JPH06232583A - Ferrite radiowave absorber - Google Patents

Abstract

PURPOSE:To provide a ferrite radiowave absorber wherein the resistivity of a baked ferrite is so controlled as to be 10<-1>-10<-2>OMEGA-m. CONSTITUTION:The resistivity of a ferrite is so adjusted as to be 10<-1>-10<-2>OMEGA-m. Thereby, the magnetic loss of the ferrite is made nearly equal to its dielectric loss and its radiowave absorbing characteristic in a comparably low-frequency region of 20M-100MHz is so improved that it can be used effectively as a radiowave absorber in that frequency region.

Description

Detailed Description of the Invention

[0001]

The present invention has a resistivity of 10 ^-1 to 10 ^-1.
A ferrite electromagnetic wave absorber made of a ferrite sintered body controlled to ^-2 Ω-m, particularly showing the same magnetic loss and dielectric loss, and effective electromagnetic wave absorption characteristics in the low frequency range, especially in the frequency range of 20M to 100MHz. The present invention relates to a ferrite electromagnetic wave absorber.

[0002]

2. Description of the Related Art As a radio wave absorber, a product in which ferrite having magnetic loss or carbon having dielectric loss is impregnated in urethane has been commercialized. However, these are two components of electromagnetic waves (magnetic field component and electric field component).
One of the characteristics is that by absorbing only one of them (ferrite only magnetic field component, carbon only electric field component), electromagnetic wave energy is absorbed.

Generally, the absorption characteristics of a radio wave absorber are 2
It is considered that a radio wave absorber requires an absorption characteristic of 0 dB or more. For example, when using an electromagnetic wave absorber in an anechoic chamber, it is necessary to use an electromagnetic wave absorber having an electromagnetic wave absorption characteristic of at least 20 dB in order to obtain the performance of the anechoic chamber. The anechoic chamber is currently required to support frequencies of 30M to 1GHz.

However, since the conventional ferrite electromagnetic wave absorbers use only the frequency dispersion of magnetic loss, the frequency range showing a characteristic of 20 dB or more is 50M to 400.
At the present, it is narrow as MHz, and in order to support frequencies other than that, it is currently handled by using another absorber or changing the shape of the anechoic chamber. In a high frequency range such as 400M to 1GHz, the wavelength becomes shorter, so even if another absorber is used, it is possible to use a thin absorber to some extent.
In a low frequency range such as 0M to 50MHz, the thickness of the absorber becomes thicker, and there is a built-in problem that the radio wave absorber is practically difficult to use. Therefore, the development of a radio wave absorber exhibiting an absorption characteristic of 20 dB or more in a low frequency region such as 30 M to 50 MHz is an important issue.

[0005]

DISCLOSURE OF THE INVENTION The present invention has a high magnetic loss and a high dielectric loss in combination, and thereby exhibits a ferrite electromagnetic wave absorption exhibiting an absorption characteristic of 20 dB or more in a low frequency range, particularly in a frequency range of 20 M to 100 MHz. The challenge is to provide the body.

[0006]

Generally, the magnetic loss (μ ″) and dielectric loss (ε ″) of a substance in a high frequency range represent the basic characteristics of the substance, and the former is a complex relative permeability. The magnetic permittivity μ _r = μ′−jμ ″ (or loss angle tan δ = μ ″ / μ ′), and the latter is the complex relative permittivity ε _r =
ε′-jε ″ (or loss angle tan δ = ε ″ / ε ′). If the complex relative permeability and the complex relative permittivity are known, the reflectance of the substance (the ratio of the incident electromagnetic wave reflected by the surface of the substance when vertically incident on the substance) is obtained, and the absorption characteristics of the substance are shown in FIG. It can be known as the characteristics of the absorber.

The radio wave absorber having a controlled resistivity of the present invention improves absorption characteristics by obtaining a desired magnetic loss μ ″ and a dielectric loss ε ″ in a target frequency range. To do.

As a result of various studies to obtain the required complex relative magnetic permeability and complex relative permittivity in each frequency range, the dielectric constant of the ferrite sintered body was controlled by controlling the resistivity of the ferrite sintered body. It was confirmed that the purpose could be achieved by adding frequency characteristics to. That is, the present invention proposes a radio wave absorber using a ferrite sintered body having a controlled resistivity of 10 ^-1 to 10 ^-2 Ω-m.

The commonly used Ni-Zn ferrite electromagnetic wave absorber has a resistivity of 10 ⁷ Ω-m or more.
The ferrite sintered body having a controlled resistivity used in the present invention can be easily obtained by sintering Ni—Zn ferrite at a high temperature in a reducing atmosphere for a long time. The ferrite having a controlled resistivity of 10 ^-1 to 10 ^-2 Ω-m obtained by the above-mentioned treatment shows the same magnetic loss and dielectric loss as shown in FIG. Frequency range, especially 20
In the frequency range of M to 100 MHz, it showed excellent electromagnetic wave absorption characteristics as shown in FIG.

The ferrite sintered body obtained by the above treatment is used by laminating it on a reflecting plate as shown in FIG. As the reflection plate, any general metal plate can be used, and the thickness of the ferrite sintered body to be laminated can be appropriately selected depending on its complex relative permeability and complex relative dielectric constant.

[0011]

[Examples] The measurement results of the relative permittivity (ε _r = ε′-jε ″) and the relative permeability (μ _r = μ′−jμ ″) of a commonly used Ni-Zn ferrite wave absorber are shown in the figure. The electromagnetic wave absorption characteristics are shown in FIG. The dielectric loss (ε ″) is close to 0, the frequency characteristic is extremely small, and the 20 dB absorption band is 5
It is clear that the anechoic chamber, which is as narrow as 0M to 400MHz and therefore is made up of only ferrite electromagnetic wave absorbers, does not have sufficient electromagnetic wave absorption characteristics on the low frequency side. FIG. 2 shows the measurement results of ε ′, ε ″, μ ′ and μ ″ of the radio wave absorber according to the present invention in which the resistivity of the Ni—Zn ferrite radio wave absorber is controlled to 10 ⁻¹ Ω-m by the above method. To
The radio wave absorption characteristics are shown in FIG. It can be seen that the relative permittivity is increased and the magnetic loss μ ″ and the dielectric loss ε ″ are overlapped with each other, thereby improving the absorption characteristics in the low frequency region, particularly in the range of 20M to 50MHz. Furthermore, in the Ni-Zn ferrite electromagnetic wave absorber, the measurement results of ε ', ε ", μ'and μ" when the resistivity is controlled to 10 ^-3 Ω-m are shown in Fig. 3, and its electromagnetic wave absorption characteristics are shown. It is shown in FIG. It can be seen that the relative magnetic permeability decreases and the absorption characteristics deteriorate.

[0012]

The ferrite wave absorber according to the present invention is
Since it has a complex relative permeability and a complex relative permittivity of the same degree, compared to the conventional ferrite wave absorber,
It has excellent absorption characteristics in the low frequency range, especially in the range of 20M to 100MHz, and can solve the drawbacks of conventional wave absorbers.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the relative magnetic permeability, relative permittivity and frequency of a conventional Ni-Zn ferrite radio wave absorber.

FIG. 2 is a graph showing the relationship between the relative permeability, relative permittivity and frequency of a Ni—Zn ferrite radio wave absorber whose resistivity is controlled to 10 ⁻¹ Ω-m according to the present invention.

FIG. 3 is a graph showing the relationship between the relative permeability, relative permittivity, and frequency of a Ni—Zn ferrite radio wave absorber whose resistivity is controlled to 10 ⁻³ Ω-m.

FIG. 4 is a graph showing a radio wave absorption characteristic of a conventional Ni-Zn ferrite radio wave absorber.

FIG. 5: Ni whose resistivity is controlled to 10 ^-1 Ω-m according to the present invention
FIG. 6 is a graph showing the electromagnetic wave absorption characteristics of a Zn-based ferrite electromagnetic wave absorber.

FIG. 6 is a graph showing a radio wave absorption characteristic of a Ni-Zn ferrite radio wave absorber whose resistivity is controlled to 10 ⁻³ Ω-m.

FIG. 7 is a diagram showing a configuration of a ferrite electromagnetic wave absorber obtained by laminating a ferrite sintered body on a reflection plate.

[Explanation of symbols]

 μ ′ Real part of relative permeability μ ″ Relative part of magnetic permeability (magnetic loss) ε ′ Real part of relative permittivity ε ″ Imaginary part of relative permittivity (dielectric loss) f Frequency (MHz) 1 Reflector 2 Burn Bonded ferrite wave absorber 3 radio wave

Claims (2)

[Claims] 1. A ferrite sintered body having a resistivity of 10 ^-1 to 1
A ferrite electromagnetic wave absorber characterized by being controlled to 0 ^-2 Ω-m. 2. A ferrite radio wave absorber having a radio wave absorption characteristic of 20 dB or more at a low frequency, especially at 20 M to 100 MHz, by controlling the magnetic loss and the dielectric loss to the same degree.