of the present invention is to provide a method for producing a radio wave absorber having conductive fibers oriented and having a desired large thickness.

[0005]

According to the present invention, a step of extruding a thin electromagnetic wave absorbing plate containing conductive fibers oriented in a flat direction, and a pair of uncured plural electromagnetic wave absorbing plates after extrusion molding. The method of manufacturing a radio wave absorber, comprising the step of pressing with a roller and superimposing them on each other to integrate them.

[0006]

According to the present invention, a thin electromagnetic wave absorbing plate containing conductive fibers oriented in a flat direction, such as carbon fibers, can be easily manufactured by extrusion molding. A desired thickness can be obtained by stacking the sheets, whereby a conductive reflector such as a carbon fiber net, a reinforcing bar, a wire mesh, a metal punching metal and By arranging a thin plate made of aluminum, etc., and setting the distance between the front surface of the electromagnetic wave absorber and the conductive reflector to be approximately 1/4 of the internal wavelength λ of the electromagnetic wave inside the electromagnetic wave absorber, the desired frequency band can be obtained. The electromagnetic wave is absorbed in the electromagnetic wave absorber and converted into heat energy, thus preventing the ghost of television broadcasting.

In the production of such a radio wave absorber, a plurality of thin radio wave absorbers in an uncured state after extrusion are pressed by a pair of rollers so that they can be bonded and integrated with each other. .

[0008]

1 is a perspective view showing a method of manufacturing a radio wave absorber 1 according to an embodiment of the present invention. Thin electromagnetic wave absorbers 4 are individually extruded from a plurality of extrusion ports 3 divided into upper and lower parts of an extrusion molding die 2, and a plurality of the electromagnetic wave absorbers thus extruded are uncured. By pressing between the rollers 5 and 6 to integrate them, it is possible to obtain the radio wave absorber 7 having a large wall thickness. The thickness D of each radio wave absorber 4 is, for example, 3 to
30 mm, and the width W is, for example, 650 to 900 m
m, and the thickness W1 of the radio wave absorber 7 shown in FIG. 2 obtained by stacking a plurality of radio wave absorbers in this way is, for example, 4
~ 20 cm. A conductive reflector 10 is fixed to the back surface of the radio wave absorber 7, and the thickness W1 of the radio wave absorber 7 is set to be approximately ¼ of the internal wavelength λ of the electromagnetic wave to be absorbed, so that the electromagnetic wave is absorbed. It can be absorbed into the inside and converted into heat energy, thus preventing the ghost of television broadcasting.

The base material which is the main component of each radio wave absorption plate 4 is mortar composed of cement, fine aggregate, admixture and water, or a hydraulic composition such as concrete in which the mortar is mixed with coarse aggregate. Alternatively, a resin such as an epoxy resin can be applied. The conductive material is, for example, carbon fiber, which is made of rayon-based polyacrylonitrile (PA).
Various carbon fibers such as N) type, phenol resin type, coal pitch type, petroleum pitch type, etc. can be used, and usually, the fiber diameter is about 2 to 30 μm and the average fiber length is 0.1 to 1.
It is preferable to use one having a diameter of about 0 mm. The content of carbon fibers is preferably 0.5 to 10% by weight based on the hydraulic composition (for example, mortar). 0.5% by weight
If it is less than 10%, it is difficult to match the radio waves, and if it exceeds 10% by weight, it becomes difficult to uniformly disperse the carbon fibers in the matrix.

When carbon fiber is contained in the resin, the content of carbon fiber in the resin is preferably 1 to 25% by weight. This is because if it is less than 1% by weight, the matching condition for radio waves is difficult, while if it exceeds 25% by weight, it becomes difficult to uniformly disperse the carbon fibers in the matrix.

