碳纖維粉末與沙塵暴之電磁波吸收散射

Scattering and Absorption of Carbon-Fiber Powder and Sand/Dust Storm

古召呈(Chao-Cheng Ku)

指導教授 ： 陳興義

元智大學/電機通訊學院/通訊工程學系/碩士(2011年)

https://doi.org/10.6838/YZU.2011.00101

摘要

本論文是利用時域有限差分法(FDTD)來研究碳纖粒子在電磁波頻率35GHz的特定消光截面(SECS)與沙塵暴在頻率10至100 GHz的電磁波衰減，並利用轉頻(Turning Bands)方法模擬碳纖粒子與沙塵粒子隨機分佈的數位模型。 針對特定消光截面的研究結果發現，柱狀之碳纖維的直徑與立方體之碳纖粒子的邊長大小在相同的狀況下，它們量測與模擬值非常吻合，另外特定消散截面在粒子大小能產生共振時有最大值。在電磁波於沙塵暴中的衰減研究中，我們提出一電磁波衰減公式，此式為能見度、頻率、沙塵粒子半徑、複數的相對介電常數等之函數。研究所獲得的電磁波衰減結果亦與其他四種研究方法所獲得的電磁波衰減做比較。 此四種研究方法分別為: 等效材料特性技術、雷利(Rayleigh)散射近似法、量測式的機率密度方程式與米式散射(Mie scattering)等理論的應用、粒子所引申的體積分式米氏散射法。 其中可以發現經由本論文所導出的公式計算出的結果在五條公式之中為電磁波衰減的中間值。 本研究證實電磁波在沙塵暴中的衰減除了在頻率30GHz以上與能見度低於0.02公里的情況下不能忽略，其他狀況下可以忽略不計。

關鍵字

特性消光截面 ； 轉頻法 ； 碳纖維粉末 ； 衰減 ； 沙塵暴 ； 時域有限差分法 ； 微波雨毫米波

並列摘要

The finite-difference time-domain (FDTD) method is used to calculate the specific extinction cross-section (SECS) of the carbon-fiber powder at 35 GHz and to investigate the wave attenuation in sand and dust storms at the frequencies of 10-100 GH. The digitized models with a random process using the turning bands method are simulated for the carbon-fiber powder and the sand and dust storm particles. It is found that the numerical result of SECS obtained by using the diameter of a cylindrical carbon-fiber particle as the cubical cell size for simulations makes good agreement with the measurement data. It is also found that the maximum extinction occurs at a resonant particle size. From the study of wave attenuation in sand and dust storms, a formula in terms of
IV
the visibility, frequency, sand and dust particle radius, and complex relative permittivity is proposed to determine the wave attenuation. Obtained results of the wave attenuation are also compared with those obtained by four other methods: the effective material property technique, the Rayleigh scattering approximation, the measured probability density function and Mie scattering theory, and the volumetric integration of Mie scattering results by individual particles. It is found that our formula produces a mean value of wave attenuation among these five formulas. It is also confirmed that the wave attenuation is negligible except for frequencies above 30 GHz and for very severe storms with visibility less than 0.02 km.

並列關鍵字

carbon-fiber power ； Attenuation ； sand and dust storms ； finite-difference time-domain ； microwave and millimeter-wave ； specific extinction cross-section ； turning bands method

參考文獻

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