高頻微波吸波器材之研究

Study of High-frequency Microwave Absorbers

沈明寬(Ming-Kuan Shen)

指導教授 ： 朱國瑞

國立臺灣大學/理學院/物理研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01219

摘要

因應高頻微波或毫米波實驗的需要，這篇論文提出了吸收高頻電磁波的方法。材料的物理性質與入射波的頻率皆會影響反射係數(reflection coefficient)與肌膚深度(skin depth)，因此可以從這兩個參數中找出適合吸收高頻電磁波的吸波材料。以往的吸波材料多半是介電質材料，雖然介電質吸收電磁波的效果很好，但是提高頻率會使的所需要的吸波材料厚度增加，如此的高頻吸波裝置會不易製造及使用。然而，在這篇論文中，我們改以導電性損耗材料(conductive lossy material)作為吸波材料，對應高頻微波其肌膚深度小於1 mm，因此只需要塗上一薄層，就可以有效地吸收高頻率的電磁波。
為了驗證這個現象我們做了微波吸波器的模擬與量測實驗；將微波吸波器放置於Ka-band 的波導管中去計算電磁波的反射損失(return loss)，使用的頻率是26.5到40 GHz，由此了解電導性損耗材料吸波器的吸波效果，並且將透過網路分析儀量測到的結果與之比較。

關鍵字

電容率 ； 導電性損耗材料 ； 肌膚深度 ； 吸波材料 ； 微波吸波器

並列摘要

Wave absorbers are widely used to attenuate and absorb the unwanted reflected waves creating a no-reflecting environment in anechoic chamber. The researches on wave absorbers for frequency below 20 GHz are extensively presented in many papers. For higher frequency, this thesis reports an applicable way to absorb the high-frequency electromagnetic waves by conductivity lossy materials and a simulation study of microwave absorbers settled in Ka-band waveguide, the recommended frequency of which is between 26.5 and 40 GHz.
In the beginning of this thesis, we present the theoretical calculation on reflection coefficients and skin depth characterized by complex permittivity of materials and the frequency of applied waves. These parameters have great help for finding the proper absorbing material for high-frequency microwave absorbers. The electromagnetic wave interactions with dielectric and electrical conductive materials are also discussed. In the second part, two types of wave absorber, wedge-shaped and pyramidal absorbers are addressed to compare their competence in absorbing electromagnetic waves. Simulation and measurement results presented in chapter 4 and 5 indicate that the shape has a great impact on the reflection and absorption performance of a wave absorber, and that, more significantly, microwave absorbers with conductivity lossy materials can effectively absorb the power in high-frequency EM waves.

並列關鍵字

complex permittivity ； conductivity lossy material ； skin depth ； wave absorbing material ； microwave absorber

參考文獻

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