JP2005012031A - Radio absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio absorber using a resistance film with capacitive susceptance which can be designed and manufactured more thinly and easily than a radio absorber using a resistance film having only resistance component. <P>SOLUTION: The radio absorber 10 is provided with a radio reflector 11, a dielectric layer 12<SB>1</SB>arranged on a radio-incoming side of this radio reflector 11, and the resistance film 22<SB>1</SB>arranged on the radio-incoming side of the dielectric layer 12<SB>1</SB>. In a frequency where reflection attenuation is maximized in the frequency area of radio of 0.8 GHz to 18 GHz, the value of the real part of the face resistance value of the resistance film 22<SB>1</SB>is within the range of 5 to 2,000 Ω square, the value of the imaginary part of the face resistance value is within the range of -15 to -1,100 Ω square, and a value obtained by dividing the value of the imaginary part by that of the real part is within the range of -0.3 to -3.1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００９２】
上記の表に示したように、導電性粉末の配合量を約５７〜７２重量％の範囲内で変化させることにより、２７０〜３５００Ω□の範囲内の直流面抵抗値を有する抵抗皮膜２２を作製することができた。
【００９３】
次に、実施例における抵抗皮膜２２の面抵抗値の評価方法について説明する。この評価方法では、まず、電波反射体１１から約１０ｍｍの距離の位置に、スペーサを介して、上記の方法で作製した抵抗皮膜２２を配置して試料を作製した。ここでは、スペーサの材料として、空気の誘電率に近い誘電率を有する発泡ポリエチレンを用いた。次に、上記試料について、電波が抵抗皮膜２２に対して垂直に入射する際の入力インピーダンスを、以下の方法で測定した。まず、上述のように配置した抵抗皮膜２２の前面に、この抵抗皮膜２２と同一の平面形状を有する金属板を配置し、この金属板の反射係数を測定した。次に、試料の反射係数を測定した。次に、金属板の反射係数と試料の反射係数との比に基づいて、試料前面の入力インピーダンスを算出した。次に、算出した入力インピーダンスから面抵抗値の複素量を計算により求めた。
【００９４】
図１３は、上述の面抵抗値の評価のために用いた測定システムの構成を示している。この測定システムは、評価しようとする試料１２０に電波を放射する送信アンテナ１２１と、試料１２０で反射された電波を受信する受信アンテナ１２２と、送信アンテナ１２１に接続されたネットワークアナライザ１２３と、入力端が受信アンテナ１２２に接続され、出力端がネットワークアナライザ１２３に接続された増幅器１２４とを備えている。送信アンテナ１２１と受信アンテナ１２２には、ダブルリジットガイドアンテナを用いた。送信アンテナ１２１と受信アンテナ１２２は、アンテナ１２１，１２２から試料１２０における電波の入射位置までの距離が等しくなるように配置される。実施例では、この距離を３ｍとしている。また、評価システムは、電波暗室１２５内に設置される。
【００９５】
ネットワークアナライザ１２３は、送信アンテナ１２１に送信用の信号を送る。受信アンテナ１２２によって得られる受信信号は、増幅器１２４によって増幅された後、ネットワークアナライザ１２３に入力される。ネットワークアナライザ１２３は、送信用の信号と受信信号とに基づいて試料の特性を測定する。測定周波数は１〜９ＧＨｚとした。
【００９６】
なお、送信アンテナ１２１から受信アンテナ１２２へ直接到達する直接波は、測定値に影響を与える。そのため、実施例では、試料１２０がない状態で直接波を測定し、試料１２０がある状態の測定値から、直接波の測定値をベクトル的に除去した。また、測定では、タイムドメイン法を併用した。
【００９７】
図１４は、作製した抵抗皮膜２２の周波数２ＧＨｚ〜８ＧＨｚにおける面抵抗値の複素量の周波数特性を示している。図１５は、作製した抵抗皮膜２２の２ＧＨｚ、５ＧＨｚ、８ＧＨｚにおける面抵抗値の複素量と直流面抵抗値との関係を示している。図１４および図１５から分かるように、作製した抵抗皮膜２２の面抵抗値の実部および虚部の値は、周波数が高くなるに従って小さくなる傾向にある。
【００９８】
また、図１５から分かるように、作製した抵抗皮膜２２の面抵抗値の複素量と直流面抵抗値には相関があり、作製した抵抗皮膜２２の面抵抗値の複素量は、直流面抵抗値に対して周波数毎の直線で表すことができる。従って、周波数を決めると、直流面抵抗値から面抵抗値の実部および虚部が求まる。この関係により、電波吸収体１０を設計する際には、抵抗皮膜の面抵抗値を１変数として取り扱うことが可能になる。その結果、電波吸収体１０の設計を、ニュートン法等で行うことが可能になる。また、上記の関係により、所望の面抵抗値を有する抵抗皮膜２２を安定して製造することが可能になる。
【００９９】
［第１の実施例］
次に、第１の実施例の電波吸収体１０として、上述の特性を有する抵抗皮膜２２を用いて、図１に示したように抵抗層１３が１層のみの構成の電波吸収体１０（以下、単層型電波吸収体と言う。）を設計および製造した。
【０１００】
まず、第１の実施例の単層型電波吸収体の設計方法について説明する。図１６は、前述のようにして作製した抵抗皮膜２２の面抵抗値の複素量をコールコールプロットとして表したものである。図１６において、記号Ｍを付した曲線は、単層型電波吸収体の整合曲線を表わしている。なお、ここで言う整合曲線とは、整合条件を満たす面抵抗値の複素量の軌跡を表わす曲線である。図１６から、周波数２ＧＨｚ〜８ＧＨｚの範囲では、抵抗皮膜２２の直流面抵抗値が約３５０〜５００Ω□の範囲内のときに整合条件を満たすことが可能であり、これにより、スペーサの厚さが０．１７λ〜０．０９λの単層型電波吸収体が得られることが分かる。また、図１６から分かるように、周波数が高くなるに従い、整合条件を満たすときのスペーサの厚さ（以下、整合厚さと言う。）が小さくなる傾向にある。
【０１０１】
以上の結果から、実施例において作製した抵抗皮膜２２を用いた単層型電波吸収体における整合厚さは０．１７〜０．０９λとなる。従って、この単層型電波吸収体では、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体と比較して、厚さを約３０〜６５％小さくすることができる。
【０１０２】
次に、周波数帯として５．８ＧＨｚ帯を使用するＤＳＲＣシステムに適用できる単層型電波吸収体について設計および製造を行った。このＤＳＲＣシステムを応用した各種アプリケーションを想定すると、不燃性を有する電波吸収体が求められる。従って、単層型電波吸収体を構成する材料には無機材料を使用した。
【０１０３】
設計および製造した単層型電波吸収体の構成は、図７に示した通りである。この単層型電波吸収体において、誘電体層１２_１は、主に無機材料によって構成され、ハニカム形状を有している。誘電体層１２_１における１つの孔の径は１５ｍｍである。また、抵抗皮膜２２_１には、厚さ２ｍｍの無機系の抵抗皮膜用基体２１_１上に形成したものを用いた。この構造において、周波数帯５．８ＧＨｚにおいて反射減衰量が最大になるように、誘電体層１２_１の最適な厚さと、抵抗皮膜２２_１の最適な直流面抵抗値Ｒｓとを、ニュートン法により求めた。その結果、誘電体層１２_１の厚さは４．３ｍｍとなり、抵抗皮膜２２_１の直流面抵抗値Ｒｓは４７０Ω□となった。なお、抵抗皮膜用基体２１_１の複素比誘電率は２．８−ｊ０．２８とし、誘電体層１２_１の複素比誘電率は１．０５−ｊ０とした。
【０１０４】
上記の設計結果から、作製した抵抗皮膜を用いた５．８ＧＨｚ帯用の単層型電波吸収体の全体の厚さは６．３ｍｍとなった。抵抗成分のみを有する抵抗皮膜を用いた５．８ＧＨｚ帯用の単層型電波吸収体では、全体の厚さは１１．３ｍｍとなる。従って、本実施例の単層型電波吸収体では、抵抗成分のみを有する抵抗皮膜を用いた単層型電波吸収体に比べて、厚さを約４５％小さくすることができることが分かる。
【０１０５】
次に、上記の設計結果に基づいて、以下のようにして、実際に単層型電波吸収体を製造した。まず、電波反射体１１としての金属板に誘電体層１２_１を接着剤にて接着した。次に、抵抗皮膜用基体２１_１上に抵抗皮膜２２_１を形成してなる抵抗層１３_１を、抵抗皮膜２２_１が誘電体層１２_１に接するように、誘電体層１２_１に対して接着剤にて接着して、図７に示した構造の単層型電波吸収体を完成させた。この電波吸収体の大きさは、縦３００ｍｍ、横３００ｍｍとした。ここで、実際に作製した抵抗皮膜２２_１の直流面抵抗値は、測定の結果、４０５Ω□であった。また、製造した単層型電波吸収体の全体の厚さは６．７ｍｍであった。
【０１０６】
次に、製造した単層型電波吸収体の電波吸収特性を、図１３に示した測定システムおよび図１３を参照して説明した測定方法を用いて測定した。この単層型電波吸収体の電波吸収特性を図１７に示す。図１７において、破線で示した曲線は、設計値に基づいて計算によって求めた電波吸収特性（以下、計算値と言う。）を表わしている。また、図１７において、実線で示した２本の曲線はいずれも、実際に製造した単層型電波吸収体の電波吸収特性（以下、測定値と言う。）を表わしている。
【０１０７】
図１７に示したように、測定値では、最大の反射減衰量が得られる周波数は５．６ＧＨｚ〜５．７ＧＨｚであり、周波数５．８ＧＨｚにおける反射減衰量は約２７〜２９ｄＢとなった。計算値に対して測定値が若干異なっている原因は、作製した抵抗皮膜の直流面抵抗値が設計値に比べて６５Ω□低く、また、製造した電波吸収体の全体の厚さが設計値に比べて０．４ｍｍ大きくなったためであると考えられる。
【０１０８】
また、製造した電波吸収体について、電界の方向に対する抵抗皮膜の方向性に起因して、電界の方向によって電波吸収特性に違いがあるか否かを調べた。その結果、電界の方向による電波吸収特性の違いは小さいことが分かった。
【０１０９】
［第２の実施例］
次に、第２の実施例の電波吸収体１０として、図３に示したように抵抗層１３が２層の構成の電波吸収体１０（以下、２層型電波吸収体と言う。）を設計および製造した。ここでは、オフィス内で使用される無線ＬＡＮの周波数帯である２．４ＧＨｚ帯と５．２ＧＨｚ帯で機能する２層型電波吸収体について設計を行った。ここで、オフィス内の壁に使用される電波吸収体では不燃性が求められることから、電波吸収体を構成する材料には無機材料を使用した。
【０１１０】
設計および製造した２層型電波吸収体の構成は、図８に示した通りである。この２層型電波吸収体において、誘電体層１２_１，１２_２はいずれも、主に無機材料によって構成され、ハニカム形状を有している。誘電体層１２_１，１２_２における１つの孔の径は１５ｍｍである。抵抗皮膜２２_１には、厚さ１ｍｍの無機系の抵抗皮膜用基体２１_１上に形成したものを用いた。また、抵抗皮膜２２_２には、厚さ２ｍｍの無機系の抵抗皮膜用基体２１_２上に形成したものを用いた。この構造において、ニュートン法を用いて、抵抗皮膜２２_１，２２_２の直流面抵抗値Ｒｓ１，Ｒｓ２と、誘電体層１２_１，１２_２の厚さｄ１，ｄ２を求めた。この２層型電波吸収体の設計結果を、下記の表に示す。この表には、抵抗成分のみを有する抵抗皮膜を用いた２層型電波吸収体の設計結果も併せて示している。
【０１１１】
【表２】

【０１１２】
上記の設計結果から、実施例において作製した抵抗皮膜を用いた２層型電波吸収体の全体の厚さは約２５ｍｍとなった。抵抗成分のみを有する抵抗皮膜を用いた２層型電波吸収体では、全体の厚さは約３５ｍｍとなる。従って、本実施例の２層型電波吸収体では、抵抗成分のみを有する抵抗皮膜を用いた２層型電波吸収体に比べて、厚さを約３０％小さくすることができることが分かる。
【０１１３】
次に、上記の設計結果に基づいて、以下のようにして、実際に２層型電波吸収体を製造した。まず、電波反射体１１としての金属板に誘電体層１２_１を接着剤にて接着した。次に、抵抗皮膜用基体２１_１上に抵抗皮膜２２_１を形成してなる抵抗層１３_１を、抵抗皮膜用基体２１_１が誘電体層１２_１に接するように、誘電体層１２_１に対して接着剤にて接着した。次に、抵抗層１３_１に誘電体層１２_２を接着剤にて接着した。次に、抵抗皮膜用基体２１_２上に抵抗皮膜２２_２を形成してなる抵抗層１３_２を、抵抗皮膜２２_２が誘電体層１２_２に接するように、誘電体層１２_２に対して接着剤にて接着して、図８に示した構造の２層型電波吸収体を完成させた。この電波吸収体の大きさは、縦３００ｍｍ、横３００ｍｍとした。ここで、実際に作製した抵抗皮膜２２_１，２２_２の直流面抵抗値は、測定の結果、それぞれ２７０Ω□，１８５９Ω□であった。また、製造した２層型電波吸収体の全体の厚さは２５ｍｍであった。
【０１１４】
次に、製造した２層型電波吸収体の電波吸収特性を、図１３に示した測定システムおよび図１３を参照して説明した測定方法を用いて測定した。この２層型電波吸収体の電波吸収特性を図１８に示す。図１８において、破線で示した曲線は、設計値に基づいて計算によって求めた電波吸収特性（計算値）を表わしている。また、図１８において、実線で示した２本の曲線はいずれも、実際に製造した２層型電波吸収体の電波吸収特性（測定値）を表わしている。
【０１１５】
図１８に示したように、測定値では、周波数２．４ＧＨｚと周波数５．２ＧＨｚにおける反射減衰量はいずれも２０ｄＢ以上となった。これにより、本実施例の２層型電波吸収体では、双峰特性が得られることが確認できた。なお、周波数５．２ＧＨｚにおいて、計算値に対して測定値が若干異なっている原因は、作製した抵抗皮膜２２_１，２２_２の直流面抵抗値が、設計値に比べて１０〜１５％程度異なっているためであると考える。
【０１１６】
また、製造した電波吸収体について、電界の方向に対する抵抗皮膜の方向性に起因して、電界の方向によって電波吸収特性に違いがあるか否かを調べた。その結果、電界の方向による電波吸収特性の違いは小さいことが分かった。
【０１１７】
ここまでは、電波吸収体１０の前面に対して電波が垂直に入射する場合について説明してきた。以下、電波吸収体１０の前面に対して電波が斜め方向から入射する場合における電波吸収体１０の設計方法について説明する。
【０１１８】
まず、図１１に簡略化して示した電波吸収体１０において、抵抗皮膜２２に対して電波が斜め方向から入射する場合を考える。ここで、抵抗皮膜２２に対する電波の入射角度、すなわち抵抗皮膜２２の法線と電波の入射方向とのなす角度をθとする。また、この場合には、入射電波を、電界が入射面に垂直な偏波すなわちＴＥ波と、磁界が入射面に垂直な偏波すなわちＴＭ波とに分けて考える必要がある。
【０１１９】
まず、入射電波がＴＥ波の場合について説明する。この場合、前出の式（１），（３）〜（５）に対応する式は、それぞれ以下の式（６）〜（９）になる。なお、ＴＥ波の場合には、スペーサを空気とした場合の整合条件は、前出の式（２）で表わされるインピーダンスＺ_ｉｎ ^＊が１／ｃｏｓθになることである。
【０１２０】
Ｚ_１ ^＊＝｛１／√（ε_ｒ´−ｓｉｎ^２θ）｝・ｔａｎｈ｛ｊ・（２πｄ／λ）・√（ε_ｒ´−ｓｉｎ^２θ）｝ …（６）
【０１２１】
Ｒｅａｌ（Ｒｓ^＊）＝｛ｓｉｎ（２πｄｃｏｓθ／λ）｝^２・３７７／ｃｏｓθ…（７）
【０１２２】
Ｉｍａｇ（Ｒｓ^＊）＝−［｛ｓｉｎ（４πｄｃｏｓθ／λ）｝／２］・３７７／ｃｏｓθ …（８）
【０１２３】
ｎλ／２ｃｏｓθ＜ｄ＜（ｎ＋１）λ／２ｃｏｓθ （ｎは０以上の整数）…（９）
【０１２４】
一方、入射電波がＴＭ波の場合は、前出の式（１），（３）〜（５）に対応する式は、それぞれ以下の式（１０）〜（１３）になる。なお、ＴＭ波の場合には、スペーサを空気とした場合の整合条件は、前出の式（２）で表わされるインピーダンスＺ_ｉｎ ^＊がｃｏｓθになることである。
【０１２５】
Ｚ_１ ^＊＝｛√（ε_ｒ´−ｓｉｎ^２θ）／ε_ｒ´｝・ｔａｎｈ｛ｊ・（２πｄ／λ）・√（ε_ｒ´−ｓｉｎ^２θ）｝…（１０）
【０１２６】
Ｒｅａｌ（Ｒｓ^＊）＝｛ｓｉｎ（２πｄｃｏｓθ／λ）｝^２・３７７・ｃｏｓθ…（１１）
【０１２７】
Ｉｍａｇ（Ｒｓ^＊）＝−［｛ｓｉｎ（４πｄｃｏｓθ／λ）｝／２］・３７７・ｃｏｓθ …（１２）
【０１２８】
ｎλ／２ｃｏｓθ＜ｄ＜（ｎ＋１）λ／２ｃｏｓθ （ｎは０以上の整数）…（１３）
【０１２９】
なお、式（６），（１０）においてθ＝０とすると式（１）と一致する。また、式（７），（１１）においてθ＝０とすると式（３）と一致する。また、式（８），（１２）においてθ＝０とすると式（４）と一致する。また、式（９），（１３）においてθ＝０とすると式（５）と一致する。従って、式（６）〜（１３）は、θ＝０の場合も含めると、電波吸収体１０の前面に対して電波が垂直に入射する場合にも適用可能である。なお、θ＝０の場合は、ＴＥ波とＴＭ波の区別はなくなる。
【０１３０】
