JPH0515491U - Broadband wave absorber - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an electromagnetic wave absorbing device having a wide band electromagnetic wave absorbing property, which can also be used for improving the characteristics of an existing electromagnetic wave absorbing device. [Structure] A sintered ferrite magnetic material (F), a resistance film (RS), a low dielectric constant dielectric material (LD) and a low magnetic permeability magnetic material (RF) are sequentially laminated on a reflection plate (C). Broadband electromagnetic wave absorber.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a multi-layered electromagnetic wave absorber using a sintered ferrite magnetic material or the like, and more particularly to a broadbanded electromagnetic wave absorber.

[0002]

[Problems to be solved by conventional techniques and devices]

 As an electromagnetic wave absorbing wall material for an anechoic chamber for measuring electromagnetic waves emitted from electronic equipment and a wall material for preventing reflection of TV electromagnetic waves from a building, it is necessary to properly absorb electromagnetic waves in a wide frequency band. In this respect, the radio wave absorber using the sintered ferrite magnetic material has an excellent characteristic of absorbing radio waves from a low frequency, for example, about 30 MHz, while having a thickness of about 5-8 mm.

FIG. 7 shows the most basic structure of a ferrite electromagnetic wave absorber, which is formed by backing a sintered ferrite magnetic material F having a thickness d with a metal conductor plate C (HANS WILHE LM). HELBERG "Die Absorption electromagnetischer Wellen in einem grossen Frequenzbereich durch eine duenne homogene Sehicht mit Velusten" Zeitschrifit fuer angewandte Physik, XIII Band Heft 5-1961, P237-245; Sue Take et al. "Magnetic Resistive Film Absorption Wall" Electronic Communication Society Microwave Research Group 1967.1; Japanese Patent Publication No. 43-26143). When the electric field reflection coefficient of the surface of the ferrite magnetic body F in this configuration is s, the power absorption coefficient of the radio wave absorber can be expressed as 1- | s | ² . Therefore, it can be said that the smaller | s |, the better the absorber. Normally, | s | ≦ 0.1, that is, the absorption coefficient ≧ 0.99 is adopted as a guide.

FIG. 8 shows the absorption characteristics of the radio wave absorber shown in FIG. 7 with the horizontal axis representing the frequency f and the vertical axis representing the magnitude of the reflection coefficient | s |. In this case, | s | = 0.1. If the lower one of the two frequencies is fl and the higher one is fh, the frequency band B satisfying | s | = 0.1 is B = fh-fl Can be represented. The relationship between this frequency band B and the material that realizes it is as follows.

(A) When fl is set to 30 MHz, the ferrite to be used is of the sintered type and is of the NiZn type or the MnZn type. According to this, fh becomes 300-400MHz.

(B) When fl is set to 90 MHz, the ferrite to be used is also of the sintered type, in which case fh is 350-520 MHz.

Among these, (a) is intended for a wall material of an anechoic chamber, and fh = 1000 MHz is required for fl = 30 MHz, but this cannot be satisfied. In the case of (b), a wall material for buildings for absorbing TV radio waves is assumed, and fl = 90MHz and fh = 800MHz are required, but these cannot be satisfied. Fig. 9 shows this improvement (Naito et al., "One Broad Band of Ferrite Absorption Wall," Institute of Electronics and Communication Engineers, Microwave Research Group 1968.1; HANS WILHELM HELBERG, "Die breitbandige Absorption electromagnetischer Wellen durch duenne Ferritschichten" Zeitschrifit. fuer angewandte Physik, XIX Band Heft 6-1965, p509-514; refer to Japanese Patent Laid-Open No. 1-101605), and the ferrite F in FIG. d2, one of the d1 is attached to the metal reflection plate, and the other d2 is arranged with a space Po. The space Po is filled with air.

According to this configuration, it has been found that fh = 1000 MHz at fl = 30 MHz or fh = 800 MHz at fl = 90 MHz. The ferrites F1 and F2 may have the same characteristics or may have slightly different characteristics. Sintered ferrite with a magnetic permeability of about 500 is used when the same characteristics are used, and sintered ferrite with a magnetic permeability of 500 is used as F1 and a magnetic permeability of 200 is used as F2 when different materials are used. The overall characteristics are almost the same as those of the above (see "Naito et al.," One Broad Band of Ferrite Absorption Wall, "Institute of Electronics and Communication Engineers, Microwave Research Group 1968.3).

This improved product has not been put to practical use for the following reason. This is because both the ferrites F1 and F2 are sintered ferrites, and if the predetermined area is constructed by this method, the number of materials of the sintered body will be doubled and the cost will be increased.

FIG. 10 shows another conventional example for widening the band, in which the dielectric D is inserted between the metal conductor plate C and the ferrite F. In this case, fl = 30 MHz and fh = 1000 MHz are gradually obtained (“HANE WILHELM HELBERG” “Die Absorpti on electromagnetischer Wellen in einem duenne Materialschieht in Kleinem Abstand vor einer Metallfaeche” Zeitschrifit fuer angewandte Physik, XVI Band Heft, XVI Band Heft -220; Japanese Patent Publication No. 50-4423; U.S. Pat. No. 3,754,225, Aug. 21,1973; Japanese Patent Laid-Open No. 2-35797; Hashimoto et al., "Practical Design of Simple Small Anechoic Chamber Using Ferrite" S. Abdul lah Mirtaheri et al. “Widening the Bandwidth of Ferrite Absorbing Wall by Adding a Dielectric layer” 1991 IEICE Spring See National Convention B-290).

The maximum frequency fh is currently set to 1000 MHz, but if the operating frequency of electronic equipment, such as the clock frequency of a personal computer, becomes higher in the future, the radiated radio waves generated by it will reach higher frequencies, Inevitably fh will be higher than 1000MHz.

Based on such an idea, a radio wave absorber of the type shown in FIGS. 11 and 12 has been provided (Japanese Patent Application No. 3-). 11 shows the one shown in FIG. 7 with the dielectric D and the rubber ferrite RF provided on the front surface, and FIG. 12 shows the one shown in FIG. 10 with the dielectric D and the rubber ferrite RF provided on the front surface. However, the frequency band of these is not wide enough.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an electromagnetic wave absorber having a wide band electromagnetic wave absorption characteristic, which can be used for improving the characteristics of an existing electromagnetic wave absorber. To aim.

[0014]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention provides a broadband electromagnetic wave absorbing device in which a sintered ferrite magnetic material, a resistance film, a low dielectric constant dielectric material and a low magnetic permeability magnetic material are sequentially stacked on a reflector. It is a thing.

[0015]

[Action]

 The radio wave from the radio wave source propagates toward the reflection plate, and sequentially passes through the low-permeability magnetic material, the low-dielectric-constant dielectric material, the resistance film, and the sintered ferrite in the middle. Radio waves are absorbed in this process. The function is that the resistance film functions from low frequency to high frequency as a whole, and at low frequencies, the low-permeability magnetic material itself has almost no effect, and the sintered ferrite with high magnetic permeability also acts to absorb radio waves. To do. On the other hand, in the high frequency range, especially in the frequency range exceeding 1500 MHz, the sintered ferrite, the low dielectric constant dielectric material and the low magnetic permeability magnetic material cooperate to absorb the radio wave. Therefore, electromagnetic waves are absorbed over a wide band from low frequencies to high frequencies.

[0016]

[Effect of the device]

 A broadband electromagnetic wave absorber was constructed by sequentially stacking a sintered ferrite magnetic material, a resistance film, a low dielectric constant dielectric material, and a low magnetic permeability magnetic material on the reflector plate. It is possible to provide a radio wave absorber having the same.

In this radio wave absorber, a laminated body including a resistance film, a low dielectric constant dielectric substance and a low magnetic permeability magnetic substance is added to an existing radio wave absorber having a sintered ferrite magnetic body as a surface element. As a result, a broadband radio wave absorber can be configured.

[0018]

【Example】

 FIG. 1 shows the configuration of an embodiment of the present invention, in which a sintered ferrite magnetic material F, a resistance film RS, a low dielectric constant LD and a low magnetic permeability RF are superposed on a reflection plate C. It was done.

FIG. 2 shows the measured characteristics of the embodiment having the configuration of FIG. 1, in which a sintered ferrite magnetic material F having a thickness of 6.6 mm is arranged on the front surface of the reflection plate C, and a surface resistance of 1900 (Ω). The resistance film RS of □) and the air layer having a thickness of 20, 28, and 35 mm are arranged, and further, the rubber ferrite RF having a thickness of 2.4 mm is arranged. It can be seen that among these three characteristics, when the thickness is 28 mm, the attenuation of 20 dB or more is obtained over the widest range.

FIG. 3 shows measured characteristics of the configuration of FIG. 1 with the resistive film removed. This is a narrow frequency band, as is clear from comparison of the characteristics of FIG. That is, in the case where there is no resistive film, the return loss becomes -20 dB or more from 30 MHz to 1200 MHz, but with the resistive film, it spreads to 1600 MHz.

FIG. 4 shows an embodiment in which an air layer serving as a dielectric D1 is provided between the reflecting plate C and the sintered ferrite F in the configuration of FIG.

FIG. 5 shows the measured characteristics of the configuration of FIG. 4, in which the thickness of the low dielectric constant dielectric material D2 between the resistance film RS and the low magnetic permeability magnetic material RF is 30 mm, 32. It shows each return loss characteristic when it is set to 2 mm and 35 mm. The return loss of 20 dB or more has the maximum frequency width when D2 is 32.2 mm.

FIG. 6 shows measured characteristics of the structure having the characteristics shown in FIG. 5 except for the resistance film RS. Also in this case, the respective return loss characteristics are shown when the thickness of the low dielectric constant LD2 between the sintered ferrite F and the low magnetic permeability RF is 40 mm, 52.5 mm and 60 mm. ing. That is, it can be seen that the band is widened from 30 MHz to 1600 MHz when the resistance film is used, while it is −20 dB or more up to 30 MHz when the resistance film is not used. This shows the usefulness of the resistance film RS.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is the embodiment of FIG.

3 is a measured characteristic diagram when the resistive film is removed from FIG.

FIG. 4 is a sectional view showing another embodiment of the present invention.

FIG. 5 shows the embodiment shown in FIG.

FIG. 6 is a measured characteristic diagram when the resistance film is removed from FIG.

FIG. 7 is a cross-sectional view showing the configuration of the most basic ferrite electromagnetic wave absorber.

8 is a characteristic diagram showing the absorption characteristics of the radio wave absorber shown in FIG. 7 with the horizontal axis representing frequency f and the vertical axis representing the magnitude of reflection coefficient | s |.

FIG. 9 is a cross-sectional view of an improvement of the configuration shown in FIG.

FIG. 10 is a cross-sectional view showing another conventional example of wide band.

11 is a cross-sectional view of what is shown in FIG. 7 with a dielectric D and rubber ferrite RF provided on the front surface.

12 is a cross-sectional view of what is shown in FIG. 10 with a dielectric D and a rubber ferrite RF provided on the front surface.

[Explanation of symbols]

 C Metallic reflector D Dielectric F Sintered ferrite magnetic material RF Low permeability magnetic material RS Resistive film

Claims (6)

[Scope of utility model registration request] 1. A broadband electromagnetic wave absorbing device comprising a reflective plate, a sintered ferrite magnetic material, a resistance film, a low dielectric constant dielectric material, and a low magnetic permeability magnetic material, which are sequentially stacked on top of each other. 2. The radio wave absorber according to claim 1, wherein a dielectric is arranged between the reflector and the sintered ferrite magnetic body. 3. The radio wave absorber according to claim 1, wherein the resistance film has a surface resistance per unit area of 900 (Ω □) or more. 4. The radio wave according to claim 1, wherein the sintered ferrite magnetic body and the low-permeability magnetic body have a relationship of satisfying μ1 ≧ 25 · μ2 when the DC permeability is μ1 and μ2, respectively. Absorber. 5. The apparatus according to claim 1, wherein the sintered ferrite magnetic body has a magnetic permeability of 500 at direct current.
The electromagnetic wave absorber described above. 6. The radio wave absorber according to claim 1, wherein the low-permeability magnetic body has a magnetic permeability of 20 or less at direct current.