JPH0399496A - Radio wave absorber - Google Patents

Abstract

PURPOSE:To obtain a radio wave absorber which is excellent in reflection property and applicable for radio waves of high power by a method wherein heat resistant base materials are formed into a multilayer, that is, the multilayer is composed of a ceramic or an inorganic binder layer, glass fiber layer, a carbon layer, a glass fiber layer, a carbon layer, and a ceramic or an inorganic binder, which are laminated in this order starting from a plane on which radio waves are incident. CONSTITUTION:When a carbon layer 13 used as a matching layer is formed into a plane board, the carbon density of it is so set as to make the transmission loss of radio waves which are vertically incident on it equal to about 14dB or above. Glass fiber layers 12 and 14 are utilized to enable carbon layers 13 and 15 to be mechanically stable in structure, and ceramic layers 11 and 16 are used as surface layers to constitute a radio wave absorbent of this design. By this constitution, a radio wave absorber becomes excellent in reflection property.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio wave absorber that can be used for high power applications.

[Prior Art] Fig. 5 is a perspective view showing a conventional radio wave absorber, and in Fig. 9, (1) is a flat foamed polyurethane base material formed into a pyramid shape and impregnated with carbon as a resistor. It is a resistance chain wheel layer type absorber.

Next, the operation will be explained.

When a radio wave is incident on the pyramidal equal-resistance chain wheel layer absorber (1), the energy of the electromagnetic wave is converted into thermal energy and absorbed due to the ohmic loss of carbon.

With this radio wave absorber, the characteristic impedance of the absorber viewed from space can be changed sequentially from low impedance to high impedance by making the shape pyramid-shaped, so it can have good reflection characteristics over a wide band, and The angle-dependent reflection characteristics are also better than that of a flat radio wave absorption band.

The height of the pyramid is usually required to be at least 9 wavelength A, which is the lower limit frequency of use, and the larger the height and the smaller the opening angle of the tip of the pyramid, the lower the reflection characteristics can be.

The conventional radio wave absorber constructed as described above uses polyurethane as a base material, and therefore has poor heat resistance.

Figure 6 shows an experimental example where the power density is 0.12W/c.
It shows the surface temperature of a radio wave absorber versus time when a continuous wave of m'' is radiated onto the radio wave absorber.

Since it reaches the upper limit temperature at which polyurethane begins to age in about 10 seconds, it cannot be used as a radio wave absorber for applications that require higher power.

[Problem to be Solved by the Invention 1] The conventional radio wave absorber is constructed as described above and uses polyurethane as the base material.

It cannot be used above the upper limit temperature of 160° C. at which polyurethane begins to age, and has problems such as being extremely sensitive to heat and not being able to be used for high power applications.

This invention was made to solve the above-mentioned problems, and aims to obtain a radio wave absorber that can be used for high power applications and has good reflection characteristics.

[Means for Solving the Problems] The radio wave absorber according to the present invention has a multilayer structure using a heat-resistant base material, and includes, in order from the radio wave incident surface, a ceramic or inorganic binder layer, a glass fiber layer, It is composed of a carbon layer, a glass fiber layer, a carbon layer, a ceramic or inorganic binder layer, etc.

[Function] The radio wave absorber of the present invention uses a heat-resistant base material and has a multilayer structure, so that it is nonflammable even when used for high power applications and has excellent mechanical strength. By configuring the carbon layer as a resistor in a multilayer structure including a matching layer and an absorbing layer, a radio wave absorber with good reflection characteristics can be obtained.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a cross-sectional view showing one embodiment of the present invention, and FIG. 1(b) is a cross-sectional view showing a nine-layer structure.

In FIG. 1(a) (bl), (11) is a layer using a ceramic or inorganic binder, (12) is a glass fiber layer, and (13) is a carbon layer used as a matching layer.

(14) is a glass fiber layer, (15) is a carbon layer as an absorber layer, and (16) is a layer using a ceramic or inorganic binder layer.

Next, the operation will be explained.

