Research On The Microstructure Array For Time Reversal Far-field Super-resolution Imaging

With the increasing development of science and technology,the resolution of traditional far-field imaging system has been limited in practical applications.Therefore,the realization of far-field super-resolution imaging is increasingly important.An efficient way to implement super-resolution characteristic of electromagnetic wave is the design of microstructure array.In this dissertation,based on the canalization regime,mode conversion and localized mode resonance,novel microsctructure arrays for time reversal far-field super-resolution imaging system in microwave range are studied.The main work of this dissertation is as follows:Firstly,a summary of the research background and significance of super-resolution characteristic is given,along with the implementation priciples and research status from several aspects.Then the background and research status of time reversal technique are briefly reviewed.The content and organization of this dissertation are summaried at last.Secondly,aiming at the imaging system of transmission mode,the methods to realize the canalization regime are derived,along with several imaging microstructure arrays of superior performance.In the canalization regime,the incident waves are coupled into the wire medium and converted into transmission modes in the wire medium.The transmission modes allow the sub-wavelength information to propagate from the source plane to the image plane,and then super-resolution imaging is realized.In allusion to the limitation of the wire medium in practical applications,novel microstructure arrays to realized super-resolution imaging are designed.Firstly,the bending wire array is designed,which verifies that the imaging ability is not affected by the bending angle.Then the planar structure is proposed,which is more convenient to fabricate and integrate.By adjust the period of the planar structure,magnification and shrink of super-resolution image are realized.Then based on stepped impedance resonantor,the size of imaging lens is reduced effectively.Finally,through the analysis of spatial dispersion relations,several methods are applied to realize the canalization regime,which can be useful as reference for the design and construction in the future.Thirdly,aiming at the imaging system of radiation mode,several imaging microstructure arrays are proposed with low profile,compact size and broadband.In this part,according to the concept of resonant metalens,the principle of mode conversion is analyzed in detail firstly.Then based on the regime of mode conversion,three one-dimensional compact and planar microstructure arrays are proposed.The property of mode conversion is verified by the near-and far-field spectra.Combined with time reversal technique,super-resolution focusing and imaging are realized by both simulations and experiments.What's more,the design of microstructure is expanded into two-dimensional case.One kind of two-dimensional planar microstructure array is presented.The analysis of Bloch modes validates the relationship between resonant frequencies and Bloch modes.Then the property of mode conversion is verified by the near-and far-field spectra.Combined with time revesal multiple signal classification method,super-resolution imaging of point-like scatters and extended target are realized,respectively.In addition,the influence on the imaging result of the antennas' polarization,location and quantity is analyzed.Finally,based on stereometamaterial,one kind of wideband stereo microstructure array is proposed.Using the concept of stereometamaterial,the unit cell has a certain frequency interval between two working frequencies.The array with this kind of unit cell can well enhance the working bandwidth.The advantages brought by the bandwidth are validated from two aspects of frequency and time domain,recpectively.Finally,aiming at the imaging system in complex environment,without the help of Green's function,several imaging microstructure arrays are proposed with compact size,high resolution and high efficiency.In this part,one kind of multi-frequency planar lens based on localized resonant mode is proposed firstly.By optimizing the period and operating frequency of each unit cell,the coupling between adjacent cells can be ignored.Thus,the location of object can be obtained from the analysis of far-field spectrum.Then,one kind of far-field scanning microstructure array is proposed.By switching the two different kinds of working states,the location of the target can be determined and far-field super-resolution imaging can be realized.The proposed array maintains excellent performance even in complex environment.At last,based on the multi-frequency characteristic of fractal structure,a multi-frequency scanning microstructure array is presented with several working frequencies.In addition,by combining the first and the third order resonance,a new scanning imaging method is designed,which can effectively improve the imaging efficiency.