JPS58173898A - 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] The present invention relates to a radio wave absorber.

Conventionally, as the radio wave absorbing material, materials such as ferrite, carbon, and polymer resin have been used, as disclosed in Japanese Patent Laid-Open No. 55-36987. This kind of radio wave absorbing material is
As shown in FIG. 1, a radio wave absorber is constructed by forming a layer 2 of a certain thickness on a conductor plate +l+. 1st
The radio wave absorber shown in the figure has a good complex dielectric constant and a complex SRS constant, where λ is the wavelength and d is the thickness of layer 2) is equal to l. However, since 1 is true only when a critical condition is satisfied, there is a drawback that the frequency range in which a good radio wave absorption effect is exhibited is very narrow.

An object of the present invention is to provide a radio wave absorber that overcomes the above-mentioned drawbacks and has good radio wave absorption characteristics over a wide frequency band. This will be explained in detail below.

The radio wave absorber provided by the present invention has a structure in which a low input impedance layer 3 and an impedance change layer 4 are laminated on a conductive plate 1, as shown in FIG.

In particular, the use of the low input impedance layer 3 is a feature of the radio wave absorber according to the present invention. The low input impedance layer refers to a layer whose input impedance characteristics are biased toward the left end of the chart, as shown by A in the Smith chart of FIG. 3, for example. This layer has a large radio wave loss, but if it is simply placed on a conductor plate, it will not match well with the air, and most of the electromagnetic waves will be reflected on its surface, making it impossible to be a good radio wave absorber. . In order to efficiently send electromagnetic waves to the low input impedance layer 3, impedance change layers 4t are laminated as shown in FIG. The impedance transformation layer 4 functions similarly to a wavelength impedance transformer used in microwave engineering. Therefore, the design method of the impedance transformation layer 4 basically follows the design method of a wavelength impedance transformer. In the low input impedance layer 30 input impedance characteristics, the imaginary part is 0.
The frequency f. If the value of the real part is R, the impedance transformation layer 4 has its wave impedance ZwftZ
Let w = ~ arm, and its thickness be f. % of the wavelength, it operates as an impedance transformer.

In a normal material, the dielectric constant is 2 or more and the wave impedance Zw is Z w =5, so considering the above relationship, B needs to be 05 or less. When four such impedance change layers are provided, the input impedance characteristics seen from the surface are shown in Figure 3 (b).
It is a characteristic of The characteristic obtained by converting this into a reflection loss is the characteristic (c) shown in FIG. 4. On the other hand, Fig. 4) is the first
These are the characteristics of the conventional radio wave absorber shown in the figure. In Figure 4 (
It can be seen that the frequency bandwidth where the p2 return loss is 20 dB or more is much wider in the radio wave absorber according to the present invention. In Figure 4, numbers 8 and 13 are.

This indicates that the frequency is 8 GHz to 13 GHz.

The characteristics of (a) in Figure 3 are not possible with ordinary polymer resins, and the inventors have made extensive efforts to realize the low input impedance layer 3. As a result, it was found that the low input impedance layer 3 can be achieved by combining a conductive substance with a polymer resin. The term "conductive substance" refers to a substance that is substantially composed of a substance with good electrical conductivity, such as a foil made of metal 1 alloy carbon.

It is a granular, short fibrous substance. Also, low input impedance characteristics can be achieved by using a ferroelectric material instead of a conductive material. Typical examples include barium titanate, lead titanate, strontium titanate, lead niobate, and lead zirconate.

There is no problem in using both a conductive substance and a strongly electroconductive substance at the same time.

