JP4319422B2 - Manufacturing method of radio wave absorber - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave absorber and a method for manufacturing the same, and relates to a radio wave absorber that has a simple structure and can be easily manufactured, and a method for manufacturing the same.
[0002]
[Prior art]
[Patent Document 1]
JP 2000-174544 A [Patent Document 2]
Japanese Patent Laid-Open No. 2000-261240
In recent years, the use range and use frequency of wireless communication using electronic devices has increased, and unnecessary radiation of radio waves generated due to higher frequency of signals used has increased, and the radio wave environment has also deteriorated accordingly. Under such circumstances, the demand for radio wave absorbers used for improving the radio wave environment is increasing, and various radio wave absorbers have been considered so far. If a magnetic loss material such as ferrite or a conductive loss material such as a resistance film is used, or a complicated structure such as a multilayer structure is used, a radio wave absorber having a good radio wave absorption characteristic can be obtained. However, since expensive materials are used and many processes and complicated and precise processing are required, there is a disadvantage that the cost is increased, which has hindered the spread of radio wave absorbers.
[0004]
[Problems to be solved by the invention]
The present invention seeks to obtain a radio wave absorber that can be manufactured with an inexpensive material, a simple structure, and a small number of man-hours, thereby providing a radio wave absorber that is inexpensive and easy to manufacture.
[0005]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems by using a sponge and a liquid containing carbon black, such as ink, as a material, thereby obtaining a sponge having a carbon black concentration gradient. That is, a radio wave absorber made of a sponge containing dispersed carbon black is characterized by having a carbon black concentration gradient from the front surface to the back surface of the sponge.
[0006]
In addition, in the method of manufacturing a radio wave absorber composed of a sponge containing dispersed carbon black, a liquid containing carbon black is dropped from the surface of the sponge, and there is a difference between the concentration of carbon black on the surface and the concentration of carbon black inside. In this state, the dropping is stopped, and the sponge is dried to form a sponge having a carbon black concentration gradient. Instead of dripping, a method by dipping may be used.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The wave absorber according to the present invention basically comprises a sponge and carbon black contained therein. The concentration of carbon black is not uniform, and a concentration gradient is provided from one surface to the opposite surface so as to gradually change from a high concentration to a low concentration.
[0008]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are front views showing a method of manufacturing a radio wave absorber according to the present invention. FIG. 1 is a dropping method and FIG. 2 is a dipping method. In the dropping method shown in FIG. 1, black ink 12 which is a liquid containing carbon black is dropped on the surface of a rectangular sponge 11 cut into a predetermined shape. Although the ink 12 penetrates from the surface of the sponge 11 to the inside, the concentration of carbon black is the highest on the surface and becomes lower as it goes inside. If dripping is stopped in this state and the sponge is dried, carbon black remains in the state when dripping is stopped inside the sponge.
[0009]
In the dipping method of FIG. 2, the lower surface of a rectangular sponge 21 cut into a predetermined shape is dipped in ink 22 which is a liquid containing carbon black. The ink 22 penetrates from the lower surface of the sponge 21 to the inside, but the concentration of carbon black is the highest on the surface (in this example, the lower surface), and decreases as it goes inside. When the immersion is stopped in this state and the sponge is dried, the carbon black remains in the state when the immersion is stopped inside the sponge. In this way, a carbon black concentration gradient is formed inside the sponge.
[0010]
FIG. 3 is a front view showing a state in which the radio wave absorber according to the present invention attached to the metal plate 33 is used. As shown in the figure, radio waves are made incident from the surface having the lower carbon black concentration as the surface. The radio wave travels while gradually attenuating from a low concentration region close to air toward a high carbon black concentration region. The change of the radio wave impedance becomes gentle with respect to the traveling direction of the radio wave, and since there is no sudden discontinuity, the reflection is reduced, and as a result, an excellent radio wave absorption performance is obtained.
[0011]
The characteristics of the radio wave absorber according to the present invention were measured with the apparatus shown in FIG. A radio wave absorber was prepared by the above method using a 12 mm thick sponge and commercially available ink. The radio wave absorption characteristics were measured using the reflected power method in the frequency range of 55 to 65 GHz in the measurement environment shown in FIG. The size of the wave absorber is 80 × 80 mm, the distance between the antenna and the wave absorber is 300 mm, and the incident angle of the radio wave is 5 °.
[0012]
FIG. 5 shows the result of the element uniformly impregnated with Chinese ink, that is, no concentration gradient, and FIG. 6 shows the result of the element according to the present invention. As shown in FIG. 5, uniform results obtained 15 dB or more in the range of 58 to 64 GHz and over 20 dB in the range of 61 to 62 GHz. On the other hand, the results according to the present invention exceeded 20 dB over the entire measurement range, and exceeded 25 dB near 60 GHz. This indicates that applying a concentration gradient broadens the frequency range where good absorption characteristics can be obtained, and the maximum amount of absorption is improved by about 5 dB.
[0013]
【The invention's effect】
Since the radio wave absorber according to the present invention uses only an inexpensive sponge and a liquid containing carbon black (for example, ink) as a material, it can be manufactured at a very low cost and with a small number of man-hours. Since the concentration gradient of carbon black is formed, the change in the radio wave impedance becomes gentle with respect to the traveling direction of the radio wave, so that the abrupt discontinuity disappears and the reflection is reduced. As described above, according to the present invention, excellent radio wave absorption characteristics can be obtained by the synergistic effect of the dielectric loss of carbon black as well as the reduction of reflection.
[Brief description of the drawings]
1 is a front view showing an embodiment (manufacturing method) of the present invention. FIG. 2 is a front view showing another embodiment (manufacturing method) of the present invention. FIG. 3 shows an embodiment (structure) of the present invention. Front view [FIG. 4] A perspective view showing a method of measuring the characteristics of the radio wave absorber [FIG. 5] An explanatory diagram of the characteristics of the radio wave absorber having a uniform concentration [FIG. 6] An explanatory diagram of the characteristics of the radio wave absorber according to the present invention Explanation of]
11, 21, 31: Sponge (radio wave absorber)
12, 22: Ink
33: Metal plate

Claims (2)

  In a method of manufacturing a radio wave absorber comprising a sponge containing dispersed carbon black, a liquid containing carbon black is dropped from the surface of the sponge, and there is a difference between the concentration of carbon black on the surface and the concentration of carbon black inside. A method for producing a radio wave absorber, wherein dripping is stopped and the sponge is dried to form a sponge having a carbon black concentration gradient.   In a method of manufacturing a radio wave absorber comprising a sponge containing dispersed carbon black, the lower surface of the sponge is immersed in a liquid containing carbon black, and there is a difference between the concentration of carbon black on the lower surface and the concentration of carbon black inside. A method of manufacturing a radio wave absorber, wherein immersion is stopped and the sponge is dried to form a sponge having a carbon black concentration gradient.

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