JPS6089902A - Material for radio wave absorber - Google Patents

Abstract

PURPOSE:To obtain a material for radio wave absorber which can effectively absorb the radio wave of low frequency region by mixing and dispersing specific quantity of tabular ferrite in a matrix. CONSTITUTION:As a matrix (base material), resin such as epoxy resin or silicone resin or a sort of rubber or a combination of two or more sorts of rubber is used. Tabular ferrite grain is mixed in the above-mentioned matrix by 10-60% in volume and dispersed. This enables to obtain a material for radio wave absorber which can absorb radio wave of low frequency region.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a radio wave absorber material (1), particularly in the low frequency region (
The present invention relates to a radio wave absorber material that satisfactorily absorbs radio waves (500 MHz to 4 GHz).

(Background Art) As a conventional radio wave absorber material, one in which, for example, ferrite powder is mixed and dispersed in a resin or the like is known. this is,
It utilizes the natural resonance of ferrite, and in a frequency region with a natural resonance frequency similar to -L, the real part of the ferrite's complex relative magnetic permeability ibr (5, = Le'1- j rL''r), 1: , This study focuses on the fact that both the imaginary part and the imaginary part decrease as the frequency increases, and this region becomes the radio wave absorption band.

Ferrite particles used in such radio wave absorber materials are generally obtained by an aqueous solution method or a solid reaction-pulverization method. Here, regarding these manufacturing methods, MzF
The case where X=O in e3-χ04, that is, magnetite (Fe3C+4) will be briefly explained as an example.

(a) Aqueous solution method Also called coprecipitation method, the black pigment magnetite is produced by this method. FeCl2 and Fe in the ratio of 1 molecule: 2 molecules
When NaOH aqueous solution is added to Cl3 aqueous solution, Fe5(
74 is obtained as a precipitate.

The reaction formula is as follows.

FeCl2 +2FeC13+ 8NaOH+Fe(O
H)2 + Fe(OH)3 +8NaCIFe(OH
)2 +2Fe(01()3 −+ Fe04 + 4
To obtain 820MzFe3-zOa, MC1z
(For example, NiCl2) may be added as a predetermined measure.

(b) Solid reaction-pulverization method The powder of α-Fe203 (Begara), which is a raw material, is reacted in a nitrogen atmosphere at a temperature of 1400°C for a firing time of 3 hours.
Obtain Fe3O4. The reaction formula is as follows.

When obtaining MzFe3-703, add M to a-Fe2O3
A predetermined amount of O (for example, NiO) is mixed and reacted. The conductive ferrite thus obtained is pulverized into particles having an average particle diameter of 0.5 to 1 OILIl using a pulverizer such as a ball mill to obtain a target object.

However, conventional radio wave absorber materials using ferrite particles manufactured by such a manufacturing method have the following first-order problems. In other words, since the ferrite particles obtained by the method (a) above have an average particle diameter of no more than 0.54 m and have a single magnetic domain structure, the rotational resonance frequency of the shaft cannot be lowered, and the ferrite particles in the low frequency region ( 500MH2~3GHz)
cannot absorb radio waves. In addition, since the method (2) involves sintering, it is possible to further select the crushing conditions to achieve zero
．． It is possible to obtain ferrite particles in a wide range of 3 to IQO #Lm, but the particle size is in the form of crushed particles in the same direction,
Aspect ratio is small. Therefore, compared to method (a), although the natural resonance frequency can be shifted to a lower frequency region, this is not a major improvement.

(Objective of the Invention) The object of the present invention is to solve such conventional problems and provide a radio wave absorber material that can satisfactorily absorb radio waves in the low frequency region, and its characteristics are as follows: The radio wave absorber material is made by mixing and dispersing 10 to 60% by volume of plate-like ferrite particles in a matrix.

Hereinafter, the present invention will be explained in detail using the drawings.

(Structure and operation of the invention) First, plate-shaped ferrite particles will be explained. A plate-shaped ferrite particle is literally a plate-shaped ferrite particle. Figures 1 and 2 show plate-shaped ferrite particles (NiO: ZnO:
Fe203 = 22.5: 22.5: 49.0
), each with a magnification of 1.50.
0 times and 3.1100 times. As can be seen from these electron micrographs, the ferrite particles are plate-shaped (single piece).
is formed.

FIG. 3 shows the frequency and complex relative magnetic permeability 4r (A-r = g'r -
7g”r). In the figure, curves A,
A' are g'r and L'r, respectively, of ferrite particles used in a conventional radio wave absorber, and curves B and B' are g'r and JL'r, respectively, of plate-shaped ferrite particles used in the present invention. As can be seen from the figure, the natural resonance frequency of normal ferrite particles is approximately 2 to 3 GH2, and the natural resonance frequency of plate-shaped ferrite particles is approximately 500M.
It is Hz. That is, the natural resonance frequency of plate-shaped ferrite particles is clearly shifted to a lower frequency than that of normal ferrite particles. This frequency control is performed by changing the diameter-to-thickness ratio of the plate-shaped ferrite particles. As mentioned above, the material properties as a radio wave absorber material require that the real part g/r and the imaginary part g'I of the complex relative magnetic permeability decrease almost in parallel. Therefore, as can be seen from Figure 3, when using ordinary Ferrite I particles, the optimum radio wave absorption region is around 4 to 8 GHz +l, whereas with plate-shaped ferrite particles, the radio wave absorption range is around 500 MHz.
A frequency around 1 to 5 GHz from Z is suitable for a radio wave absorber. Therefore, plate-shaped ferrite particles can absorb radio waves in a low frequency range well, and the present invention focuses on the characteristics of such plate-shaped ferrite particles. still,
In each case shown in FIG. 3, 40% by volume of ferrite powder was mixed and dispersed in 80% by volume of epoxy resin.

Here, a method for manufacturing plate-shaped ferrite particles will be explained. The plate-shaped ferrite particles are made from natural or synthetically obtained plate-shaped hematite, and a method called the flux method is used. The flux method uses Fe2O3 and NO (=Ni), which are the raw materials for ferrite.

In this method, ferrite is obtained by mixing powders of Go, Mn, Cu, Mg, Zn, etc. with flux such as sulfate, nitride, halide, etc., and reacting at a predetermined temperature. When plate-shaped hematite is used in this method, plate-shaped ferrite is obtained. If the MO is not changed, iron ferrite or magnetite is obtained.

An example of a plate-shaped ferrite obtained in this way will be shown.

Blending ratio: FezO3; 48 mold, NiO;
25.5 mold.

ZnO; 25.5 mold Furanx: Li2SO4-Na2s04 Heat treatment conditions: 800°C for 1 hour Electron micrographs: Figures 1 and 2, diameter 1-4 μm,
Thickness: about Q, 5 pLm Such plate-shaped ferrite particles are placed in the matrix with lθ
Mix and disperse at ~60% by volume. Here, the average diameter to thickness ratio of the plate-shaped ferrite particles is preferably such that the average diameter is 3 times or more the average thickness, and the average diameter is about 0.5 to 5007 Lm. It is preferable. This is because, as shown in Figure 3, the larger the diameter-to-thickness ratio of the plate-shaped ferrite, the higher the effective magnetic permeability, and accordingly the natural resonance frequency shifts to a lower frequency, increasing the frequency band of the radio wave absorber. This is because it can be made lower. Further, when a magnetic domain wall is generated in a particle, not only rotational resonance of the magnetic domain but also resonance due to movement of the magnetic domain wall occurs, which is more effective, but in a region of 0.5 μm or less, no domain wall is generated. As the matrix (material 81), one or a combination of two or more of various resins such as epoxy resin and silicone resin, or various rubbers is used. 10 to 6 plate-like ferrite particles in the matrix
The reason for mixing and dispersing at 0% by volume is that this amount is suitable for mixing and dispersing, and good radio wave absorption characteristics can be obtained.

Next, a preferred example of a radio wave absorber using two consecutive radio wave absorber materials according to the present invention will be described. Figure 4 shows a radio wave absorber using commonly used granular ferrite particles,
It is a graph showing experimental results of frequency (GHz) and return loss (dB) with a radio wave absorber using plate-shaped ferrite particles according to the present invention. As a conventional example, the diameter is 2J.
The radio wave absorbers (curves C1 and 02) are formed by mixing and dispersing LIo granular ferrite particles in a resin at a rate of 40% by volume into sheets with thicknesses of 4.5 mm and 8.5 mm (curves C1 and 02). Average diameter 3 pLm, average thickness 0.4
This is a radio wave absorber (Curve Rho and [12) made by mixing and dispersing gm plate-like ferrite particles in a resin at a concentration of 40% by volume and forming sheets with thicknesses of 4.8 mm and 7 mm.

As can be seen from the figure, the radio wave absorber using the radio wave absorber material according to the present invention has a center frequency of 7.
It can be seen that although it is inferior to the conventional one in the high frequency region near GHz+1, it is superior to the conventional one in the low frequency region where the center frequency is around 3 GHz.

The present invention has been described in detail above. In the above-mentioned radio wave absorber material, plate-shaped ferrite particles are mixed and dispersed in any direction, but as another embodiment, the direction may be aligned in the direction of one leg.

This can be obtained by applying a magnetic field or rolling during molding. If the plate-like ferrite particles are aligned parallel to the plane of the radio wave absorber from which radio waves arrive, better characteristics can be obtained.

(Effects of the Invention) As explained above, according to the present invention, it is possible to provide a radio wave absorber material that can satisfactorily absorb radio waves in a low frequency region.

[Brief explanation of drawings]

Figures 1 and 2 have magnifications of 1550x and 38x, respectively.
Electron micrograph of plate-shaped ferrite at 00x, No. 3
The figure shows the relationship between frequency and complex magnetic permeability of a conventional radio wave absorber material using ordinary ferrite and a radio wave absorber material according to the present invention using plate-shaped ferrite, and Fig. 4 shows a conventional radio wave absorber material using plate-shaped ferrite. FIG. 3 is a diagram showing the relationship between frequency and return loss of a radio wave absorber using a body material and a radio wave absorber material according to the present invention. μr --- Complex relative permeability 1. ．． ;, +-real part, 1
IR-M - Imaginary Part Patent Applicant Takashi Yamaguchi Co., Ltd. Patent Application Agent Megumi Yamamoto - 0 Procedural Amendment (Method) February 10, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 1, Indication of the case 1982 Patent Application No. 197595 2, Name of the invention Radio wave absorber material 3, Amendment yli:' Relationship to the case Patent applicant name (306) TDC Co., Ltd. (Other 1)
Name) 6. Column 7 for a brief explanation of the drawings in the specification subject to amendment.
``Photograph'' is changed to ``Figure 1 and Figure 2 each have a magnification of 1550.
"Electron micrograph of grain structure of plate-shaped ferrite magnified at 3900 times and 3900 times." Below

Claims (2)

[Claims] (1) A radio wave absorber material comprising 10 to 60% by volume of plate-shaped ferrite mixed and dispersed in a matrix. (2) The radio wave absorber material according to claim 1, wherein the plate-like ferrite is dispersed so as to be aligned in a substantially constant direction.