JP2903738B2 - Radio wave absorber - Google Patents
Radio wave absorberInfo
- Publication number
- JP2903738B2 JP2903738B2 JP4873891A JP4873891A JP2903738B2 JP 2903738 B2 JP2903738 B2 JP 2903738B2 JP 4873891 A JP4873891 A JP 4873891A JP 4873891 A JP4873891 A JP 4873891A JP 2903738 B2 JP2903738 B2 JP 2903738B2
- Authority
- JP
- Japan
- Prior art keywords
- radio wave
- wave absorber
- polystyrene
- resin
- conductive
- 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.)
- Expired - Fee Related
Links
Description
【産業上の利用分野】本発明は電波吸収体に関し、特に
電波暗室に使用する電波吸収体の材料に関するものであ
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorber, and more particularly to a material for an electromagnetic wave absorber used in an anechoic chamber.
【従来の技術】従来、ＥＭＩノイズ（電磁波ノイズ）測
定やアンテナ評価試験測定のために電波暗室が使用され
ている。この電波暗室は壁からの反射を防ぐため電波吸
収体を壁や床に張り付けた構造をしている。このような
電波暗室に使用される電波吸収体には形状や材質が異な
る種々のものが提案されている。図４（ａ）に示すよう
なウェッジ形状の電波吸収体としては、発泡ポリスチレ
ンの一次発泡ビーズの表面に導電性カーボンと熱可塑性
樹脂（例えば、酢酸ビニール）の混合物からなる導電性
塗料を塗布し、摂氏１００〜１１０°Ｃで蒸気加熱成形
した材料が使われている。この電波吸収体はクローズド
セル構造の発泡ポリスチレンを用いているので、耐候性
が極めて優れているという特徴を持っている。しかしな
がら、ポリスチレンビーズの表面に熱可塑性の導電性塗
料を塗布し、摂氏１００°Ｃで蒸気加熱すると、その導
電性塗料（酢酸ビニール＋カーボン）は摂氏７０〜８０
°Ｃで軟化するため、成形の際に金型への融着が生じ金
型からの離着が悪く、場合によっては成形物の一部が金
型にとられ、歩留りが悪いという問題がある。また、発
泡ポリスチレンはもろいという性質を有しており、例え
ば、ピラミッド形状の電波吸収体の先端が欠けるという
問題がある。一方、図４（ｂ）に示すようなピラミッド
形状の電波吸収体には、発泡ポリウレタンを導電性塗料
中に含浸し乾燥硬化させた材料や、特開昭６３−１９２
２９９号公報に開示されているような発泡ポリエチレン
に導電性カーボンを練り込んだ材料が使われている。発
泡ポリウレタンを使用した電波吸収体は、含浸によって
導電性を付与するため、手軽に製造できる反面、オープ
ンセル構造であるため吸湿による電波吸収性能の劣化及
び耐候性が悪いという問題点をもっている。図５に発泡
ポリウレタンからなるピラミッド形状電波吸収体を温度
４０°Ｃ、湿度９０％RHの条件下に５００時間放置した
前後の電波吸収特性の比較を示す。図５中、実線は試験
（放置）前を示し、破線は試験（放置）後を示してい
る。図５から明らかなように、放置後５GHz 以上の周波
数において、反射減衰量（特性）が大幅に劣化している
ことがわかる。最後に発泡ポリエチレンに導電性カーボ
ンを練り込んだ材料からなる電波吸収体は、クローズド
セル構造の発泡ポリエチレンで構成されているため耐候
性がよく、また導電性カーボンを練り込んでいるため材
料表面からの導電性カーボンの脱落がないというメリッ
トがある。しかしながら、ポリエチレンに導電性カーボ
ンを練り込んだ材料を金型内で発泡させると金型に接す
る表面に内部より抵抗が低く、また密度の高いスキン層
を形成するため、この面からの電磁波の反射が生ずると
いう問題点がある。従って、この問題点を解決するため
スキン層を除去しなければならず、材料の歩留りが悪い
という問題がある。2. Description of the Related Art Conventionally, an anechoic chamber has been used for EMI noise (electromagnetic noise) measurement and antenna evaluation test measurement. This anechoic chamber has a structure in which a radio wave absorber is attached to the wall or floor to prevent reflection from the wall. Various types of electromagnetic wave absorbers having different shapes and materials have been proposed for use in such an anechoic chamber. As a wedge-shaped radio wave absorber as shown in FIG. 4A, a conductive paint made of a mixture of conductive carbon and a thermoplastic resin (for example, vinyl acetate) is applied to the surface of primary expanded beads of expanded polystyrene. A material formed by steam heating at 100 to 110 ° C is used. Since this radio wave absorber uses foamed polystyrene having a closed cell structure, it has a feature that weather resistance is extremely excellent. However, when a thermoplastic conductive paint is applied to the surface of polystyrene beads and steam-heated at 100 ° C., the conductive paint (vinyl acetate + carbon) becomes 70 to 80 ° C.
Because of softening at ° C, there is a problem that fusion occurs to the mold during molding and separation from the mold is poor, and in some cases, a part of the molded product is taken into the mold, resulting in poor yield. . In addition, expanded polystyrene has a fragile property. For example, there is a problem in that the tip of a pyramid-shaped radio wave absorber is chipped. On the other hand, a radio wave absorber having a pyramid shape as shown in FIG. 4B is made of a material obtained by impregnating a foamed polyurethane in a conductive paint and drying and curing the same.
No. 299 discloses a material obtained by kneading conductive carbon into foamed polyethylene. The radio wave absorber using foamed polyurethane imparts conductivity by impregnation, so that it can be easily manufactured. On the other hand, it has an open cell structure, so that it has a problem that radio wave absorption performance deteriorates due to moisture absorption and weather resistance is poor. FIG. 5 shows a comparison of the radio wave absorption characteristics before and after the pyramid-shaped radio wave absorber made of foamed polyurethane was left for 500 hours under conditions of a temperature of 40 ° C. and a humidity of 90% RH. In FIG. 5, the solid line indicates the state before the test (leaving), and the broken line indicates the state after the test (leaving). As is clear from FIG. 5, the return loss (characteristic) is significantly deteriorated at a frequency of 5 GHz or more after standing. Finally, a radio wave absorber made of a material in which conductive carbon is kneaded with foamed polyethylene has good weather resistance because it is made of foamed polyethylene with a closed cell structure, and also has a good surface resistance because it is kneaded with conductive carbon. There is an advantage that the conductive carbon does not fall off. However, if a material in which conductive carbon is kneaded with polyethylene is foamed in a mold, the surface in contact with the mold has a lower resistance than the inside and a high-density skin layer is formed. Is caused. Therefore, in order to solve this problem, the skin layer must be removed, and there is a problem that the yield of the material is poor.
【発明が解決しようとする課題】上述したように発泡ポ
リスチレンを基材とした電波吸収体材料は、耐候性に優
れている反面、成形性、歩留りに問題があり、更に柔軟
性がなく、もろく欠けが生じるという問題点もあり、他
の発泡ポリウレタン、または発泡ポリエチレンを使用し
た電波吸収体材料についても、信頼性、歩留りに問題が
ある。本発明の目的は、このような従来の問題を解決
し、信頼性に優れ、成形性も良好で柔軟性があり、もろ
さを改善した電波吸収体を提供することにある。As described above, the radio wave absorber material based on expanded polystyrene is excellent in weather resistance, but has problems in moldability and yield, and is not flexible and brittle. There is also a problem of chipping, and other radio wave absorber materials using foamed polyurethane or foamed polyethylene also have problems in reliability and yield. An object of the present invention is to solve such a conventional problem and to provide a radio wave absorber having excellent reliability, good moldability, flexibility, and improved fragility.
【課題を解決するための手段】上記目的を達成するた
め、本発明の電波吸収体は、電波到来方向に導電性発泡
樹脂からなるウェッジ形状又はピラミッド形状の電波導
入部と該電波導入部の背面に配置した上記導電性発泡樹
脂からなる平板状のフラット部と該フラット部の背面に
配置した完全反射体で裏打ちされた焼結体フェライトと
から構成された電波吸収体において、上記導電性発泡樹
脂は、ポリスチレン樹脂又はポリスチレンとポリエチレ
ンの共重合樹脂中に導電性カーボンを練り込み分散さ
せ、発泡剤を加え、ビーズ状にした後、蒸気加熱により
２０〜８０倍の倍率に発泡して構成し、該構成された導
電性発泡樹脂の体積固有抵抗が１０4 Ω・cm 〜１０8 Ω
・cm であることに特徴がある。In order to achieve the above object, a radio wave absorber according to the present invention comprises a wedge-shaped or pyramid-shaped radio wave introduction portion made of a conductive foamed resin in a radio wave arrival direction and a back surface of the radio wave introduction portion. A radio wave absorber composed of a flat plate-shaped flat portion made of the above-mentioned conductive foamed resin and a sintered ferrite lined with a perfect reflector disposed on the back of the flat portion. Is kneaded and dispersed in a conductive resin in a polystyrene resin or a copolymer resin of polystyrene and polyethylene, added a foaming agent, formed a bead, and foamed by steam heating to a magnification of 20 to 80 times, The volume resistivity of the formed conductive foamed resin is 10 4 Ω · cm to 10 8 Ω.
・ It is characterized by cm.
【作用】本発明においてはポリスチレン樹脂又はポリス
チレンとポリエチレンの共重合樹脂中に導電性カーボン
を練り込むため、成形の際に金型への融着がなく、通常
の発泡ポリスチレンの成形と同様に複雑形状の成形が容
易であり、耐候性に優れた電波吸収体（材料）を構成で
きる。In the present invention, since conductive carbon is kneaded into a polystyrene resin or a copolymer resin of polystyrene and polyethylene, there is no fusion to a mold at the time of molding. It is easy to form the shape, and a radio wave absorber (material) having excellent weather resistance can be formed.
【実施例】以下、本発明の一実施例を、図面により詳細
に説明する。図１は、本発明の一実施例を示す電波吸収
体の構造図である。これはウェッジ形状の電波吸収体の
部分断面構造を示している。図２に全体構造を示す。図
１、図２において、１は電波を完全に反射する反射体、
２は反射体１上に配置された焼結フェライト、３は本発
明による１０5 〜１０7 Ω・cmの体積固有抵抗を有する
発泡倍率４０倍の導電性発泡ポリスチレンとポリエチレ
ンの共重合体からなる平板状のフラット部、４は本発明
による１０5 〜１０7 Ω・cmの体積固有抵抗を有する発
泡倍率４０倍の導電性発泡ポリスチレンとポリエチレン
の共重合体からなるウェッジ形状の電波導入部である。
本実施例の電波吸収体は、ポリスチレンとポリエチレン
の共重合体中に導電性カーボンを練り込み分散させ、発
泡剤を加え、ビーズ状にした後、蒸気加熱により４０倍
の倍率に発泡し成形することにより製造できる。図３は
図２の構造の電波吸収体の反射減衰量の周波数特性を示
す図である。ここで、破線は発泡ポリスチレンによる従
来例を示し、実線は本実施例を示している。また、本実
施例で測定に用いたウェッジ形状の電波吸収体は、６０
cm角で長さ１m 程度のものである。図３から明らかなよ
うに、５０MHz 以上の周波数帯域において反射減衰量が
通常電波吸収体の機能として必要な２０dB以上を維持し
ている。さらに本実施例では、図３中に破線で示した、
従来の発泡ポリスチレンを基材とした電波吸収体の特性
と比較して同等の特性が得られていることがわかる。本
実施例のポリスチレン−ポリエチレン共重合体からなる
電波吸収体は従来のポリスチレンからなる電波吸収体に
比較して柔軟性が大幅に増加している。このことを示す
ため、３点曲げ試験における破壊までの変形量について
従来のポリスチレンからなる電波吸収体との比較を行な
った。その結果、従来のポリスチレン電波吸収体２０m
m、ポリスチレン−ポリエチレン共重合体からなる電波
吸収体２８mmと従来のポリスチレン電波吸収体に比較し
て大幅に柔軟性が増加していることがわかった。電波吸
収体が反射体、フェライト、フラット部、電波導入部か
ら成る構成は特公昭４６−１２２２８号公報に開示され
たもので、その構造はフェライト板電波吸収壁の前面に
ジグザグ形電波吸収壁を配置したフェライトと誘電損失
料からなるものである。この複合電波吸収体は、フェラ
イト層および誘電体層（フラット部、電波導入部）を適
切に選択することにより広帯域な特性が得られる。この
場合、誘電体層とフェライト層のインピーダンスマッチ
ングはフェライト層のインピーダンス、誘電体層の形
状、体積固有抵抗を適切に選択することにより得られ
る。誘電体層の適切な体積固有抵抗は、誘電体層の形状
およびフェライト層のインピーダンスとの関係で、その
範囲が決められる。本実施例においては１０5 〜１０7
Ω・cm のものを使用したが、これ以外の形状、フェライ
ト層のインピーダンスを考えると１０4 〜１０8 Ω・cm
の範囲でインピーダンスマッチングを得ることが可能で
ある。さらに周知のとおり電波吸収体の材料としては誘
電率の低いものが望ましい。従って発泡材料の発泡倍率
を20倍以下にすると、誘電率が大きくなり電波吸収体表
面からの反射が大きくなるだけでなく重量も重くなり好
ましくない。一方、発泡倍率を８０倍以上にすると強度
が弱くなり実用性がなくなる。本実施例では発泡倍率が
４０倍のものを使用したが、２０〜８０倍の範囲であれ
ば、本実施例を適用可能である。本実施例では、ポリス
チレンとポリエチレンの共重合樹脂を使用したが、ポリ
スチレン樹脂を使用して本実施例の製法により製造して
も良い。上記実施例では、ウェッジ形状の電波吸収体に
ついて説明したが、ピラミッド形状の電波吸収体にも同
様に本実施例を適用できることは言うまでもない。ま
た、ポリエチレンを含んでいるので柔軟性もある。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a structural diagram of a radio wave absorber showing one embodiment of the present invention. This shows a partial cross-sectional structure of a wedge-shaped radio wave absorber. FIG. 2 shows the overall structure. 1 and 2, reference numeral 1 denotes a reflector that completely reflects radio waves;
Reference numeral 2 denotes a sintered ferrite disposed on the reflector 1, and reference numeral 3 denotes a copolymer of conductive expanded polystyrene and polyethylene having an expansion ratio of 40 and having a volume resistivity of 10 5 to 10 7 Ω · cm according to the present invention. The flat flat portion 4 is a wedge-shaped radio wave introducing portion made of a copolymer of conductive expanded polystyrene and polyethylene having a volume resistivity of 10 5 to 10 7 Ω · cm and a foaming ratio of 40 according to the present invention. .
The radio wave absorber of the present example is obtained by kneading and dispersing conductive carbon in a copolymer of polystyrene and polyethylene, adding a foaming agent, forming a bead, foaming to a 40-fold magnification by steam heating, and molding. Can be manufactured. FIG. 3 is a diagram showing the frequency characteristic of the return loss of the radio wave absorber having the structure of FIG. Here, the broken line shows a conventional example using expanded polystyrene, and the solid line shows this example. The wedge-shaped radio wave absorber used for the measurement in this example is
It is about 1 m in length in cm square. As is apparent from FIG. 3, in the frequency band of 50 MHz or more, the return loss is maintained at 20 dB or more which is necessary for the function of the normal radio wave absorber. Further, in the present embodiment, a broken line shown in FIG.
It can be seen that the same characteristics as those of the conventional electromagnetic wave absorber using expanded polystyrene as a base material are obtained. The radio wave absorber made of the polystyrene-polyethylene copolymer of the present embodiment has greatly increased flexibility as compared with the conventional radio wave absorber made of polystyrene. In order to show this fact, the amount of deformation up to breaking in the three-point bending test was compared with that of a conventional radio wave absorber made of polystyrene. As a result, the conventional polystyrene wave absorber 20 m
m, a wave absorber made of a polystyrene-polyethylene copolymer of 28 mm was found to have significantly increased flexibility as compared with the conventional polystyrene wave absorber. The configuration in which the radio wave absorber comprises a reflector, a ferrite, a flat portion, and a radio wave introduction portion is disclosed in Japanese Patent Publication No. 46-12228, and its structure is a zigzag radio wave absorption wall in front of a ferrite plate radio wave absorption wall. It consists of ferrite and dielectric loss material. In this composite radio wave absorber, a wideband characteristic can be obtained by appropriately selecting a ferrite layer and a dielectric layer (flat portion, radio wave introduction portion). In this case, impedance matching between the dielectric layer and the ferrite layer can be obtained by appropriately selecting the impedance of the ferrite layer, the shape of the dielectric layer, and the volume resistivity. The appropriate volume resistivity of the dielectric layer is determined by the relationship between the shape of the dielectric layer and the impedance of the ferrite layer. In this embodiment, 10 5 to 10 7
Ω · cm was used, but considering other shapes and the impedance of the ferrite layer, 10 4 to 10 8 Ω · cm
It is possible to obtain impedance matching in the range of Further, as is well known, a material having a low dielectric constant is desirable as a material of the radio wave absorber. Therefore, if the expansion ratio of the foam material is set to 20 times or less, the dielectric constant increases, the reflection from the surface of the radio wave absorber increases, and the weight increases, which is not preferable. On the other hand, when the expansion ratio is 80 times or more, the strength becomes weak and the practicality is lost. In this embodiment, a foaming ratio of 40 is used, but the present embodiment is applicable as long as the expansion ratio is in the range of 20 to 80 times. In this embodiment, a copolymer resin of polystyrene and polyethylene is used. However, a polystyrene resin may be used and manufactured according to the manufacturing method of this embodiment. Although the wedge-shaped radio wave absorber has been described in the above embodiment, it goes without saying that this embodiment can be similarly applied to a pyramid-shaped radio wave absorber. It also has flexibility because it contains polyethylene.
【発明の効果】以上説明したように、本発明によれば、
信頼性に優れ、成形性の良好な電波吸収体を提供するこ
とができる。また、共重合体を用いることにより、強度
を増大するとともに、柔軟性も増すことができる。As described above, according to the present invention,
It is possible to provide a radio wave absorber having excellent reliability and good moldability. In addition, by using a copolymer, strength can be increased and flexibility can be increased.
【図１】本発明の一実施例を示す電波吸収体の構造図で
ある。FIG. 1 is a structural view of a radio wave absorber according to an embodiment of the present invention.
【図２】図１の電波吸収体の各部の構成図である。FIG. 2 is a configuration diagram of each part of the radio wave absorber of FIG. 1;
【図３】本発明の実施例における周波数−反射減衰量特
性と従来例との比較図である。FIG. 3 is a diagram illustrating a comparison between a frequency-return loss characteristic according to an embodiment of the present invention and a conventional example.
【図４】電波吸収体の具体的構成例を示す図である。FIG. 4 is a diagram showing a specific configuration example of a radio wave absorber.
【図５】従来の発泡ポリウレタンによるピラミッド形電
波吸収体の特性図である。FIG. 5 is a characteristic diagram of a conventional pyramid-shaped electromagnetic wave absorber made of foamed polyurethane.
１ 反射体 ２ フェライト ３ フラット部 ４ 電波導入部 DESCRIPTION OF SYMBOLS 1 Reflector 2 Ferrite 3 Flat part 4 Radio wave introduction part
Claims (1)
ウェッジ形状又はピラミッド形状の電波導入部と該電波
導入部の背面に配置した上記導電性発泡樹脂からなる平
板状のフラット部と該フラット部の背面に配置した完全
反射体で裏打ちされた焼結体フェライトとから構成され
た電波吸収体において、上記導電性発泡樹脂は、ポリス
チレン樹脂又はポリスチレンとポリエチレンの共重合樹
脂中に導電性カーボンを練り込み分散させ、発泡剤を加
え、ビーズ状にした後、蒸気加熱により２０〜８０倍の
倍率に発泡して構成し、該構成された導電性発泡樹脂の
体積固有抵抗が１０4 Ω・cm 〜１０8 Ω・cmであること
を特徴とする電波吸収体。1. A wedge-shaped or pyramid-shaped radio wave introducing portion made of a conductive foam resin in a direction of arrival of a radio wave, a flat flat portion made of the conductive foam resin disposed on the back of the radio wave introducing portion, and the flat portion. In a radio wave absorber composed of a sintered ferrite lined with a perfect reflector disposed on the back surface of the electromagnetic wave absorber, the conductive foamed resin is made by kneading conductive carbon in a polystyrene resin or a copolymer resin of polystyrene and polyethylene. After adding the foaming agent, adding a foaming agent, forming a bead, and foaming by steam heating to a magnification of 20 to 80 times, the conductive foamed resin thus formed has a volume resistivity of 10 4 Ω · cm 2 to A radio wave absorber characterized by having a resistivity of 10 8 Ω · cm.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4873891A JP2903738B2 (en) | 1991-02-22 | 1991-02-22 | Radio wave absorber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4873891A JP2903738B2 (en) | 1991-02-22 | 1991-02-22 | Radio wave absorber |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04267596A JPH04267596A (en) | 1992-09-24 |
| JP2903738B2 true JP2903738B2 (en) | 1999-06-14 |
Family
ID=12811631
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP4873891A Expired - Fee Related JP2903738B2 (en) | 1991-02-22 | 1991-02-22 | Radio wave absorber |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2903738B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002190691A (en) * | 2000-12-22 | 2002-07-05 | Tdk Corp | Wave absorber |
| AT6727U1 (en) * | 2003-01-30 | 2004-03-25 | Plansee Ag | METHOD FOR PRODUCING POROUS SINTERED BODIES |
-
1991
- 1991-02-22 JP JP4873891A patent/JP2903738B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04267596A (en) | 1992-09-24 |
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