Preliminary Theoretical Research And Application Of Time Reversal Method

Since it was introduced into electromagnetism in 2004,the time-reversal method has attracted extensive attention of researchers,and has been applied to wireless communication,target detection,underwater location and other areas.However,compared with the rapid development in applications of the time-reversal method,the theoretical research on the time-reversal method is relatively slow,which greatly limits the further applications of the time-reversal technique.In this paper,the time-reversal method is first theoretically and then experimentally analyzed.The three issues of the time-reversal method are addressed: large errors in some situations,incapability of handling bandlimited signals and localization of non-impulse sources.The detailed work is described in the following paragraphs.Firstly,the digital signal processing(DSP)method is applied to show theoretically synchronous focusing with the time-reversal method in the time domain and frequency domain.At the same time,localization of the two-dimensional point sources is also extended to that of the three-dimensional point sources,line sources and surface sources.As a result,the space-time synchronous focusing with the time-reversal method is verified experimentally in the higher dimensions.In addition,an practical example of the time-reversal method in diagnosis of faulty antenna array elements is presented.Secondly,based on the derived energy equation in the time-reversal process,a precision improved algorithm is proposed,which greatly reduces the errors for the time-reversal reconstructions of clustered sources with the time-reversal source reconstruction.However,although the error of this improved algorithm is low,its complexity is high.Therefore,another precision improved algorithm is proposed with calibration,which can provide both fast and more accurate calculation results than the direct time-reversal method in reconstructing clustered sources.Thirdly,this paper proposes a method to handle the signals of limited bandwidth.The method extends the received band-limited signal to an unlimited-bandwidth signal which is real;then with the use of the time-reversal mirror antennas,the signal is retransmitted and source reconstruction is conducted.Finally,a deconvolution between the received signal and the source signal isproposed to deal with the source reconstruction of non-impulse sources.In addition,by defining the entropy of the field value in the cavity and looking for the minimum entropy of the backwards process,the paper locates the pulse sources,which is excited at an unknown time;in other words,the source reconstruction of the pulse sources excited at an unknown time is reconstructed.