Time Reversal Synthesis Method And Implemention Of Microwave Uniform Fields

The spatial control of electromagnetic fields refers to the synthesis of electromagnetic fields that meet the expected distribution in a specified spatial area according to demands,which has great potential in many engineering applications.In recent years,microwave medical,microwave heating,secure communications,equipment testing and other application scenarios have become more and more demanding for the spatial field control,which has led to a series of methods and techniques to achieve field control.Several existing spatial field control technologies have their own limitations.Based on the line array plane wave field synthesis technology,it mainly relies on the optimization algorithm,for the simple electromagnetic wave field distribution with huge computations and is not suitable for synthesizing the complex space field distribution.Based on the spatial field control method of metamaterials,due to the tedious design process,the design scheme is not universal,which makes its applications quite limited.Based on the time reversal point-focusing fields,the spatial electromagnetic field shaping technology can realize most classic field distributions.The basic principle of the spatial electromagnetic field shaping method is the linear superposition of the point-focusing field.For complex electromagnetic distribution,the diffraction limit between the probing antennas will limit the accuracy of the shaped spatial electromagnetic field.Meanwhile,the irrelevance between the point-focusing fields causes the generation of uncontrollable side lobes,resulting in a decrease in the quality of the desired shaped electromagnetic field.Therefore,how to achieve efficient and economic control of the spatial electromagnetic fields is still a challenging topic.For solving the above problems,this thesis studied the synthesis of electromagnetic fields from the perspective of wavenumber domain synthesis,and utilized the AF(arriving fields)as the basic fields for spatial electromagnetic field synthesis.Combining the advantages of adaptive localization and space-time focusing of time ireversal technique,this thesis proposes a time reversal arriving field synthesis method.Finally,generating a one-dimensional uniform field of a specified width in a specified spatial domain is demonstrated by a simple array structure.The main contents include:First,the field shaping technology based on TR point-focusing fields is briefly introduced,and its advantages and disadvantages are discussed.The theory of wave-number spectrum projection and the spatial field composition theory in wavenumber domain are presented.The arriving fields of uniform plane wave,ideal point source,dipole antenna and arbitrary linearly polarized antenna are studied.With the uniform field composed by uniform plane wave fields as the example,the basic properties of the synthesized one-dimensional uniform field are studied.Second,based on the theory of time reversal wavenumber domain synthesis,a one-dimensional uniform field synthesis scheme is proposed.By comparing the one-dimensional uniform fields synthesized by different array elements and different array arrangements,a one-dimensional uniform field physics synthesis scheme by using the semicircular array of dipole antennas is given.Then,the key factors affecting the accuracy of one-dimensional uniform field are studied.The factors including the arrangement of the antenna array,the number of elements,the width of the target composite field is studied,and the distortion of the wavenumber spectrum of the arrival field as the key factor is revealed.Finally,aiming at further improving the uniformity of one-dimensional uniformity,we obtain the one-dimensional uniform field with ripple coefficient <0.1dB by optimizing the design of the feed signals of the array element with the genetic algorithm,,and the optimization results are verified by simulations.By analyzing the wavenumber spectra of the synthesized one-dimensional uniform field before and after optimization,it is proved that the key to improving the quality of one-dimensional uniform fields is to reduce the synthetic error caused by the overlap and offset of the wavenumber spectra of the arriving fields.