Investigations On The EM Scattering Of Partially Charged Sand Particle And Its Applications

Electromagnetic signal attenuation in sandstorms is a key problem in the application of wireless communications, the remote sensing of sandstorms and the detection of outer space, the effects of electromagnetic wave attenuation and depolarization from the sand particles and the dust storms have a direct influence on the accuracy of electromagnetic signal reception. To accurately calculate the scattering field is an important precondition.Based on the Rayleigh Approximation and the Mie model, this dissertation is devoted to dealing with the problem concerning the scattering and absorption effects of electromagnetic wave (signed as EM wave in short) by the charged spherical sand particles in sandstorms, the scattering field of a partially charged spherical particles is derived and the effects of surface charge density and charge distribution angle on the spatial distribution of the scattering field intensity and these ones on the differential scattering across section are calculated. Then we found that the surface charge on the particles have different degrees of impact on the scattering field intensity and the differential scattering across section, and it is related to not only charge quality, distributed angle and the particle radius but also the frequency.After derived the expressions of scattering cross section, absorption cross section and extinction efficiency for the partially charged spherical sand, we discussed the attenuation efficiency of different frequency EM wave illuminate on the charged sand, the attenuation coefficient of different frequency EM wave propagating on the sandstorms, and the cross depolarization degrees for the linear/circular polarization wave transmitting in the dust storms. We found that the electric charges on the sand surface almost didn't affect the higher frequency EM waves'extinction, but it have a significant effect on the attenuation of the lower frequency EM waves, especially for the EM wave whose frequency lower than 100GHz, and the attenuation coefficients increase with the magnitude of charges carried by the dust characterized by the charge-to-mass ratio). In addition the partially charged spherical particles can make the incident microwave depolarized, and this effect increased with the increasing of particles'charge-to-mass ratio and the incident wave'frequency, but decreased with the increase of visibility. It is the first time to report the depolarization influence of partially charged spherical sand particles on the microwave.After considering the effect of multiple scattering and the charge on particle surface, we derived the T-matrix for the partially charged particles to compute the extinction efficiency for different frequency EM waves illumination on the partially charged two-sphere systems and propagating in the sandstorms with different visibility. The results showed that in a same condition, the results obtained from multiple scattering theory is larger than the one from single scattering hypothesis. This difference between multiple scattering and single scattering increased with the increasing of charge quantity, but decreased with the frequency increasing. However, even for a strong dust storm,the volume fraction of dust particles is still very small, so we can ignore the multiple scattering effects when we calculate the attenuation rate of electromagnetic wave propagation in the sandstorm.Moreover the charge on particle surface can largely enhance the radar back scattering cross section,for spherical grains, the influence on radar measurement results increased with the surface charge density increasing. These results in the thesis are firstly given.These results are helpful for the theoretical study to verify the sands' electrification mechanism and to confirm the charge distribution zone on the particle surface; moreover, they are particularly useful for the design of satellite communication channel and the effective correction of the results of sandstorms' remote sensing monitoring.