膜面微波吸收器材之研究

Abstract

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 deep)，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，但是提高頻率會使得所需要的吸波材料厚度增加，如此高頻吸波裝置不易製造及使用。然而這篇論文中，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１mm，因此只要塗上一薄層，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；將為吸波器放置於C-band、X-band、K-band、Ka-band的波導管中去實驗電磁波的反射耗損(return loss)，使用的頻率是10GHz、15GHz、21 GHz、30 GHz；並且以電腦模擬相同的頻率，再模擬更高頻的50GHz~1000 GHz觀察其趨勢以驗證未來兆赫茲波的吸波材料結構與製作。 關鍵字：電容率、導電性損耗材料、肌膚深度、吸波材料、為波吸波器

Wave absorbers are widely used to attenuate and absorb the unwanted reflected wave creating a no-reflecting environment in anechoic chamber. The researches on wave absorbers for frequency below 20GHz 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 40GHz. 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 address to compare their competence in absorbing electromagnetic wave. 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 wave.