Extraordinary Transmission In Composite Structure Bragg Waveguides

The volatility problem in the periodic structure has been widely concerned by researchers because the band gap structure similar to the electron band appears when the wave propagates in the periodic structure.By studying the fluctuation characteristics in the periodic structure,functional devices such as optical microcavity structures,optical switches,filters,and silencers can be realized.The composite periodic structure has more important research significance and application value because of its different structure and characteristics.In this paper,a composite structure Bragg waveguide is designed,and the regulation of its anomalous transmission characteristics is realized by changing the geometric parameters of the waveguide.The main contents of the paper are as follows:First,the background and significance of the research are briefly described,and several different composite periodic structures and research status at home and abroad are introduced.The necessity and urgency of designing composite periodic waveguides for functional waveguide devices are expounded.The main contents of the papers and the arrangement of each chapter are summarized.Second,in theory,the transmission of waves in a cylindrical variable-section periodic waveguide is deduced and analyzed.Firstly,the mechanism of Bragg resonance and non-Brad resonance and the conditions of resonance occur are expounded.The dispersion curve of periodic waveguide is obtained,and the modulation of the passband and forbidden frequency range in the dispersion curve is realized by changing the geometric parameters of the waveguide.Subsequently,the finite element method and related COMSOL Multiphysics multiphysics software were introduced.Finally,the transmission spectrum and field distribution of the waveguide were obtained by numerical simulation of the periodic waveguide,and the analysis was carried out.Third,Through the design of the geometric parameters of the waveguide structure,the extraordinary transmission characteristics in the composite Bragg waveguide are fully studied.Firstly,we design two single waveguides with the same Bragg resonance frequency but different sizes,connect them to form a composite waveguide,and analyze the transmission line and field distribution of the composite waveguide.We have found that heterostructures atthe junction of composite waveguides result in localization of energy,resulting in interface states,resulting in extraordinary transmission.On this basis,we discuss the effects of the two waveguide duty cycles on the characteristics of the composite waveguide.Finally,by studying the different phase combinations of the two waveguides,the modulation of the characteristics of the composite waveguide is realized.Fourth,the extraordinary transmission phenomenon was experimentally studied.The band and field distribution of the composite waveguide were measured in the experiment.First,the experimental device system is briefly introduced,and the specific process of the experiment is explained.The process design and fabrication of the two single waveguides and their phase modules are then performed.Finally,the transmission spectrum and longitudinal sound pressure of the composite waveguide were measured,and the experimental results were in agreement with the simulation results.In summary,the extraordinary transmission characteristics of the composite waveguide are studied by numerical simulation and experimental measurement,and the characteristics of the composite waveguide are controlled by changing the phase combination of the two waveguides.The research results can provide reference for design of various new waveguide devices.