JPS59215798A - Radio wave absorber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a radio wave absorber.

(Background Art) As a conventional radio wave absorber, for example, a rubber sheet made of a mixture of ferrite and rubber is known.

However, this rubber sheet has the disadvantage that it is heavy, and due to this, installation using ordinary adhesives is unreliable and construction is difficult.

To improve this drawback, approximately λ/4 is applied to the conductor surface.
A radio wave absorber has been proposed in which a foam with a thickness of (λ is the free space wavelength of the operating center frequency) is placed, and a carbon coating film whose characteristic impedance is approximately equal to 377Ω, which is the characteristic impedance in free space, is provided on the surface of the foam. There is. However, there is a drawback that the characteristic impedance changes greatly with changes in the thickness of the resistive film applied, and that the manufacturing process must be strictly controlled.

In order to improve this drawback, the present applicant previously filed Japanese Patent Application No. 57-92964 for the purpose of providing a radio wave absorber that is easy to manufacture, lightweight, has excellent workability, and has excellent impedance matching. , its feature is that the resistive film, which is composed of conductive fibers arranged in a plane, is placed parallel to the conductor surface at λ7.
We are proposing a radio wave absorber placed at a distance of 4 or less.

(Purpose of the Invention) This invention is a further development of the radio wave absorber proposed by the applicant mentioned above, and its purpose is to provide a radio wave absorber with particularly good radio wave absorption characteristics. The radio wave absorber is characterized in that the electromagnetic wave absorber is provided with a resistive cloth made of conductive fibers or conductive fibers and synthetic fibers on the surface opposite to the surface of a foamed dielectric material provided with a conductor on the surface. The reason is that the spacing between the fibers is λ/4 (λ is the free space wavelength of the operating center frequency) or less.

(Structure and operation of the invention) The present invention will be explained below based on the drawings.

FIG. 1 is a longitudinal cross-sectional view of an embodiment of a radio wave absorber previously proposed by the present applicant. In the figure, IO is a resistive fabric, 12 is an adhesive, 14 is a dielectric foam, and 16 is a conductor. As shown in Fig. 2, the resistance woven fabric is made up of conductive fibers 18 in the warp and conductive fibers 18 in the weft made of conductive single fibers bundled with tens of water and weft conductive fibers 20 woven in a lattice shape with approximately equal spacing. It is a woven fabric. FIG. 3 shows a longitudinal cross-sectional view of the resistive fabric IO.

In addition, in FIG. 2, a woven fabric made of synthetic fibers such as nylon or acrylic may be provided between each conductive fiber. Here, the conductive fiber used is, for example, a synthetic fiber such as nylon or acrylic fiber with a conductive film such as CuS adhered to the surface by a dyeing technique. As shown in FIG. 3, a resin 21 having a dielectric constant of 5 or less, a paint, or an adhesive is coated or impregnated on the surface and inside of the resistance woven body IO. The above-mentioned radio wave absorber was previously proposed by the present applicant, and can provide excellent radio wave absorption characteristics.

Next, one embodiment of the present invention will be described in detail with reference to FIGS. 4 to 7.

FIG. 4 shows a longitudinal sectional view of a radio wave absorber according to an embodiment of the present invention, which has the same structure as the radio wave absorber shown in FIG. 1 except for the structure of the resistance cloth 28. That is, a conductor 26 is provided on one surface of the foamed dielectric 24, and a resistance cloth 28 is provided with an adhesive 22 on the surface of the foamed dielectric 24 opposite to the surface on which the conductor 26 is provided. There is. The feature of this invention is the resistance cloth body 28, which consists of vertical conductive fibers 830 and horizontal conductive fibers in which several tens of conductive fibers are bundled together, as shown in FIG. 32 is a woven fabric body equally woven in a lattice shape at predetermined intervals of λ/4 (λ is the free space wavelength of the operating center frequency) or less, approximately 8 mm in this embodiment. This is because the distance between the conductive fibers and the resistance value are approximately proportional to each other, and the resistance value of the resistance fabric when the distance between the conductive fibers is approximately 8 points is approximately equal to the free space impedance of 377Ω.

