Time Reversal Based Algorithms For Controlling Electromagnetic Wave Propagation

With the development of wireless technology, electromagnetic(EM) waves gain widespread applications in our life. In addition to applications in wireless communications, remote sensing, and target tracking, the new applications in the medical, industrial and agricultural as well as some basic science have been exploited in recent years. These applications are closely related to the electromagnetic waves control. EM waves control has always been an attractive topic. However, how to control the EM waves for specific purpose has become a critical issue.EM waves control methods mainly include: antenna array technology, metamaterial technology, and time reversal technique. Antenna array technology is limited to far-field control, and it also requires tedious optimization process in solving the problem of EM waves control. However, limited to the fundamental principles, only the narrowband EM waves control can be realized by the metamaterial technology. Besides, the structures of the metamaterials are not flexible and universal. By means of spatial-temporal focusing properties and adaptive transmission capability, time reversal technique can simply achieve a broadband EM waves control. This thesis aims to develop the algorithms for controlling EM waves using time reversal technique. The contents include:First, a general method of controlling broadband EM waves is introduced from Uniqueness Theorem of EM fields and spatial-temporal focusing properties of time reversal electromagnetic waves.Second, based on the above principles, a simplified algorithm of controlling the EM waves’ distributions is presented by combing the Green function, and the time reversal technique. With this algorithm, some factors that impact-on the focal spot of the focused fields have been analyzed. Further, the focused fields of linearly approximate uniformity of intensity distribution are achieved through simulations.Finally, based on the time reversal technique, a moving control algorithm for a focal spot of focused EM fields is developed. The effectiveness of the algorithm is verified through numerical simulations in free space and a semi-enclosed metal chamber. Meanwhile, the correctness of the algorithm is analyzed through the simulation results. Further, the algorithm is demonstrated through the experiment in the semi-enclosed metal chamber environment.