JPS5927597A - 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, and particularly to a radio wave absorber effective for microwaves.

(Background Art) The applicant has previously determined that by adjusting only the thickness of the radio wave absorber, the center frequency of the absorber (the frequency at which the amount of electromagnetic wave absorption is maximum)
We swept a microwave absorber that can determine (
Patent application 1982- (IJ 3777).

As shown in Figure 1, this has a radio wave absorbing layer 1 of equal thickness and a metal plate 2 bonded to one side of the layer 1, and the wave absorbing layer 1 is made of rubber or plastic as a base. o in volume ratio, 15 to 0.35 ferrite and 0.1 in volume ratio
It is formed by dispersing and mixing 0.25 to 0.25 carbonyl iron. With such a configuration, the radio wave absorbing layer 10
If there is an incident wave a on the surface, the surface wave due to this incident wave a passes through the absorption layer 1 and is generated by the metal plate 2. The second-order reflected wave b' reflected by the antenna cancels each other and operates as a radio wave absorber.

As shown in Figure 2, the radio wave absorber with the above structure can change the center frequency by simply adjusting the thickness t of the absorption layer, which simplifies the manufacturing process, improves yield, and reduces manufacturing costs. can have a great effect. Figure 2 shows nickel zinc ferrite with a volume ratio of 0.18 and nickel zinc ferrite with a volume ratio of 0.18.
These are the results of measurements conducted on a radio wave absorber constructed by dispersing and mixing No. 22 carbonyl iron into an epoxy resin.

(Problem of the Invention) The present invention is a further development of Japanese Patent Application No. 56-013777, and an object of the present invention is to provide a radio wave absorber that effectively functions over a wider range of microwaves.

A feature of the present invention for achieving this object is that a radio wave absorber includes a dielectric material having a substantially uniform thickness in which ferromagnetic powder is dispersed, and a conductor coupled to the negative surface of the dielectric material. The radio wave absorber is characterized in that an array of concave portions and convex portions are formed on the entire surface of the radio wave absorber, and the area of the convex portions is smaller than the area of a square with a side of 1.5λ (λ is the free space wavelength).

(Structure and operation of the invention) FIGS. 3(A) and 3(Bl are one embodiment of the radio wave absorber according to the present invention, FIG. 3(Al is a side view,
shows a plan view.

Reference number 10 in the figure is a radio wave absorbing layer, which is formed by dispersing and mixing ferrite with a volume ratio of 0.15 to 0.35 and carbonyl iron with a volume ratio of 0.1 to 0.25 in rubber or plastic. The composition is the same as that of Application No. 56-013777. As the ferrite, nickel zinc type can be used. An uneven surface is formed on one surface of the absorbing layer 10 by Oa (worked metal plate 2° bonded, and a convex portion on the other surface) and the concave portions 10b. Electromagnetic waves are incident on this uneven surface.

Both the convex portion 10a and the concave portion 10b are squares with the same area,
FIG. 3 (as shown in Bl (diagonal lines indicate the recess 10b)
They are arranged in an alternating grid pattern in the vertical and horizontal directions.

The length l of one side of the square is desirably approximately equal to or larger than the wavelength of the incident wave in order to expect an effective function as an absorber.

Note that the shape of the concave portion and the convex portion can be any shape other than square and have the same area, and it is not always necessary to arrange them alternately in the vertical and horizontal directions.

In other words, even if there is some disorder in the arrangement, considering that it is actually used in radio waves, it can be expected that it will function as a broader band absorber than one with a flat entrance surface. can. However, considering that the absorber does not have polarization characteristics and is easy to manufacture, it is desirable that the concave portions and the convex portions be squares having approximately the same area and arranged in the vertical and horizontal directions.

If the depth Δd of the concave portion 10b relative to the convex portion 10a is adjusted in the above configuration, as is clear from the experimental example described later, as Δd increases, the center frequency can be increased while broadening the bandwidth at a return loss of 20 dB. Therefore, a broadband radio wave absorber can be obtained.

Next, it will be confirmed through an experimental example that the above configuration effectively operates as a broadband microwave absorber.

Figure 4 shows an example of the experimental configuration of a radio wave absorber.The absorbing layer 10 is made by dispersing and mixing 17.5% of nickel zinc ferrite and 21.5% of carbonyl iron in chloroprene rubber in terms of volume ratio. = 3.3%, and the uneven surface explained in Fig. 3 (Al) and Fig. 3 (Bl) was formed on the radio wave incident surface. The frequency (G1
-1z) and return loss (dB) and frequency (
The relationship between G11z) and the fractional band at 20 dB was measured.

Figure 5 shows the experimental results, and as Δ(I increases, 2od
It can be seen that the center frequency changes while the bandwidth at B increases. The straight line (A) in the figure is Δd ==
It can be seen that a value of 0.21 or more can be obtained as an average of the fractional bands at each 20 dB from 0.3% to 1.0X.

Figure 6 shows an example in which the absorption layer is constructed with the same composition as in Figure 5 without making the incident surface uneven, and the frequency (G
Hz) and return loss (dB) and frequency (GH
z) and the fractional band at 20 dB.

