Research On Electromagnetic Field Shaping Based On Time Reversal Electromagnetic Theory

The propagation control of electromagnetic waves is one of the fundamental topics that has always been concerned in electromagnetic region. As the scope of electromagnetic wave applications has been increasingly expanded in recent years, the research on electromagnetic wave propagation and spatial field control encounters unprecedented technical challenges, especially for applications in the medical, industrial, agricultural, chemistry, and so on. Although the use of subwavelength techniques combined metamaterials is an effective method, the following limitations prevent it from widespread applications. First, it currently limits to the generation of only single frequency or narrowband electromagnetic fields. Second, a specific shaping field requires a corresponding specific electromagnetic structure. Once the electromagnetic structure is well designed, it cannot be flexibly changed for other shaping fields. In theory, the use of Green’s functions can be used for generation and control of arbitrary shaping fields, but it needs tremendous calculation and optimization. How to break through these limitations is an extremely challenging scientific issue.In order to deal with the above difficult technical problems, a novel method capable of shaping broadband electromagnetic fields is proposed in this paper. This method is based on the theory of space-time focusing of time reversal(TR) and has been successfully applied to generate several wideband electromagnetic fields of different shapes in a limited region. The new method breaks through the narrow-band limit of existing methods for electromagnetic filed generation and control. It can build various electromagnetic fields of different geometrical shapes without changing the system structure, exhibiting high flexibility and universality. The contents of this paper include:First, the space-time focusing mechanism of TR transmission has been theoretically analyzed according to the uniqueness theorem and a method for design of broadband electromagnetic field shaping is proposed by utilizing the focusing principle.Second, the proposed method is applied for an L-shaped electromagnetic filed generation in free space and the effects of some important parameters on the field shaping performance have been discussed in detail.Next, the same method is employed for shaping the electromagnetic fields of the specified geometrical figures in complex scattering environments. Meanwhile, a method to construct the source-shaped fields is proposed for improving the profile of the wanted shaping fields.Finally, an experimental system is well established for experimental study on L-shaped electromagnetic fields based on the TR technique. The comparison between simulations and experiments verifies the effectiveness of the proposed method.