JP2806528B2 - Magnesium-zinc ferrite material for radio wave absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to, but is not limited to, a magnesium-zinc ferrite material having high noise absorption performance suitable as, for example, a radio wave absorber for an anechoic chamber. Things.

[Prior art] At present, radiation noise regulations such as CISPR
The range from 0 MHz to 1 GHz is subject to regulation, and there is an increasing need to measure radiation noise from various electronic devices within the above frequency range.

The standard is to measure at an open site, but an anechoic chamber at 30 MHz to 1 GHz without reflection of electromagnetic waves is widely used as a substitute. In this type of anechoic chamber, a radio wave absorber is used to make the inner wall a non-reflective wall.

If radio wave absorption is to be realized only by dielectric loss, the required thickness of the dielectric is about the wavelength of the electromagnetic wave to be absorbed. For example, it is very thick to absorb 100 MHz (wavelength λ = 3 m) or less. Indoor effective volume decreases.

For this reason, recently, a laminated structure of a dielectric and a ferrite has been used. In this case, the ferrite is made to have a thickness of about 8 mm and is responsible for absorption in a low frequency band. Therefore, since the ferrite material is required to have a material property of μ ′ of about 1000, a nickel-zinc-based material has been exclusively used.

[Problems to be Solved by the Invention] It is said that a radio wave absorber requires a reflection loss of about 20 dB or more. In order to obtain the above attenuation around 30 to 40 MHz, it is necessary for μ ″ to decrease with frequency around this band. For this purpose, as long as the μ′-f characteristic curve obeys the limit of Snake, About 1000 is required as μ ′.

Therefore, in the prior art, a nickel-zinc ferrite material was used to satisfy the above characteristics. With this type of material, the matching band is about 5 mm and the absorption band is 40 to 500 MHz.
Although a grade of about a degree is obtained, there is a major drawback that nickel as a raw material is expensive.

An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and the matching thickness is about 8 mm, but the absorption band is 30 to 400 MHz.
Another object of the present invention is to provide a magnesium-zinc-based ferrite material which is favorable especially on a low frequency side and whose raw material is less expensive than nickel.

[Means for Solving the Problems] The present invention, which can achieve the above objects, comprises: heat of oxidation: 47 to 50 mol% magnesium oxide: 20 to 23 mol% zinc oxide: 24 to 27 mol% manganese oxide ... Composition of 3 to 6 mol%, 30MHz to 400MHz
Magnesium for radio wave absorber used in low frequency band of-
It is a zinc-based ferrite material.

More preferably, there is a composition in which 3 mol% or less of copper oxide is added to the above composition.

The reason for limiting the basic composition in the present invention as described above is that each component is related to each other, and μ ′ required for absorption in a low frequency band in a composition region outside the above range.
Is decreased, or the peak width of μ ″ required for absorbing electromagnetic waves is narrowed, resulting in a reduction in absorption performance.

For example, when the amount of iron oxide is out of the above composition range, a decrease in μ ′ is observed. With respect to the amount of zinc oxide, if the amount is less than the specified amount, μ ′ decreases. If the amount exceeds the specified amount, the Curie temperature Tc decreases, and the absorption width decreases due to the narrow μ ″ peak width. If the other two components are out of the specified range, the characteristics of μ ′ and μ ″ will not be optimal and high absorption performance will not be obtained.

The addition of copper oxide enhances sinterability. However, if the amount is more than the specified amount, sinterability is increased, and physical properties such as strength are deteriorated due to grain growth, which is not preferable.

[Action] Within the above composition range, μ ′ can be set to about 1000 even with a magnesium-zinc ferrite material. Incidentally, in the case of a conventional general magnesium-zinc ferrite material, it is about 200 to 500.

The non-reflection condition for a normal incidence plane wave can be approximated by the following equation when the complex relative permittivity (ε′−jε ″) is relatively small.

Here, c is a light flux, and d is a thickness.

It is considered that a magnetic material satisfying the expression (1) over a wide frequency range becomes a broadband absorber. Equation (1) is lo
When the g μ ″ -log f plot is plotted, it is a straight line that descends by 45 ° to the right. In the magnesium-zinc ferrite material of the present invention, the log μ ″ -log f extends linearly even at the low frequency side, so that broadband absorption is achieved. It is thought that the body was realized.

By the way, the frequency of radiation noise from digital equipment such as a personal computer is said to be tens to hundreds of MHz, and by forming an absorption wall by sticking only a ferrite plate to a metal plate as in the present invention, Although it is inferior in the high frequency range, it can exhibit good radio wave absorption characteristics in the low frequency range.

