JPH0992996A - Wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb an electric wave of a specific frequency by a small thickness wave absorber by a method wherein the wave absorber is composed of a dielectric unit made of foamed phenolic resin in which carbon fibers are dispersed and a conducting unit which is stuck to one of the surfaces of the dielectric unit. SOLUTION: A wave absorber is composed of a dielectric unit 3 made of foamed phenolic resin 1 in which carbon fibers 2 are dispersed and a conducting unit 4 which is stuck to one of the surfaces of the dielectric unit 3. The foamed phenolic resin 1 can be made by adding foaming agent such as n-hexane and hardner such as inorganic acid to resol-type phenolic resin and heating the mixture for foaming and hardening. As phenol resin is semi-incombustible, it can be used as outer wall material. As phenol resin has a relatively large dielectric constant, i.e., 4-6, among resin family, the effect of wave absorption is high and the thickness of a wave absorber can be reduced. Especially, an electric wave with a frequency about 100-900MHz can be absorbed with a small thickness.

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 attached to a building or the like in order to prevent the reflection of radio waves on the surface of the building such as a high-rise building, a bridge, or an elevated highway.

[0002]

2. Description of the Related Art Heretofore, a radio wave absorber has been known in which a thin metal plate is attached to one side of a dielectric material in which ferrite powder, carbon powder, etc. are dispersed in a resin. If the thickness is thick, the frequency band of radio waves that can be absorbed becomes several GHz, which is effective in preventing ghosts on TV.
It has been difficult to absorb radio waves with a frequency of about 00 to 900 MHz. Therefore, a thin thickness of 100-900
There is a demand for a radio wave absorber capable of absorbing a radio wave having a frequency of about MHz. In addition, since the above resins are generally flammable, it is also required to make them semi-inflammable as a radio wave absorber for use in a building or the like.

On the other hand, a ferrite sintered body may be used as an absorber of radio waves in a relatively low frequency band such as television radio waves. In this case, the thickness is about 10 mm and the radio wave absorption performance is excellent, but there is a drawback that it is very heavy because it is a sintered body of metal, and its improvement is required.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to absorb a radio wave having a thin thickness and a frequency of about 100 to 900 MHz. It is possible to provide a lightweight, quasi-incombustible radio wave absorber that can be manufactured.

[0005]

According to a first aspect of the present invention, there is provided a radio wave absorber of a dielectric material in which carbon fibers are dispersed in a phenol resin foam, and a conductive material attached to one surface of the dielectric material. It is characterized by consisting of a body.

A radio wave absorber according to a second aspect of the present invention is the radio wave absorber according to the first aspect, characterized in that the content of carbon fiber in the dielectric is 0.5 to 10% by weight.

A radio wave absorber according to a third aspect of the present invention is the radio wave absorber according to the first or second aspect, wherein the conductor is a metal plate.

[0008]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic view showing the structure of the radio wave absorber of the present invention. As shown in FIG. 1, the radio wave absorber of the present invention has a carbon fiber 2 dispersed in a phenol resin foam 1. It is composed of a dielectric 3 and a conductor 4 attached to one surface of the dielectric 3. This phenol resin foam 1
Is a phenol resin such as a resole type phenol resin or a novolac type phenol resin, a foaming agent such as n-hexane, methylene chloride, trichloromethane or dinitropentamethylenetetramine, a curing agent such as an inorganic acid, an aromatic sulfonic acid or hexamethylenetetramine. It can be manufactured by heating and foaming and curing a mixture of
In addition, since a mixture of a phenol resin with a foaming agent and a curing agent is commercially available as a phenol resin foam material,
This commercially available phenol resin foam material may be used.

Since the phenol resin is quasi-incombustible, the radio wave absorber of the present invention made of a phenol resin foam can be used as a quasi-incombustible material as an outer wall material. Since the phenolic resin has a large dielectric constant of 4 to 6 among the resins, it has a high effect of absorbing radio waves, so that the radio wave absorber of the present invention can be easily thinned. Further, since the specific gravity of the phenol resin foam is small, the radio wave absorber of the present invention can be easily reduced in weight.

