JPH05335776A - Dielectric compound material - Google Patents

Abstract

PURPOSE:To improve dielectric loss by simple constitution and thin an electric wave absorber by mixing metal alloy needle-shaped powder which has high resistibility and sphere-shaped metal powder which has a high dielectric constant by almost same quantity with dielectric. CONSTITUTION:As for needle-shaped metal powder A, metal alloy which has a resistibility of rho>=80muOMEGA-cm, or desirably rho>=100muOMEGA-cm is used and when Co- Fe-Si-B amorphous metal alloy is used, especially excellent results are attained as electric wave absorbing material. The desirable shape of the needle-shaped metal powder A is a flake or a needle of which the longest axis is 30mm or shorter, shortest axis is 1-20mum with an aspect ratio of 50 or more. The metal alloy needle-shaped powder A and sphere-shaped metal powder B such as highly conductive Cu powder are mixed with dielectric C by almost same quantity and dielectric compound material with an improved dielectric constant is provided. The desirable resistibility of the highly conductive metal B to be mixed in the dielectric C is 10X10<-6>OMEGA-cm or lower. Therefore, dielectric loss contributes to the absorption of electric field components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric composite used as a material for absorbing radio waves in a high frequency band.

[0002]

2. Description of the Related Art As a material for absorbing radio waves in a high frequency band,
A composite material in which a conductive material, for example, a conductive particle such as a metal is mixed in a dielectric has been put into practical use.

The electromagnetic wave absorbing action of these composites utilizes the effect of converting the energy of the electromagnetic waves passing through it into heat energy. This phenomenon cannot be explained only by the eddy current loss based on the electromagnetic dielectric effect of the electromagnetic wave passing through the conductor in the composite, and is understood to be caused by the dielectric loss. Therefore, although a composite material of a conductive material and a dielectric material as described above has been adopted or proposed, dielectric absorption is insufficient in many cases and sufficient absorption characteristics cannot be obtained.

For example, a composite material obtained by adding and mixing carbon as a conductor into a dielectric material such as expanded polystyrene or rubber has been put into practical use as a radio wave absorber, but the required thickness as an absorber is 1 m. Reached the above, improved absorption characteristics,
That is, it is desired to increase the dielectric loss.

[0005]

SUMMARY OF THE INVENTION The present invention improves the dielectric loss with a simple structure in view of the above-mentioned drawbacks of the dielectric composite as a radio wave absorber having the above-mentioned structure which has been put into practical use and proposed. An object of the present invention is to provide a dielectric composite that requires a small thickness as a radio wave absorber.

[0006]

In order to solve the above-mentioned problems, the dielectric composite of the present invention comprises a high electric resistance metal alloy needle-shaped powder and a spherical metal powder having a high electrical conductivity, which are substantially the same in the dielectric. It is characterized in that the amounts are mixed. The term "needle-like" as used herein is a generic term for needle-like, fibrous, flake-like, and other shapes having a large aspect ratio.

[0007]

In general, the magnetic loss and dielectric loss of a substance in a high frequency range represent the basic characteristics of this substance. The former is complex permeability μ ^* = μ′−jμ ″ (or loss angle tan
δ = μ ″ / μ ′), and for the latter, complex permittivity ε ^* =
It is known to be represented by ε'-jε ″ (or loss angle tan δ = ε ″ / ε ′). If the complex magnetic permeability and complex permittivity are known, the reflectance of this substance (the ratio of the incident electromagnetic wave reflected on the surface of the substance when it is vertically incident on the substance) and the skin depth (the incident electromagnetic wave is 1 / m in the substance) The thickness of the absorption layer until it decays to e) is obtained, and the absorption characteristics of the substance can be known.

As shown in FIG. 1, an electromagnetic wave is a wave having an electric field component E and a magnetic field component H together, and the ratio of the electric field component and the magnetic field component is expressed as a spatial impedance Zo,
It is 377Ω in the far field. The magnetic loss contributes to the magnetic field component, and the dielectric loss contributes to the absorption of the electric field component. Since the ratio of the electric field component and the magnetic field component of the electromagnetic wave is constant, the electromagnetic wave can be absorbed by absorbing only one of them.

The acicular metal powder used in the present invention has an electrical resistivity ρ ≧ 80 μΩ-cm, preferably ρ ≧ 10.
A metal alloy with 0 μΩ-cm is used. Well-known high permeability amorphous metals such as Fe-Si-B
System, metal alloys such as Co-Fe-Si-B system, Fe-Al-Si system (Sendust system), etc. are preferable metal alloys for use.
In particular, Co-Fe-Si-B based amorphous metal alloys can obtain good results as radio wave absorbing materials. Even if it is a metal alloy, permalloy has a low electric resistivity, and a desired result cannot be obtained.

The shape and size of the metal alloy powder used have an important influence on the dielectric loss (complex dielectric constant) characteristics of the electromagnetic wave absorber, and even if spherical or lumpy ones are used, favorable results cannot be obtained, and needle-like shapes are obtained. Those having a large aspect ratio such as a fibrous shape or a flake shape give preferable results.

The shape and size of the acicular metal powder mixed in the dielectric is an important factor for maintaining the properties of the dielectric composite. In the present invention, the shape of the acicular metal powder is preferably flake or acicular having a longest axis of 30 mm or less, a shortest axis of 1 to 20 μm and an aspect ratio of 50 or more.

The alloy has a cavitation method disclosed in Japanese Unexamined Patent Publication No. Sho 58-6907, that is, it has a surface layer having a low wettability with respect to the molten metal, and the molten metal is formed on the surface of the roll rotating at high speed. It is desirable to manufacture by a method in which the molten metal is supplied and the molten metal is divided into fine molten metal droplets, and subsequently the molten metal droplets are collided with a metal rotating body rotating at high speed to rapidly solidify. In particular, in order to manufacture an alloy having a shortest axis, it can be realized by increasing the rotation speed of the metal rotating body. It is also possible to make the shortest axis of the alloy small by a chemical method such as etching.

By mixing the above-mentioned acicular powder of a metal alloy with Cu powder having a high conductivity into a dielectric, a dielectric composite having an improved dielectric constant can be obtained. Incidentally, the electric resistivity of Cu is 1.7 × 10 ⁻⁶ Ω-cm. The high conductivity metal mixed with the acicular powder of the above metal alloy in the dielectric is not limited to Cu, but has an electric resistivity of 1
It is preferably 0 × 10 ⁻⁶ Ω-cm or less.

In the dielectric composite of the present invention, as a means for mixing a high conductivity metal such as Cu with a needle powder of a metal alloy into the dielectric, a high electric resistance metal alloy needle powder and a high conductivity spherical metal are used. The powder and the dielectric are mixed in substantially the same amount.

[0015]

Embodiments of the present invention will be described in detail below with reference to the drawings and tables.

Co-based amorphous alloy flakes (longest axis 2
0 mm, shortest axis 10 μm) A and spherical Cu with a diameter of 20 μm
Powder B was prepared, and as shown in FIG. 2, A and B were mixed in the same amount in the dielectric C, A was mixed in C, and B was mixed in C, respectively. Ten types of dielectric composite specimens were prepared by changing the volume mixing ratio to several types. For each of these specimens, magnetic permeability μ ', μ "and dielectric constant ε'for radio waves in the frequency band of 100 to 3000 MHz,
ε ″ was measured. Table 1 shows changes in the magnetic permeability and the dielectric constant depending on the volume ratio with respect to the measurement frequency of 200 MHz.
Table 2 shows the No. 8 specimen (volume ratio of both A and B powders is 5
The frequency characteristics of the magnetic permeability and the dielectric constant are shown for (% of the above).

[0017]

[Table 1]

[0018]

[Table 2]

From these tables, a mixture of spherical metal powder B and acicular metal powder A in the same amount in dielectric C is A or B.
Is more effective than the one in which only the dielectric C is mixed, and the effect of adding the powder is not observed when the mixing ratio of A and B is 3% or less, respectively, and the conductivity is high when it exceeds 10%. Nari ε
It is difficult to control as a finite value, and it has been shown that the characteristics cannot be improved.

Although not shown in the table, as a result of various experiments, the outer diameter of the spherical metal powder is not limited to 20 μm, but may be 5 to 2
The same effect can be obtained even when the thickness is 0 μm, and it does not matter if the shape is not a perfect sphere but a flat shape. It was also confirmed that the volume ratios of A and B do not have to be completely the same, but may be substantially the same.

As described above, according to the present invention, it is possible to improve the dielectric loss of the dielectric composite and reduce the required thickness of the radio wave absorber with a simple structure.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating the properties of electromagnetic waves.

FIG. 2 is a conceptual diagram showing the composition of the dielectric composite of the present invention.

[Explanation of symbols]

 A Magnetic metal alloy acicular powder B High conductivity spherical metal powder C Dielectric

Claims (4)

[Claims] 1. A dielectric composite characterized in that a needle-like powder of a high electric resistance metal alloy and a spherical metal powder having a high conductivity are mixed in substantially the same amount in a dielectric. 2. The electrical resistivity of the above metal alloy is 80 μΩ.
-Cm or more, the longest axial dimension of the acicular powder is 30 mm or less,
The dielectric composite according to claim 1, wherein the shortest axis dimension is 1 to 20 µm and the aspect ratio is 50 or more. 3. The spherical metal powder has an outer diameter of 5 to 20 μm.
The dielectric composite according to claim 1, wherein m is m. 4. The dielectric composite according to claim 1, wherein the volume ratio of each of the metal alloy acicular powder and the spherical metal powder is 3 to 10%.