[Example] First, iron oxide (Fe ₂ O ₃ ) 48 mol%, magnesium oxide (M
gO) 22 mol%, zinc oxide (ZnO) 25 mol%, manganese oxide (MnO) 4 mol%, and copper oxide (CuO) 1 mol%. And polyvinyl alcohol and water). After joining to form the desired shape, 1250-1350 ℃
It was fired for up to 3 hours to obtain a product of the present invention. Such a manufacturing method is similar to a general ferrite core manufacturing method.

For comparison, a magnesium-zinc ferrite material outside the composition range of the present invention (comparative example) and a conventional nickel-zinc ferrite material (conventional product) were similarly manufactured and their characteristics were measured. The comparative example is a conventional representative magnesium-zinc ferrite material, and its composition is Fe ₂ O
₃ is 47 mol%, MgO is 29 mol%, ZnO is 20 mol%, and MnO is 4 mol%.

Μ ′, μ ″-
FIG. 1 shows the f characteristic curve. Here, the solid line is the μ′-f characteristic curve, and the broken line is the μ ″ -f characteristic curve.

FIG. 2 shows the results of measuring the radio wave absorption performance in a state where the back surfaces were short-circuited in the shape of a flat plate having each matching thickness.

As can be seen from FIGS. 1 and 2, as described above, the present invention can realize μ ′ ≒ 1000 even though it is a magnesium-zinc ferrite material, and the bandwidth of μ ″ is 20 dB or more attenuated by the conventional nickel-zinc. It can be seen that it has good performance equivalent to that of the system ferrite and slightly shifted to the lower frequency side.

Such a ferrite material is, for example, a plate having a thickness of about 8 mm as a radio wave absorber on the low frequency side (30 to 400 MHz) for an anechoic chamber, a metal is adhered to the back surface, and a high frequency side absorber is used. A structure in which an absorber (such as a mixture of styrene foam and carbon) utilizing dielectric loss is formed in a conical shape and bonded (such as a pyramid-type radio wave absorber described in JP-A-58-199000). ) Can be used.

In addition, this plate-shaped ferrite material alone can be used by attaching it to a metal plate or the like.

FIG. 3 is a graph showing the effect of adding copper oxide. In the figure, the product A of the present invention has a composition in which 1 mol% of copper oxide is added, and the product B of the present invention has a composition in which copper oxide is not added. The respective compositions are shown in Table 1.

In terms of characteristics, the product A of the present invention to which copper oxide is added is almost the same as the product B of the present invention without addition. The effect of the addition is to increase the sinterability. In the case where copper oxide is not added, good firing conditions are 1340 ° C. for 2 hours. For example, when 1 mol% of copper oxide is added, sintering can be performed at a relatively low temperature of 1300 ° C. for 2 hours, and μ ′ is slightly increased. Get higher. Therefore, by adding an appropriate amount of copper oxide, sintering can be performed under conventional general ferrite sintering conditions, so that there is an advantage that a common sintering furnace can be used.

[Effects of the Invention] Since the present invention is a magnesium-zinc ferrite material having a specific composition as described above, the raw material cost is lower than that of a nickel-zinc ferrite material, and μ′μ1000 equivalent thereto can be realized. However, the bandwidth where μ ″ is attenuated by 20 dB or more shifts to a slightly lower frequency, such as 30 MHz to 400 MHz,
Excellent radio wave absorption performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph of μ ′, μ ″ -f characteristic curves, FIG. 2 is a graph of absorption performance curves, and FIG. 3 is a graph of μ ′, μ ″-showing the effect of addition of copper oxide.
It is an f characteristic curve figure.

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Masayuki Inagaki 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (56) References JP-A-58-123550 (JP, A) JP-A Showa 61-48430 (JP, A) Japanese Patent Publication 28-3234 (JP, B1) Showa 34-9303 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 49 / 00-49/08 C04B 35/26-35/40

Claims (2)

(57) [Claims] 1. 47-50 mol% of iron oxide, magnesium oxide 20
~ 23 mol%, zinc oxide 24-27 mol%, manganese oxide3 ~
A magnesium-zinc ferrite material for a radio wave absorber, comprising 6 mol% and used as a plate-like sintered body in a low frequency band of 30 MHz to 400 MHz. 2. A magnesium-zinc ferrite material for a radio wave absorber, wherein copper oxide is added to the composition according to claim 1 in an amount of 3 mol% or less to form a plate-like sintered body in a low frequency band of 30 MHz to 400 MHz.