JPH05251888A - Thin narrow band radio wave absorber - Google Patents

Abstract

PURPOSE:To absorb and take away only the radio wave of narrow band frequency by mixing material of high magnetic permiability and high dielectric constant with high polymer material. CONSTITUTION:Ethylene propylene diene rubber is mingled with permally and barium titanate in weight ratio of 1:1 so that the latter weight is equivalent to the 80% of the entire weight. And then, they are kneaded and pressed to obtain a sheet. Its thickness is 2mm. Or, chloprene rubber is mingled with titanate and Mn-Zn ferrite group alloy in weight ratio of 1:1 so that the latter weight is equivalent to the 80% of the entire weight. And then, they are kneaded and pressed to obtain a sheet of 2mm in thickness. So, since only the radio wave of very narrow frequency can be absorbed and taken away, and at the same time, it can be formed to a thin one, electromagnetic fault problem is effectively solved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel thin thin band electromagnetic wave absorber.

[0002]

In recent years, electromagnetic interference (EM
C) The problem has been highlighted, and a radio wave absorber that absorbs radio waves in a certain frequency band has become the main focus for solving the problem.

In the prior art, there are only 1 GHz band electromagnetic wave absorber.
It usually has a bandwidth of about 2 GHz (absorption band of 20 dB or more). In addition, most of the main development efforts are aimed at widening the band.

For example, according to Japanese Patent Application Laid-Open No. 51-121200, a composite ferrite in which a ferrite powder is dispersed in a non-magnetic material, or a carbonyl iron-based magnetic material in which a carbonyl iron powder is dispersed in a non-magnetic material is used. The following radio wave absorbers have been known, but since all of them have a narrow frequency band and are limited in their practical range, they contain both ferrite powder and carbonyl iron powder and have good radio wave absorption characteristics over a wide frequency range. An electromagnetic wave absorber is obtained.

However, when attempting to remove unwanted radio waves, the use of such a broadband radio wave absorber also removes radio waves in the frequency band in the vicinity thereof.
For example, since the conventional radio wave absorber has a bandwidth of about 1 to 2 GHz, there is a disadvantage that even if only 5 GHz radio waves are desired to be removed, 4 GHz to 6 GHz radio waves are also removed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is thus to provide a radio wave absorber having an absorption band as narrow as possible.

According to the present invention, it has been found that such a purpose can be achieved when mixing a high magnetic permeability material and a high dielectric constant material into a polymeric material.

[0008] The present invention in μ'is more than 10,000 high permeability material and a high dielectric constant material as described above _as-Shi was mixed Mel of a and high permeability (high mu) material in the polymeric material what is _use-Irare, Ipushiron' is is _... Ru with more than 5.000 as high permeability (high epsilon) materials. Where μ and ε are the complex permeability and complex permittivity, respectively, and are expressed by the following equations.

[0009] _{· · μ = μ'-iμ "} , ε = ε'-iε" as such high-permeability material is preferably used generally typical magnetic alloy of Ni-Fe system called permalloy. The standard composition of this alloy is 60 to 90% Ni and the balance of Fe, and in addition to this, small amounts of Mo, Cr, Mn, Cu, etc. are added as necessary. This permalloy is usually 10,000
It has a magnetic permeability of zero.

Besides, Ni-Co alloy or Mn-Zn ferrite may be used.

As the high dielectric constant material, for example, 5000
It is preferable to use barium titanate (BaTiO ₃ ) having a dielectric constant of. Also lead titanate (PbTiO ₃ )
Can also be used. Both of the above high-performance materials are generally used in the form of powder.

As the polymer material to which these materials are mixed, for example, synthetic resin such as epoxy resin and unsaturated polyester resin, or synthetic rubber such as chloroprene rubber, ethylene propylene diene rubber (EPDM) and silicone rubber is used. Various resins or rubbers may be used alone or in combination of two or more kinds.

The high magnetic permeability material and the high dielectric constant material are used in a weight ratio of 1: 1 to 1: 4. The radio wave absorption characteristics (matching frequency) can be changed by the mixture ratio of both. When the high-performance material and the high-polymer material are mixed, it is appropriate to add the high-performance material in an amount of 70 to 90% by weight based on the total amount of the high-performance material and the high-molecular material. .. At this time, a high magnetic permeability material may be mixed with the polymer material, a high dielectric constant material may be separately mixed with the polymer material, and both may be further mixed. In this case, the polymer materials may be the same or different.

Incidentally, ethylene propylene diene rubber (EP
For a mixture of DM) and permalloy, μ'is about 1000, and for a mixture of the same rubber and BaTiO ₃ ε'is about 80.
It is 0. The outer EPDM and Mn-Zn ferrite, chloroprene rubber (CR) and BaTiO _3, a mixture of silicone rubber and Ni-Co alloy has a good characteristic.

The radio wave absorber thus obtained absorbs only radio waves of a narrow band of frequency and can be formed with a thin sheet.

Examples will be shown below.

[0017]

Example 1 Permalloy and barium titanate (BaTiO ₃ ) were added to ethylene propylene diene rubber (EPDM) in a weight ratio of 1: 1.
80% by weight of the total amount was mixed, and kneading and pressing were performed to obtain a sheet. Its thickness was 2 mm.

In this case, μ ′ = 1000 μ ″ = 100 ε ′ = 800 ε ″ = 80.

The results of measuring the radio wave absorption characteristics of the obtained radio wave absorber are shown in the graph of FIG. The radio wave absorption characteristics had a center frequency at 4 GHz and a band of 20 dB or more was 3.8 to 4.1 GHz, which was a narrow band.

Example 2 Lead titanate (PbTi) was added to chloroprene rubber (CR).
The O ₃₎ and Mn-Zn ferrite based alloy in a weight ratio of 1: 1
80% by weight of the total amount was mixed and kneaded and pressed to obtain a sheet having a thickness of 2 mm.

In this case, μ ′ = 900 μ ″ = 90 ε ′ = 600 ε ″ = 60.

The results of measuring the radio wave absorption characteristics of the obtained radio wave absorber are shown in FIG. The radio wave absorption characteristics had a center frequency at 4 GHz, and a band of 20 dB or more was a narrow band of 3.6 to 4.4 GHz.

[0023]

As is apparent from the above, according to the radio wave absorber of the present invention, it is possible to absorb and remove only radio waves having a frequency of a very narrow band width, and further, it is possible to form a thin film, which causes electromagnetic interference Can solve problems effectively. Moreover, the absorption bandwidth can be appropriately changed by changing the ratio of both high-performance materials to be mixed or the sheet thickness.

[Brief description of drawings]

FIG. 1 is a graph showing radio wave absorption characteristics of a radio wave absorber made according to Example 1 of the present invention.

FIG. 2 is a graph showing the radio wave absorption characteristics of a radio wave absorber made according to Example 2 of the present invention.

Claims (3)

[Claims] 1. A thin narrow-band electromagnetic wave absorber obtained by mixing a high magnetic permeability material and a high dielectric constant material with a polymer material. 2. The high magnetic permeability material is permalloy.
The thin narrow-band electromagnetic wave absorber described. 3. The thin narrow band electromagnetic wave absorber according to claim 1, wherein the high dielectric constant material is barium titanate.