Electromagnetic Scattering Model For Charged Sand-dust Particles:Analysis And Application

Electromagnetic waves（EMWs）propagating in the medium can transmit a variety of information.In addition,due to their wide spectrums,different transmitting power characteristics in different bands and adaptation to different purposes,EMW technology has already been widely used in various fields.When EMWs propagate through sandy weather,they will be scattered and absorbed by dust particles,further affecting their propagation characteristics.In addition,in a sandy environment,the particles do carry a certain amount of charges,making the scattering characteristics more complicated.More accuracy is needed to further guide the application of EMWs in sand environments.To achieve this goal,applicable scattering models for charged sand particles need to be developed and refined.On the one hand,there are many scattering models,but there are still few studies on model classification and analysis of model-solving ability;on the other hand,as a natural product,the composition of sand and dust particles is complex causing their physical and chemical properties varying,which influence the scattering characteristics of sand particles.At the same time,in practical problems,measuring the combined and individual effects of these factors on EMWs is of profound significance to establish a more accurate scattering model for sand particles.Therefore,this paper starts from the charged sand particles’scattering models,analyzing different assumptions,advantages and disadvantages,and solution capabilities of the models,as well as discussing the problem-solving capabilities and the application of different models to practical problems.The main contents of this paper are as followed.First,this paper summarizes the commonly used scattering models for charged spherical particles with models classified by the way the particles carry extra charge.On this basis,from the perspective of the size parameter,suggestions for the selection of different charged spherical particle scattering models in sand and dust systems are given:the charged Mie scattering model is advised to select when the size parameter x is larger than 3×10^-4,the core-shell model should be selected when x is smaller than 2×10^-5,and the equivalent medium model is supposed to select when 5×10^-6<x<3×10^-4.Then,this paper also summarizes the existing modelling for solving the electromagnetic scattering problem for non-spherical particles.In addition,a COMSOL model is put forward based on the finite element method.Its calculation accuracy has been confirmed by comparing its computational results with the analytical solutions:charged Mie theory and charged T-Matrix.At last,several relevant typical scattering problems for charged particle in the context of sand and dust particles are discussed,with the conclusions as follow:（1）the distribution of extra charge affects the scattering cross-section of spheroid dust particles scarcely;（2）when its aspect ratio is between 0.8 and 1.2,and its particle surface charge and particle equal volume radius R satisfy ln（η）≤1.5ln（r）-0.03,the scattering caused by charged spheroid dust particles can be approximated by the scattering caused by equal-volume neutral spherical dust particles;（3）when the particle shape is constant,the amount of charges carry by particles can only affect the extinction resonance’s position but not degree,unless the shape been changed.At last,the models are further applicated in practice,as for the attenuation when microwave propagating through dust storms been discussed in this paper:（1）on the basis of the charged T-Matrix scattering model,it is a comprehensive attenuation model that has been proposed with a variety of factors taken into account;（2）the extent of the effect of multiple factors on EMW attenuation is also discussed.The calculation results find that the non-spherical characteristics of dust particles cannot be negligible when calculating the attenuation values,and the increasing effects of excess charges as well as high relative humidity on attenuation contribute to each other;（3）the microwave attenuation model is proposed by taking microwave attenuation of water vapor into consideration,which also well explains the significant discrepancy between the experimental and calculated results;（4）based on the Islam model,an improved model for EMW attenuation is given by multiple linear fitting,which is accurate and easy to calculate for practical engineering applications.