JPH0613780A - Radio wave absorbent - Google Patents
Radio wave absorbentInfo
- Publication number
- JPH0613780A JPH0613780A JP19024792A JP19024792A JPH0613780A JP H0613780 A JPH0613780 A JP H0613780A JP 19024792 A JP19024792 A JP 19024792A JP 19024792 A JP19024792 A JP 19024792A JP H0613780 A JPH0613780 A JP H0613780A
- Authority
- JP
- Japan
- Prior art keywords
- radio wave
- absorbent
- sintered body
- powder
- field component
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Landscapes
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は、高周波数域の電波を吸
収するための電波吸収体に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber for absorbing radio waves in a high frequency range.
【0002】[0002]
【従来の技術】電波(電磁波)は、図5に示す如く、電
界成分Eと磁界成分Hとを合せ持った波であり、この電
界成分Eと磁界成分Hとの比は、空間インピーダンスZo
として表され、遠方界においては377Ωとなる。物質
の磁気損失は磁界成分の吸収に、誘電損失は電界成分の
吸収に寄与する。2. Description of the Related Art A radio wave (electromagnetic wave) is a wave having an electric field component E and a magnetic field component H as shown in FIG. 5, and the ratio of the electric field component E and the magnetic field component H is the spatial impedance Zo.
And becomes 377Ω in the far field. The magnetic loss of a substance contributes to the absorption of a magnetic field component, and the dielectric loss contributes to the absorption of an electric field component.
【0003】一般に、高周波数域における物質の磁気損
失μ* や誘電損失ε* は、この物質の基本的特性を表す
ものである。前者は、複素透磁率μ* =μ′−jμ″
(又は損失角 tanδ=μ″/μ′)、後者は、複素誘電
率ε* =ε′−jε″(又は損失角 tanδ=ε″/
ε′)で表されることが知られている。複素透磁率及び
複素誘電率が判れば、この物質の反射率(入射電磁波が
物質に垂直入射した場合に物質表面で反射される割合)
や、表皮深さ(入射電磁波が物質中で1/eに減衰する
迄の吸収層の厚み)が求められ、また物質の吸収特性
は、図4に示す電波吸収体1の特性として知ることがで
きる。Generally, the magnetic loss μ * and the dielectric loss ε * of a substance in a high frequency range represent the basic characteristics of this substance. The former is complex permeability μ * = μ′−jμ ″
(Or loss angle tan δ = μ ″ / μ ′), the latter is complex permittivity ε * = ε′−jε ″ (or loss angle tan δ = ε ″ /
It is known to be represented by ε '). If the complex permeability and complex permittivity are known, the reflectance of this substance (the ratio of the incident electromagnetic wave reflected on the substance surface when it is vertically incident on the substance)
Or the skin depth (thickness of the absorption layer until the incident electromagnetic wave is attenuated to 1 / e in the substance) is obtained, and the absorption characteristic of the substance can be known as the characteristic of the radio wave absorber 1 shown in FIG. it can.
【0004】従来、電波吸収体としては、磁気損失を利
用したフェライトや、誘電損失を持つカーボンをウレタ
ンなどに含浸させたものなどが製品化されている。しか
し、これらは、電磁波の持つ磁界成分と電界成分の2つ
の成分の一方のみを損失させる事(フェライトは磁界成
分のみ、カーボンは電界成分のみ)により電磁波エネル
ギーを吸収するという特徴があるため、図4に示す如
く、吸収体1の裏側(電波2の入射側の反対側)に反射
板3を取付ける必要がある。また整合厚さ(吸収体とし
て使用できる厚さ)が複素透磁率μ* と複素誘電率ε*
によって必然的に決るという問題点があった。Conventionally, as a radio wave absorber, a ferrite utilizing magnetic loss, a carbon impregnated with urethane having a dielectric loss, and the like have been commercialized. However, these are characterized by absorbing electromagnetic wave energy by causing loss of only one of the two components of the electromagnetic field, the magnetic field component and the electric field component (ferrite has only the magnetic field component, and carbon has only the electric field component). As shown in FIG. 4, it is necessary to mount the reflector 3 on the back side of the absorber 1 (the side opposite to the incident side of the radio wave 2). In addition, the matching thickness (thickness that can be used as an absorber) is complex permeability μ * and complex permittivity ε *.
There was a problem that it was inevitably decided by.