Next, experimental results regarding the relationship between the size of the uneven shape and the fractional band will be explained.

Curves a, b, c, and d in FIGS. 7 and 8 show experimental examples of the relationship between the size of the convex portion and the fractional band. The radio wave absorbing material used in these experiments was a mixture of Ni-Zn ferrite powder and chloroprene rubber at a volume ratio of 40% to 60%.

Curve (a) in Figure 7 shows the thickness of the concave portion of the radio wave absorbing material, which is 2.9 mm.
In the case where the thickness of the convex part is d==4.4 mm, the convex part is a square, and the length of one side of the convex part is l=30 mm, the center frequency is f-7.5 GHz (λ=40 mm), and the fractional band (Δ /
// )2od++=0.29 is obtained. At this time, the ratio of the length l of the convex portion to the center wavelength is as follows.

The curve in Figure 7 (in the case of BL, the thickness of the concave part is 2.9 mm, the thickness of the convex part is 3.3 mm, the length of the convex part is 30 mm, and the center frequency is 9 mm.
Fractional band (Δ//f,) at 5 GHz (λ=32im)
20 dn = 0.29 is obtained l - i.e. = 0.95
It is.

At this time, T32 The curves (C1 and (d) in Fig. 8 have a length of 90
In the case of (C), the fractional band (Δf
/f) zoan-0, 160, 185 makes completion = 3.

Figure 9 shows the relationship between the length l+ of the convex portion and the fractional band with respect to the center wavelength, based on the experimental results shown in Figures 7 and 8.
From the figure, it can be seen that when l≦1.5λ, a fractional bandwidth of 0.25 or more is obtained, and if lbl is thicker than this, the fractional bandwidth deteriorates rapidly.Therefore, the length l of the convex portion is 1. It is preferable that it is 5λ or less.The shape of the convex portion is not limited to a square, but any shape having an area smaller than the above-mentioned square is possible.

When the length l of the convex part is determined, the size a of the four parts or the interval between the convex parts (C1 is a2 732-12 from FIG. 1O since the areas of the convex part and the concave part are equal).

The radio wave absorbing material is preferably a mixture of Ni-Zn ferrite powder or a mixture of Ni-Zn ferrite powder and carbonyl iron powder with a polymeric material such as rubber or plastic. In the case of Ni-Zn ferrite,
While it is easy to align with the F=00 line for all frequencies,
Mn--Zn ferrite is disadvantageous because it has a high dielectric constant and is difficult to align with the 1'=0 line.

(Effects of the Invention) As explained above, according to the present invention, the incident surface of the radio wave absorbing layer is an uneven surface with convex portions and concave portions having the same area, and the length of one side of the convex portion is 1.5λ or less. Therefore, it is possible to provide a radio wave absorber that functions over a wider range of microwaves.

[Brief explanation of the drawing]

FIG. 1 shows a conventional example of a radio wave absorber, FIG. 2 shows an example of characteristics of the configuration shown in FIG. 1, FIG. The figure shows an example of the experimental configuration of a radio wave absorber, Figure 5 shows the measurement results showing the relationship between the frequency and return loss, and the frequency and fractional band of the radio wave absorber in Figure 4. Figure 6 shows the same as Figure 5. Figures 7, 8, and 9 show the measurement results showing the relationship between frequency, return loss, and frequency and fractional bandwidth using the thickness of the radio wave absorber of the composition as a parameter. Figures 7, 8, and 9 show the relationship between pattern size and fractional bandwidth. Figure 10 shows the relationship between
. FIG. 2 is an explanatory diagram of the relationship in size. 10...Radio wave absorbing layer ioa...Convex portion 10b...Concave portion 11...Metal plate patent applicant Tokyo Denki Kagaku Kogyo Co., Ltd. Company Patent Application Agent ° Patent Attorney Megumi Yamamoto -wh1 Figure 1-+ Figure 2 Figure 3 (A) Figure 3 (B) Figure 4 Figure 9 (a) (b) 03 \1 Ratio 02 (d) 1 Ko Acupuncture Qi 1 (c) Figure 10

Claims (6)

[Claims] (1) In a radio wave absorber that has a dielectric material that has ferromagnetic powder dispersed therein and has a substantially uniform thickness, and a conductor that is coupled to the negative surface of the dielectric material, concave portions and convex portions are arranged on the entire surface of the dielectric material. 1. A radio wave absorber characterized in that the area of the convex portion is smaller than the area of a square having a side of 1.5λ (λ is the free space wavelength) and φ. (2) The radio wave absorber according to claim 1, wherein the ferromagnetic powder is a Ni-Zn ferrite powder. (3) The radio wave absorber according to claim 1, wherein the ferromagnetic powder is a mixture of Ni-Zn ferrite powder and carbonyl iron powder. (4) The radio wave absorber according to claim 1, wherein the dielectric material is a polymeric material such as rubber or plastic. (5) The radio wave absorber according to claim 1, wherein the areas of the concave portion and the convex portion are approximately equal to each other. (6) The radio wave absorber according to claim 1, wherein the convex portion is a square with a side length of 15λ or less.