Time Reversal Based Algorithms For Generating High-precision Electromagnetic Shaped Field

Shaping which is usually used for form simulation,scene reproduction or some other special purposes refers to giving a certain material or object a specific geometric shape.It has an extremely important application in many subject areas.The key technology to generate shaped field is related to the control of the generation and propagation of intra-field waves.How to realize arbitrary wave generation and control in space and time has always been a research subject of great concern in various fields.In several important physical fields such as acoustic field,water wave field and electromagnetic field,there have been significant breakthroughs in the arbitrary generation and control of acoustic field and water wave field.With the continuous expansion of the electromagnetic waves' application,especially in the fields of agriculture,industry,chemistry,energy,biology,medicine,and secure communication,there is an urgent need for a high-precision electromagnetic shaped field which has a controlled field intensity and a specific geometrical shape.How to effectively and efficiently control the electromagnetic field to achieve the prospective application has become one of the most challenging scientific problems in the electromagnetic area.At present,there are two well-developed methods to achieve the control of electromagnetic waves by means of antenna array and electromagnetic metamaterial,respectively.Among them,antenna array mainly controls the radiation pattern and electromagnetic metamaterial mainly controls the abnormal properties of materials.These two methods both require specific structures or materials for a specific field,which are not flexible and universal.For the existing problems and the limitation of the traditional methods,a novel method to generate electromagnetic shaped field is proposed based on the spatial-temporal focusing theory and adaptive transmission characteristic of Time Reversal(TR)in this thesis.And achieve the goal of generating high-precision electromagnetic shaped field through the modern intelligent optimization algorithm.The main content of this paper are summarized as follows:First,from the uniqueness theorem of time-varying electromagnetic field,the time symmetry of the wave equation and the reciprocity of the Green's function are proven and typically analyze the spatial-temporal focusing properties of time reversalelectromagnetic waves.Second,based on the vector superposition principle of electromagnetic field,a novel method to generate electromagnetic shaped field in free space,closed boxes,or arbitrary reciprocal electromagnetic environments is proposed.Further analyze the flexibility and universality of it compared with the traditional methods and its existing problems.Finally,by designing TR return signals through two intelligent optimization algorithms represented by genetic algorithm and simplex method,a high-precision single-point focused field and a “?”-shaped uniform field are generated,respectively.And analyse the accuracy of the algorithms through simulation results in MATLAB.