JPS60120597A - 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.

In order to improve this drawback, it is possible to
A radio wave absorber has been proposed in which a foam with a thickness of (input 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.

The disadvantage is that the characteristic impedance changes greatly with changes in the thickness of the resistive film applied, and the manufacturing process must be strictly controlled.

In order to improve this drawback, the present applicant previously filed Japanese Patent Application No. 57-112984 with the aim of providing a radio wave absorber that is easy to manufacture, lightweight, has excellent workability, and has excellent impedance consistency. The authors propose a radio wave absorber in which a resistor consisting of conductive fibers arranged in a planar manner is arranged parallel to the conductor surface and at a distance of less than /4.

(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 resistance cloth made of conductive fibers or conductive fibers and synthetic m fibers on the surface opposite to the surface of a dielectric body provided with a conductor on the surface. The reason is that the series resistance of the conductive fibers is set to 30Ω/m or more.

In this invention, the spacing between the conductive fibers is λ/4
It is preferable that it is below.

(Structure and operation of the invention) Fig. 1 shows a dielectric material 2 having a conductor l provided on the negative side, and conductive fibers or conductive fibers and synthetic fibers woven at predetermined intervals on the surface facing the negative side. A cross-sectional view of a radio wave absorber provided with a resistance cloth body 3 is shown. The sheet resistance of the resistance cloth 3 in such a radio wave absorber is determined by the resistance value and spacing of the conductive fibers, and is theoretically given by the following equation.

Rs=R/n Here, Rs is the sheet resistance (Ω10), R is the resistance of the conductive fiber (07m), and n is the number of fibers stretched over 1m.

FIG. 2 is a diagram showing the sheet resistance when conductive #lims having different resistance values are arranged in a lattice shape at different intervals in the above-described resistor cloth. 0 in the same figure is 0 at R= +14
Measured value for 7 m, fist is measured value for R = 109 and 07 m, Δ is measured value for R = 87 and 07 m, mouth is R
=33 shows the measured values in the case of 07m, and A, B, C, and D show the theoretical values in each case.

The conductive ma used here is one in which a conductive layer of copper sulfide (CuS) is adhered to the surface of an acrylic fiber using a dyeing technique. As is clear from FIG. 2, the sheet resistance of the resistance cloth can be changed to a desired value by adjusting the resistance value and spacing of the conductive fibers.

The measurement results of the radio wave absorption characteristics (reflection amount) in the X-band (8 GHz to 12 GHz) of the radio wave absorber (7) provided with the resistive cloth having the above structure are shown in FIGS. In the same figure, E is the thickness of the dielectric (t)=8+nm, the resistance of the conductive fiber (R)==114 and 07m, and the distance between the conductive fibers (d
) = 3mm; F is t = 8mm, R =
10! IKΩ/m, data when d = 3.5 mm; G is t = 8 mm, R = 8? 07m, d
Data when = 5.5mm; H is t = 9mm, R = 3
3 is the data when Ω/m and d=6 mm. As is clear from FIG. 3, the radio wave absorbers (E, F, G) with R=07m at +14, 07m at 10θ, and 07m at +17 exhibit extremely wide-band characteristics. In the case of R-33 and 07m radio wave absorber (H), the band is narrower than in the above three cases, but a reflection amount of 20 dB or less can be obtained. Although not shown, measurements were also carried out using conductive fibers with R = 30 and Ω/m or less, but a reflection amount of less than 20 dB could not be obtained and the fiber was unsuitable as a radio wave absorber.

From the above, it is understood that a radio wave absorber using conductive fibers with a resistance value of 30 Ω/m or more has good broadband absorption characteristics. Note that if the resistance value of the conductive fiber is too large, the stability of the resistance of the conductive fiber will be lost and it will be difficult to obtain the characteristics of the absorber, so it is preferably up to about 500.07 m. Furthermore, if the spacing is greater than or equal to 1/4, the thickness of the absorber becomes thicker and the specific band becomes narrower, so it is desirable that the spacing is less than or equal to 1/4.

FIG. 4 is a diagram showing data of a radio wave absorber according to an embodiment of the present invention, which has very wide-band characteristics. This radio wave absorber consists of a resistor 108 and a conductive fiber of 3.5 mm long.
It is constructed by adhering resistor cloth arranged at intervals of .about.0.5 mm to the opposite surface of a 7.5 mm thick dielectric material provided with a conductor on one surface.

Furthermore, this radio wave absorber is extremely lightweight with a maximum weight of 500g/m2.

In the above examples, conductive fibers made by adhering copper sulfide (CuS) to the surface of acrylic fibers were used, but the conductive fibers that can be used in the present invention are not limited to this, and for example, Nylon fibers coated with copper sulfide or other conductive layers can also be used. Further, if the dielectric material l is made of foam, it will be more lightweight, but it may be made of a hard material.

(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 the drawing]

Fig. 1 is a cross-sectional view of the radio wave absorber of the present invention, Fig. 2 is a diagram showing the relationship between the sheet resistance of the resistive cloth and the spacing between conductive fibers, and Fig. 3 is a diagram showing the relationship between the sheet resistance of the resistive cloth and the spacing between the conductive fibers. FIG. 4 is a diagram showing the frequency characteristics of the amount of reflection of the radio wave absorber according to an embodiment of the present invention. 1-m-dielectric 2-m-conductor 3-11 resistance cloth Qin l Zudo + d8 + 2nd Leap conductive rare transfer rumor (egg) Tool 3 closed O "□□ Ichitsu J Kanto -

Claims (3)

[Claims] (1) A radio wave absorber in which a resistive cloth made of conductive fibers or conductive fibers and synthetic fibers is provided on the surface of a dielectric material having a conductor provided on its surface opposite to the surface thereof. A radio wave absorber characterized in that the DC resistance of the fiber is 30Ω/m or more. (2) The radio wave absorber according to claim 1, characterized in that the conductive fibers are bordered in a lattice shape at intervals of 1/4 (where 1 is the free space wavelength of the operating center frequency) or less. . (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.