As described above, the base material contains carbon fibers, and by extrusion molding from the relatively small extrusion port 3, the carbon fibers are flattened (left and right in FIG. 1, left and right in FIG. 2). Direction). According to an experiment by the inventor of the present invention, the electromagnetic wave absorber 7 of the electromagnetic wave absorber 7 is aligned so that the orientation direction of the carbon fiber 8 which is schematically shown in FIG. It was confirmed that the electromagnetic wave absorption performance can be improved by determining the arrangement. The magnetic field direction 10H is the vertical direction. The dielectric constant ε of the radio wave absorber 7 is expressed separately for its real part ε1 and its imaginary part ε2.

[0012]

[Equation 1] ε = ε1-jε2 According to the present inventor, as shown in FIG. 3, when a sample piece of the radio wave absorber 7 is cut along an arbitrary plane, two axes orthogonal to each other are X-axis. -X1, Y-Y1, with X-X1 as the reference line, the intersection angle with the cutting line P-P1 is θ, and ε1, which is the maximum when θ is changed in the range of 0 to 180 degrees.
Let the values of ε2 be ε1max and ε2max, and obtain the minimum ε
It has been confirmed that when 1, 1 and ε 2 are ε 1 min and ε 2 min, the degree of orientation S ε 1, S ε 2 shown in Formula 2 and Formula 3 satisfies at least one of Formula 2 and Formula 3, the absorption is good. .

[0013]

## EQU00002 ## S.epsilon.1 = .epsilon.1max-.epsilon.1min> 25

[0014]

## EQU00003 ## S.epsilon.2 = .epsilon.2max-.epsilon.2min> 5

[0015]

As described above, according to the present invention, it is possible to easily mass-produce a thin electromagnetic wave absorbing plate containing conductive fibers such as carbon fibers oriented in a flat direction by extrusion molding. It is possible to obtain a radio wave absorber having a desired thickness by stacking a plurality of such thin radio wave absorbers. A conductive reflector is arranged on the back surface of such an electromagnetic wave absorber, and the distance between the front surface and the conductive reflector is set to approximately 1/4 of the internal wavelength λ of the electromagnetic wave inside the electromagnetic wave absorber.
By selecting, the electromagnetic wave is absorbed in the electromagnetic wave absorber and converted into heat energy, so that the electromagnetic wave is prevented from being reflected to the outside of the electromagnetic wave absorber, and thus the ghost of television broadcasting can be prevented. Become.

After such extrusion molding, a plurality of such thin electromagnetic wave absorbing plates are stacked in an uncured state and pressed by a pair of rollers to be integrated. In this way, a radio wave absorber having a desired thickness can be easily obtained. According to such extrusion molding, the orientation of the conductive fibers is improved, and therefore, the orientation direction of the conductive fibers is made to coincide with the electric field direction of an electromagnetic wave such as a television broadcast having a horizontal electric field strength, thereby efficiently. The electromagnetic wave can be favorably absorbed in the radio wave absorber.

[Brief description of drawings]

FIG. 1 is a simplified perspective view showing a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a perspective view of a radio wave absorber 7 according to an embodiment of the present invention.

FIG. 3 is a diagram showing an experimental result of the present inventor.

[Explanation of symbols]

 7,9 Radio wave absorber 2 Dice 3 Extrusion port 4 Radio wave absorber 5 Roller 8 Carbon fiber 10 Conductive reflector

Front Page Continuation (72) Inventor Junichi Fujita 4-1-2 Hiranocho, Chuo-ku, Osaka-shi, Osaka Within Osaka Gas Co., Ltd. (72) Inventor Mitsuo Kiura 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka No. Osaka Gas Co., Ltd. (72) Inventor Tsuneo Nakama 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture Yuji Ichikawa, Examiner, Osaka Gas Co., Ltd. (56) Reference JP-A-58-188193 ( JP, A)

Claims (1)

[Claims] 1. A step of extruding a thin electromagnetic wave absorbing plate containing conductive fibers oriented in a flat direction, and a plurality of uncured plural electromagnetic wave absorbing plates after extrusion are pressed by a pair of rollers to be superposed. A method of manufacturing a radio wave absorber, comprising: