JP2556571Y2 - Broadband radio wave absorber - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber having a multilayer structure using a sintered ferrite magnetic material or the like, and more particularly to a radio wave absorber having a wide band characteristic.

[0002]

2. Description of the Related Art As an electromagnetic wave absorbing wall material for an anechoic chamber for measuring an electromagnetic wave radiated from an electronic device and a wall material for preventing reflection of a TV electric wave from a building, there are wide materials. It is necessary to absorb radio waves in the frequency band well. In this regard, the radio wave absorber using the sintered ferrite magnetic material has excellent characteristics of absorbing radio waves from a low frequency, for example, about 30 MHz, while having a thickness of about 5 to 8 mm.

FIG. 7 shows the most basic structure of a ferrite electromagnetic wave absorber, in which a sintered ferrite magnetic material F having a thickness d is lined with a metal conductor plate C (see HANS W).
“Die Absorption electromagnetisch” by ILHELM HELBERG
er Wellen in einem grossenFrequenzbereich durch ei
ne duenne homogene Sehicht mit Velusten ”Zeitschrifit fuer angewandte Physik, XIII Band Heft
5-1961, P237-245; Suetake et al., "Magnetic Resistive Coating Absorbing Wall", The Institute of Electronics, Communications and Engineers, 1967.1;
-26143). Assuming that 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. In the normal case, | s | ≦ 0.1, that is, absorption coefficient ≧ 0.99, is adopted as a standard.

FIG. 8 shows the absorption characteristics of the radio wave absorber shown in FIG. 7 with the frequency f on the horizontal axis and the reflection coefficient | s | on the vertical axis. In this case, of the two frequencies where | s | = 0.1, the lower one is fl and the higher one is f
Assuming that h, the frequency band B satisfying | s | = 0.1 can be expressed as B = fh-fl. The relationship between this frequency band B and the material for realizing it is as follows.

(A) When fl is set to 30 MHz,
Ferrite to be used is sintered type, NiZn type or MnZn
System. According to this, fh is 300-400MHZ
z.

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

[0007] Of these, (a) assumes a wall material of an anechoic chamber.
000MHz is required but cannot be met. In the case of (b), a wall material for a building for absorbing TV radio waves is assumed, where fl = 90 MHz and fh = 800 MHz.
z is required but cannot be met.
FIG. 9 is a diagram of this improvement (Naito et al., "One-band broadening of ferrite absorption wall", The 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;
7, the ferrite F in FIG. 7 is divided into two parts, F1 and F2, as shown in the figure, and the thicknesses are d1 and d2, respectively. And place d2 on the other side. The space Po is filled with air.

[0008] According to this configuration, at fl = 30 MHz, fh
= 1000MHz or fl = 90MHz and fh = 800
MHz has been found to be satisfactory. Ferrite F1 and F
2 may have the same characteristics or may have slightly different characteristics. When the same ferrite is used, it is a sintered ferrite having a magnetic permeability of about 500. When different ferrites are used, a sintered ferrite having a magnetic permeability of 500 as F1 and a magnetic permeability of 200 as F2 are used. And the overall characteristics are almost the same (Naito et al., "One-band broadening of ferrite absorption wall", The Institute of Electronics, Communication Engineers, Microwave Research Group 19)
See 68.3).

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

FIG. 10 shows another conventional example of widening the band, in which a dielectric D is inserted between a metal conductor plate C and a ferrite F. In this case, fl = 30
MHz, fh = 1000MHz is finally obtained (HANS WILHEL
M Die Absorption electromagnetischer We by M HELBERG
llen in einem duenne Materialschieht in KleinemAbs
tand vor einer Metallfaeche ”Zeitschrifit fuer a
ngewandte Physik, XVI Band Heft 4-1963, P214-220;
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 Compact Anechoic Chamber Using Ferrite", IEICE, Vo1.J73-
B No. 8 P421-431 (Heisei 2-08); S. Abdullah Mirtaheri et al., “Widening the Bandwidth of Ferrite Absorbing”
Wall by Adding a Dielectric layer ”(see 1991 IEICE Spring Conference B-290).

The maximum frequency fh is currently set to 1000 MHz, but if the operating frequency of electronic equipment, for example, the clock frequency of a personal computer, becomes higher in the future, the radiated radio waves generated thereby will spread over higher frequencies. Inevitably, fh will be higher than 1000 MHz.

Based on such a concept, a radio wave absorber of the type shown in FIGS. 11 and 12 has been provided (Japanese Patent Application No. 3-129509). FIG. 11 shows the structure shown in FIG. 7 in which a dielectric D and a rubber ferrite RF are provided on the front surface, and FIG. 12 shows the structure shown in FIG. 10 in which a dielectric material D and a rubber ferrite RF are provided on the front surface. However, these do not have a sufficiently wide frequency band.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a radio wave absorbing device having a wide band radio wave absorbing characteristic and which can be used for improving the characteristics of an existing radio wave absorbing device. Aim.

[0014]

In order to achieve the above object, in the present invention, a sintered ferrite magnetic material, a resistive film, a low dielectric constant dielectric material and a low magnetic permeability magnetic material are sequentially laminated on a reflector. A broadband radio wave absorber.

[0015]

The radio wave from the radio wave source propagates toward the reflector and passes through the low magnetic permeability magnetic material, low dielectric constant dielectric, resistance film and sintered ferrite in the middle. In this process, radio wave absorption is performed. The effect is that the resistive film functions from low to high frequencies as a whole, and at low frequencies, the low-permeability magnetic material itself has almost no effect and the sintered ferrite with high permeability also acts to absorb radio waves. Do. On the other hand, in a high frequency range, particularly in a frequency range exceeding 1500 MHz, sintered ferrite, a low dielectric constant dielectric and a low magnetic permeability magnetic material cooperate to absorb radio waves. Therefore, radio wave absorption over a wide band from low frequency to high frequency is performed.

[0016]

[Effect of the Invention] A broadband radio wave absorber is formed by sequentially laminating a sintered ferrite magnetic material, a resistive film, a low dielectric constant dielectric material and a low magnetic permeability magnetic material on a reflector, and especially by the presence of the resistive film. It is possible to provide a radio wave absorber having a wide band frequency characteristic.

This radio wave absorber is formed on an existing radio wave absorber having a sintered ferrite magnetic material as a surface element.
By adding a laminate composed of a resistive film, a dielectric having a low dielectric constant, and a magnetic material having a low magnetic permeability, a broadband radio wave absorber can be formed.

[0018]

FIG. 1 shows the structure of an embodiment of the present invention, in which a sintered ferrite magnetic material F and a resistive film R are formed on a reflector C.
S, a low-permittivity dielectric LD and a low-permeability magnetic body RF are superimposed.

FIG. 2 shows the measured characteristics of the embodiment having the structure shown in FIG. 1. A sintered ferrite magnetic material F having a thickness of 6.6 mm is arranged on the front surface of the reflector C, and the sheet resistance is 1900 (Ω). □), a resistance film RS, an air layer having a thickness of 20, 28, and 35 mm are provided, and a rubber ferrite RF having a thickness of 2.4 mm is further provided. Among these three characteristics, when the thickness is set to 28 mm, attenuation of 20 dB or more is obtained over the widest range.

FIG. 3 shows measured characteristics obtained by removing the resistive film from the configuration of FIG. This is narrow in the frequency band, as is clear from the comparison of the characteristics in FIG.
That is, when there is no resistive film, the amount of return loss becomes -20 dB or more from 30 MHz to 1200 MHz, but if there is a resistive film, it spreads to 1600 MHz.

FIG. 4 shows an embodiment in which an air layer as a dielectric D1 is provided between the reflector 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-permittivity dielectric D2 between the resistive film RS and the low-permeability magnetic material RF is 30 mm, 32.2 mm. , 3
It shows the return loss characteristics when the distance is 5 mm. The return loss of 20 dB or more has the maximum frequency width when D2 is 32.2 mm.

FIG. 6 shows the measured characteristics of the configuration having the characteristics shown in FIG. 5 but excluding the resistance film RS. Also in this case, the sintered ferrite F and the low-permeability magnetic material R
F, the thickness of the low dielectric constant dielectric LD2 is 40 mm,
The graph shows the respective return loss characteristics at 52.5 mm and 60 mm. That is, up to 30 MHz is -20 dB or more without using a resistive film.
It can be seen that the band extends from z to 1600 MHz. This indicates the usefulness of the resistance film RS.

[Brief description of the drawings]

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

FIG. 2 is an embodiment of FIG.

FIG. 3 is an actual measurement 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.

6 is an actual measurement characteristic diagram when the resistive film is removed from FIG.

FIG. 7 is a 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 frequency f on the horizontal axis and the reflection coefficient | s | on the vertical axis.

FIG. 9 is a cross-sectional view of an improvement of the configuration shown in FIG. 7;

FIG. 10 is a cross-sectional view showing another conventional example of widening the bandwidth.

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

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

[Explanation of symbols]

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

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-12996 (JP, A) JP-A-1-241199 (JP, A)

Claims (6)

(57) [Scope of request for utility model registration] 1. A broadband radio wave absorber comprising a sintered ferrite magnetic material, a resistive film, a low dielectric constant dielectric material and a low magnetic permeability magnetic material sequentially laminated on a reflector. 2. The radio wave absorber according to claim 1, wherein a dielectric is disposed between said reflector and the sintered ferrite magnetic material. 3. The radio wave absorber according to claim 1, wherein the resistance film has a sheet resistance per unit area of 900 (Ω □) or more. 4. The apparatus according to claim 1, wherein when the magnetic permeability of the sintered ferrite magnetic material and the low magnetic permeability magnetic material at the time of DC are μ1 and μ2, respectively, the radio waves satisfying the relation of μ1 ≧ 25 · μ2. Absorber. 5. The apparatus according to claim 1, wherein the sintered ferrite magnetic material has a magnetic permeability at a direct current of 500.
Above is a radio wave absorber. 6. The radio wave absorber according to claim 1, wherein the low-permeability magnetic material has a magnetic permeability at a direct current of 20 or less.