JPH01187896A - Material for radio wave absorber - Google Patents

Abstract

PURPOSE:To lighten an absorber compared with a sheetlike absorber having used gum or paint, and to obtain the absorber with excellent wide-band characteristics and oblique-incidence characteristics, by making a sheetlike substance contain conductive fibers with the coating of a good conductor metal on the surfaces of long and slender fiberlike resins, and insulating fiberlike resins without the coatings of a good conductor metal. CONSTITUTION:A good conductor metal such as cupper, nickel etc., is coated on the surface of a fiberlike resin being an insulator electrically, to make a conductive fiber A. Then, the fibers A are mixed with fiberlike resins B being an insulator, to make a nonwoven fabric sheetlike absorbing material. When used as a material for a radio wave absorber, it is effective that the above- mentioned conductive fibers A and insulating fibers B are mixed in the range of 0.5 to 10% by weight. Four layers from the first layer 1 to the fourth layer 4, for example, are laminated to make an absorber. Each layer is a mixture of the good conductive fibers A and the insulating fibers B in the weight ratios of 5%, 3%, 1.5$% and 1% respectively, and each layer is equally 3nm in thick ness. Polyacrylonitrile and polyethylene are used for the firbers A and B, and nickel is used as a coating metal of the fiber A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio wave absorber material that suppresses unnecessary reflection and scattering of electromagnetic waves.

[Conventional technology]

The characteristics required of a radio wave absorber include the frequency band used, the amount of absorption, and changes in the amount of absorption at normal and oblique incidence, as well as weight, size, and shape from a practical standpoint.

Durability during outdoor use, etc.

[Problem that the invention seeks to solve]

However, an absorber that satisfies all of these characteristics has not yet been obtained, and materials and construction methods are selected depending on the purpose of use. For example, absorbers used in anechoic chambers are particularly required to have broadband properties, so a pyramid-shaped structure is used, but since this is large, a lightweight structure made of polyurethane foam or the like is used. is often used. On the other hand, to prevent false images formed on a ship's mast, an absorber with a narrow band characteristic is used, which is formed into a thin sheet made of weather-resistant rubber or paint.

An object of the present invention is to provide an absorber that is lighter in weight than the sheet-like absorber using rubber or paint, and has excellent broadband characteristics and oblique incidence characteristics.

[Means for solving problems]

The present invention consists of a sheet-like material of non-woven fabric, and the sheet-like material includes a conductive fiber whose surface is coated with a good conductor metal and an insulating fibrous resin which is not coated with a good conductor metal. This is a radio wave absorber material characterized by the following.

In Figure 1, the surface of a fibrous resin that is an electrical insulator is coated with a good conductor metal such as copper or nirasil to form a conductive fiber A, and this is mixed with a fibrous resin B that is an insulator. death,
It was made into a sheet-like absorbent material made of non-woven fabric. Experimental results have been obtained showing that it is effective when the conductive fiber and insulating fiber are mixed in a weight ratio of 0.5 to 10% for use as a material for a radio wave absorber. Normally, when designing an absorbent material, it is necessary to determine the values of complex permittivity (ffi) and complex permeability (μ), which include loss terms, but in the nonwoven fabric sheet of the present invention, the density of conductive fibers is low. It is not very accurate to measure ε and μ assuming that the medium is homogeneous. Here, we actually constructed an absorber and confirmed that it is an effective material as an absorbent based on its absorption properties.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing the cross-sectional structure of an absorbent body using the material of the present invention. The absorbent body is made by laminating four layers, first layer 1 to fourth layer 4. In each layer of the first layer 1 to the fourth layer 4, the weight ratio of the conductive fiber A to the insulating fiber B is 5%, 3%, and 1% in order.
．． They were mixed at a ratio of 5% and 1%. Each layer has an equal thickness of 3
There are m layers, and the total thickness is about 15 nn. Polyacrylonitrile and polyethylene were used for both fibers A and B, and nickel was used as a metal to coat the fibrous resin of conductive fiber A. Of course, in the present invention, various resins and good conductor metals can be used for the fibers A and B, and they are not limited to the resins and metals used in this example. do not have.

FIG. 3 shows the radio wave absorption characteristics when the absorber shown in FIG. 2 is placed on a metal plate and electromagnetic waves are perpendicularly incident on the fourth layer 4. As is clear from the figure, 10GIIz ~
It shows good absorption characteristics at 15 GHz.

FIG. 4 shows the absorption characteristics at oblique incidence. Characteristic (a) of the present invention shows good absorption characteristics even at an incident angle of 45°. For comparison, the oblique incidence characteristic of a two-layer radio wave absorber (Japanese Patent Application No. 109686/1986) using rubber as a base material, which is used in the same frequency band, is shown by the broken line (b). ).

Comparing the characteristics (b), it can be seen that the absorber using the material according to the present invention has better oblique incidence characteristics than the rubber type absorber.

FIG. 5 shows an example of an absorbent body formed into a corrugated shape using the same material of the present invention. The mixing ratio of conductive fibers is 1.5%. Here, since the design was aimed at the 10 to 15 GHz band, the height h and width W of the waveform were both approximately the same as the wavelength, and were 35 m+ and 24 nn, respectively. The thickness d of the layer was 3 mm. FIG. 6 shows the characteristics of the absorber shown in FIG. 5, and with the help of the shape effect, the absorber has good characteristics even when the light is incident obliquely.

All of the above have broadband characteristics and good oblique incidence characteristics, but in addition to radio wave characteristics, they are also characterized by being extremely lightweight, and have high practical value. For example, in the configuration shown in FIG. 2, the weight is 470 g/m, which is significantly lighter than the 8 kg/m of a two-layer absorbent body made of rubber as a base material.

In the material according to the present invention, it is thought that the radio wave loss is caused by the fact that the fibers coated with a good conductive metal are loaded and a current is induced in the conductive fibers when electromagnetic waves are incident. Since radio wave loss increases in proportion to the density of the conductive fibers, in the laminated absorber shown in FIG. 2, the fourth layer 4, the third layer 3. Second layer 2. The mixing ratio of the conductive fibers A is increased so that the loss increases in the order of the first layer 1.

As shown in FIG. 4, the absorber using the material according to the invention is superior to the rubber-type absorber in oblique incidence characteristics. This includes the possibility that the effect of the conductive fibers dispersed in the nonwoven sheet is dependent on the incident angle, and the characteristic of using a fibrous conductive substance as a loss material arises.

[Effects of the Invention] As described above, according to the present invention, an absorber having broadband characteristics and good oblique incidence characteristics can be obtained, and the absorber can be reduced in weight.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of the material of the present invention, Figure 2 is a sectional view of a radio wave absorber constructed by laminating the material, Figures 3 and 4.
The figure shows the absorption characteristics of the absorber shown in Fig. 2, Fig. 5 is a perspective view of a radio wave absorber constructed by corrugating the material of the present invention, and Fig. 6 shows the absorber shown in Fig. 5. FIG. A... Conductive fiber B... Insulating fiber 1 to 4
...1st layer to 4th layer

Claims (1)

[Claims] (1) Consisting of a sheet of nonwoven fabric, the sheet includes conductive fibers in which the surface of elongated fibrous resin is coated with a good conductor metal and an insulating fibrous resin that is not coated with a good conductor metal. A radio wave absorber material characterized by: