JPH07302992A - Porous ferrite radio-wave absorber - Google Patents
Porous ferrite radio-wave absorberInfo
- Publication number
- JPH07302992A JPH07302992A JP11343794A JP11343794A JPH07302992A JP H07302992 A JPH07302992 A JP H07302992A JP 11343794 A JP11343794 A JP 11343794A JP 11343794 A JP11343794 A JP 11343794A JP H07302992 A JPH07302992 A JP H07302992A
- Authority
- JP
- Japan
- Prior art keywords
- radio wave
- ferrite
- wave absorber
- coo
- radio
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
- Compounds Of Iron (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、高周波数帯域で優れた
電波吸収特性を有し、軽量、小型、不燃性の電波吸収体
に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight, compact, nonflammable electromagnetic wave absorber having excellent electromagnetic wave absorption characteristics in a high frequency band.
【０００２】[0002]
【従来の技術】電波吸収体としては、磁気損失を利用し
たフェライトや、誘電損失を持つカーボンなどをウレタ
ンなどに含浸させたものや、それをピラミッド状または
三角プリズム状に形成したもの（以後「カーボン含浸タ
イプ」と呼ぶ）などが製品化されている。その電波吸収
体を反射板面に隙間なく並べて構成した電波吸収壁は、
電波の反射がない電波暗室などに応用されている。2. Description of the Related Art As an electromagnetic wave absorber, a ferrite that uses magnetic loss, carbon that has a dielectric loss, or the like is impregnated in urethane, or one that is formed into a pyramid shape or a triangular prism shape. We call it "carbon impregnated type"). The electromagnetic wave absorbing wall, which is constructed by arranging the electromagnetic wave absorbers on the reflector surface without any gap,
It is applied to anechoic chambers where there is no reflection of radio waves.
【０００３】上述のカーボン含浸タイプは、ウレタンを
ピラミッド状または三角プリズム状に成形しているた
め、経時的に先端部が変形したり、簡単に燃える等の問
題点がある。耐燃性を増すために難燃剤を塗布すること
も行なわれてはいるが、経時変化が大きく数年で交換が
必要となる。The above-mentioned carbon impregnated type has a problem in that the tip portion is deformed with time and is easily burned because urethane is molded into a pyramid shape or a triangular prism shape. Although a flame retardant has been applied to increase the flame resistance, the change over time is large and replacement is required within several years.
【０００４】ところで、電波吸収体は、通常、電波吸収
特性として、２０dB以上の吸収率を要求されるが、カー
ボン含浸タイプのみでの場合、電波吸収特性は低周波帯
域（３０Ｍ〜５０ＭHz）での吸収特性が低く、電波吸収
体の厚さが１ｍ以上となるなどの問題点を持っている。
フェライトタイルの場合、６〜８mmの厚さで、２０dB以
上の吸収率を示す周波数帯域幅は、最多でも３０Ｍ〜６
００ＭHz前後であり、フェライトとカーボン含浸タイプ
とを組合せた場合でも、厚さが６０cm以上となる問題点
がある。By the way, a radio wave absorber is usually required to have an absorption rate of 20 dB or more as a radio wave absorption characteristic. However, in the case of only a carbon impregnated type, the radio wave absorption characteristic has a low frequency band (30 M to 50 MHz). It has problems such as low absorption characteristics and a thickness of the electromagnetic wave absorber of 1 m or more.
In the case of ferrite tile, the frequency bandwidth showing the absorption rate of 20 dB or more at a thickness of 6 to 8 mm is 30 M to 6 at the maximum.
The frequency is around 00 MHz, and there is a problem that the thickness becomes 60 cm or more even when the ferrite and the carbon-impregnated type are combined.
【０００５】電波暗室は、電子機器から放射される電磁
波ノイズを測定する半無響室と電子機器等の耐ノイズ性
を試験する全無響室とに大別される。耐ノイズ性試験で
は、高電界を掛けるため、電波吸収体が発熱するという
問題があり、電波吸収体が不燃性であることは極めて重
要である。An anechoic chamber is roughly classified into a semi-anechoic chamber for measuring electromagnetic noise emitted from electronic devices and a fully anechoic chamber for testing noise resistance of electronic devices. In the noise resistance test, since a high electric field is applied, there is a problem that the radio wave absorber generates heat, and it is extremely important that the radio wave absorber is nonflammable.
【０００６】また、電波吸収体の厚さが厚くなること
は、電波暗室等の室内の有効面積が狭くなることであ
り、建屋の大きさが大きくなり、敷地、建造費が増大す
るという大きな欠点がある。Further, the increase in the thickness of the electromagnetic wave absorber means that the effective area in the room such as the anechoic chamber is narrowed, the size of the building is increased, and the site and the construction cost are increased. There is.
【０００７】さらに近年においては、電波利用の多様化
はマイクロ波領域に迄及び、それらの領域に対応した電
波吸収体さらには電波暗室の必要性が高まってきてい
る。本発明者は、別途２０ＧHz迄に対応した電波吸収体
を提案しているが、衛星通信などの利用周波数範囲は３
０ＧHzに迄及んでいる。Further, in recent years, the diversification of use of radio waves extends to the microwave region, and the need for a radio wave absorber and an anechoic chamber corresponding to these regions is increasing. The present inventor has separately proposed a radio wave absorber corresponding to up to 20 GHz, but the frequency range used for satellite communication is 3
It extends to 0 GHz.
【０００８】[0008]
【発明が解決しようとする課題】本発明は、上記の実情
にかんがみ、１Ｇ〜３０ＧHzの高周波帯域において２０
dBの電波吸収特性を有し、不燃性で、小型、軽量、耐久
性に優れた電波吸収体を提供することを課題とする。SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention has been proposed in the high frequency band of 1 to 30 GHz.
It is an object of the present invention to provide a non-flammable, small-sized, lightweight, and excellent radio wave absorber having a radio wave absorption characteristic of dB.
【０００９】[0009]
【課題を解決するための手段】上記の課題を解決するた
め、本発明の電波吸収体は、NiX Zn1-X Fe2O4 （Ｘ＝0.
３６〜1.００）を主成分とし、CoO を５〜４０重量％添
加した組成から成るフェライトを多孔質化した材料で形
成され、１Ｇ〜３０ＧHzの周波数帯域で２０dB以上の電
波吸収特性を有するようにされている。In order to solve the above problems, the electromagnetic wave absorber of the present invention has a Ni X Zn 1-X Fe 2 O 4 (X = 0.
36 to 1.00) as the main component, and made of a porous ferrite material composed of 5 to 40% by weight of CoO, and has a radio wave absorption characteristic of 20 dB or more in the frequency band of 1 GHz to 30 GHz. Has been
【００１０】上記の多孔質フェライトの形状は、ピラミ
ッド状、または三角プリズム状とするのが有利である。The above-mentioned porous ferrite is advantageously shaped like a pyramid or a triangular prism.
【００１１】上記の多孔質フェライトの気孔率は重量及
び加工上の見地から３０〜９０％とする必要がある。The porosity of the above porous ferrite must be 30 to 90% from the viewpoint of weight and processing.
【００１２】[0012]
【作用】一般に、複素比透磁率μｒ＝μ′−ｊμ″（ま
たは損失角 tanδ＝μ″／μ′）及び複素比誘電率εｒ
＝ε′−ｊε″（または損失角 tanδ＝ε″／ε′）
は、高周波における物質の基本特性である。複素比透磁
率及び複素比誘電率が分れば、その物質の反射率（入射
電波が物質に垂直入射した場合に物質表面で反射される
割合）が求められ、また物質の吸収特性として知ること
ができる。In general, complex relative permeability μr = μ'-jμ "(or loss angle tan δ = μ" / μ ') and complex relative permittivity εr
= Ε′-jε ″ (or loss angle tanδ = ε ″ / ε ′)
Is the basic property of a material at high frequencies. If the complex relative permeability and complex relative permittivity are known, the reflectance of the substance (the ratio of the incident radio wave reflected by the surface of the substance when vertically incident on the substance) can be obtained, and also known as the absorption characteristics of the substance. You can
【００１３】多孔質フェライトは、フェライトの磁気特
性を利用して吸収効果を向上させるため、その電波吸収
特性は材料となるフェライトの比透磁率の周波数特性に
依存する。従って、マイクロ波以上の周波数帯で吸収効
果を得るには、比透磁率の損失項のピークが高い周波数
であるほど向上する。また、多孔質化により比誘電率を
下げることができ、高周波での電波吸収特性を改善して
いる。Since the porous ferrite improves the absorption effect by utilizing the magnetic characteristic of the ferrite, its radio wave absorption characteristic depends on the frequency characteristic of the relative permeability of the material ferrite. Therefore, in order to obtain the absorption effect in the frequency band higher than the microwave, the higher the frequency is, the higher the peak of the loss term of the relative permeability is. In addition, the relative permittivity can be lowered by making it porous, and the radio wave absorption characteristics at high frequencies are improved.
【００１４】本発明は、CoO を添加して高周波特性とし
たNi−Zn系フェライトを材質として多孔質フェライトを
作成し、電波吸収体を形成したことにより、高周波での
電波吸収特性を改善したものである。さらに電波吸収体
の形状をピラミッド状、又は三角プリズム状にしたこと
により、高周波での電波吸収特性がさらに改善され、小
型、軽量化を図ることができた。According to the present invention, a radio-wave absorber is formed by forming a porous ferrite by using Ni-Zn-based ferrite with CoO added as a high-frequency characteristic to form a radio-wave absorber. Is. Furthermore, by making the shape of the radio wave absorber into a pyramid shape or a triangular prism shape, the radio wave absorption characteristics at high frequencies were further improved, and it was possible to reduce the size and weight.
【００１５】本発明の電波吸収体に使用されるCoO を添
加したNiX Zn1-X Fe2O4 （Ｘ＝0.３６〜1.００）フェラ
イトは数ＧHzの周波数帯で高い透磁率を有し、透磁率の
周波数特性はCoO の添加量により制御される。特にCoO
の添加量が５重量％以上になると、透磁率のピークを示
す周波数帯が高周波となり、これにより高周波での電波
吸収効果を高めることができる。ただし、添加量を多く
し過ぎると、低周波側の特性が悪化するため、４０重量
％が限界である。The CoO-added Ni X Zn 1-X Fe 2 O 4 (X = 0.36 to 1.00) ferrite used in the radio wave absorber of the present invention has a high magnetic permeability in the frequency band of several GHz. The frequency characteristic of magnetic permeability is controlled by the amount of CoO 2 added. Especially CoO
When the addition amount of is 5% by weight or more, the frequency band showing the peak of the magnetic permeability becomes a high frequency, whereby the radio wave absorption effect at the high frequency can be enhanced. However, if the amount of addition is too large, the characteristics on the low frequency side are deteriorated, so 40% by weight is the limit.
【００１６】これらの材質による多孔質フェライトは、
１００mm以下の厚さで、２０dB以上の吸収率が得られる
周波数帯域幅は１Ｇ〜３０ＧHzであり、小型で優れた電
波吸収特性を示す。Porous ferrite made of these materials is
With a thickness of 100 mm or less, a frequency bandwidth capable of obtaining an absorptivity of 20 dB or more is 1 GHz to 30 GHz, which is small and exhibits excellent electromagnetic wave absorption characteristics.
【００１７】これらの材質による多孔質フェライトの気
孔率は、３０％以下では重量が重くなり、９０％以上で
は成形できない。したがって、気孔率を３０〜９０％と
すれば、軽量で成形可能な多孔質フェライトとなる。If the porosity of the porous ferrite made of these materials is 30% or less, the weight becomes heavy, and if it is 90% or more, it cannot be molded. Therefore, when the porosity is 30 to 90%, the porous ferrite becomes lightweight and can be formed.
【００１８】本発明の電波吸収体は多孔質化したフェラ
イトの焼結体であるから、不燃性であることはもとよ
り、充分な強度を有し、経時的変形も少ない。Since the radio wave absorber of the present invention is a sintered body of porous ferrite, it has not only incombustibility but also sufficient strength and little deformation over time.
【００１９】また、本発明による多孔質フェライトは、
フェライトタイルと組合わせた場合、３０Ｍ〜３０ＧHz
の帯域で２０dB以上の吸収特性を示し、広周波数帯域対
応の電波暗室用吸収体としても利用可能である。Further, the porous ferrite according to the present invention is
30M-30GHz when combined with ferrite tile
It exhibits an absorption characteristic of 20 dB or more in the band, and can be used as an absorber for an anechoic chamber compatible with a wide frequency band.
【００２０】[0020]
【実施例】以下に、本発明の実施例を、図面に基づいて
詳細に説明する。Embodiments of the present invention will be described below in detail with reference to the drawings.
【００２１】＜実施例１＞Ni−ZnフェライトNi18Zn32Fe
2O4 （Ni比0.３６）に添加量を０から４０重量％の間の
５種類に変えてCoO を添加した組成のフェライトの透磁
率の周波数特性を図１に示す。この図より、CoO の添加
量を多くするほど、透磁率のピークが高周波側へ移行し
てゆくことが判る。<Example 1> Ni-Zn ferrite Ni 18 Zn 32 Fe
FIG. 1 shows the frequency characteristics of the magnetic permeability of the ferrite of the composition in which CoO is added by changing the addition amount to 2 O 4 (Ni ratio 0.36) in 5 types from 0 to 40 wt%. From this figure, it can be seen that the peak of magnetic permeability shifts to the high frequency side as the amount of CoO added increases.
【００２２】これらのCoO を添加したNi−Znフェライト
を材料とした気孔率６０％の多孔質体を、図３に示す如
く底面１００mm×１００mm、高さ１００mmのピラミッド
形状に成形して電波吸収体１を形成し、これを反射板２
の一方の面に隙間なく取り付け、反射板２の面に垂直に
電波を入射させ、吸収率を測定した。その測定結果に基
づく電波吸収特性曲線を図２に示す。図には、CoO の添
加量が０、５、２５、４０重量％の４種の場合につい
て、横軸に周波数、縦軸に電波吸収率をとって電波吸収
特性曲線を示した。As shown in FIG. 3, a porous body made of Ni—Zn ferrite containing CoO and having a porosity of 60% is molded into a pyramid shape having a bottom surface of 100 mm × 100 mm and a height of 100 mm, as shown in FIG. 1 to form a reflector 2
The sample was attached to one surface without gaps, radio waves were made to enter the surface of the reflection plate 2 perpendicularly, and the absorption rate was measured. A radio wave absorption characteristic curve based on the measurement result is shown in FIG. In the figure, the radio wave absorption characteristic curve is shown with the horizontal axis representing the frequency and the vertical axis representing the radio wave absorptivity for four types of CoO added in the amounts of 0, 5, 25 and 40 wt%.
【００２３】この図より明らかなように、CoO の添加量
が５〜４０重量％での２０dBの吸収帯域は１Ｇ〜３０Ｇ
と広帯域であり、優れた電波吸収特性を示す。５重量％
未満のCoO 添加量では、高周波数側の特性が悪く、４０
重量％を越すと、低周波数側の特性が悪化する。As is clear from this figure, the absorption band of 20 dB when the added amount of CoO is 5 to 40% by weight is 1 G to 30 G.
It has a wide band and exhibits excellent electromagnetic wave absorption characteristics. 5% by weight
If the amount of CoO added is less than 40%, the characteristics on the high frequency side will be
When it exceeds the weight percentage, the characteristics on the low frequency side are deteriorated.
【００２４】＜実施例２＞NiX Zn1-X Fe2O4 フェライト
のNi比Ｘが0.３６、0.８０及び1.００の３種類の夫々に
CoO を５重量％添加した材料の透磁率の周波数特性を、
横軸に周波数、縦軸に複素比透磁率をとって図４に示
す。これらのNi比の異るNi−Zn系フェライトにCoO を５
重量％添加したものを材料とした気孔率６０％の多孔質
体を、図３に示す如く底面１００mm×１００mm、高さ１
００mmのピラミッド形状の電波吸収体１に成形し、これ
を反射板２に取付けて、電波を反射板２の面に垂直に入
射させて吸収率を測定した。それらの電波吸収特性曲線
を横軸に周波数、縦軸に電波吸収率をとって図５に示
す。この図より明らかなように、Ni比が0.３６以上で
は、２０dBの吸収帯域は１Ｇ〜３０ＧHzと広帯域であ
る。因みに、CoO を添加しない場合は、Ni比が0.３６〜
1.００で同じ形状に形成した電波吸収体の２０dBの吸収
帯域は１Ｇ〜２０ＧHzであり、CoO を添加したことによ
り、高周波域の特性が顕著に改善された。<Example 2> Ni X Zn 1-X Fe 2 O 4 ferrite has a Ni ratio X of 0.36, 0.80 and 1.00, respectively.
The frequency characteristic of magnetic permeability of the material with 5% by weight of CoO added,
The frequency is plotted on the abscissa and the complex relative permeability is plotted on the ordinate, which are shown in FIG. CoO is added to these Ni-Zn ferrites with different Ni ratios.
A porous body having a porosity of 60% made of a material added by weight% has a bottom surface of 100 mm x 100 mm and a height of 1 as shown in Fig. 3.
A radio wave absorber 1 having a pyramid shape of 00 mm was formed, and this was attached to a reflection plate 2, and a radio wave was made incident on the surface of the reflection plate 2 perpendicularly to measure the absorption rate. The radio wave absorption characteristic curves are shown in FIG. 5 with the horizontal axis representing frequency and the vertical axis representing radio wave absorption rate. As is clear from this figure, when the Ni ratio is 0.36 or more, the absorption band of 20 dB is a wide band of 1 GHz to 30 GHz. By the way, when CoO is not added, the Ni ratio is 0.36 ~
The absorption band of 20 dB of the electromagnetic wave absorber formed in the same shape at 1.00 is 1 G to 20 GHz, and the addition of CoO significantly improved the characteristics in the high frequency range.
【００２５】＜実施例３＞実施例１のCoO を５重量％添
加したNi−Znフェライト（Ni比0.３６）のピラミッド型
多孔質体及び実施例２の中のCoO を５重量％添加したNi
比1.００のNi−Znフェライトのピラミッド型多孔質体
を、図６に示すようにフェライトタイル３と組合せ、夫
々について電波吸収率を測定した。その吸収特性曲線
を、図７に、横軸に周波数を、縦軸に電波吸収率をとっ
て示す。この図より明らかな如く、２０dBの吸収帯域は
３０ＭHz〜３０ＧHzの広帯域に亘っており、フェライト
タイルとの組合せにより、１ＧHz以下の低周波域の吸収
特性が著しく向上している。<Example 3> A pyramidal porous body of Ni-Zn ferrite (Ni ratio: 0.36) containing 5% by weight of CoO of Example 1 and 5% by weight of CoO of Example 2 were added. Ni
A Ni-Zn ferrite pyramid-type porous body having a ratio of 1.00 was combined with a ferrite tile 3 as shown in FIG. 6, and the radio wave absorption rate was measured for each. The absorption characteristic curve is shown in FIG. 7 with the horizontal axis representing frequency and the vertical axis representing radio wave absorption rate. As is clear from this figure, the absorption band of 20 dB extends over a wide band of 30 MHz to 30 GHz, and the combination with the ferrite tile significantly improves the absorption characteristics in the low frequency region of 1 GHz or less.
【００２６】[0026]
【発明の効果】以上説明した如く、本発明によれば、１
Ｇ〜３０ＧHzの高周波帯域において、２０dBの電波吸収
特性を有し、不燃性、小型、軽量の優れた電波吸収体を
得ることができ、高周波帯域に対応する電波暗室の経済
的な建造に効果が得られる。As described above, according to the present invention, 1
In the high frequency band of G to 30 GHz, it has an electromagnetic wave absorption characteristic of 20 dB, and it is possible to obtain an excellent non-flammable, small and lightweight electromagnetic wave absorber, which is effective for economical construction of an anechoic chamber corresponding to the high frequency band can get.
【図１】種々の添加量でCoO を添加したNi−Zn系フェラ
イトの複素比透磁率の周波数特性を示す曲線図である。FIG. 1 is a curve diagram showing frequency characteristics of complex relative permeability of Ni—Zn ferrites with various amounts of CoO added.
【図２】種々の添加量でCoO を添加したNi−Zn系フェラ
イト多孔質体の電波吸収特性を示す曲線図である。FIG. 2 is a curve diagram showing radio wave absorption characteristics of Ni—Zn ferrite porous bodies to which CoO is added at various addition amounts.
【図３】本発明による電波吸収体の一実施例の構成を示
す断面図である。FIG. 3 is a sectional view showing a configuration of an embodiment of a radio wave absorber according to the present invention.
【図４】５重量％のCoO を添加した種々のNi比のNi−Zn
系フェライトの複素比透磁率の周波数特性を示す曲線図
である。FIG. 4 Ni-Zn with various Ni ratios with addition of 5 wt% CoO
It is a curve figure which shows the frequency characteristic of the complex relative permeability of system ferrite.
【図５】５重量％のCoO を添加した種々のNi比のNi−Zn
系フェライトの多孔質体の電波吸収特性を示す曲線図で
ある。FIG. 5: Ni-Zn with various Ni ratios added with 5 wt% CoO
FIG. 3 is a curve diagram showing the radio wave absorption characteristics of a porous body of a system ferrite.
【図６】本発明による電波吸収体の他の実施例の構成を
示す断面図である。FIG. 6 is a cross-sectional view showing the configuration of another embodiment of the radio wave absorber according to the present invention.
【図７】CoO を添加したNi−Zn系フェライト多孔質体と
フェライトタイルとを組合せた構成の電波吸収特性を示
す曲線図である。FIG. 7 is a curve diagram showing radio wave absorption characteristics of a configuration in which a Ni—Zn ferrite porous body to which CoO 3 is added and a ferrite tile are combined.
１ ピラミッド状多孔質フェライト電波吸収体 ２ 反射板 ３ フェライトタイル 1 Pyramid porous ferrite wave absorber 2 Reflector 3 Ferrite tile
Claims (3)
０）を主成分とし、CoO を５〜４０重量％添加した組成
から成るフェライトを多孔質化した材料で形成され、１
Ｇ〜３０ＧHzの周波数帯域で２０dB以上の電波吸収特性
を有する電波吸収体。1. Ni X Zn 1-X Fe 2 O 4 (X = 0.36 to 1.0)
0) as a main component and CoO in an amount of 5-40% by weight.
A radio wave absorber having a radio wave absorption characteristic of 20 dB or more in the frequency band of G to 30 GHz.
ッド形又は三角プリズム形であることを特徴とする請求
項１に記載の電波吸収体。2. The radio wave absorber according to claim 1, wherein the shape of the porous ferrite is a pyramid shape or a triangular prism shape.
％〜９０％であることを特徴とする請求項１又は２に記
載の電波吸収体。3. The porosity of the porous ferrite is 30.
% To 90%, The radio wave absorber according to claim 1 or 2, characterized in that
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11343794A JPH07302992A (en) | 1994-05-02 | 1994-05-02 | Porous ferrite radio-wave absorber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11343794A JPH07302992A (en) | 1994-05-02 | 1994-05-02 | Porous ferrite radio-wave absorber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH07302992A true JPH07302992A (en) | 1995-11-14 |
Family
ID=14612207
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP11343794A Pending JPH07302992A (en) | 1994-05-02 | 1994-05-02 | Porous ferrite radio-wave absorber |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH07302992A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5892188A (en) * | 1996-07-24 | 1999-04-06 | Kabushiki Kaisha Riken | Porous ferrite wave absorber |
| JP2000022380A (en) * | 1998-06-30 | 2000-01-21 | Riken Corp | Radio wave absorber |
| JP2009177105A (en) * | 2008-01-25 | 2009-08-06 | Matsuoka Roofing Inc | Electromagnetic wave absorber |
-
1994
- 1994-05-02 JP JP11343794A patent/JPH07302992A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5892188A (en) * | 1996-07-24 | 1999-04-06 | Kabushiki Kaisha Riken | Porous ferrite wave absorber |
| JP2000022380A (en) * | 1998-06-30 | 2000-01-21 | Riken Corp | Radio wave absorber |
| JP2009177105A (en) * | 2008-01-25 | 2009-08-06 | Matsuoka Roofing Inc | Electromagnetic wave absorber |
| JP4602429B2 (en) * | 2008-01-25 | 2010-12-22 | 松岡瓦産業株式会社 | Radio wave absorber |
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