ここで、単層型電波吸収体について、入射角度θが３０°、４０°、５０°、６０°、７０°、８０°の各場合における面抵抗値の複素量と規格化整合厚さとの関係を求めた結果を図１９〜図３０に示す。図１９は、入射角度θが３０°で、ＴＥ波の場合について示している。図２０は、入射角度θが３０°で、ＴＭ波の場合について示している。図２１は、入射角度θが４０°で、ＴＥ波の場合について示している。図２２は、入射角度θが４０°で、ＴＭ波の場合について示している。図２３は、入射角度θが５０°で、ＴＥ波の場合について示している。図２４は、入射角度θが５０°で、ＴＭ波の場合について示している。図２５は、入射角度θが６０°で、ＴＥ波の場合について示している。図２６は、入射角度θが６０°で、ＴＭ波の場合について示している。図２７は、入射角度θが７０°で、ＴＥ波の場合について示している。図２８は、入射角度θが７０°で、ＴＭ波の場合について示している。図２９は、入射角度θが８０°で、ＴＥ波の場合について示している。図３０は、入射角度θが８０°で、ＴＭ波の場合について示している。
【０１３１】
本実施の形態において、電波吸収体１０に対する入射電波がＴＥ波の場合には、０．８ＧＨｚ〜１８ＧＨｚの電波の周波数領域内で反射減衰量が最大となる周波数において、抵抗皮膜２２の面抵抗値の実部および虚部が、それぞれ、式（７），（８）より得られる値を含む所定の許容範囲内の値となるようにする。許容範囲は、式（７），（８）より得られる値に対して±３０％の範囲であることが好ましく、±２０％の範囲であることがより好ましく、±１０％の範囲であることが更に好ましい。
【０１３２】
また、本実施の形態において、電波吸収体１０に対する入射電波がＴＭ波の場合には、０．８ＧＨｚ〜１８ＧＨｚの電波の周波数領域内で反射減衰量が最大となる周波数において、抵抗皮膜２２の面抵抗値の実部および虚部が、それぞれ、式（１１），（１２）より得られる値を含む所定の許容範囲内の値となるようにする。許容範囲は、式（１１），（１２）より得られる値に対して±３０％の範囲であることが好ましく、±２０％の範囲であることがより好ましく、±１０％の範囲であることが更に好ましい。
【０１３３】
ここで、上記の許容範囲について説明する。まず、計算によって、抵抗皮膜の面抵抗値の実部および虚部を設計値に対して変化させたときの、反射減衰量（電波吸収量）が最大となる周波数における反射減衰量の最低値を求めた。その結果、スペーサの厚さが０．０５λの場合には、抵抗皮膜の面抵抗値の実部および虚部を設計値に対して±１０％の範囲内で変化させたときの反射減衰量の最低値は１５．３（≒１５）ｄＢとなった。また、スペーサの厚さが０．１λの場合には、抵抗皮膜の面抵抗値の実部および虚部を設計値に対して±２０％の範囲内で変化させたときの反射減衰量の最低値は１４．５（≒１５）ｄＢとなった。また、スペーサの厚さが０．２λの場合には、抵抗皮膜の面抵抗値の実部および虚部を設計値に対して±３０％の範囲内で変化させたときの反射減衰量の最低値は１４．６（≒１５）ｄＢとなった。
【０１３４】
ここで、面抵抗値の実部および虚部の許容範囲を、反射減衰量が最大となる周波数における反射減衰量として１５ｄＢ以上を確保できる範囲とする。この場合、許容範囲は、スペーサの厚さが０．０５λの場合には±１０％となり、スペーサの厚さが０．１λの場合には±２０％となり、スペーサの厚さが０．２λの場合には±３０％となる。従って、本実施の形態において、スペーサの厚さを０．２λとするには許容範囲は±３０％以内とする必要がある。また、スペーサの厚さを０．１λ〜０．２λの範囲内の任意の厚さとするには許容範囲は±２０％以内とする必要がある。また、スペーサの厚さを０．０５λ〜０．２λの範囲内の任意の厚さとするには許容範囲は±１０％以内とする必要がある。以上のことから、本実施の形態において、許容範囲は、±３０％以内とすることが好ましく、±２０％以内とすることがより好ましく、±１０％以内とすることが更に好ましい。
【０１３５】
次に、図３１および図３２を参照して、本実施の形態における抵抗皮膜の面抵抗値の実部と虚部との関係について考察する。図３１は、入射電波がＴＥ波の場合について、入射角度θが０〜８０°の範囲において、整合条件を満たす抵抗皮膜の面抵抗値の複素量をコールコールプロットとして表したものである。図３１中の注釈において、“０°”はθが０°の場合を表わしている。また、“ＴＥα°（α＝３０，４０，５０，６０，７０，８０）”は、それぞれＴＥ波の場合で、入射角度θが３０°、４０°、５０°、６０°、７０°、８０°の場合を表わしている。
【０１３６】
また、図３２は、入射電波がＴＭ波の場合について、入射角度θが０〜８０°の範囲において、整合条件を満たす抵抗皮膜の面抵抗値の複素量をコールコールプロットとして表したものである。図３２中の注釈において、“０°”はθが０°の場合を表わしている。また、“ＴＭα°（α＝３０，４０，５０，６０，７０，８０）”は、それぞれＴＭ波の場合で、入射角度θが３０°、４０°、５０°、６０°、７０°、８０°の場合を表わしている。
【０１３７】
なお、図３１および図３２では、スペーサの厚さを、０．０５λ／ｃｏｓθ〜０．２λ／ｃｏｓθの範囲内としている。抵抗成分のみを有する抵抗皮膜を用いた電波吸収体では、整合条件を満たすスペーサの厚さは０．２５λ／ｃｏｓθとなる。従って、０．０５λ／ｃｏｓθ〜０．２λ／ｃｏｓθというスペーサの厚さの範囲は、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体におけるスペーサの厚さの２０〜８０％の範囲である。本実施の形態では、このように、単層型電波吸収体におけるスペーサの厚さを、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体におけるスペーサの厚さの２０〜８０％とすることを目標とする。以下、その理由について説明する。
【０１３８】
本実施の形態におけるスペーサの厚さが、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体におけるスペーサの厚さの８０％を超える場合には、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体に比べて、本実施の形態に係る電波吸収体の厚みは顕著には小さくならない。一方、本実施の形態におけるスペーサの厚さが、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体におけるスペーサの厚さの２０％未満となる場合には、そのような薄いスペーサを作製することが非常に困難になる。また、この場合には、スペーサの厚さの誤差および抵抗皮膜の面抵抗値の誤差が電波吸収体の電波吸収特性に与える影響が大きくなり、スペーサの厚さの制御も非常に困難になる。これらのことから、製造および取り扱いが容易で、且つ抵抗成分のみを有する抵抗皮膜を用いた電波吸収体に比べて十分薄い電波吸収体を実現するには、スペーサの厚さを、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体におけるスペーサの厚さの２０〜８０％とするのが好ましい。
【０１３９】
ここで、入射角度θを０〜８０°の範囲内とし、スペーサの厚さを０．０５λ／ｃｏｓθ〜０．２λ／ｃｏｓθの範囲内とする条件の下で、整合条件を満たす抵抗皮膜の面抵抗値の実部と虚部との関係について考察する。図３１および図３２から分かるように、ＴＥ波の場合もＴＭ波の場合も、虚部の値を実部の値で除した値“虚部／実部”（図では傾きと記す。）は、−０．３〜−３．１の範囲内となっている。また、図３１から分かるように、ＴＥ波の場合には、整合条件を満たす抵抗皮膜の面抵抗値の実部の値は３５〜２０００Ω□の範囲内であり、整合条件を満たす抵抗皮膜の面抵抗値の虚部の値は−１１０〜−１１００Ω□の範囲内である。また、図３２から分かるように、ＴＭ波の場合には、整合条件を満たす抵抗皮膜の面抵抗値の実部の値は５〜３５０Ω□の範囲内であり、整合条件を満たす抵抗皮膜の面抵抗値の虚部の値は−１５〜−１９０Ω□の範囲内である。
【０１４０】
以上のことから、本実施の形態にかかる電波吸収体１０では、ＴＥ波とＴＭ波の少なくとも一方の電波を吸収できるように、抵抗皮膜の面抵抗値は、以下の条件を満たすことが好ましい。その条件とは、０．８ＧＨｚ〜１８ＧＨｚの電波の周波数領域内で反射減衰量が最大となる周波数において、抵抗皮膜の面抵抗値の実部の値は５〜２０００Ω□の範囲内であり、面抵抗値の虚部の値は−１５〜−１１００Ω□の範囲内であり、虚部の値を実部の値で除した値は−０．３〜−３．１の範囲内であることである。
【０１４１】
また、本実施の形態にかかる電波吸収体１０では、ＴＥ波の電波を吸収する場合には、抵抗皮膜の面抵抗値は、以下の条件を満たすことが好ましい。その条件とは、０．８ＧＨｚ〜１８ＧＨｚの電波の周波数領域内で反射減衰量が最大となる周波数において、抵抗皮膜の面抵抗値の実部の値は３５〜２０００Ω□の範囲内であり、面抵抗値の虚部の値は−１１０〜−１１００Ω□の範囲内であり、虚部の値を実部の値で除した値は−０．３〜−３．１の範囲内であることである。
【０１４２】
また、本実施の形態にかかる電波吸収体１０では、ＴＭ波の電波を吸収する場合には、抵抗皮膜の面抵抗値は、以下の条件を満たすことが好ましい。その条件とは、０．８ＧＨｚ〜１８ＧＨｚの電波の周波数領域内で反射減衰量が最大となる周波数において、抵抗皮膜の面抵抗値の実部の値は５〜３５０Ω□の範囲内であり、面抵抗値の虚部の値は−１５〜−１９０Ω□の範囲内であり、虚部の値を実部の値で除した値は−０．３〜−３．１の範囲内であることである。
【０１４３】
以上説明したように、本実施の形態によれば、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体に比べて薄く、且つ容易に設計および製造することのできる電波吸収体を実現することができる。
【０１４４】
電波吸収体１０が複数組の誘電体層および抵抗皮膜を備えている場合には、そのうちの少なくとも１組の誘電体層および抵抗皮膜が、ここまで説明してきた条件を満たすことが好ましい。
【０１４５】
なお、本発明は、上記実施の形態に限定されず、種々の変更が可能である。例えば、電波吸収体１０を構成する各層の材料は、実施の形態に示したものに限らず、適宜選択することができる。
【０１４６】
【発明の効果】
以上説明したように、本発明の電波吸収体によれば、抵抗成分のみを有する抵抗皮膜を用いた電波吸収体に比べて薄く、且つ容易に設計および製造することのできる電波吸収体を実現することができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る電波吸収体の基本構成の第１の例を示す断面図である。
【図２】本発明の一実施の形態に係る電波吸収体の基本構成の第２の例を示す断面図である。
【図３】本発明の一実施の形態に係る電波吸収体の基本構成の第３の例を示す断面図である。
【図４】本発明の一実施の形態に係る電波吸収体の基本構成の第４の例を示す断面図である。
【図５】本発明の一実施の形態に係る電波吸収体の構成の他の例を示す断面図である。
【図６】本発明の一実施の形態における抵抗層の形成方法を示す説明図である。
【図７】複数の孔を有する板状の部材によって形成された誘電体層を有する電波吸収体の構成の第１の例を示す斜視図である。
【図８】複数の孔を有する板状の部材によって形成された誘電体層を有する電波吸収体の構成の第２の例を示す斜視図である。
【図９】複数の孔を有する板状の部材によって形成された誘電体層を有する電波吸収体の構成の第３の例を示す斜視図である。
【図１０】複数の孔を有する板状の部材によって形成された誘電体層を有する電波吸収体の構成の第４の例を示す斜視図である。
【図１１】本発明の一実施の形態に係る電波吸収体の構成を簡略化して示す斜視図である。
【図１２】本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図１３】抵抗皮膜の面抵抗値の評価のために用いられる測定システムの構成を示す説明図である。
【図１４】本発明の一実施の形態における実施例で作製した抵抗皮膜の面抵抗値の複素量の周波数特性を示す特性図である。
【図１５】本発明の一実施の形態における実施例で作製した抵抗皮膜の面抵抗値の複素量と直流面抵抗値との関係を示す特性図である。
【図１６】本発明の一実施の形態における実施例で作製した抵抗皮膜の面抵抗値の複素量をコールコールプロットとして表した特性図である。
【図１７】本発明の一実施の形態における実施例で製造した単層型電波吸収体の電波吸収特性を示す特性図である。
【図１８】本発明の一実施の形態における実施例で製造した２層型電波吸収体の電波吸収特性を示す特性図である。
【図１９】入射角度θが３０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２０】入射角度θが３０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２１】入射角度θが４０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２２】入射角度θが４０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２３】入射角度θが５０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２４】入射角度θが５０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２５】入射角度θが６０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２６】入射角度θが６０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２７】入射角度θが７０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２８】入射角度θが７０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図２９】入射角度θが８０°で入射電波がＴＥ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図３０】入射角度θが８０°で入射電波がＴＭ波の場合について、本発明の一実施の形態における抵抗皮膜の面抵抗値の複素量と規格化整合厚さとの関係を示す特性図である。
【図３１】入射電波がＴＥ波の場合について、入射角度θが０〜８０°の範囲において、整合条件を満たす抵抗皮膜の面抵抗値の複素量をコールコールプロットとして表した特性図である。
【図３２】入射電波がＴＭ波の場合について、入射角度θが０〜８０°の範囲において、整合条件を満たす抵抗皮膜の面抵抗値の複素量をコールコールプロットとして表した特性図である。
【符号の説明】
１０…電波吸収体、１１…電波反射体、１２，１２_１，１２_２…誘電体層、１３，１３_１，１３_２…抵抗層、２１，２１_１，２１_２…抵抗皮膜用基体、２２，２２_１，２２_２…抵抗皮膜。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave absorber used in EMC (electromagnetic compatibility) technology for reducing radio wave interference and radio wave interference in the field of information communication.
[0002]
[Prior art]
In recent years, as microwave and millimeter wave radio waves have been used, problems such as radio wave interference and radio wave interference have occurred. As one of means for solving these problems, a radio wave absorber is used, which has a great effect. In general, radio wave absorbers used for microwaves and millimeter waves have a wave length of 1/4 wavelength from a wave absorber formed by mixing a loss material such as ferrite or carbon with a holding material such as resin, or a wave reflector. There is a λ / 4 type wave absorber having a resistive film disposed at a position.
[0003]
It is considered that a radio wave absorber using a resistance film has existed for a long time and was put into practical use in the early 1940s. It seems that paper and the like into which oil smoke was injected were used as the initial resistance film. Thereafter, wave absorbers using resistance cloths or carbon fiber resistors woven with conductive fibers and polyester yarn have been developed and put into practical use. In recent years, with the development of transparent touch panels and display elements such as electroluminescence elements, transparent wave absorbers using transparent conductive films, which are thin films having both transparency and conductivity, have been researched and developed as resistance films. .
[0004]
Various materials are used as the material of the transparent conductive film, and the material having the best performance is indium tin oxide (hereinafter referred to as ITO), which is used for, for example, a transparent conductive film. In this transparent conductive film, polyethylene terephthalate is generally used as a base material. A transparent conductive film is manufactured by forming an ITO film on the surface of the base material by a vacuum deposition method, a sputtering method, an ion plating method or the like. This λ / 4 type wave absorber using a conductive film is constructed by attaching a radio wave reflector to one surface of a dielectric layer called a spacer and attaching a conductive film to the other surface of the spacer. .
[0005]
Usually, the electrical characteristics of the conductive film are characterized by its resistance component. Therefore, most of the conductive films do not have a capacitive susceptance. In the λ / 4 type wave absorber using such a conductive film, the thickness of the spacer is 1/4 of the wavelength in the spacer.
[0006]
In Non-Patent Document 1, when cloth or paper is used as the resistance film, the resistance film has a capacitive susceptance of about 10% with respect to the resistance value due to the dielectric constant thereof. Are listed. Non-Patent Document 1 describes that when a resistance fiber array is used as the resistance film, the resistance film has an inductive susceptance. Further, in Non-Patent Document 1, when the resistive film has a capacitive susceptance, the thickness of the spacer can be made smaller than ¼ of the wavelength in the spacer, and the resistive film has an inductive susceptance. It is described that the thickness of the spacer can be made larger than 1/4 of the wavelength in the spacer.
[0007]
Patent Document 1 describes a radio wave absorber (electromagnetic wave absorber) thinner than 1/5 of the wavelength in the spacer. Patent Document 1 describes that the reason why the radio wave absorber can be made thin is that the resistance layer (resistance film) has a high-capacity susceptance.
[0008]
[Patent Document 1]
JP 2001-320191 A
[Non-Patent Document 1]
Shimizu, Sugiura, Ishino, "Latest absorption and shielding of electromagnetic waves", Nikkei Technical Books, 1999, p. 135-138
[0009]
[Problems to be solved by the invention]
In particular, it is preferable that the radio wave absorber used indoors is thin. However, in a λ / 4 type wave absorber using a resistive film having no capacitive susceptance, it cannot be made thinner than ¼ of the wavelength in the spacer. Therefore, in the λ / 4 type wave absorber, for example, a frequency selection plate is inserted into the spacer so as to be in parallel with the conductive film as the resistance film, and the phase of the radio wave is changed in the spacer by the frequency selection plate. Thus, a device for reducing the thickness of the radio wave absorber has been made. However, in this method, it is necessary to insert the frequency selection plate between the radio wave reflector and the conductive film with high accuracy. Therefore, when this method is used, it is difficult to manufacture the radio wave absorber, and there is a problem that the manufacturing cost of the radio wave absorber including the manufacturing cost of the frequency selection plate is high.
[0010]
Non-Patent Document 1 describes a resistive film having a capacitive susceptance of about 10% of the resistance value. However, even if a resistive film having such a susceptance is used, the radio wave absorber is not so thin.
[0011]
Patent Document 1 suggests that an electromagnetic wave absorber thinner than ¼ of the wavelength in the spacer can be obtained when the resistive film has a capacitive susceptance. However, Patent Document 1 does not describe a theoretical explanation that a radio wave absorber thinner than ¼ of the wavelength in the spacer can be obtained. Patent Document 1 describes that it is extremely difficult to accurately and directly obtain a susceptance of a material suitable for a thin film. For these reasons, from the description in Patent Document 1, what is necessary is to use a resistive film having a capacitive susceptance with respect to the frequency of the radio wave to be absorbed, and to what extent the spacer thickness should be. I do n’t know. That is, from the description of Patent Document 1, it is difficult to design and manufacture a desired radio wave absorber.
[0012]
Patent Document 1 discloses, as an example, a radio wave absorber having a wavelength / thickness value of 22.5 to 80, that is, an extremely thin radio wave absorber having a thickness of 0.044 to 0.0125. Is described. However, such an extremely thin wave absorber has a problem that it is very difficult to manufacture a spacer. Further, in this radio wave absorber, there is a problem that the influence of the spacer thickness error on the radio wave absorption characteristics of the radio wave absorber becomes large, and it becomes very difficult to control the thickness of the spacer.
[0013]
The present invention has been made in view of such problems, and an object thereof is a radio wave absorber using a resistive film having a capacitive susceptance, and a radio wave absorber using a resistive film having only a resistive component. An object of the present invention is to provide a radio wave absorber that is thinner than the above and can be easily designed and manufactured.
[0014]
[Means for Solving the Problems]
Each of the first to fifth wave absorbers of the present invention is disposed on the radio wave arrival side of the radio wave reflector, the dielectric layer disposed on the radio wave arrival side of the radio wave reflector, and the dielectric layer. And a resistive film.
[0015]
In the first electromagnetic wave absorber of the present invention, the real part of the resistance value of the resistance film is 5 to 2000 Ω □ at a frequency at which the return loss is maximum in the frequency range of radio waves of 0.8 GHz to 18 GHz. Within the range, the value of the imaginary part of the sheet resistance value is within the range of −15 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is −0.3 to −3.1. Within range.
[0016]
In the second wave absorber of the present invention, the real part value of the surface resistance value of the resistive film is 35 to 2000 Ω □ at the frequency at which the return loss is maximum in the frequency range of the radio wave of 0.8 GHz to 18 GHz. Within the range, the value of the imaginary part of the sheet resistance value is within the range of −110 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is −0.3 to −3.1. Within range.
[0017]
In the third wave absorber of the present invention, the real part value of the surface resistance value of the resistance film is 5 to 350 Ω □ at the frequency at which the return loss is maximum in the frequency range of the radio wave of 0.8 GHz to 18 GHz. The value of the imaginary part of the sheet resistance value is in the range of −15 to −190Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is −0.3 to −3.1. Within range.
[0018]
In the fourth radio wave absorber of the present invention, when the thickness of the dielectric layer is d, the wavelength of the radio wave in the dielectric layer is λ, and the incident angle of the radio wave to the resistance film is θ, 0.8 GHz to 18 GHz The real part and the imaginary part of the surface resistance value of the resistance film are each within a range of ± 30% of the value obtained from the following equation at the frequency at which the return loss amount is maximum within the frequency range of the radio wave.
Real part: {sin (2πd cos θ / λ)}²・ 377 / cosθ
Imaginary part:-[{sin (4πdcosθ / λ)} / 2] · 377 / cosθ
However, nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer of 0 or more)
[0019]
In the fifth wave absorber of the present invention, when the thickness of the dielectric layer is d, the wavelength of the radio wave in the dielectric layer is λ, and the incident angle of the radio wave to the resistance film is θ, 0.8 GHz to 18 GHz The real part and the imaginary part of the surface resistance value of the resistance film are each within a range of ± 30% of the value obtained from the following equation at the frequency at which the return loss amount is maximum within the frequency range of the radio wave.
Real part: {sin (2πd cos θ / λ)}²・ 377 ・ cos θ
Imaginary part:-[{sin (4πdcosθ / λ)} / 2] · 377 · cosθ
However, nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer of 0 or more)
[0020]
The radio wave absorber of the present invention further includes one or more second dielectric layers and a second resistive film disposed between the radio wave reflector and the dielectric layer or on the radio wave arrival side of the resistive film. It may be.
[0021]
The radio wave absorber according to the present invention further includes another dielectric layer disposed on the radio wave arrival side of the resistive film disposed on the surface farthest from the radio wave reflector, and radio wave arrival at the other dielectric layer. And a radio wave absorption characteristic adjusting dielectric layer disposed on the side.
[0022]
The radio wave absorber of the present invention further includes a plate-shaped or sheet-shaped resistance film substrate, and the resistance film is formed by mixing a conductive material with a coating agent and applied to the resistance film substrate. It may be formed of a conductive paint.
[0023]
The coating agent may contain at least one of an inorganic coating agent and an organic coating agent. The conductive material may contain at least one of a scale-like conductive powder and a granular conductive powder. The material of the scale-like conductive powder or the granular conductive powder may contain graphite, carbon, metal powder or metal oxide. The conductive material includes both flaky conductive powder and granular conductive powder, and the flaky conductive powder material and granular conductive powder material include graphite, carbon, metal powder and metal. Different materials of oxides may be used. Moreover, 85 weight% or more may be sufficient as the ratio of the scale-like electroconductive powder in an electroconductive material. The resistance film substrate is mainly made of an inorganic material and may be nonflammable.
[0024]
In the radio wave absorber of the present invention, the thickness of the resistance film may be 70 μm or more and 200 μm or less.
[0025]
In the radio wave absorber of the present invention, the dielectric layer is mainly made of an inorganic material and may be nonflammable.
[0026]
In the radio wave absorber of the present invention, the dielectric layer may be formed of a plate-like member having a plurality of holes penetrating in the radio wave traveling direction or a plate-like foam. In this case, the dielectric layer has a first surface on the radio wave arrival side and a second surface on the opposite side, and at least the first surface of the first surface and the second surface is: It may be covered with a plate-like or sheet-like member mainly made of an inorganic material.
[0027]
The radio wave absorber of the present invention may further include an interior material arranged so as to cover the surface farthest from the radio wave reflector.
[0028]
In the radio wave absorber of the present invention, the surface farthest from the radio wave reflector may be coated.
[0029]
In the radio wave absorber of the present invention, the radio wave reflector includes a plate-like radio wave reflector base mainly made of an inorganic material, and a conductive film disposed on the radio wave arrival side surface of the radio wave reflector base. And may be nonflammable.
[0030]
In this application, “non-combustible” means that it has non-combustible performance that conforms to the non-combustible material specified in the Building Standard Law, and that is equivalent to the non-combustible performance of the non-combustible material specified in the Building Standard Law. Say that you have.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, the configuration of the radio wave absorber according to the present embodiment will be described with reference to FIGS. 1 to 4. 1 to 4 are sectional views showing first to fourth examples of the basic configuration of the radio wave absorber according to the present embodiment. 1 to 4, the arrow indicated by reference numeral 1 represents the traveling direction of radio waves.
[0032]
A radio wave absorber 10 shown in FIG. 1 includes a nonflammable radio wave reflector 11 and a nonflammable dielectric layer 12 disposed on the radio wave arrival side of the radio wave reflector 11.₁And dielectric layer 12₁Resistance layer 13 arranged on the radio wave arrival side₁And. Dielectric layer 12₁Is mainly composed of an inorganic material. Resistance layer 13₁As will be described in detail later, it includes a plate-shaped or sheet-shaped resistance film substrate mainly made of an inorganic material and a resistance film formed on the resistance film substrate. The radio wave absorber 10 is nonflammable as a whole.
[0033]
The radio wave absorber 10 according to the present embodiment may be configured as shown in FIGS. 2 to 4 by adding another layer to the configuration shown in FIG.
[0034]
The radio wave absorber 10 shown in FIG. 2 includes a nonflammable radio wave reflector 11 and two layers of nonflammable dielectric layers 12 disposed on the radio wave arrival side of the radio wave reflector 11.₁, 12₂And adjacent dielectric layer 12₁, 12₂Resistive layer 13 disposed between₁And. The radio wave absorber 10 shown in FIG. 2 further includes a dielectric layer 12 farthest from the radio wave reflector 11.₂The electromagnetic wave absorption characteristic adjusting dielectric layer 14 is provided on the radio wave arrival side. Dielectric layer 12₁, 12₂Is mainly composed of an inorganic material. Resistance layer 13₁The structure of the resistance layer 13 in FIG.₁It is the same. The dielectric layer 14 for adjusting radio wave absorption characteristics is mainly made of an inorganic material and has a plate shape or a sheet shape. The radio wave absorption characteristic adjusting dielectric layer 14 is the dielectric layer 12 farthest from the radio wave reflector 11.₂Protect. The radio wave absorber 10 shown in FIG. 2 is also nonflammable as a whole.
[0035]
The radio wave absorber 10 shown in FIG. 3 includes a non-flammable radio wave reflector 11 and n layers (n is an integer of 2 or more) of non-flammable dielectric layers 12 arranged on the radio wave arrival side of the radio wave reflector 11.₁~ 12_nAnd a dielectric layer 12 disposed between the adjacent dielectric layers and at a position farthest from the radio wave reflector 11_nResistance layer 13 arranged on the radio wave arrival side₁~ 13_nAnd. Dielectric layer 12₁~ 12_nIs mainly composed of an inorganic material. Resistance layer 13₁~ 13_nThe structure of the resistance layer 13 in FIG.₁It is the same. The radio wave absorber 10 shown in FIG. 3 is also nonflammable as a whole.
[0036]
The radio wave absorber 10 shown in FIG. 4 includes a nonflammable radio wave reflector 11 and m layers (m is an integer of 3 or more) of nonflammable dielectric layers 12 arranged on the radio wave arrival side of the radio wave reflector 11.₁~ 12_mAnd a resistive layer 13 disposed between adjacent dielectric layers₁~ 13_m-1And. The radio wave absorber 10 shown in FIG. 4 further includes a dielectric layer 12 farthest from the radio wave reflector 11._mThe electromagnetic wave absorption characteristic adjusting dielectric layer 14 is provided on the radio wave arrival side. Dielectric layer 12₁~ 12_mIs mainly composed of an inorganic material. Resistance layer 13₁~ 13_m-1The structure of the resistance layer 13 in FIG.₁It is the same. The configuration of the radio wave absorption characteristic adjusting dielectric layer 14 is the same as that of the radio wave absorption characteristic adjusting dielectric layer 14 in FIG. The radio wave absorption characteristic adjusting dielectric layer 14 has a function of arbitrarily adding one frequency at which the return loss reaches a peak by adjusting the input impedance expected from the radio wave arrival side of the radio wave absorber 10. The dielectric layer 14 for adjusting radio wave absorption characteristics is a dielectric layer 12 farthest from the radio wave reflector 11._mIt also has a function to protect. The radio wave absorber 10 shown in FIG. 4 is also nonflammable as a whole.
[0037]
The configurations of the radio wave absorber 10 shown in FIG. 2 and the radio wave absorber 10 shown in FIG. 4 are collectively expressed as follows. That is, the radio wave absorber 10 shown in FIG. 2 or 4 includes a non-combustible radio wave reflector 11 and an incombustible material of n layers (n is an integer of 2 or more) arranged on the radio wave arrival side of the radio wave reflector 11. Dielectric layer 12 of₁~ 12_nAnd a resistive layer 13 disposed between adjacent dielectric layers₁~ 13_n-1And. The radio wave absorber 10 shown in FIG. 2 or 4 further includes a dielectric layer 12 farthest from the radio wave reflector 11._nThe electromagnetic wave absorption characteristic adjusting dielectric layer 14 is provided on the radio wave arrival side.
[0038]
Hereinafter, the dielectric layers in FIGS. 1 to 4 are representatively referred to as dielectric layers 12. Also, the resistance layers in FIGS. 1 to 4 are referred to as resistance layers 13 as representatives.
[0039]
In the radio wave absorber 10 according to the present embodiment, the thickness of the dielectric layer 12, the thickness of the resistance film substrate in the resistance layer 13, the thickness of the dielectric layer 14 for adjusting radio wave absorption characteristics, and the resistance in the resistance layer 13. The surface resistance value of the film is set to a predetermined value so that the radio wave absorber 10 can exhibit a desired radio wave absorption characteristic in a predetermined frequency region. These will be described in detail later.
[0040]
The radio wave absorption characteristic of the radio wave absorber 10 having the configuration shown in FIG. 1 has a peak of return loss at an arbitrary frequency. On the other hand, the radio wave absorber 10 having the configuration shown in FIG. 2 can realize the radio wave absorption characteristic in which the peak of the return loss exists at any two frequencies. In addition, in the radio wave absorber 10 having the configuration shown in FIG. 3, it is possible to realize a radio wave absorption characteristic in which a peak of return loss exists at any n frequencies. In addition, the radio wave absorber 10 having the configuration shown in FIG. 4 can realize a radio wave absorption characteristic in which a peak of return loss exists at an arbitrary m frequencies.
[0041]
The radio wave absorber 10 according to the present embodiment is used, for example, to reduce radio wave interference and radio wave interference in a DSRC (dedicated narrow area communication) system or a wireless LAN (local area network) system. In the DSRC system, the 5.8 GHz band is used as the frequency band. In the wireless LAN system, the 2.4 GHz band and the 5.2 GHz band are used as frequency bands. It is preferable that the radio wave absorber 10 has a characteristic that the return loss is 15 dB or more in a desired frequency or frequency range corresponding to the purpose of use within a frequency range of radio waves of 0.8 GHz to 18 GHz. Further, the radio wave absorber 10 shown in any of FIGS. 2 to 4 has a characteristic that the return loss is 15 dB or more at a plurality of frequencies or frequency ranges in the frequency range of radio waves of 0.8 GHz to 18 GHz. In particular, it is preferable that the reflection attenuation amount be 15 dB or more at each frequency of 2.4 GHz and 5.2 GHz.
[0042]
The radio wave absorber 10 according to the present embodiment can be used as at least a part of any one of a partition, a wall, a ceiling, and a floor. Moreover, you may comprise the electromagnetic wave absorption panel which contains the electromagnetic wave absorber 10 which concerns on this Embodiment, and makes | forms the plate | board shape of a predetermined | prescribed magnitude | size. This radio wave absorption panel is used as at least a part of any of partitions, walls, ceilings, and floors.
[0043]
As shown in FIG. 5, the radio wave absorber 10 according to the present embodiment may further include an interior material 15 arranged so as to cover the surface farthest from the radio wave reflector 11. 5 shows an example in which the interior material 15 is provided so as to cover the surface farthest from the radio wave reflector 11 in the radio wave absorber 10 having the configuration shown in FIG. However, in the radio wave absorber 10 shown in FIG. 1, FIG. 2, or FIG. 4, the interior material 15 may be provided so as to cover the surface farthest from the radio wave reflector 11.
[0044]
The interior material 15 plays a role as a decorative material when the radio wave absorber 10 is used as at least a part of an indoor wall surface or a partition. As the interior material 15, a non-combustible cloth such as a glass cloth or a decorative cloth can be used, but a non-combustible cloth is preferably used.
[0045]
In the radio wave absorber 10 according to the present embodiment, the surface farthest from the radio wave reflector 11 may be coated. The surface to which this coating is applied is the surface on the radio wave arrival side of the resistance layer 13, the radio wave absorption characteristic adjusting dielectric layer 14, or the interior material 15. When coating the surface of the resistance layer 13 or the dielectric layer 14 for adjusting radio wave absorption characteristics, a primer treatment is applied to the surface of the resistive layer 13 or the dielectric layer 14 for adjusting radio wave absorption characteristics as a pretreatment for coating. Also good.
[0046]
In the radio wave absorber 10 according to the present embodiment, the resistance film in the resistance layer 13 has a capacitive susceptance.
[0047]
Next, a method for forming the resistance layer 13 in the present embodiment will be described with reference to FIG. As shown in FIG. 6, the resistance layer 13 includes a plate-shaped or sheet-shaped resistance film substrate 21 mainly made of an inorganic material, and a resistance film 22 formed on the resistance film substrate 21. Yes.
[0048]
The resistance film 22 is formed by, for example, applying a liquid conductive coating material 23 formed by uniformly mixing and dispersing a conductive material in a coating agent on the resistance film substrate 21 and solidifying it in a planar shape. It is formed. The coating agent contains at least one of an inorganic coating agent and an organic coating agent. The conductive material includes at least one of a scale-like conductive powder and a granular conductive powder. The material of the scale-like conductive powder or granular conductive powder may contain, for example, graphite, carbon, metal powder, or metal oxide. Further, when the conductive material includes both flaky conductive powder and granular conductive powder, the flaky conductive powder material and the granular conductive powder material are graphite, carbon, metal powder and metal. Different materials of oxides may be used. Moreover, 85 weight% or more may be sufficient as the ratio of the scale-like electroconductive powder in an electroconductive material. Moreover, the thickness of the resistance film 22 is, for example, 70 μm or more and 200 μm or less.
[0049]
As shown in FIG. 6, as a method for applying the conductive paint 23, spray coating is preferable. By using spray coating, the radio wave absorber 10 having a very small difference in radio wave absorption characteristics depending on the application direction of the conductive paint 23 can be manufactured. In FIG. 6, reference numeral 24 indicates a discharge portion of the conductive paint 23 in the spray coating apparatus. In particular, it is possible to obtain a stable surface resistance value of the resistance film 22 by forming the resistance film 22 by applying the conductive paint 23 on the resistance film substrate 21 by spray coating using a robot coating apparatus. .
[0050]
There is no restriction | limiting in particular as an inorganic coating agent used for the conductive paint 23, The thing conventionally used as an inorganic coating agent which has nonflammability can be used. Here, an example of an inorganic coating agent used for the conductive coating material 23 will be described. This inorganic coating agent includes an alkyl silicate as a main agent, water for hydrolyzing the alkyl silicate, and this hydrolysis reaction. It contains an aluminum chelate as a reaction catalyst to be promoted, methyl acid phosphate as a reaction inhibitor that suppresses hydrolysis reaction, and an alcohol as a solvent that dissolves alkyl silicate and water. Examples of the alkyl silicate include methyltrimethoxysilane and phenyltrimethylsilane. As an inorganic coating agent used for the conductive paint 23, a water-based inorganic coating agent may be used in addition to the above example.
[0051]
There is no restriction | limiting in particular as an organic type coating agent used for the conductive coating material 23, For example, a commercially available organic type coating material can be used.
[0052]
Moreover, as a coating agent used for the conductive paint 23, a hybrid coating agent obtained by mixing an inorganic coating agent and an organic coating agent may be used.
[0053]
Further, when the conductive film 23 is applied to the thin resistance film substrate 21 to form the resistance film 22, it is possible to prevent the resistance film 22 from being cracked or bent due to warping or bending of the resistance film substrate 21. Therefore, it is preferable to use a flexible coating agent.
[0054]
Here, an example of the manufacturing method of the base 21 for resistance films is given. In this example, the resistance film substrate 21 is made using a slurry mainly composed of a hydrous inorganic compound. The slurry contains 60 to 90% by weight of sepiolite, and further contains a binder and reinforcing materials such as inorganic fibers and glass fibers. The binder includes a thermoplastic resin for reinforcing the resistance film substrate 21 and a thermosetting resin having a network-like three-dimensional structure and imparting cohesiveness and water resistance. As the thermoplastic resin, for example, an anionic thermoplastic resin such as polyacrylimide (having a molecular weight of about 800,000 to 1,000,000) can be used. As the thermosetting resin, for example, a cationic thermosetting resin such as polyamide polyamine epichlorohydrin can be used. A sheet is formed by paper making using such a slurry, and the sheet is heated and dried at a predetermined temperature, whereby the evaporation of moisture and the reaction of the binder proceed, the sheet is solidified, and the substrate for the resistance film 21 is obtained.
[0055]
The fact that the resistance film substrate 21 is mainly made of an inorganic material means that an auxiliary material such as a binder may contain an organic material, but the main component is an inorganic material.
[0056]
The resistance layer 13 is bonded to the dielectric layer 12 with, for example, an inorganic adhesive or an organic adhesive.
[0057]
The material and manufacturing method of the radio wave absorption characteristic adjusting dielectric layer 14 are the same as those of the resistance film substrate 21. Further, the radio wave absorption characteristic adjusting dielectric layer 14 is also bonded to the dielectric layer 12 by, for example, an inorganic adhesive or an organic adhesive.
[0058]
There is no restriction | limiting as an inorganic adhesive, The thing conventionally used as an inorganic adhesive which has a nonflammability can be used. As the inorganic adhesive, for example, a water-soluble or water-dispersed inorganic adhesive configured by mixing an aluminum phosphate solution, colloidal silica, colloidal alumina or the like with a curing agent, a catalyst, or the like can be used. .
[0059]
When the resistance layer 13 or the dielectric layer 14 for adjusting radio wave absorption characteristics is bonded to the dielectric layer 12 with an organic adhesive, it is necessary to make the adhesive layer thin so that the non-combustibility of the radio wave absorber 10 can be maintained. is there.
[0060]
Next, the dielectric layer 12 will be described in detail with reference to FIGS. In order to reduce the weight of the radio wave absorber 10 and to give the radio wave absorber 10 heat insulation properties, the dielectric layer 12 is a plate-like member having a plurality of holes penetrating in the traveling direction of the radio wave, or a plate-like member. It is preferable to form with a foam. FIGS. 7 to 10 are perspective views showing first to fourth examples of the configuration of the radio wave absorber 10 having the dielectric layer 12 formed by the plate-like member having a plurality of holes as described above. It is.
[0061]
The radio wave absorber 10 of the first example shown in FIG. 7 includes a radio wave reflector 11 and a dielectric layer 12 disposed on the radio wave arrival side of the radio wave reflector 11.₁And dielectric layer 12₁Resistance layer 13 arranged on the radio wave arrival side₁And. Dielectric layer 12₁Has a honeycomb shape having a plurality of holes penetrating in the traveling direction of radio waves. Resistance layer 13₁Is a resistance film substrate 21₁And this resistance film substrate 21₁Resistive film 22 formed thereon₁Including. Resistance film 22₁Is the dielectric layer 12₁Is joined to the surface on the radio wave arrival side.
[0062]
The radio wave absorber 10 of the second example shown in FIG. 8 includes a radio wave reflector 11 and a dielectric layer 12 disposed on the radio wave arrival side of the radio wave reflector 11.₁And dielectric layer 12₁Resistance layer 13 arranged on the radio wave arrival side₁And the resistance layer 13₁The dielectric layer 12 disposed on the radio wave arrival side in FIG.₂And dielectric layer 12₂Resistance layer 13 arranged on the radio wave arrival side₂And. Dielectric layer 12₁, 12₂Each have a honeycomb shape having a plurality of holes penetrating in the traveling direction of radio waves. Resistance layer 13₁Is a resistance film substrate 21₁And this resistance film substrate 21₁Resistive film 22 formed thereon₁Including. Resistance film substrate 21₁Is the dielectric layer 12₁Is joined to the surface on the radio wave arrival side. Resistance film 22₁Is the dielectric layer 12₂Is joined to the surface opposite to the radio wave arrival side. Resistance layer 13₂Is a resistance film substrate 21₂And this resistance film substrate 21₂Resistive film 22 formed thereon₂Including. Resistance film 22₂Is the dielectric layer 12₂Is joined to the surface on the radio wave arrival side.
[0063]
The radio wave absorber 10 of the third example shown in FIG. 9 is the same as the radio wave absorber 10 shown in FIG.₁, 12₂Instead of the corrugated (corrugated) dielectric layer 12 having a plurality of holes penetrating in the traveling direction of the radio wave.₁, 12₂Is provided.
[0064]
The radio wave absorber 10 of the fourth example shown in FIG. 10 is the same as the radio wave absorber 10 shown in FIG.₁, 12₂Instead of the lattice-shaped dielectric layer 12 having a plurality of holes penetrating in the traveling direction of the radio wave₁, 12₂Is provided.
[0065]
As in the example shown in FIGS. 7 to 10, by using a plate-like member having a plurality of holes penetrating in the traveling direction of the radio wave as the dielectric layer 12, as described above, The structural strength and load resistance of the radio wave absorber 10 can be made sufficient while enabling weight reduction.
[0066]
The honeycomb-shaped, corrugated-shaped, or lattice-shaped dielectric layer 12 is formed of, for example, a hydrous inorganic compound. Examples of the hydrous inorganic compound include sepiolite, hydrates of aluminum hydroxide, magnesium hydroxide, and calcium hydroxide, dihydrate gypsum, calcium aluminate, and wollastonite. Of these, sepiolite is particularly preferable. Since sepiolite is a water-containing inorganic compound having flexibility, it has a high bending strength. Therefore, when sepiolite is used as the hydrous inorganic compound, the honeycomb-shaped dielectric layer 12 can be formed as follows. That is, first, a plurality of sheets made of a hydrous inorganic compound are manufactured. Next, a plurality of sheets are laminated while adhering adjacent sheets partially along a plurality of straight lines arranged at predetermined intervals. Next, a laminate of a plurality of sheets is stretched in the thickness direction. Thereby, the honeycomb-shaped dielectric layer 12 is formed.
[0067]
When the dielectric layer 12 is formed of a plate-like foam, the radio wave absorber 10 can have a sound absorbing function. As the foam used for the dielectric layer 12, for example, a magnesium hydroxide inorganic foam plate having the following composition can be used. This magnesium hydroxide inorganic foam plate contains 60% by weight magnesium hydroxide, 25% by weight calcium carbonate, 10% by weight aluminum hydroxide, 3% by weight vinyl chloride resin and 2% by weight silicon resin. To do. As the foam used for the dielectric layer 12, in addition to the above examples, flame retardant foams such as inocyanurate foams and phenol foams can be used.
[0068]
When the dielectric layer 12 is formed of a plate-like member having a plurality of holes penetrating in the traveling direction of the radio wave, or a plate-like foam, the first on the radio wave arrival side of the dielectric layer 12 Of the surface and the second surface on the opposite side, at least the first surface is preferably covered with a plate-like or sheet-like member mainly made of an inorganic material. In this case, the plate-like or sheet-like member covering the surface of the dielectric layer 12 may be the resistance layer 13, the radio wave absorption characteristic adjusting dielectric layer 14, or the radio wave reflector 11.
[0069]
The dielectric layer 12 is mainly made of an inorganic material, as in the case of the resistive film substrate 21, although an auxiliary material such as a binder may contain an organic material, the main component is an inorganic material. It means that.
[0070]
Next, the radio wave reflector 11 will be described in detail. The radio wave reflector 11 may be a metal plate such as a steel plate, but is a plate-like radio wave reflector base mainly made of an inorganic material, and a conductive material disposed on the radio wave arrival side surface of the radio wave reflector base. A structure having a film is preferable. The material and manufacturing method of the radio wave reflector substrate are the same as those of the resistive film substrate 21. The conductive film may be formed by a metal foil bonded to the radio wave reflector substrate, or may be formed by applying a conductive paint on the radio wave reflector substrate and solidifying it. For reducing the weight of the radio wave reflector 11, a method of forming a conductive film by applying a conductive paint on the radio wave reflector substrate is effective.
[0071]
When the metal foil is bonded to the radio wave reflector substrate, for example, an inorganic adhesive or an organic adhesive is used. In the case of using an organic adhesive, it is necessary to make the adhesive layer thin so that the non-flammability of the radio wave absorber 10 can be maintained.
[0072]
The conductive paint may be organic, but is preferably inorganic. When using an organic conductive paint, it is necessary to reduce the coating thickness of the conductive paint so that the non-flammability of the radio wave absorber 10 can be maintained.
[0073]
The radio wave reflector 11 is bonded to the dielectric layer 12 with, for example, an inorganic adhesive or an organic adhesive. In the case of using an organic adhesive, it is necessary to make the adhesive layer thin so that the non-flammability of the radio wave absorber 10 can be maintained.
[0074]
Hereinafter, a design method of the radio wave absorber 10 according to the present embodiment will be described. Here, a case where a radio wave enters perpendicularly to the front surface of the radio wave absorber 10 will be described. FIG. 11 is a perspective view showing a simplified configuration of the radio wave absorber 10. FIG. 11 shows only the radio wave reflector 11 and the resistance film 22 among the components of the radio wave absorber 10. Hereinafter, the dielectric layer between the radio wave reflector 11 and the resistance film 22 is referred to as a spacer. The distance between the radio wave reflector 11 and the resistance film 22, that is, the thickness of the spacer is represented by the symbol d. The wavelength of the radio wave in the spacer is represented by the symbol λ.
[0075]
Now, as shown in FIG. 11, consider a case where a plane wave is vertically incident on the resistive film 22 as a radio wave. In FIG. 11, an arrow indicated by reference numeral 1 represents the traveling direction of the radio wave.
[0076]
Normalized input impedance Z at the front of the spacer₁ ^*(* Represents a complex number) is the dielectric constant of the spacer material ε_rIf it is set to ′, it is expressed by the equation (1) from the transmission line theory. “J” represents √ (−1). In addition, normalization in the normalized input impedance means that the normalized input impedance is normalized by the characteristic impedance (≈377Ω) in free space.
[0077]
Z₁ ^*= {1 / √ (ε_r′)} · Tanh {j · (2πd / λ) · √ (ε_r')} ... (1)
[0078]
Next, the sheet resistance value Rs of the resistance film 22^*Is a complex quantity having a real part and an imaginary part, the normalized input impedance Z at the front surface of the resistive film 22_in ^*Is the input impedance Z₁ ^*Element and resistance value Rs^*This can be regarded as the input impedance of a circuit in which these elements are connected in parallel. Therefore, normalized input impedance Z_in ^*Is represented by the following equation (2).
[0079]
Z_in ^*= {(Rs^*/ 377) ・ Z₁ ^*} / {(Rs^*/ 377) + Z₁ ^*} ... (2)
[0080]
Impedance Z_in ^*Becomes 1, the reflection coefficient on the surface of the resistance film 22 becomes 0. Where impedance Z_in ^*The condition that the radio wave absorber 10 satisfies when 1 becomes 1 is referred to as a matching condition.
[0081]
When the spacer is air, the complex amount (real part and imaginary part) of the surface resistance value of the resistance film 22 when the expression (2) satisfies the matching condition is expressed by the following expressions (3) and (4). It can be expressed simply as follows. Real (Rs^*) Represents the real part of the sheet resistance value, and Imag (Rs^*) Represents the imaginary part of the sheet resistance value.
[0082]
Real (Rs^*) = {Sin (2πd / λ)}²・ 377 (3)
[0083]
Imag (Rs^*) = − [{Sin (4πd / λ)} / 2] · 377 (4)
[0084]
The thickness d is in the range represented by the following formula (5).
[0085]
nλ / 2 <d <(n + 1) λ / 2 (n is an integer greater than or equal to 0) (5)
[0086]
Here, a value d / λ obtained by dividing the spacer thickness d by the wavelength λ is called a normalized matching thickness. FIG. 12 shows the result of obtaining the relationship between the complex amount of the sheet resistance value and the normalized matching thickness from the equations (3) and (4).
[0087]
As can be seen from the equations (3), (4) and FIG. 12, the real part and the imaginary part of the sheet resistance value change periodically with respect to the change in the normalized matching thickness. Here, from FIG. 12, when the imaginary part of the sheet resistance value is a negative value, that is, when it is capacitive, the spacer thickness d becomes smaller than ¼ of the wavelength λ, and the imaginary part of the sheet resistance value. When is a positive value, that is, inductive, the thickness d of the spacer is found to be larger than ¼ of the wavelength λ. Thus, by using the resistive film 22 having a capacitive susceptance, the radio wave absorber 10 having a spacer thickness d smaller than ¼ of the wavelength λ can be realized.
[0088]
In the present embodiment, when the radio wave is incident on the front surface of the radio wave absorber 10 vertically, the resistance film 22 is used at a frequency at which the return loss is maximum within the frequency range of the radio wave of 0.8 GHz to 18 GHz. The real part and the imaginary part of the sheet resistance value are set to values within a predetermined allowable range including the values obtained from the equations (3) and (4). The allowable range is preferably a range of ± 30%, more preferably a range of ± 20%, and a range of ± 10% with respect to the values obtained from the formulas (3) and (4). Is more preferable.
[0089]
Hereinafter, examples of the radio wave absorber 10 according to the present embodiment will be described.
First, a method for producing the resistance film 22 in the embodiment will be described. As the conductive material used for the resistance film 22 in the examples, scaly graphite powder was used. In the examples, this powder was uniformly dispersed in a binder to form a liquid paint. Next, this liquid paint was applied to an inorganic resistive film substrate 21 having a length of 300 mm, a width of 300 mm, and a thickness of 2 mm by spray coating using a robot coating apparatus. Next, the liquid paint was dried at a temperature of 105 ° C. to form a resistance film 22. The thickness of the resistive film 22 was about 70 to 90 μm.
[0090]
The blending amounts of the conductive powder and the binder in the resistive film 22 produced by the above method are shown in the following table. Moreover, in the Example, the surface resistance value in direct current (henceforth DC surface resistance value) of the produced resistance film 22 was measured. The following table also shows the DC surface resistance values.
[0091]
[Table 1]

[0092]
As shown in the above table, the resistance film 22 having a direct current surface resistance value in the range of 270 to 3500 Ω □ is produced by changing the blending amount of the conductive powder within the range of about 57 to 72% by weight. We were able to.
[0093]
Next, a method for evaluating the sheet resistance value of the resistance film 22 in the embodiment will be described. In this evaluation method, first, a sample was prepared by disposing the resistive film 22 produced by the above-described method via a spacer at a distance of about 10 mm from the radio wave reflector 11. Here, foamed polyethylene having a dielectric constant close to that of air was used as the spacer material. Next, with respect to the sample, the input impedance when radio waves were incident on the resistance film 22 perpendicularly was measured by the following method. First, a metal plate having the same planar shape as the resistance film 22 was arranged on the front surface of the resistance film 22 arranged as described above, and the reflection coefficient of the metal plate was measured. Next, the reflection coefficient of the sample was measured. Next, the input impedance of the front surface of the sample was calculated based on the ratio between the reflection coefficient of the metal plate and the reflection coefficient of the sample. Next, the complex amount of the surface resistance value was calculated from the calculated input impedance.
[0094]
FIG. 13 shows the configuration of the measurement system used for the above-described evaluation of the sheet resistance value. This measurement system includes a transmission antenna 121 that radiates radio waves to a sample 120 to be evaluated, a reception antenna 122 that receives radio waves reflected by the sample 120, a network analyzer 123 connected to the transmission antenna 121, and an input terminal. Is connected to the receiving antenna 122, and an amplifier 124 whose output end is connected to the network analyzer 123. A double rigid guide antenna was used for the transmission antenna 121 and the reception antenna 122. The transmitting antenna 121 and the receiving antenna 122 are arranged so that the distances from the antennas 121 and 122 to the incident position of the radio wave on the sample 120 are equal. In the embodiment, this distance is 3 m. The evaluation system is installed in the anechoic chamber 125.
[0095]
The network analyzer 123 sends a transmission signal to the transmission antenna 121. A reception signal obtained by the reception antenna 122 is amplified by the amplifier 124 and then input to the network analyzer 123. The network analyzer 123 measures the characteristics of the sample based on the transmission signal and the reception signal. The measurement frequency was 1 to 9 GHz.
[0096]
A direct wave that directly reaches the receiving antenna 122 from the transmitting antenna 121 affects the measured value. Therefore, in the example, the direct wave was measured without the sample 120, and the measured value of the direct wave was vector-wise removed from the measured value with the sample 120 present. In the measurement, the time domain method was used in combination.
[0097]
FIG. 14 shows the frequency characteristics of the complex amount of the surface resistance value at a frequency of 2 GHz to 8 GHz of the produced resistive film 22. FIG. 15 shows the relationship between the complex amount of the sheet resistance value and the DC sheet resistance value at 2 GHz, 5 GHz, and 8 GHz of the manufactured resistive film 22. As can be seen from FIGS. 14 and 15, the real part and imaginary part values of the sheet resistance value of the produced resistive film 22 tend to decrease as the frequency increases.
[0098]
Further, as can be seen from FIG. 15, there is a correlation between the complex amount of the surface resistance value of the manufactured resistive film 22 and the DC surface resistance value, and the complex amount of the surface resistance value of the manufactured resistive film 22 is the DC surface resistance value. Can be represented by a straight line for each frequency. Therefore, when the frequency is determined, the real part and the imaginary part of the sheet resistance value can be obtained from the DC sheet resistance value. Due to this relationship, when designing the radio wave absorber 10, the surface resistance value of the resistance film can be handled as one variable. As a result, the radio wave absorber 10 can be designed by the Newton method or the like. In addition, the above-described relationship makes it possible to stably manufacture the resistive film 22 having a desired sheet resistance value.
[0099]
[First embodiment]
Next, as the radio wave absorber 10 of the first embodiment, the resistance film 22 having the above-described characteristics is used, and the radio wave absorber 10 (hereinafter, referred to as the resistance layer 13 having only one layer as shown in FIG. 1). This is called a single-layer type electromagnetic wave absorber).
[0100]
First, the design method of the single layer type wave absorber of the first embodiment will be described. FIG. 16 shows a complex amount of the sheet resistance value of the resistance film 22 produced as described above as a Cole-Cole plot. In FIG. 16, a curve with a symbol M represents a matching curve of a single layer type electromagnetic wave absorber. The matching curve referred to here is a curve representing a locus of complex amounts of surface resistance values that satisfy the matching conditions. From FIG. 16, in the frequency range of 2 GHz to 8 GHz, it is possible to satisfy the matching condition when the direct current surface resistance value of the resistance film 22 is in the range of about 350 to 500 Ω □. It can be seen that a single-layer wave absorber of 0.17λ to 0.09λ can be obtained. Also, as can be seen from FIG. 16, as the frequency increases, the spacer thickness (hereinafter referred to as the matching thickness) when the matching condition is satisfied tends to be reduced.
[0101]
From the above results, the matching thickness in the single-layer wave absorber using the resistance film 22 produced in the example is 0.17 to 0.09λ. Therefore, in this single layer type wave absorber, the thickness can be reduced by about 30 to 65% as compared with the wave absorber using the resistance film having only the resistance component.
[0102]
Next, a single-layer wave absorber that can be applied to a DSRC system that uses the 5.8 GHz band as a frequency band was designed and manufactured. Assuming various applications to which this DSRC system is applied, a radio wave absorber having nonflammability is required. Therefore, an inorganic material is used as the material constituting the single-layer type electromagnetic wave absorber.
[0103]
The structure of the designed and manufactured single-layer wave absorber is as shown in FIG. In this single-layer type electromagnetic wave absorber, the dielectric layer 12₁Is mainly composed of an inorganic material and has a honeycomb shape. Dielectric layer 12₁The diameter of one hole in is 15 mm. Also, the resistance film 22₁2 mm thick inorganic resistance film substrate 21.₁The one formed above was used. In this structure, the dielectric layer 12 has a maximum reflection loss in the frequency band of 5.8 GHz.₁Optimal thickness and resistive coating 22₁The optimum DC surface resistance value Rs was determined by the Newton method. As a result, the dielectric layer 12₁The thickness becomes 4.3 mm, and the resistance film 22₁The DC surface resistance value Rs was 470Ω □. Resistive film substrate 21₁The complex relative dielectric constant of 2.8-j0.28 and the dielectric layer 12₁The complex relative dielectric constant of was set to 1.05-j0.
[0104]
From the above design results, the overall thickness of the single-layer type wave absorber for the 5.8 GHz band using the produced resistive film was 6.3 mm. In a single layer type wave absorber for a 5.8 GHz band using a resistance film having only a resistance component, the overall thickness is 11.3 mm. Therefore, it can be seen that the thickness of the single-layer wave absorber of this example can be reduced by about 45% compared to the single-layer wave absorber using a resistance film having only a resistance component.
[0105]
Next, based on the above design results, a single-layer wave absorber was actually manufactured as follows. First, a dielectric layer 12 is formed on a metal plate as the radio wave reflector 11.₁Were bonded with an adhesive. Next, the resistance film substrate 21₁On top of the resistive film 22₁Resistive layer 13 formed of₁Resistance film 22₁Is the dielectric layer 12₁The dielectric layer 12 is in contact with₁The single layer type electromagnetic wave absorber having the structure shown in FIG. 7 was completed. The size of the radio wave absorber was 300 mm in length and 300 mm in width. Here, the actually produced resistance film 22₁As a result of the measurement, the DC surface resistance value was 405Ω □. The total thickness of the manufactured single-layer wave absorber was 6.7 mm.
[0106]
Next, the radio wave absorption characteristics of the manufactured single-layer type radio wave absorber were measured using the measurement system shown in FIG. 13 and the measurement method described with reference to FIG. FIG. 17 shows the radio wave absorption characteristics of this single-layer type radio wave absorber. In FIG. 17, a curve indicated by a broken line represents a radio wave absorption characteristic (hereinafter referred to as a calculated value) obtained by calculation based on a design value. In FIG. 17, the two curves shown by solid lines both represent the radio wave absorption characteristics (hereinafter referred to as measured values) of the actually manufactured single-layer type radio wave absorber.
[0107]
As shown in FIG. 17, in the measured value, the frequency at which the maximum return loss was obtained was 5.6 GHz to 5.7 GHz, and the return loss at the frequency of 5.8 GHz was about 27 to 29 dB. The reason why the measured value is slightly different from the calculated value is that the DC resistance value of the manufactured resistive film is 65Ω □ lower than the designed value, and the total thickness of the manufactured wave absorber is the designed value. This is considered to be due to 0.4 mm increase.
[0108]
Further, the manufactured radio wave absorber was examined for whether there is a difference in radio wave absorption characteristics depending on the direction of the electric field due to the directionality of the resistance film with respect to the direction of the electric field. As a result, it was found that the difference in radio wave absorption characteristics depending on the direction of the electric field was small.
[0109]
[Second Embodiment]
Next, as the radio wave absorber 10 of the second embodiment, as shown in FIG. 3, the radio wave absorber 10 having a structure in which the resistance layer 13 has two layers (hereinafter referred to as a two-layer type radio wave absorber) is designed. And manufactured. Here, a two-layer wave absorber functioning in the 2.4 GHz band and the 5.2 GHz band, which are the frequency bands of the wireless LAN used in the office, was designed. Here, since the radio wave absorber used for the wall in the office is required to be nonflammable, an inorganic material is used as a material constituting the radio wave absorber.
[0110]
The structure of the designed and manufactured two-layer type electromagnetic wave absorber is as shown in FIG. In this two-layer type electromagnetic wave absorber, the dielectric layer 12₁, 12₂Each is mainly composed of an inorganic material and has a honeycomb shape. Dielectric layer 12₁, 12₂The diameter of one hole in is 15 mm. Resistance film 22₁1 mm thick inorganic resistance film substrate 21.₁The one formed above was used. Also, the resistance film 22₂2 mm thick inorganic resistance film substrate 21.₂The one formed above was used. In this structure, using the Newton method, the resistive film 22₁, 22₂DC surface resistance values Rs1, Rs2 and the dielectric layer 12₁, 12₂The thicknesses d1 and d2 were determined. The design results of this two-layer type electromagnetic wave absorber are shown in the following table. This table also shows the design results of the two-layered electromagnetic wave absorber using a resistance film having only a resistance component.
[0111]
[Table 2]

[0112]
From the above design results, the overall thickness of the two-layered electromagnetic wave absorber using the resistance film produced in the example was about 25 mm. In a two-layer type electromagnetic wave absorber using a resistance film having only a resistance component, the overall thickness is about 35 mm. Therefore, it can be seen that the thickness of the two-layer type wave absorber of this example can be reduced by about 30% compared to the two-layer type wave absorber using a resistance film having only a resistance component.
[0113]
Next, based on the above design results, a two-layer type electromagnetic wave absorber was actually manufactured as follows. First, a dielectric layer 12 is formed on a metal plate as the radio wave reflector 11.₁Were bonded with an adhesive. Next, the resistance film substrate 21₁On top of the resistive film 22₁Resistive layer 13 formed of₁The resistance film substrate 21₁Is the dielectric layer 12₁The dielectric layer 12 is in contact with₁It adhered with an adhesive. Next, the resistance layer 13₁Dielectric layer 12₂Were bonded with an adhesive. Next, the resistance film substrate 21₂On top of the resistive film 22₂Resistive layer 13 formed of₂Resistance film 22₂Is the dielectric layer 12₂The dielectric layer 12 is in contact with₂The two-layered electromagnetic wave absorber having the structure shown in FIG. 8 was completed. The size of the radio wave absorber was 300 mm in length and 300 mm in width. Here, the actually produced resistance film 22₁, 22₂The DC surface resistance values of 270Ω □ and 1859Ω □ were measured, respectively. The total thickness of the manufactured two-layer type electromagnetic wave absorber was 25 mm.
[0114]
Next, the radio wave absorption characteristics of the manufactured two-layer type radio wave absorber were measured using the measurement system shown in FIG. 13 and the measurement method described with reference to FIG. The radio wave absorption characteristics of this two-layer type radio wave absorber are shown in FIG. In FIG. 18, the curve indicated by the broken line represents the radio wave absorption characteristic (calculated value) obtained by calculation based on the design value. In FIG. 18, the two curves indicated by solid lines both represent the radio wave absorption characteristics (measured values) of the actually manufactured two-layer type radio wave absorber.
[0115]
As shown in FIG. 18, in the measured values, the return loss at the frequency of 2.4 GHz and the frequency of 5.2 GHz is both 20 dB or more. Thereby, it was confirmed that the two-layered electromagnetic wave absorber of this example can obtain the bimodal characteristics. The reason why the measured value is slightly different from the calculated value at the frequency of 5.2 GHz is that the produced resistive film 22₁, 22₂It is considered that this is because the direct current surface resistance value differs from the designed value by about 10 to 15%.
[0116]
Further, the manufactured radio wave absorber was examined for whether there is a difference in radio wave absorption characteristics depending on the direction of the electric field due to the directionality of the resistance film with respect to the direction of the electric field. As a result, it was found that the difference in radio wave absorption characteristics depending on the direction of the electric field was small.
[0117]
Up to this point, the case where radio waves are incident on the front surface of the radio wave absorber 10 vertically has been described. Hereinafter, a design method of the radio wave absorber 10 when radio waves are incident on the front surface of the radio wave absorber 10 from an oblique direction will be described.
[0118]
First, let us consider a case where radio waves are incident on the resistance film 22 from an oblique direction in the radio wave absorber 10 shown in a simplified manner in FIG. Here, the incident angle of the radio wave with respect to the resistance film 22, that is, the angle between the normal line of the resistance film 22 and the incident direction of the radio wave is defined as θ. Further, in this case, it is necessary to consider the incident radio wave separately into polarized waves, ie, TE waves, whose electric field is perpendicular to the incident surface, and polarized waves, ie, TM waves, whose magnetic field is perpendicular to the incident surface.
[0119]
First, the case where the incident radio wave is a TE wave will be described. In this case, the expressions corresponding to the above expressions (1) and (3) to (5) are the following expressions (6) to (9), respectively. In the case of the TE wave, the matching condition when the spacer is air is the impedance Z expressed by the above equation (2)._in ^*Is 1 / cos θ.
[0120]
Z₁ ^*= {1 / √ (ε_r'-Sin²θ)} · tanh {j · (2πd / λ) · √ (ε_r'-Sin²θ)} (6)
[0121]
Real (Rs^*) = {Sin (2πdcos θ / λ)}²・ 377 / cos θ (7)
[0122]
Imag (Rs^*) = − [{Sin (4πdcos θ / λ)} / 2] · 377 / cos θ (8)
[0123]
nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer greater than or equal to 0) (9)
[0124]
On the other hand, when the incident radio wave is a TM wave, the expressions corresponding to the above expressions (1) and (3) to (5) are the following expressions (10) to (13), respectively. In the case of the TM wave, the matching condition when the spacer is air is the impedance Z expressed by the above equation (2)._in ^*Is cos θ.
[0125]
Z₁ ^*= {√ (ε_r'-Sin²θ) / ε_r′} · Tanh {j · (2πd / λ) · √ (ε_r'-Sin²θ)} (10)
[0126]
Real (Rs^*) = {Sin (2πdcos θ / λ)}²・ 377 ・ cos θ (11)
[0127]
Imag (Rs^*) = − [{Sin (4πdcos θ / λ)} / 2] · 377 · cos θ (12)
[0128]
nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer greater than or equal to 0) (13)
[0129]
It should be noted that if θ = 0 in the equations (6) and (10), the equation (1) coincides. Further, when θ = 0 in the equations (7) and (11), it agrees with the equation (3). Further, in the equations (8) and (12), when θ = 0, the equation agrees with the equation (4). Further, in the equations (9) and (13), when θ = 0, the equation agrees with the equation (5). Therefore, Expressions (6) to (13) can be applied to a case where radio waves are incident on the front surface of the radio wave absorber 10 including the case where θ = 0. When θ = 0, the TE wave and TM wave are not distinguished.
[0130]
Here, regarding the single-layer type wave absorber, the relationship between the complex amount of the surface resistance value and the normalized matching thickness when the incident angle θ is 30 °, 40 °, 50 °, 60 °, 70 °, and 80 °. The results obtained are shown in FIGS. FIG. 19 shows a case where the incident angle θ is 30 ° and the TE wave. FIG. 20 shows the case of the TM wave when the incident angle θ is 30 °. FIG. 21 shows a case where the incident angle θ is 40 ° and the TE wave. FIG. 22 shows the case where the incident angle θ is 40 ° and the TM wave. FIG. 23 shows a case where the incident angle θ is 50 ° and the TE wave. FIG. 24 shows the case where the incident angle θ is 50 ° and the TM wave. FIG. 25 shows a case where the incident angle θ is 60 ° and the TE wave. FIG. 26 shows the case where the incident angle θ is 60 ° and the TM wave. FIG. 27 shows a case where the incident angle θ is 70 ° and the TE wave. FIG. 28 shows the case of the TM wave when the incident angle θ is 70 °. FIG. 29 shows a case where the incident angle θ is 80 ° and the TE wave. FIG. 30 shows the case where the incident angle θ is 80 ° and the TM wave.
[0131]
In the present embodiment, when the incident radio wave to the radio wave absorber 10 is a TE wave, the sheet resistance value of the resistive film 22 is at a frequency at which the return loss is maximum within the frequency range of the radio wave of 0.8 GHz to 18 GHz. The real part and the imaginary part are set to values within a predetermined allowable range including values obtained from the expressions (7) and (8). The allowable range is preferably a range of ± 30%, more preferably a range of ± 20%, and a range of ± 10% with respect to the values obtained from the formulas (7) and (8). Is more preferable.
[0132]
Further, in the present embodiment, when the incident radio wave to the radio wave absorber 10 is a TM wave, the surface of the resistance film 22 at a frequency at which the return loss is maximum in the frequency range of the radio wave of 0.8 GHz to 18 GHz. The real part and the imaginary part of the resistance value are set to values within a predetermined allowable range including the values obtained from the equations (11) and (12), respectively. The allowable range is preferably a range of ± 30%, more preferably a range of ± 20%, and a range of ± 10% with respect to the values obtained from the formulas (11) and (12). Is more preferable.
[0133]
Here, the allowable range will be described. First, the minimum value of the return loss at the frequency at which the return loss (radio wave absorption) is the maximum when the real and imaginary parts of the surface resistance value of the resistance film are changed with respect to the design value is calculated. Asked. As a result, when the thickness of the spacer is 0.05λ, the return loss when the real part and the imaginary part of the surface resistance value of the resistance film are changed within a range of ± 10% with respect to the design value. The lowest value was 15.3 (≈15) dB. When the spacer thickness is 0.1λ, the minimum return loss when the real part and the imaginary part of the surface resistance value of the resistive film are changed within a range of ± 20% of the design value. The value was 14.5 (≈15) dB. When the spacer thickness is 0.2λ, the minimum return loss when the real part and the imaginary part of the surface resistance value of the resistive film are changed within a range of ± 30% of the design value. The value was 14.6 (≈15) dB.
[0134]
Here, the allowable range of the real part and the imaginary part of the sheet resistance value is set to a range in which 15 dB or more can be secured as the return loss at the frequency at which the return loss is maximum. In this case, the allowable range is ± 10% when the spacer thickness is 0.05λ, ± 20% when the spacer thickness is 0.1λ, and the spacer thickness is 0.2λ. In this case, ± 30%. Therefore, in the present embodiment, the allowable range needs to be within ± 30% in order to set the spacer thickness to 0.2λ. In addition, in order to set the spacer thickness to an arbitrary thickness within the range of 0.1λ to 0.2λ, the allowable range needs to be within ± 20%. In addition, the allowable range needs to be within ± 10% in order to set the spacer thickness to an arbitrary thickness within the range of 0.05λ to 0.2λ. From the above, in the present embodiment, the allowable range is preferably within ± 30%, more preferably within ± 20%, and even more preferably within ± 10%.
[0135]
Next, with reference to FIGS. 31 and 32, the relationship between the real part and the imaginary part of the sheet resistance value of the resistance film in the present embodiment will be considered. FIG. 31 shows a Cole-Cole plot of the complex amount of the surface resistance value of the resistance film satisfying the matching condition when the incident radio wave is a TE wave and the incident angle θ is in the range of 0 to 80 °. In the annotation in FIG. 31, “0 °” represents the case where θ is 0 °. “TEα ° (α = 30, 40, 50, 60, 70, 80)” is the case of TE wave, and the incident angle θ is 30 °, 40 °, 50 °, 60 °, 70 °, 80, respectively. Indicates the case of °.
[0136]
FIG. 32 is a Cole-Cole plot showing the complex amount of the surface resistance value of the resistance film satisfying the matching condition when the incident radio wave is TM wave and the incident angle θ is in the range of 0 to 80 °. . In the annotation in FIG. 32, “0 °” represents the case where θ is 0 °. “TMα ° (α = 30, 40, 50, 60, 70, 80)” is the case of TM waves, and the incident angle θ is 30 °, 40 °, 50 °, 60 °, 70 °, 80. Indicates the case of °.
[0137]
In FIGS. 31 and 32, the thickness of the spacer is in the range of 0.05λ / cos θ to 0.2λ / cos θ. In the radio wave absorber using the resistance film having only the resistance component, the thickness of the spacer that satisfies the matching condition is 0.25λ / cos θ. Therefore, the range of the spacer thickness of 0.05λ / cos θ to 0.2λ / cos θ is a range of 20 to 80% of the thickness of the spacer in the radio wave absorber using the resistance film having only the resistance component. In the present embodiment, the thickness of the spacer in the single-layer wave absorber is thus set to 20 to 80% of the thickness of the spacer in the wave absorber using the resistance film having only the resistance component. Goal. The reason will be described below.
[0138]
When the thickness of the spacer in this embodiment exceeds 80% of the thickness of the spacer in the radio wave absorber using the resistance film having only the resistance component, the radio wave absorption using the resistance film having only the resistance component Compared with the body, the thickness of the radio wave absorber according to the present embodiment is not significantly reduced. On the other hand, when the thickness of the spacer in this embodiment is less than 20% of the thickness of the spacer in the radio wave absorber using the resistance film having only the resistance component, such a thin spacer is manufactured. Becomes very difficult. Further, in this case, the influence of the error in the spacer thickness and the error in the surface resistance value of the resistance film on the radio wave absorption characteristics of the radio wave absorber becomes large, and it becomes very difficult to control the thickness of the spacer. For these reasons, in order to realize a radio wave absorber that is easy to manufacture and handle and that is sufficiently thin compared to a radio wave absorber that uses a resistance film having only a resistance component, the thickness of the spacer is reduced only to the resistance component. The thickness of the spacer in the radio wave absorber using the resistance film is preferably 20 to 80%.
