JPH023560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite radio wave absorber, and in particular to improvements in radio wave absorber materials that can be used as manufacturing materials.

When the outer shell or parts of ships, aircraft, vehicles, buildings, etc. are made of FRP (Fiber reinforced plastic), the reflection of radio waves can generally be reduced more than when made of metal, suppressing unnecessary radio wave reflection. It is known to be effective when desired. However, glass fibers used as ordinary reinforcing fibers and carbon fibers with high conductivity reflect radio waves quite strongly, so in order to suppress radio wave reflection as mentioned above, it is necessary to change the electrical constants of the material and the composite material. Special consideration must be given to the composition of the

In view of the above points, the present invention aims to provide a composite radio wave absorber that can effectively reduce radio wave reflection over a wide range of microwave bands.

Examples of the composite radio wave absorber according to the present invention will be described below along with comparative examples.

FIG. 1 shows a known composite radio wave absorber as Comparative Example 1. In this figure, a ferromagnetic powder 3 (ferrite powder, carbonyl iron powder, etc.) is contained in a polymeric binder 2 on the surface of a metal plate or metal foil 1.
A composite radio wave absorber is constructed by attaching a magnetic absorber made by dispersing and forming layers. In this case, by dispersing and mixing the ferromagnetic powder 3 in the binder 2 at a volume ratio of about 30 to 40% and designing the thickness to be about 2 to 4 mm, the X-band ( It is possible to provide radio wave absorption characteristics having a peak of 20 dB or more at 8 to 12.5 GHz). but,
As is clear from FIG. 4a, the frequency band exceeding 20 dB (hereinafter referred to as the 20 dB band) is about 2 GHz, which has the disadvantage that it cannot necessarily be said to be a sufficiently wide band.

FIG. 2 shows Comparative Example 2. In this case, a cloth woven with carbon-containing fibers 5 such as carbon fibers and silicon carbide fibers is laminated on the surface of the metal plate or metal foil 1, and a polymeric material 4 (not necessarily the same as the binder 2) is applied. The impregnated material is closely attached and molded as one piece. In Comparative Example 2, when 10 sheets of silicon carbide fiber cloth with a specific resistance of about 360 Ω/cm ² are stacked and molded, a design with a thickness of about 3 to 8 mm will have the radio wave absorption characteristics as shown in Figure 4b. be able to. According to FIG. 4b, the broadband performance is sufficient, but the amount of radio wave absorption is a small value of about 5 to 8 dB.

As described above, with the structures of Comparative Examples 1 and 2 shown in FIGS. 1 and 2, it is not easy to satisfy both the amount of radio wave absorption and the broadband performance.

FIG. 3 shows an embodiment of the composite radio wave absorber according to the present invention. As shown in this figure, the composite radio wave absorber is made by dispersing ferromagnetic powder 3 (ferrite powder, carbonyl iron powder, etc.) in a polymer binder 2 on the surface of a metal plate or metal foil 1 and forming it into a layer. A magnetic absorber (first layer) is attached, and a cloth woven with carbon-containing fibers 5 such as carbon fibers and silicon carbide fibers is further laminated on the surface layer and impregnated with a polymeric material 4 (second layer). ) are closely attached and molded.

That is, the real number part of the dielectric constant of the binder 2 of the first layer is 2.5 to 3.5, the ferromagnetic powder 3 is ferrite, the thickness is 3 mm, and the specific resistance of the material of the carbon-containing fiber 5 of the second layer is When 300 to 400 Ωcm, the number of laminated sheets is 10, the real part of the dielectric constant of polymer material 4 is 2.5 to 3.5, and the thickness is 8 mm, the radio wave absorption characteristics are as shown in Figure 4 c. , the 20dB band is 4GHz or higher, satisfying both radio wave absorption and wideband performance. In this case, the first
The polymeric material used for the layer (a layer in which ferromagnetic powder 3 is dispersed in a binder 2 made of a polymeric material) and the second layer (a layer in which a cloth made of carbon-containing fibers 5 is impregnated with a polymeric material 4) is dielectric. Preferably, the real part of the ratio is in the range of 2-4. As this value increases, broadband performance generally suffers. Note that the specific resistance of the carbon-containing fiber material may be changed for each sheet.

If the configuration of the present invention as described above is used, the thickness of the first layer is 10 mm or less, the thickness of the second layer is 15 mm or less (that is, the total thickness is 25 mm or less), and the dielectric constant of the polymeric material used as the binder is The real part of the rate is in the range of 2 to 4,
It is possible to find experimentally the design specifications that allow the specific resistance of the carbon-containing fiber material to be within the range of 10Ωcm to 1KΩcm and the 20dB band to be 4GHz or higher, providing a means to construct a composite radio wave absorber with good performance. It is something.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the structure of a composite radio wave absorber of Comparative Example 1, Fig. 2 is a perspective view showing the structure of Comparative Example 2, and Fig. 3 shows an example of the composite radio wave absorber according to the present invention. A perspective view, FIG. 4a is a graph showing the radio wave absorption characteristics of Comparative Example 1, FIG. 4b is a graph showing the radio wave absorption characteristics of Comparative Example 2, and FIG. 4c is a graph showing the radio wave absorption characteristics of the example of the present invention. This is a graph showing. 1...Metal plate or metal foil, 2...Polymer material,
3...Ferromagnetic powder, 4...Polymer material (not necessarily the same as 2), 5...Carbon-containing fiber.

Claims (1)

[Claims] 1 The first layer is made by dispersing ferromagnetic powder in a polymer material with a real number part of dielectric constant of 2 to 4 and forming it into a layer with a thickness of 10 mm or less, and a carbon-containing material such as carbon fiber or silicon carbide fiber is added to the first layer. The specific resistance of fiber material is 10Ωcm ~
A second layer impregnated with a polymer material with a real number part of dielectric constant of 2 to 4 is laminated with 10 kΩcm woven cloth, and the total thickness is 25 mm or less. A composite radio wave absorber featuring: