JPH04361595A - Copper-zinc ferrite radio wave absorbent - Google Patents

Abstract

PURPOSE:To enable the radio wave absorption property of a radio wave absorbent to be enhanced in bandwidth and the radio wave absorbent to be lessened in thickness and manufactured at a low cost. CONSTITUTION:A copper-zonc ferrite radio wave absorbent is formed of a plate-like sintered body formed of 47-50mol.% iron oxide, 29-32mol.% zinc oxide, and 18-21mol.% copper oxide in composition, In some cased, 3% or below of manganese oxide is additionally given to the above composition.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber made of a plate-shaped sintered body of copper-zinc ferrite. This ferrite radio wave absorber is mainly used in radio anechoic chambers and the like.

0002

[Prior art] FCC (Federal Communications Commission), CIS
The frequency band subject to radiation noise regulations such as PR (International Special Committee on Radio Interference) is 30MHz to 1GHz.
There is an increasing need to measure radiation noise from various electronic devices in the above frequency band. Open sites or anechoic chambers are used for this measurement, but recently problems such as the environment (in addition to the effects of the ground, topography, surrounding buildings, etc.)
(Depending on the weather, measurements may not be possible), so the use of anechoic chambers is increasing. This anechoic chamber is a room surrounded by radio wave absorbers that do not reflect incident radio waves.

Conventionally, radio wave absorbers used in anechoic chambers include types using only dielectrics, types using only ferrite, and types using laminated layers of dielectric and ferrite. The ferrites used here include magnesium-zinc type and nickel-zinc type, which have a large value of magnetic loss (imaginary part of complex relative magnetic permeability) μ'' in the target frequency band, and have a large value of magnetic loss (imaginary part of complex relative permeability μ). ′ is selected.

0004

[Problem to be solved by the invention] A radio wave absorber made only of dielectric material requires a constant thickness depending on the wavelength.
When absorbing radio waves of 100 MHz or less, the wall thickness increases and the indoor effective volume decreases, resulting in the building becoming larger.

[0005] On the other hand, in the case of laminating a dielectric and a ferrite, a thin radio wave absorber can be produced even in a relatively low frequency band. However, in the case of magnesium-zinc ferrite, the matching thickness is approximately 8 mm, resulting in a thick plate and a high firing temperature. Further, in the case of nickel-zinc ferrite, it can be made thinner, but it has the disadvantage of increasing cost.

An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a ferrite radio wave absorber that is relatively thin, has a wide radio wave absorption range, and is inexpensive.

[0007]

[Means for Solving the Problems] The present invention provides iron oxide 47-
50 mol%, zinc oxide 29~32 mol%, copper oxide 18~
This is a copper-zinc based ferrite radio wave absorber made of a plate-shaped sintered body having a composition of 21 mol%. In addition to the above composition, manganese oxide may also be contained in an amount of 3 mol % or less.

[0008] The reason for limiting the composition of each component as described above is that in the composition range outside these ranges, the Curie temperature decreases, the temperature characteristics at high temperatures deteriorate, and the magnetic loss (complex magnetic permeability) required for radio wave absorption is reduced. This is because the imaginary part) μ'' also decreases, and the absorption frequency range shifts to the high frequency side, resulting in a decrease in absorption performance in the low frequency band.

The above-mentioned ferrite radio wave absorber may be used alone, or may be used in a multi-layered manner with a dielectric material.

[Effect]

[0010] If the amount of iron oxide is greater than the specified range, the magnetic loss μ''
If the amount of zinc oxide is less than the specified range, the magnetic loss μ'' will also decrease.If the amount of zinc oxide is more than the specified range, the Curie temperature will decrease and the magnetic loss μ'' will decrease. Even if it is small, the magnetic loss μ'' decreases, causing deterioration of the absorption properties.If other elements are outside the specified range, the magnetic properties will not be optimal, and high absorption performance cannot be obtained.

The ferrite radio wave absorber having the above structure has a matching thickness of about 7 mm. The absorption frequency band also extends to higher frequencies than conventional products, exhibiting broadband absorption characteristics.

[0012] Manganese oxide has a real part μ of complex magnetic permeability.
′ and the imaginary part μ″.

[0013]

[Example] A calcined powder having a composition of 49 mol% iron oxide, 30 mol% zinc oxide, 20 mol% copper oxide, and 1 mol% manganese oxide was added with 1 to 2 mol% of polyvinyl alcohol as a binder.
After adding weight% and water and granulating it and forming it into a plate shape, 900 ~
It was fired at 1000°C for 1 to 3 hours to obtain a ferrite radio wave absorber. The matching thickness of this copper-zinc based ferrite radio wave absorber (product of the present invention) was 7 mm. The results of measuring the frequency characteristics of reflection loss and magnetic permeability of the product of the present invention with a plate thickness of 7 mm are shown in FIGS. 1 and 2, respectively. For comparison, a conventional magnesium-zinc (Mg-Zn)-based ferrite radio wave absorber (plate thickness: 8 mm) and a nickel-zinc (Ni-Zn)-based ferrite radio wave absorber (plate thickness: 5.4 m) were used for comparison.
The characteristics of m) are also shown at the same time. The reflection loss is usually 1
It is said that about 5 to 20 dB or more is necessary.

In particular, as is clear from FIG. 1, the absorption frequency band of the product of the present invention is expanded to the high frequency side compared to the conventional product.
It can be seen that it exhibits broadband absorption characteristics. The plate thickness is only 1mm compared to conventional magnesium-zinc ferrite.
However, the specific gravity of ferrite is about 5, and considering that it will be attached to the entire wall, the effect of weight reduction is significant.

[0015]

[Effects of the Invention] Since the present invention is a copper-zinc ferrite radio wave absorber as described above, it can be made thinner than the conventional magnesium-zinc ferrite, and it can be made thinner than the conventional magnesium-zinc ferrite. It can be manufactured at low cost because it does not use. Furthermore, since the copper-zinc ferrite of the present invention can be fired at a low temperature, costs can be reduced in this respect as well. As described above, the radio wave absorber of the present invention has the effect of compensating for each of the drawbacks of the prior art and widening the radio wave absorption characteristic.

[Brief explanation of the drawing]

FIG. 1 is a graph showing frequency characteristics of return loss.

FIG. 2 is a graph showing frequency characteristics of complex magnetic permeability.

Claims (2)

[Claims] [Claim 1] Iron oxide 47-50 mol%, zinc oxide 2
A copper-zinc based ferrite radio wave absorber comprising a plate-shaped sintered body having a composition of 9 to 32 mol% and 18 to 21 mol% of copper oxide. 2. A ferrite radio wave absorber having the composition according to claim 1, further containing 3 mol % or less of manganese oxide.