Extraction And Analysis Of The Instantaneous Spectrum Of Echo In Medical Characteristics Under Near-Field Microwave Sounding

With the development of science and technology,nonlinear and non-stationary signal processing and its application in engineering gain more and more attention. Researchers and scholars achieve the purpose of processing different signals through analyzing characteristics of time-varying signals,constructing suitable time-frequency distribution and processing properly.Therefore,it is a significant study to find suitable and excellent-performance time-frequency distribution for nonlinear and non-stationary signal analysis and processing——time-frequency analysis.It is the analytical theory of non-stationary signal analysis.Time-frequency analysis is highly efficient in processing the nonlinear and non-stationary signals,more and more research has been put on this topic. Time-frequency analysis method based on Hilbert-Huang Transform(HHT) is a new analysis method of signals.After several years' development,the HHT method shows its advantage in non-stationary signal processing,and has important theoretical research value and broad prospects.The HHT method is deeply studied both in theory and application in this paper.Firstly,this paper reviews the several most representative analysis methods of non-stationary and nonlinear signals in time-frequency analysis,which is short time Fourier transform,Winger-Ville distribution and wavelet transform,and deeply discusses their own advantages and limitations.Secondly,the introduction of proposed background and related theory of HHT are presented.The basic concepts of instantaneous frequency and intrinsic mode function are illustrated.Then,the algorithm principle and the meanings in physics of Hilbert time-frequency spectrum and marginal spectrum are described.Finally,the improved Hilbert-Huang Transform algorithm based on wavelet packet decomposition is proposed by analyzing the defect of the EMD method.The numerical simulation software is established and the GUI-based signal processing system is developed.It is used to import medical experimental data for processed and analyzed.The purpose is to complete extracting and analyzing the instantaneous spectrum of the signal acquired and to get relevant experimental results,combined with specific cases,the analysis of its physical and medical meanings is studied deeply for application research on medical imaging,data classification and inversion, data mining and non-real-time processing.