In addition, between each conductive fiber is a synthetic material such as nylon or acrylic.
A woven fabric body made of #I may be provided. Also, as the conductive fiber, for example, a conductive film such as CuS is attached on the surface of composite fibers such as nylon and acrylic using a dyeing technique. You can use things.

The surface and interior of the resistance cloth body 28 may be coated with or impregnated with a resin, paint, or adhesive having a dielectric constant of 5 or less.

FIG. 6 shows the above resistance cloth 28 with a thickness of 1
'5mm, 10+sm, and! /8mm polyethylene, shows the frequency characteristics of the amount of reflection when adhered to the surface of the sheet.

The matching frequency is 5GH2 when the thickness is 15mm, l O+u
+ is 9AU, thickness is 8I1m is 13GH.

(1) Shows good characteristics at 5GH when the thickness is 15 layers. Regarding the relationship with the thickness, λ/4 in 5 GH is 15 layers, which agrees with the theory.

(2) Good characteristics are shown at 9GH when the thickness is 1OII11. 9GH, λ/4 is 8.3 mm, which is thicker than the theoretical value.

(3) When wearing shoes with a thickness of 81I, the amount of reflection is about -15dB at 13GH, and 15m+
++, the characteristics are significantly deteriorated compared to the case of 10 mm. The input/4 at 13GH is 5.8m+i.

As described above, when the distance between the conductive fibers approaches λ/4, the thickness of the absorber must be made thicker than the theoretical value, and when it becomes larger than λ/4, the amount of reflection increases and the performance of the absorber deteriorates. Therefore, it can be seen that in order to obtain a thin absorbent material with good characteristics, it is preferable to set the spacing between the conductive fibers to 1/4 or less.

Next, the relationship between the amount of reflection and the frequency when a resistance cloth in which the number of conductive single fibers contained in conductive lA11M is 172 and the interval between conductive fibers is 4 mm is adhered to a foamed polyethylene sheet with a thickness of 6 mm is shown in the seventh figure. As shown in the figure.

Note that λ/4 for a thickness of 12.5 GH is 6 mm.

As can be seen from the figure, good characteristics are shown at 12.5GH1. In this way, if the amount of conductive single fibers contained in a unit area is constant and the interval between the conductive fibers is set to 1/4 or less, a good absorbent body can be obtained.

(Effects of the Invention) As explained above, according to the present invention, it is possible to provide a lightweight radio wave absorber with extremely excellent radio wave absorption characteristics.
It is effective for purposes such as preventing false images from ship masts and other structures, and reducing side lobes of parabolic antennas.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a radio wave absorber previously proposed by the applicant, FIGS. 2 and 3 are diagrams showing the structure of a resistance woven body, and FIG.
The figure is a longitudinal sectional view of a radio wave absorber according to an embodiment of the present invention.
The figure is a diagram for explaining the structure of the resistive fabric body of the radio wave absorber of FIG. 4, and FIGS. 6 and 7 are diagrams showing the absorption characteristics of the radio wave absorber according to the present invention. 24... Foamed dielectric 26... Conductor 28... Resistance cloth Patent applicant TDC Co., Ltd. Patent application agent Megumi Yamaki - 1l&1Fig.0 Condolences 3 1/\ni8 Fig. 4 8 Figure 2 Figure 5

Claims (3)

[Claims] (1) Conductive fibers or conductive m-fibers and synthetic am
What is claimed is: 1. A radio wave absorber provided with a resistive cloth made of woven fabric, characterized in that the spacing between the conductive m fibers is equal to or less than 1/4 (λ is the free space wavelength of the operating center frequency). (2) The radio wave absorber according to claim 1, wherein the conductive fibers are woven in a grid pattern. (3) The radio wave absorber according to claim 1 or 2, wherein the conductive fiber is a nylon or acrylic fiber whose surface has been surface-treated with copper sulfide.