Research On Novel Detection Method And Information Transmission Method Based On Time Reversal Technology

Time reversal technique (TR) is a kind of reverse operation for the received signalsin the time domain. This operation allows the system utilizing some physicalinformation, like the multi-path effect to extend the effective array size. The mostimportant characteristics of the time reversal technique is temporal and spatial focusingproperties. To date, those focusing properties have been used to improve theperformance of the detection systems and the communication systems.In this dissertation, based on the current investigations about the time reversaltechnique, several novel time reversal detection methods and information anti-detectionmethod have been presented. Firstly, in order to overcome the shortcomings of thetraditional time reversal mirror detection methods and the time reversal multiple targetsdetection technologies, we proposed two new time reversal mirror detection methods.Then, in order to compensate deficiencies of the information security method based onTR, we improved the information anti-detection method based on time reversal withusing the pattern reconfigurable antenna. The work of this dissertation can besummarized into four sections:1. The investigation on time reversal theory and the research progress of theimaging detection technology and wireless information transmission technology basedon TR are introduced. Furthermore, the deficiencies of the current time reversaldetection technique about the amount of data from the target and the detected targetnumber have been discussed.2. To reduce the number of the detection elements and the amount of data required,the novel time reversal mirror detection method based on the temporal focusing isdeveloped. In this investigation, the physical and mathematical models of the detectionmethod are studied, firstly. Then, the performances of the new method in acoustics andelectromagnetic fields are investigated by using the numerical imaging simulationsoftware. Finally, the electromagnetic experiments are taken to prove the new detectionmethod. Compared with the traditional time reversal mirror detection technology, thenew time reversal mirror detection method can effectively reduce the number ofelements of the detection array. Furthermore, its detection performance isn’t affected by the array structure. Therefore, the novel time reversal mirror detection method cangreatly reduce the cost of the time reversal detection system, and the amount ofdetection data.3. In order to overcome the shortcoming of the current time reversal multi-targetdetection method, the sub-array time reversal mirror detection method is developed. Themethod points out the multiple targets’ locations by calculating the superimposedstrength of the time reversal signal. Firstly, the physical and mathematical models of thedetection method are investigated. Then, the performances of the method in the acousticimpact simulation detection, the acoustic crack simulation detection and theelectromagnetic wave simulation detection are discussed. Finally, the acoustic impactdetection experiment was taken to verify the feasibility of the new detection method.The results show that the sub-array time reversal mirror detection method can detect thetarget, and its performances for multiple passive target detection and multiple activetarget detection are superior to those of the traditional time reversal mirror method andthe current time reversal multi-target detection method. It is worthwhile to mention thatthe number of detective targets of the sub-array time reversal mirror detection method ismore than that of the current time reversal multi-target detection method, when nomutual scatter exist among the targets.4. On the hand, the pattern reconfigurable antenna is able to choose thecommunication channel. On the other hand, the spatial focusing ability of the timereversal technology can reconstruct the communication channel. Thus, the combinationof the pattern reconfigurable antenna and the time reversal technique can be utilized toimprove wireless information dissemination security. In this dissertation, two novelbroadband pattern reconfigurable antennas are designed, and their performances totransmit the time reversed signals are investigated in order to prove the feasibility thatthe pattern reconfigurable antennas are applied to the time reversal technique. Then,through theoretical derivation and FDTD simulation, the anti-detection effect of the newalgorithm is studied. As shown in simulation results, since the propagation path of theinformation is inconsistent in various modes and the detection area is reduced, thechanging direction of the pattern mode can change the path of the transmission ofinformation. it can make it difficult to catch all the information in the same location, soas to enhance the security of information dissemination.