| Summary: | 碩士 === 元智大學 === 通訊工程學系 === 99 === 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.
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