The materials for achieving low input impedance characteristics have been described above. If low input impedance characteristics can be obtained, the radio wave absorber shown in FIG. 2 can be constructed, and better radio wave absorption characteristics can be obtained over a wider band than the conventional ones. The inventors have discovered that the broadband characteristics can be further increased by not only making the low input impedance layer 3 low in input impedance, but also adding magnetic loss to it. (A) and (A) in Figure 3 are the input impedance characteristics when (A) has magnetic loss and (R) has no magnetic loss. The values of the real part at frequencies where the imaginary part is O are both approximately 0 and 3, but there is a difference in the characteristics at 8 to 13 GHz, so impedance transformation layers are stacked to form a radio wave absorber. There is also a difference in the radio wave absorption characteristics when the low input impedance transformation layer 3 includes magnetic loss.The results of numerical calculations are shown in (E) and (E) in Figure 5 for cases in which magnetic loss is included in the low input impedance transformation layer 3 and cases in which it is not included. Figure 5 shows the frequency bandwidth resulting in a return loss of 20 dB or more divided by its center frequency in relation to the input impedance R. #
Comparing (e) and (f) in Figure c5, it is clear that (f), which includes magnetic loss, has a wider band characteristic. Therefore, in the radio wave absorber according to the present invention, it is desirable that the low input impedance layer 3 includes magnetic loss. Incorporating magnetic loss can be achieved by compounding the polymer resin with a magnetic material such as ferrite, iron, cobalt, nickel, etc. in the form of particles, foil, or short fibers. Since iron and nickel have good electrical conductivity, they can also serve as the highly specialized materials mentioned above.

Next, the impedance transformation layer 4 will be described.

The impedance transformation layer 4 has a wave impedance Zw of the low input impedance layer 30 (for reference), if the impedance value of the low input impedance layer 4 is R, its wave impedance Zw is f.

= J. Therefore, depending on the average value,
The polymer resin alone can be used, or in order to satisfy the above-mentioned conditions, the polymer resin is combined with a magnetic substance in the form of particles, foil, or short fibers, and a conductive substance in the shape described above. By making a composite material of a polymer resin and the above-mentioned substances, it is effective as an absorber to include radio wave loss as well as the effect of impedance modification. In particular, as a result of various numerical calculations, we discovered that including magnetic loss has the effect of widening the frequency band. (to) in Figure 5.

(G) shows this, and (G) has a wider frequency band. Therefore, in the radio wave absorber according to the present invention, it is desirable that the impedance change layer 4 includes magnetic loss. Inclusion of magnetic loss can be realized by compounding the same material as in the case of including magnetic loss in the low input impedance layer 3.

The polymer resin used for the low input impedance layer 3 and the impedance modification layer 4 is thermoplastic.

Both thermosetting types can be used and have the same radio wave characteristics. When using a radio wave absorber, it may be easier to handle if it has elasticity, and in such cases, natural rubber or synthetic rubber can be used.

Examples are described below.

Example 1 Weight ratio of polyethylene, ferrite, and short brass fibers is 30
The low input impedance layer 3 is made of a material with a thickness of 1.011 mixed at a ratio of 0:24, and a material with a thickness of 3.6 mixed with polyethylene and ferrite at a ratio of 60:40 by weight.
A radio wave absorber in which the material of m is an impedance change layer 4.

FIG. 6 shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 7 shows the reflection loss.

Example 2 The low input impedance layer 3 was made of a material with a thickness of 0.9 mg, which was a composite of polybutadiene resin, ferrite, and short iron fibers at a weight ratio of 30:0:15, and polybutadiene resin, ferrite, and short iron fibers were composited at a weight ratio of 70:0:15. A radio wave absorber whose impedance transformation layer 4 is made of a material with a thickness of 38 mm mixed at a ratio of :30. FIG. 8 shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 9 shows the reflection loss.

Example 3 A 1.4M thick material made by combining polybutadiene resin and short iron fibers at a weight ratio of 75:25 was used as the low input impedance layer 3, and a 4.61m thick butadiene resin was used as the impedance modified layer 4. radio wave absorber. FIG. 10 shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 11 shows the reflection loss.

Example 4 An impedance modification layer was made of Atsushi 15 Tsuru material, which is a composite of epoxy resin, ferrite, and aluminum foil at a weight ratio of 30:0:0:35, and an epoxy resin and ferrite were mixed at a weight ratio of 50:50. Radio wave absorber 0 No. 12 with impedance change layer 4 made of material with a thickness of 4.0111
The figure shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 13 shows the reflection loss.

Example 5 Chloroprene rubber, ferrite, carphone.

Thickness: 1.5mm thick brass short fibers are composited at a weight ratio of 30nia0:5:10. OH material low input impedance layer 3
and a thickness of 3.61E made by mixing chloroprene rubber, ferrite, and carbon in a weight ratio of 70:30:5.
A radio wave absorber in which impedance change layer 4 is made of material ll. FIG. 14 shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 5 shows the reflection loss.

