JPH0222130A - Nickel-zinc-based ferrite material - Google Patents

Abstract

PURPOSE:To exhibit sufficient absorption performance as a wave absorber in a wide band by providing Fe2O3, ZnO and NiO with specific composition ratios. CONSTITUTION:A nickel-zinc-based ferrite substance obtained by providing respective composition ratios of 48-50mol% Fe2O3, 32-37mol% ZnO and 13-20mol% NiO (which may be substituted by CuO up to 11mol%). Since the above-mentioned ferrite material has wideband wave absorption properties alone and the thickness thereof can be reduced to provide a lightweight, the material is advantageous due to no structural load applied in execution of especially outer walls, etc., of buildings and also effectively used as housing inner wall materials of various electronic devices.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nickel-zinc ferrite material with high noise absorption performance suitable as a radio wave absorber for an anechoic chamber.

[Prior art] Radiated noise regulations such as Cl5PR currently cover frequencies from 30 MHz to IGHz, and there is an increasing need to measure radiated noise from various electronic devices within the above frequency range. ing.

The standard for measurements is to take measurements at an open site, but as an alternative, an anechoic chamber with 30 Ml (z = l GHz and no reflection of electromagnetic waves) is also widely used.

In this type of anechoic chamber, a radio wave absorber is used to make the inner wall non-reflective.

If we try to achieve radio wave absorption using only dielectric loss,
The necessary thickness of the dielectric is approximately equal to the wavelength of the electromagnetic waves to be absorbed, so in order to absorb, for example, 100 MHz (wavelength λ=3 m) or less, the dielectric must be extremely thick, reducing the effective indoor volume.

Therefore, recently, a laminated structure of dielectric and ferrite has been used, and in this case, the ferrite is made to have a thickness of about 81 mm and is responsible for absorption in the low frequency band.

[Problems to be Solved by the Invention] As a radio wave absorber, it is said that a reflection loss of about 20 dB is required on the board. 30~IGHz by magnetic material only
To obtain the above attenuation in the range of μ
It is necessary for " to decrease with frequency. To this end, as long as the .mu.'-f characteristic curve follows the Snoek limit, .mu.' must be about 1000 or more.

However, in the prior art, no material has been found that satisfies the above characteristics and has sufficient absorption performance over a wide band.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to achieve a matching thickness of about 5 to 6 mm and an absorption band of 30 to IGHz.
The purpose of the present invention is to provide a wide range of nickel-zinc ferrite materials.

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes: Iron oxide... 48 to 50 mol% zinc oxide
... 32-37 mol% nickel oxide ... 1
It is a nickel-zinc ferrite material having a composition of 3 to 20 mol%.

In addition, in the above composition, 13 to 20 mol% of nickel oxide
Of this, up to 11 mol% may be replaced with copper oxide.

The reason why the basic composition is limited as described above in the present invention is that each component is related to each other, and in the composition region outside the above range, the absolute level of μ' decreases, and accordingly, the low frequency band As the level of μ" required for absorption of electromagnetic waves decreases, the absorption band shifts to the high frequency side, and the
This is because the amount of absorption below 12 is reduced.

For example, when the amount of iron oxide deviates from the above composition range, μ' decreases regardless of whether it is large or small.

Moreover, when the amount is large, the resistivity increases and the dielectric constant increases. Regarding the amount of zinc oxide, if it is less than the specified amount, μ' will decrease, and if it exceeds the specified amount, the Curie temperature Tc will decrease. Regarding nickel oxide, if it deviates from the specified range, the characteristics of μ' and μ'' will not be optimal, and high absorption performance will not be obtained.

Addition of copper oxide increases sinterability. However, if the amount exceeds the specified amount, the sinterability increases too much, growth of giant particles is observed, and the strength level of the product decreases, which is not preferable.

[Operation] The no-reflection condition for a normal incident plane wave is the complex dielectric constant (
When t'-jε'') is relatively small, it can be approximated as shown in the following equation.

2　π　d　　　　　f However, C is the speed of light and d is the thickness.

A magnetic material that satisfies this equation (1) over a wide frequency range is considered to be a broadband absorber.

Equation (1) is a straight line that slopes downward by 45° to the right when log μ −1og f is plotted. The nickel-zinc ferrite material of the present invention has a lo
g μ −1og r extends linearly, which is considered to be the reason why a broadband absorber was realized.

By the way, the frequency of radiated noise from digital devices such as personal computers is said to be several tens to hundreds of MHz, and by configuring an absorption wall by attaching only a ferrite plate to a metal plate as in the present invention, it can be effectively It is possible to express radio wave absorption characteristics.

[Example] First, raw materials were prepared to have a composition of 49 mol% iron oxide (FewOs), 34 mol% zinc oxide (ZnO), 9 mol% nickel oxide (NiO), and 8 mol% Mj4 (CuO) oxide. The product of the present invention is prepared by blending, kneading with a binder (1 to 2% by weight of polyvinyl alcohol and water), and granulating it.Then, it is molded into a desired shape, and then baked at 1000 to 1100°C for 1 to 3 hours to obtain the product of the present invention. did. Such a manufacturing method is similar to that of a general ferrite core.

For comparison, a nickel-zinc ferrite material (Comparative Example 1) and a magnesium-zinc ferrite material (Comparative Example 2) outside the composition range of the present invention were also produced in the same manner and their properties were measured. Comparative Example 1 is a typical conventional nickel-zinc ferrite material used in general-purpose cores such as drum cores, and its composition is 49 mol% Fe, O,
NiO is 23 mol% and ZnO is 28 mol%. This composition has more nickel oxide and less zinc oxide than the present invention, and the composition of Comparative Example 2 has 45 mol% of Fe, O,
, MgO is 25 mol%, ZnO is 24 mol%, and MnO is 6 mol%.

μ′, μ″− of each ferrite material obtained in this way
The f characteristic curve is shown in FIG. 1, where the solid line is the .mu.'-f characteristic curve and the broken line is the .mu.''-r characteristic curve.

In addition, Fig. 2 shows the matching thickness (the product of the present invention is 5.4 + * m).
, Comparative Example 1 is 6.0 mm, Comparative Example 2 is 8.0 mm), and the radio wave absorption performance was measured in a flat plate shape with the back side short-circuited.

From these FIGS. 1 and 2, it can be seen that in the present invention, μ'>1000 as described above, and the bandwidth in which μ” is attenuated by 20 dB or more is extremely wide and exhibits good performance.

Such a ferrite material can be used as a radio wave absorber for an anechoic chamber, for example, by forming a plate-like material with a thickness of about 5 to 6 IwII and pasting a metal on the back surface.

Of course, a structure in which the dielectric material and the product of the present invention are laminated may also be used.

[Effects of the Invention] Since the present invention is a nickel-zinc ferrite material having a specific composition as described above, μ′>1000 can be realized.
The bandwidth in which μ" is attenuated by 20 dB or more is extremely wide, and excellent radio wave absorption performance can be obtained.

Further, the ferrite material according to the present invention exhibits broadband radio wave absorption performance by itself, and can be made thinner and lighter, so it is particularly advantageous in construction of external walls of buildings, etc., since it does not impose a structural burden. Of course, it is also effective as a wall material inside the housing of various electronic devices.

[Brief explanation of the drawing]

Figure 1 is a μ'8 μ''-f characteristic curve diagram, and Figure 2 is an absorption performance curve diagram.

Claims (3)

[Claims] 1. Nickel consisting of 48-50 mol% iron oxide, 32-37 mol% zinc oxide, and 13-20 mol% nickel oxide.
Zinc-based ferrite material. 2. In the composition according to claim 1, nickel oxide 13 to
A nickel-zinc ferrite material in which 11 mol% or less of 20 mol% is replaced with copper oxide. 3. A radio wave absorber using the nickel-zinc ferrite material according to claim 1 or 2.