【0005】[0005]
【発明が解決しようとする課題】本発明は、従来の電波
吸収体の上記の問題点にかんがみ、電磁波の持つ2つの
成分、すなわち磁界成分と電界成分の2つの成分を損失
させることにより電磁波エネルギーを吸収することがで
き、又反射板による多重反射や整合厚さ等を考慮する必
要のない電波吸収体を提供することを課題とする。SUMMARY OF THE INVENTION In view of the above problems of the conventional electromagnetic wave absorber, the present invention eliminates two components of an electromagnetic wave, that is, two components, a magnetic field component and an electric field component, so that electromagnetic wave energy is lost. It is an object of the present invention to provide a radio wave absorber that can absorb the electromagnetic wave and does not need to consider the multiple reflection by the reflector and the matching thickness.
【0006】[0006]
【課題を解決するための手段】前者の課題を解決するた
めの本発明の電波吸収体は、フェライト焼結体中に導電
性セラミックスを分散して形成したことを特徴とする。A radio wave absorber of the present invention for solving the former problem is characterized in that conductive ceramics are dispersed in a ferrite sintered body.
【0007】後者の課題を解決するための本発明の電波
吸収体は、上記構成の電波吸収体において、磁気損失と
誘電損失とが等しくなるようにしたことを特徴とする。A radio wave absorber of the present invention for solving the latter problem is characterized in that, in the radio wave absorber having the above-mentioned structure, the magnetic loss and the dielectric loss are made equal to each other.
【0008】[0008]
【作用】フェライト焼結体中に導電性セラミックスを分
散して電波吸収体を形成したことにより、目的とする周
波数域で所望の複素透磁率(磁気損失)μ* を得るとと
もに、複素誘電率(誘電損失)ε* をも生じさせる事が
でき、その結果、電磁波の持つ磁界成分と電界成分の両
方を損失させて電磁波エネルギーを吸収することが可能
となり、吸収特性が改善される。[Function] By forming a radio wave absorber by dispersing conductive ceramics in a ferrite sintered body, a desired complex magnetic permeability (magnetic loss) μ * can be obtained in a target frequency range, and a complex dielectric constant ( (Dielectric loss) ε * can also be generated, and as a result, both the magnetic field component and the electric field component of the electromagnetic wave can be lost to absorb the electromagnetic wave energy, and the absorption characteristics are improved.
【0009】物質に電磁波が垂直に入射した場合のイン
ピーダンスZは、次式により与えられる。 Z=√μ* /ε* 真空の場合 μ* =μ0 =4π×10-7 ε* =ε0 =8.85×10-12 故に Z =377Ω 物質のインピーダンスは、比透磁率(真空の透磁率μ0
との比)と比誘電率(真空の誘電率ε0 との比)とから
上式により求まる。そして磁気損失μ* 及び誘電損失ε
* が等しければ、空間インピーダンスと整合となり、反
射がなくなる。従って、反射板による多重反射や整合厚
さなどを考える必要がなくなり、電波吸収体の設計が簡
単になる。The impedance Z when an electromagnetic wave is vertically incident on a substance is given by the following equation. Z = √μ * / ε * In the case of vacuum μ * = μ 0 = 4π × 10 −7 ε * = ε 0 = 8.85 × 10 −12 Therefore Z = 377Ω Impedance of a material is Permeability μ 0
And the relative permittivity (ratio with the permittivity ε 0 of vacuum) from the above equation. And magnetic loss μ * and dielectric loss ε
If * is equal, it matches the spatial impedance and there is no reflection. Therefore, it is not necessary to consider multiple reflections by the reflector and matching thickness, and the design of the electromagnetic wave absorber is simplified.
【0010】導体の誘電率は高周波数においては、無限
大であることが知られている。しかし、その場合、透磁
率は0となり、損失材料としては成り立たなくなる。従
って、導体を絶縁または、それに近い状態とすることに
よって、誘電率を有限な値とする必要がある。It is known that the permittivity of a conductor is infinite at high frequencies. However, in that case, the magnetic permeability becomes 0, and it cannot be used as a loss material. Therefore, it is necessary to make the permittivity a finite value by insulating the conductor or in a state close to it.
【0011】本発明で使用される導電性セラミックスの
電気抵抗率は、ρ≧100μΩ−cmとするのが良い。こ
れ以下であると、分散したセラミックス間の接触抵抗が
下り、望ましい誘電損失が得られない。The electrical resistivity of the conductive ceramics used in the present invention is preferably ρ ≧ 100 μΩ-cm. If it is less than this, the contact resistance between the dispersed ceramics decreases, and a desired dielectric loss cannot be obtained.
【0012】導電性セラミックスの形状は、最長軸が1
0〜100μm、最短軸が1〜30μmで、アスペクト
比が50以上である針状もしくはファイバー状等である
ことが望ましい。アスペクト比が小さい粒状である場合
は、誘電率が上がらない。また最長軸の長さが100μ
m以上となると、厚さ数mmのフェライト焼結体内での分
散がうまくゆかない等の問題があり、上記の如く寸法を
設定した。The longest axis of the conductive ceramics has a shape of 1
Desirably, the shape is needle-like or fiber-like with 0 to 100 μm, the shortest axis of 1 to 30 μm, and an aspect ratio of 50 or more. If the particles have a small aspect ratio, the dielectric constant does not increase. The length of the longest axis is 100μ
If it is more than m, there is a problem that the dispersion in the ferrite sintered body having a thickness of several mm does not work properly, and the dimensions are set as described above.
【0013】導電性セラミックスの体積比が5%以下で
は、誘電率を上げることができず、30%を越えると、
セラミックス間の接触抵抗が下り、特性を維持すること
ができない。If the volume ratio of the conductive ceramics is 5% or less, the dielectric constant cannot be increased, and if it exceeds 30%,
The contact resistance between ceramics decreases, and the characteristics cannot be maintained.
【0014】また導電性セラミックス、例えば TiC(焼
結温度約3140℃)等を利用した場合は、融点がNi−
Znフェライトの焼結温度(1300℃前後)より高いた
め、焼結時に形状が変形することや、母材と反応するこ
となく、安定した焼結体を作ることができる。When conductive ceramics such as TiC (sintering temperature of about 3140 ° C.) is used, the melting point is Ni--
Since the temperature is higher than the sintering temperature of Zn ferrite (around 1300 ° C.), a stable sintered body can be produced without deforming the shape during sintering or reacting with the base material.
【0015】[0015]
【実施例】以下に、本発明の具体的実施例を、図面に基
づいて詳細に説明する。電波吸収体1は、図1に概念的
に示すように、Ni−Znフェライト焼結体4を母材とし、
導電性セラミックスである TiC粉末5を分散した複合体
として構成した。DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described in detail below with reference to the drawings. The radio wave absorber 1 has a Ni-Zn ferrite sintered body 4 as a base material, as conceptually shown in FIG.
It was configured as a composite body in which TiC powder 5 which is a conductive ceramic was dispersed.
【0016】TiC粉末は、ファイバー粉末(A)と粒状
粉末(B)の2種類を用いて、体積比を5%から40%
迄の範囲で種々に変えて、夫々厚さ10mmの電波吸収体
を作成し、周波数200MHz の電波に対して吸収率を測
定した。As the TiC powder, two kinds of fiber powder (A) and granular powder (B) are used, and the volume ratio is 5% to 40%.
By making various changes within the range up to the above, radio wave absorbers having a thickness of 10 mm were created, and the absorption rate was measured for radio waves with a frequency of 200 MHz.
【0017】その測定結果を図2に示す。図中・印はフ
ァイバー粉末(A)を使用した電波吸収体に対するも
の、×印は粒状粉末(B)を使用した電波吸収体に対す
るものである。この図より、粒状粉末を使用したものは
吸収率が上らず、又ファイバー粉末を使用した場合も5
%未満及び30%以上では特性を維持することができな
いことが判る。The measurement results are shown in FIG. In the figure, the mark indicates the electromagnetic wave absorber using the fiber powder (A), and the mark x indicates the electromagnetic wave absorber using the granular powder (B). From this figure, it can be seen that the one using the granular powder does not have a high absorptivity, and that the one using the fiber powder is 5
It can be seen that the characteristics cannot be maintained at less than 30% and at 30% or more.
【0018】図3は、前記の TiCのファイバー粉末をフ
ェライト焼結体中に分散した電波吸収体のうち粉末の体
積比が15%のものについて、電波の周波数を変化させ
て測定した吸収率より作成した電波吸収特性曲線であ
る。この図より、吸収する目的の電波の周波数が300
MHz 近傍の場合、 TiCのファイバー粉末を体積比で15
%分散したものが最適であることが判る。FIG. 3 shows the absorptance measured by changing the frequency of the radio wave for the radio wave absorber having the TiC fiber powder dispersed in the ferrite sintered body and having a powder volume ratio of 15%. It is the electromagnetic wave absorption characteristic curve created. From this figure, the frequency of the target radio wave to be absorbed is 300
In the vicinity of MHz, the volume ratio of TiC fiber powder is 15
It can be seen that the one with% dispersion is optimal.
【0019】[0019]
【発明の効果】以上の如く、本発明によれば、目的とす
る周波数域の電波を磁界成分と電界成分の2つを損失さ
せることにより電磁波エネルギーを吸収することがで
き、吸収特性を改善することができる。As described above, according to the present invention, it is possible to absorb electromagnetic wave energy by making radio waves in a target frequency range lose two components, a magnetic field component and an electric field component, and improve absorption characteristics. be able to.
【図1】本発明の電波吸収体の構成を示す概念図であ
る。FIG. 1 is a conceptual diagram showing a configuration of a radio wave absorber of the present invention.
【図2】本発明の電波吸収体の導電性セラミックスの体
積比に関する電波吸収特性を粉末の形状2種類に対して
示す曲線図である。FIG. 2 is a curve diagram showing the radio wave absorption characteristics relating to the volume ratio of the conductive ceramics of the radio wave absorber of the present invention for two types of powder shapes.
【図3】本発明の電波吸収体の電波周波数に関する電波
吸収特性の一例を示す曲線図である。FIG. 3 is a curve diagram showing an example of the radio wave absorption characteristics of the radio wave absorber according to the present invention with respect to the radio frequency.
【図4】電波に対する電波吸収体と反射板の配置を説明
する説明図である。FIG. 4 is an explanatory diagram illustrating the arrangement of a radio wave absorber and a reflection plate for radio waves.
【図5】電波の電界成分と磁界成分を説明する説明図で
ある。FIG. 5 is an explanatory diagram illustrating an electric field component and a magnetic field component of a radio wave.
1 電波吸収体 2 電波 4 フェライト 5 導電性セラミックス 1 Radio wave absorber 2 Radio wave 4 Ferrite 5 Conductive ceramics
Claims (5)
スを分散して形成したことを特徴とする電波吸収体。1. A radio wave absorber formed by dispersing conductive ceramics in a ferrite sintered body.
100μΩ−cm以上で、最長軸が10〜100μm、最
短軸が1〜30μmであり、アスペクト比が50以上で
あることを特徴とする請求項1に記載の電波吸収体。2. The conductive ceramics according to claim 1, which has an electric resistance of 100 μΩ-cm or more, a longest axis of 10 to 100 μm, a shortest axis of 1 to 30 μm, and an aspect ratio of 50 or more. The electromagnetic wave absorber according to 1.
〜30%であることを特徴とする請求項1に記載の電波
吸収体。3. The volume ratio of the conductive ceramics is 5
The radio wave absorber according to claim 1, wherein the radio wave absorber is -30%.
バーであることを特徴とする請求項1に記載の電波吸収
体。4. The radio wave absorber according to claim 1, wherein the conductive ceramic is TiC fiber.
徴とする請求項1に記載の電波吸収体。5. The radio wave absorber according to claim 1, wherein the magnetic loss and the dielectric loss are equal to each other.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP19024792A JPH0613780A (en) | 1992-06-25 | 1992-06-25 | Radio wave absorbent |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP19024792A JPH0613780A (en) | 1992-06-25 | 1992-06-25 | Radio wave absorbent |
Publications (1)
Publication Number | Publication Date |
---|---|
JPH0613780A true JPH0613780A (en) | 1994-01-21 |
Family
ID=16254960
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP19024792A Pending JPH0613780A (en) | 1992-06-25 | 1992-06-25 | Radio wave absorbent |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH0613780A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7218266B2 (en) | 2000-04-10 | 2007-05-15 | Hitachi, Ltd. | Electromagnetic wave absorber, method of manufacturing the same and appliance using the same |
-
1992
- 1992-06-25 JP JP19024792A patent/JPH0613780A/en active Pending
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7218266B2 (en) | 2000-04-10 | 2007-05-15 | Hitachi, Ltd. | Electromagnetic wave absorber, method of manufacturing the same and appliance using the same |
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