The carbon fiber used in the radio wave absorber of the present invention is not particularly limited, but has a diameter of 1 to 50 μm,
A length of 0.1 to 2 mm is desirable. This is because if the aspect ratio is too small, the dielectric constant of the dielectric does not increase, making it difficult to reduce the thickness of the electromagnetic wave absorber, and if the fiber becomes too long, it becomes difficult to disperse it in the phenol resin foam. Because. The content of carbon fibers in the dielectric material of the radio wave absorber is not particularly limited, but is preferably 0.5 to 10% by weight. This is because if it is less than 0.5% by weight, the dielectric constant of the dielectric does not increase, making it difficult to reduce the thickness of the radio wave absorber, and if it exceeds 10% by weight, it becomes conductive and radio waves are reflected. In some cases, the function as a radio wave absorber may be deteriorated.

The conductor attached to one surface of the dielectric in the present invention may be any one having conductivity and reflecting radio waves, and various metal plates such as copper plate and iron plate can be used, There is no particular limitation on the sticking method, and the sticking may be performed using an adhesive or the like.

[0013]

The present invention will be described below based on examples and comparative examples.

(Example 1) Phenolic resin foam material (manufactured by Toyo Tire & Rubber Co., Ltd., product number A-491) and carbon fiber having a diameter of 13 μm and a length of 0.7 mm were added to the total amount of the phenol resin foam material and the carbon fiber. Carbon fiber content is 3% by weight
The mixture was mixed and mixed so as to be The obtained phenol resin foam containing carbon fiber was used as a plate-shaped dielectric having a thickness of 4 cm, and then a copper plate having a thickness of 0.2 mm was attached to one surface of this dielectric using an adhesive. To produce a radio wave absorber. The measurement result of the reflection coefficient of the obtained electromagnetic wave absorber is shown in FIG.

(Example 2) Phenolic resin foam material (manufactured by Toyo Tire & Rubber Co., Ltd., product number A-491) and carbon fiber having a diameter of 13 μm and a length of 0.7 mm were used with respect to the total amount of the phenol resin foam material and the carbon fiber. Carbon fiber content is 3% by weight
The mixture was mixed and mixed so as to be The obtained phenol resin foam containing carbon fiber was used as a plate-shaped dielectric having a thickness of 2 cm, and then a copper plate having a thickness of 0.2 mm was attached to one surface of this dielectric using an adhesive. To produce a radio wave absorber. The measurement result of the reflection coefficient of the obtained electromagnetic wave absorber is shown in FIG.

(Comparative Example) Phenolic resin foam material (manufactured by Toyo Tire & Rubber Co., Ltd., product number A-491) and carbon powder were used, and the carbon powder content was 3% by weight based on the total amount of the phenol resin foam material and carbon powder. So that after mixing and mixing,
It was heated and foamed in free foam. The obtained phenol resin foam containing carbon powder is used as a plate-shaped dielectric having a thickness of 6 cm, and then a copper plate having a thickness of 0.2 mm is attached to one surface of the dielectric with an adhesive. To produce a radio wave absorber. The measurement result of the reflection coefficient of the obtained electromagnetic wave absorber is shown in FIG.

As is clear from the results of FIGS. 2 to 4, in Examples 1 and 2 in which the phenol resin foam containing carbon fibers was used as the dielectric, the phenol resin foam containing carbon powder was used as the dielectric. The thickness of the dielectric is smaller than that of the comparative example, which is a body, and it is a radio wave absorber capable of absorbing radio waves having a frequency of about 100 to 900 MHz.

[0018]

The radio wave absorber of the invention according to claims 1 to 3 is a dielectric material in which carbon fibers are dispersed in a phenol resin foam, and a conductive material attached to one surface of the dielectric material. As it consists of a body, it has a thin thickness of 100-900M.
It is possible to absorb radio waves with a frequency of about Hz,
Further, it is a radio wave absorber having suitable performances that are lighter weight and quasi-incombustible.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of a radio wave absorber of the present invention.

FIG. 2 is a graph showing the measurement results of the reflection coefficient of the radio wave absorber obtained in Example 1.

FIG. 3 is a graph showing the measurement results of the reflection coefficient of the radio wave absorber obtained in Example 2.

FIG. 4 is a graph showing a measurement result of a reflection coefficient of a radio wave absorber obtained in a comparative example.

[Explanation of symbols]

 1 Phenolic resin foam 2 Carbon fiber 3 Dielectric 4 Conductor

Claims (3)

[Claims] 1. A radio wave absorber comprising a dielectric material in which carbon fibers are dispersed in a phenol resin foam and a conductor attached to one surface of the dielectric material. 2. The content of carbon fiber in the dielectric is 0.
The radio wave absorber according to claim 1, which is 5 to 10% by weight. 3. The radio wave absorber according to claim 1, wherein the conductor is a metal plate.