When a radio wave is incident, it is absorbed by the ohmic loss of the carbon layer of the resistance layer in the same manner as a conventional radio wave absorber.

In this example, a carbon layer (1
3) When the carbon layer (15) used as the absorber layer is used as a flat plate, the density of carbon is selected so that the transmission loss of radio waves incident perpendicularly to it is approximately 1 dB. The density of carbon is selected so that the transmission loss of radio waves incident perpendicularly to it is approximately 14 dB or more.
In addition, in order to make the carbon layers (13) and (15) mechanically stable, glass fiber layers (12) and (14) are used.
Ceramic layers (11) and (1
6).

FIG. 2 is a diagram showing the frequency-dependent reflection characteristics of a radio wave absorber in an embodiment of the present invention.

FIG. 3 is a diagram showing the reflection characteristics with respect to the incident angle of radio waves. In FIG. 3, (a) shows the reflection characteristics of the radio wave absorber of the present invention, and (b) shows the reflection characteristics of the conventional radio wave absorber.

It is clear from the figure that the radio wave absorber according to the present invention has good 1 reflection characteristics.

FIG. 4 shows the surface temperature of the radio wave absorber with respect to time when a continuous wave with a power density of 0.8 W/cm2 is radiated onto the radio wave absorber according to the present invention.

Even after about 60 minutes, the temperature remained at about 160°C, which shows that the heat resistance has been significantly improved with a large amount of power compared to the conventional one.

The characteristics shown in FIG. 4 are test results under a heat dissipation state by natural convection, and there is no need to perform forced air cooling.

In the above embodiments, the shape of the radio wave absorber is described as being pyramidal, but the same effect can be obtained even if the radio wave absorber is configured to have a flat plate shape or any other shape.

In addition, in the above embodiment, the carbon layer (13) used as a matching layer and the carbon layer (15) used as an absorber layer were shown, but only the carbon layer (15) used as an absorber layer was shown. It may be configured by providing.

In this case, the reflection characteristics with respect to the angle of incidence of radio waves are only slightly worse than those composed of carbon layers (13) and (14), and it goes without saying that it can be used for high power applications.

[Effect of the invention 1 As described above, according to the present invention, a heat-resistant base material is used to form a multilayer structure, and radio waves are transmitted sequentially from the incident surface to a ceramic or inorganic binder layer, a glass fiber layer, a carbon layer, and a glass fiber layer. Since it is composed of a fiber layer, a carbon layer, a ceramic or inorganic binder layer, etc., a radio wave absorber with good reflection characteristics can be obtained, and it can also be used for high power applications.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are cross-sectional views showing one embodiment of the present invention, FIG. 2 is a diagram showing the reflection characteristics with respect to frequency of one embodiment of the present invention, and FIG. 3 is a diagram showing one embodiment of the present invention. FIG. 4 is a diagram showing the surface temperature versus time according to an embodiment of the present invention, FIG. 5 is a perspective view of a conventional radio wave absorber, and FIG. 6 is a diagram of a conventional radio wave absorber. FIG. 3 is a diagram showing the surface temperature of a radio wave absorber versus time. In the figure, (1) is a uniform resistance chain wheel layered absorber. (Ill and (16) are layers using ceramic or inorganic binder layers, (12) and (14) are glass fiber layers, and (13) and (15) are carbon layers. Parts are shown with the same reference numerals.

Claims (2)

[Claims] (1) In a radio wave absorber in which a resistor is provided on a base material of arbitrary shape, from the radio wave incident surface, a ceramic or inorganic binder layer, a glass fiber layer, a carbon layer as a resistance layer, and then a ceramic or inorganic binder layer are used as the resistance layer. A radio wave absorber comprising a binder layer. (2) In a radio wave absorber in which a resistor is provided on a base material of an arbitrary shape, in order from the radio wave incident surface, a ceramic or inorganic binder layer, a glass fiber layer, a carbon layer as a matching layer, a glass fiber layer, and a resistance layer. 1. A radio wave absorber comprising a carbon layer and a ceramic or inorganic binder layer.