[0139]
Here, the surface of the resistance film satisfying the matching condition under the condition that the incident angle θ is in the range of 0 to 80 ° and the thickness of the spacer is in the range of 0.05λ / cos θ to 0.2λ / cos θ. Consider the relationship between the real part and the imaginary part of the resistance value. As can be seen from FIGS. 31 and 32, in both the case of the TE wave and the case of the TM wave, a value “imaginary part / real part” (denoted as a slope in the figure) obtained by dividing the value of the imaginary part by the value of the real part. , −0.3 to −3.1. Further, as can be seen from FIG. 31, in the case of the TE wave, the real part value of the surface resistance value of the resistance film satisfying the matching condition is in the range of 35 to 2000Ω □, and the surface of the resistance film satisfying the matching condition. The value of the imaginary part of the resistance value is within a range of −110 to −1100Ω □. Further, as can be seen from FIG. 32, in the case of TM waves, the real part of the surface resistance value of the resistance film satisfying the matching condition is in the range of 5 to 350Ω □, and the surface of the resistance film satisfying the matching condition The value of the imaginary part of the resistance value is in the range of −15 to −190Ω □.
[0140]
From the above, in the radio wave absorber 10 according to the present embodiment, the surface resistance value of the resistance film preferably satisfies the following conditions so that at least one of the TE wave and the TM wave can be absorbed. The condition is that the value of the real part of the surface resistance value of the resistive film is within the range of 5 to 2000 Ω □ at the frequency where the return loss is maximum within the frequency range of the radio wave of 0.8 GHz to 18 GHz. The value of the imaginary part of the resistance value is in the range of −15 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. is there.
[0141]
Moreover, in the radio wave absorber 10 according to the present embodiment, the surface resistance value of the resistance film preferably satisfies the following condition when absorbing TE wave radio waves. The condition is that the value of the real part of the surface resistance value of the resistive film is in the range of 35 to 2000 Ω □ at the frequency where the return loss is maximum in the frequency range of radio waves of 0.8 GHz to 18 GHz. The value of the imaginary part of the resistance value is in the range of −110 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. is there.
[0142]
In the radio wave absorber 10 according to the present embodiment, the surface resistance value of the resistance film preferably satisfies the following conditions when absorbing TM wave radio waves. The condition is that the value of the real part of the surface resistance value of the resistive film is within the range of 5 to 350 Ω □ at the frequency where the return loss is maximum within the frequency range of the radio wave of 0.8 GHz to 18 GHz. The value of the imaginary part of the resistance value is in the range of −15 to −190Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. is there.
[0143]
As described above, according to the present embodiment, it is possible to realize a radio wave absorber that is thinner than a radio wave absorber using a resistance film having only a resistance component and can be easily designed and manufactured. it can.
[0144]
When the radio wave absorber 10 includes a plurality of sets of dielectric layers and resistance films, it is preferable that at least one of the dielectric layers and the resistance films satisfy the conditions described so far.
[0145]
In addition, this invention is not limited to the said embodiment, A various change is possible. For example, the material of each layer constituting the radio wave absorber 10 is not limited to that shown in the embodiment, and can be appropriately selected.
[0146]
【The invention's effect】
As described above, according to the radio wave absorber of the present invention, a radio wave absorber that is thinner than a radio wave absorber using a resistance film having only a resistance component and can be easily designed and manufactured is realized. There is an effect that can be.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first example of a basic configuration of a radio wave absorber according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a second example of the basic configuration of the radio wave absorber according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a third example of the basic configuration of the radio wave absorber according to the embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a fourth example of the basic configuration of the radio wave absorber according to the embodiment of the present invention.
FIG. 5 is a cross-sectional view showing another example of the configuration of the radio wave absorber according to the embodiment of the present invention.
FIG. 6 is an explanatory diagram showing a method of forming a resistance layer in one embodiment of the present invention.
FIG. 7 is a perspective view showing a first example of a configuration of a radio wave absorber having a dielectric layer formed by a plate-like member having a plurality of holes.
FIG. 8 is a perspective view showing a second example of a configuration of a radio wave absorber having a dielectric layer formed by a plate-like member having a plurality of holes.
FIG. 9 is a perspective view showing a third example of a configuration of a radio wave absorber having a dielectric layer formed by a plate-like member having a plurality of holes.
FIG. 10 is a perspective view showing a fourth example of the configuration of the radio wave absorber having a dielectric layer formed by a plate-like member having a plurality of holes.
FIG. 11 is a perspective view showing a simplified configuration of a radio wave absorber according to an embodiment of the present invention.
FIG. 12 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in one embodiment of the present invention.
FIG. 13 is an explanatory diagram showing a configuration of a measurement system used for evaluating a surface resistance value of a resistance film.
FIG. 14 is a characteristic diagram showing a frequency characteristic of a complex amount of a surface resistance value of a resistance film produced in an example of one embodiment of the present invention.
FIG. 15 is a characteristic diagram showing the relationship between the complex amount of the sheet resistance value and the DC sheet resistance value of the resistance film produced in the example of the embodiment of the present invention.
FIG. 16 is a characteristic diagram showing a complex amount of the surface resistance value of the resistance film produced in the example of the embodiment of the present invention as a Cole-Cole plot.
FIG. 17 is a characteristic diagram showing radio wave absorption characteristics of a single-layer radio wave absorber manufactured in an example of one embodiment of the present invention.
FIG. 18 is a characteristic diagram showing radio wave absorption characteristics of the two-layer type radio wave absorber manufactured in the example of the embodiment of the present invention.
FIG. 19 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 30 ° and the incident radio wave is a TE wave. is there.
FIG. 20 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in one embodiment of the present invention when the incident angle θ is 30 ° and the incident radio wave is a TM wave. is there.
FIG. 21 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 40 ° and the incident radio wave is a TE wave. is there.
FIG. 22 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 40 ° and the incident radio wave is a TM wave. is there.
FIG. 23 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 50 ° and the incident radio wave is a TE wave. is there.
FIG. 24 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 50 ° and the incident radio wave is a TM wave. is there.
FIG. 25 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 60 ° and the incident radio wave is a TE wave. is there.
FIG. 26 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 60 ° and the incident radio wave is a TM wave. is there.
FIG. 27 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 70 ° and the incident radio wave is a TE wave. is there.
FIG. 28 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 70 ° and the incident radio wave is a TM wave. is there.
FIG. 29 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in an embodiment of the present invention when the incident angle θ is 80 ° and the incident radio wave is a TE wave. is there.
FIG. 30 is a characteristic diagram showing the relationship between the complex amount of the surface resistance value of the resistive film and the normalized matching thickness in one embodiment of the present invention when the incident angle θ is 80 ° and the incident radio wave is a TM wave. is there.
FIG. 31 is a characteristic diagram representing, as a Cole-Cole plot, a complex amount of a surface resistance value of a resistance film satisfying a matching condition when an incident radio wave is a TE wave and an incident angle θ is in a range of 0 to 80 °.
FIG. 32 is a characteristic diagram showing a complex amount of the surface resistance value of the resistance film satisfying the matching condition as a Cole-Cole plot when the incident radio wave is a TM wave and the incident angle θ is in the range of 0 to 80 °.
[Explanation of symbols]
10 ... Radio wave absorber, 11 ... Radio wave reflector, 12,12₁, 12₂... Dielectric layers 13, 13₁, 13₂... Resistivity layer, 21, 21₁, 21₂... Substrate for resistance film, 22, 22₁, 22₂... resistance film.

Claims (21)

Radio wave reflector,
A dielectric layer disposed on the radio wave arrival side of the radio wave reflector,
A radio wave absorber comprising a resistive film disposed on the radio wave arrival side in the dielectric layer,
In the frequency range where the return loss is maximum within the frequency range of radio waves of 0.8 GHz to 18 GHz, the real part of the surface resistance value of the resistance film is in the range of 5 to 2000 Ω □, The value of the imaginary part is in the range of −15 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. Radio wave absorber. Radio wave reflector,
A dielectric layer disposed on the radio wave arrival side of the radio wave reflector,
A radio wave absorber comprising a resistive film disposed on the radio wave arrival side in the dielectric layer,
In the frequency range where the return loss is maximum within the frequency range of radio waves of 0.8 GHz to 18 GHz, the real part of the surface resistance value of the resistance film is in the range of 35 to 2000 Ω □, The value of the imaginary part is in the range of −110 to −1100Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. Radio wave absorber. Radio wave reflector,
A dielectric layer disposed on the radio wave arrival side of the radio wave reflector,
A radio wave absorber comprising a resistive film disposed on the radio wave arrival side in the dielectric layer,
In the frequency range where the return loss is maximum in the frequency range of radio waves of 0.8 GHz to 18 GHz, the real part of the surface resistance value of the resistance film is in the range of 5 to 350 Ω □, The value of the imaginary part is in the range of −15 to −190Ω □, and the value obtained by dividing the value of the imaginary part by the value of the real part is in the range of −0.3 to −3.1. Radio wave absorber. Radio wave reflector,
A dielectric layer disposed on the radio wave arrival side of the radio wave reflector,
A radio wave absorber comprising a resistive film disposed on the radio wave arrival side in the dielectric layer,
Reflecting within the frequency range of radio waves from 0.8 GHz to 18 GHz, where d is the thickness of the dielectric layer, λ is the wavelength of the radio wave in the dielectric layer, and θ is the incident angle of the radio wave with respect to the resistive film. The radio wave absorber, wherein a real part and an imaginary part of the surface resistance value of the resistive film are within a range of ± 30% of a value obtained from the following expression at a frequency at which the attenuation amount is maximum. .
Real part: {sin (2πd cos θ / λ)} ² · 377 / cos θ
Imaginary part:-[{sin (4πdcosθ / λ)} / 2] · 377 / cosθ
However, nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer of 0 or more) Radio wave reflector,
A dielectric layer disposed on the radio wave arrival side of the radio wave reflector,
A radio wave absorber comprising a resistive film disposed on the radio wave arrival side in the dielectric layer,
Reflecting within the frequency range of radio waves from 0.8 GHz to 18 GHz, where d is the thickness of the dielectric layer, λ is the wavelength of the radio wave in the dielectric layer, and θ is the incident angle of the radio wave with respect to the resistive film. The radio wave absorber, wherein a real part and an imaginary part of the surface resistance value of the resistive film are within a range of ± 30% of a value obtained from the following expression at a frequency at which the attenuation amount is maximum. .
Real part: {sin (2πdcosθ / λ)} ² · 377 · cosθ
Imaginary part:-[{sin (4πdcosθ / λ)} / 2] · 377 · cosθ
However, nλ / 2 cos θ <d <(n + 1) λ / 2 cos θ (n is an integer of 0 or more) Furthermore, it comprises one or more sets of a second dielectric layer and a second resistive film disposed between the radio wave reflector and the dielectric layer or on the radio wave arrival side of the resistive film. The radio wave absorber according to any one of claims 1 to 5. Further, the other dielectric layer disposed on the radio wave arrival side of the resistive film disposed on the surface farthest from the radio wave reflector, and the radio wave absorption characteristic adjustment disposed on the radio wave arrival side of the other dielectric layer 7. The radio wave absorber according to claim 1, further comprising a dielectric layer for use. In addition, a resistive film substrate in the form of a plate or a sheet is provided, and the resistive film is formed of a conductive paint mixed with a coating agent and coated on the resistive film substrate. The radio wave absorber according to any one of claims 1 to 7, wherein The radio wave absorber according to claim 8, wherein the coating agent includes at least one of an inorganic coating agent and an organic coating agent. 10. The radio wave absorber according to claim 8, wherein the conductive material includes at least one of a scale-like conductive powder and a granular conductive powder. 11. The radio wave absorber according to claim 10, wherein the material of the scale-like conductive powder or granular conductive powder includes graphite, carbon, metal powder, or metal oxide. The conductive material includes both the flaky conductive powder and the granular conductive powder, and the flaky conductive powder material and the granular conductive powder material include graphite, carbon, and metal. 11. The radio wave absorber according to claim 10, wherein the radio wave absorber is made of different materials of powder and metal oxide. The radio wave absorber according to any one of claims 10 to 12, wherein a ratio of the scale-like conductive powder in the conductive material is 85% by weight or more. 14. The radio wave absorber according to claim 8, wherein the resistance film substrate is mainly made of an inorganic material and is nonflammable. The electromagnetic wave absorber according to any one of claims 1 to 14, wherein the resistance film has a thickness of 70 µm or more and 200 µm or less. The radio wave absorber according to any one of claims 1 to 15, wherein the dielectric layer is mainly made of an inorganic material and is nonflammable. 17. The dielectric layer according to claim 1, wherein the dielectric layer is formed of a plate-like member having a plurality of holes penetrating in a traveling direction of radio waves or a plate-like foam. Radio wave absorber. The dielectric layer has a first surface on the radio wave arrival side and a second surface on the opposite side, and at least the first surface of the first surface and the second surface is mainly composed of The radio wave absorber according to claim 17, which is covered with a plate-like or sheet-like member made of an inorganic material. 19. The radio wave absorber according to claim 1, further comprising an interior material arranged so as to cover a surface farthest from the radio wave reflector. The radio wave absorber according to any one of claims 1 to 19, wherein a surface farthest from the radio wave reflector is coated. The radio wave reflector has a plate-shaped radio wave reflector base mainly made of an inorganic material, and a conductive film disposed on the radio wave arrival side surface of the radio wave reflector base, and is nonflammable. The radio wave absorber according to claim 1, wherein the radio wave absorber is provided.

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