Example 6 Ebony/ferrite, iron grain 11 lid ratio 30 near 0:3
The low input impedance layer 3 is made of a material with a thickness of 12 mm, which is composited at a ratio of 5.
Radio wave absorber with impedance change layer 4 made of materials with a thickness of 3.3 mm mixed at a ratio of 0.

FIG. 116 shows the input impedance characteristics of only the low input impedance layer 3, and FIG. 17 shows the reflection loss.

[Brief explanation of drawings]

FIG. 1 shows the structure of a conventional single layer radio wave absorber, and FIG. 2 shows the structure of a multilayer radio wave absorber according to the present invention. Fig. 3 Smith chart showing the input impedance characteristics seen from the surface of the low input impedance layer provided on the metal plate and the input impedance characteristics seen from the surface of the impedance transformation layer laminated on top of it. , Figure 4 shows the characteristics obtained by converting (b) in Figure 3 into reflection loss, and
This is the reflection loss characteristic of the conventional radio wave absorber shown in the figure. Figure 5 compares the frequency bandwidths when magnetic loss is included in the low input impedance layer and the impedance transformation layer and when it is not included. Figures 6 and 7 show the input impedance characteristics and reflection loss of only the low input impedance layer for Example 1, and Figures 8 and 9 show the reflection loss for Example 2.
FIGS. 10 and 11 show the input impedance characteristics and reflection loss of only the low input impedance layer, and the reflection loss t, #! for the case of Example 3. Figure 12, 1st
For the case shown in Figure 3 and Figure 13, the input impedance characteristics of only the low input impedance layer and the reflection loss tube %
14 and 15 show the input impedance characteristics and reflection loss of only the low input impedance layer in the case of Example 5, and FIG. 16 shows the reflection loss. The 17th rIA shows the input impedance characteristics and reflection loss of only the low input impedance layer for the case of Example 6. 1...Conductor plate, 2...Conventional radio wave absorbing material, 3...Low input impedance layer, 4...
...Impedance transformation stratification, (I, (I)...
... Input impedance characteristics of the low input impedance layer, (b) ...... (-(Input impedance characteristics modified by the 1fr impedance modification layer, 1/1...
...Characteristics obtained by converting (b) into reflection loss)...
・・Characteristics of return loss of conventional radio wave absorbers, (E), (F), (G)・・・・When magnetic loss is included in the low input impedance layer and the impedance transformation layer and when it is not included. Frequency bandwidth of the case Fig. 1 Fig. 2 Fig. 4 (2) The same frequency band (GHz) Fig. 51 Kuzu 7 Fig. Circumference warp (GHz) Whistle 91!1 Circumference number (GHz) Certain l1 Fig. Circumference 5 Number of stages (GHz) Number of stages in the circumference (GHz) Number of stages in the concave direction (GHz) Number of stages in the 771st direction (GHz) Procedural amendment (method) Commissioner of the Japan Patent Office 1, Indication of the case 1988 Patent application No. 5617
5 No. 2, Title of the invention: Radio wave absorber 3, Relationship to the amended person's case Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4, Agent & Date of amendment order: July 27, 1982 (shipment date) 6 Specification subject to amendment 7 Contents of amendment I will submit the entire text of the typed specification as shown in the attached sheet.

Claims (4)

[Claims] (1) In a radio wave absorber formed by laminating a low input impedance layer and an impedance modification layer on 4 body plates, the low input impedance layer i- is guided to a molecular resin and 8 substances 1
A radio wave absorber characterized by containing at least one of a strong #S electric material and a magnetic substance. (2) The impedance modification layer is made of a polymer resin, or a mixture of a polymer resin and a magnetic material in the form of particles, foil, or short fibers, and a conductive material in the above shape. A radio wave absorber according to claim 1 consisting of: (3) Magnetic materials include ferrite, iron, and cobalt. The radio wave absorber according to claims 1 and 2, which is made of a substance containing at least one of foil-like nine grain-like and short-fiber-like substances made of a ferromagnetic material such as nickel. (4) Conductive Materials Co., Ltd., a patent claim consisting of a substance containing at least one of the following: a substantially conductive metal alloy, a carbon-based foil-like grain, and a short fiber-like conductive material. The radio wave absorber according to range 1 and 2.