The Studies Of TRM Imaging Technique In The Complex And Multi-scattering Environments

The detection of concealed targets in the complex and multi-scattering environments is of great importance in theory and applications. Its theoretical significance lies in exploring the methods to detect targets in the background with significant multipaths. The corresponding theoretical achievements will greatly support its applications in the fields of imaging in inhomogeneous media, through the wall radar imaging and the detection of concealed targets in forest environment and so on.Time Reversal Mirror (TRM) technique is derived from the Phase Conjugation Mirror (PCM). It is a combination of the physical procedure of wave multi-propagation and the array signal processing. Compared with the traditional array signal processing methods, the fundamental difference is that TRM well employs the wave propagation information, can achieve much higher resolution than the real aperture. This technique greatly improved the imaging ability of the detecting system for concealed targets. TRM technique firstly appeared in the fields of Acoustics and got a lot of experimental validations. Recently, it was introduced to the fields of Electromagnetics.Based on the theoretical analysis, this paper studied the TRM technique in the three fields: Microwave-Induced Thermo-Acoustic Tomography (MITAT), the Ultra-Wideband Through the Wall Radar (UWB-TWR) imaging and concealed targets detection in multi-scattering forest environment. We focused on resolving TRM model in the different random backgrounds, the analysis of the model stability and the preset of system Green's Function. We also studied the impacts to the imaging caused by the mismatch of the backgrounds associated with the forward and inverse phases of TRM. This paper is divided into following five parts:1. We introduced three types of complex environments, namely, Microwave-Induced Thermo-Acoustic Tomography, the Ultra-Wideband Through the Wall Radar and the multi-scattering forest environment. We analyzed the traditional imaging methods in those fields and pointed out their disadvantages.We clared that TRM beard greatly advantages when imaging in the complex environments. Next, we mainly reviewed the origin, development and experimental studies of TRM technique. And we also introduced the theoretical research achievements of TRM. Recently, TRM was introduced to the fields of Electromagnetics. However, the research was still on the early stage.2. Capter 2 gave a systematic and comprehensive analysis of the TRM theory foundamental, the super resolution and the statistical stability properties. We carried out several numerical simulations to illustrate the super resolution phenomenon of TRM imaging in the random media. For reaching a better understanding of the TRM imaing processing in the random or mismatched media, we introduced the Incidence-respond Operator.3. Studied the application of TRM technique in the field of Microwave-Induced Thermo-Acoustic Tomography. Firstly, we reviewed the basic foundamental of TRM in MITAT. Then, the Pseudo-Spectral Time Domain (PSTD) combined with TRM was employed for the imaging of layered tissues. This technique yielded nice two dimensional imaging results. Next, we mathematically described the TRM technique in the three dimensional MITAT imaging system. The PSTD-TRM imaging results in the three dimensional MITAT system beard higher imaging quality than those of Back Projection method. For real application, a breast model was added. For targets with different sizes, we analyzed the impacts to the imaging from the randomness of the inhomogeneous biological tissue.4. TRM technique was introduced to the UWB-TWR for the first time in the Chapter 4. We analyzed its theoretical foundamental in detail. Combined with the FDTD (Finite Difference Time Domain) method, we studied TRM imaging under the environments of the single-layered and multi-layered walls. The imaging results were much better that those of Back Projection. At the same time, TRM under the complex conditions of random wall, the noise-polluted received signals and the mismatched case were well studied. We also evaluated the impacts of the array to the TRM imaging.5. We preliminarily studied the TRM in the random and multi-scatting forest environment. We demonstrated the mathpathing phenomenon of microwave signal in the forest environment by numerical simulations. A forest model based on the Ray-tracing method was built and validated by the FDTD algorithm. Based on this model, we achieved the TRM imaging for the single and multi targets in the forest environment. This paper studied the problem of TRM imaging in the complex and multi-scattering environment in detail. Through numerical simulations, we validated the powerful ability of TRM imaging, especially in the complex environments. We discussed the impacts to TRM imaging from some relevant factors. The results of this paper will provide a reference for the imaging in the complex environment.