Research On Terahertz Device With Adjustable Cross-section Periodic Waveguide Structure

In recent years,with the development of terahertz radiation sources and detection technology,the superior characteristics of terahertz waves have shown great prospects,the terahertz functional devices are widely used in the terahertz technology.The research of terahertz micro-structured functional devices has become a major development trend of terahertz devices and the important research frontiers in the terahertz field.Based on the research progress of terahertz micro-structure functional devices at home and abroad,this paper studies the transmission mechanism of terahertz waves in variable-section periodic waveguides in theory,and designs the terahertz waveguides involved in terahertz functional devices.A series of scientific and technical problems such as the physical mechanism of mode resonance and magnetic field distribution,terahertz material properties,frequency regulation and simulation.The main contents in this paper include the following aspects:1.The transmission characteristics of a terahertz wave in a variable cross-section periodic waveguide are studied.The Bragg resonance generated by the same two transverse mode resonance interactions and the Non-Bragg resonance occurring between different transverse modes are introduced.Then,the waveguide period is adjusted by Length and average radius to control the range of the forbidden band and the frequency position of the passband in the forbidden band,to achieve the regulation of the propagation mode of the terahertz wave in the waveguide.Based on the principle of multimode resonance,a terahertz waveguide capable of achieving single high-order mode transmission is designed.2.The single-mode transmission terahertz waveguide structure is studied,and a magnetic field-sensitive nematic liquid crystal E7 is added to the waveguide.The special type of the frequency shift of the center frequency of the passband is studied by increasing the angle?between the external magnetic field and the terahertz wave propagation direction,after that,the longitudinal distribution and cross-section of the magnetic field at the center frequency was analyzed,and electromagnetic field change along the radial direction at the maximum of the magnetic field in the axial direction was taken to indicate that the waveguide can transmit a single high-order mode and the frequency can be adjusted.3.The defects are introduced in the perfect periodic structure,and the defect modes are generated in the Prague forbidden band and the non-Bragg forbidden band.The result by numerical simulation shows that the resonant frequency of the non-Bragg defect mode can be controlled by the temperature characteristics of the metal tube wall.After that,we fixed the defect radius to reduce the defect length.When L=0.2?and L=0.8?,the highest tunability is11.5 MHz/K.Then,when the length of the defect is fixed to reduce the defect radius.When R=0.7r₀,the sensitivity is 10.15 MHz/K.4.Finally,two simple waveguide structures are designed to realize the effect of double-passband filtering and dual-band impedance filtering.One is to introduce the"work"type defect in the variable-section periodic waveguide structure.The structural parameters are reasonably designed to pass the fixed frequency wave,and the double pass is designed.With a filter;the other is composed of two sets of periodic variable-section waveguides with a sinusoidal function of Asin(2?x/50).The fluctuation parameters of the composite waveguide,the period of the sinusoidal function and the influence of the amplitude on the forbidden band width are studied.The maximum forbidden band bandwidth is 1.6 THz,and the ratio of the broadband to the center frequency is as high as 40%.Based on the above results,we obtain a composite waveguide structure.High efficiency band stop filter.In short,we theoretically design variable-section waveguides with different structural parameters,and use numerical simulation methods to analyze the field distribution,mode resonance mechanism and band characteristics in the waveguide.Besides,the tunable of the functional device was realized by applying mechanical stress,changing the temperature characteristics of the gold tube wall and adding the magnetic control characteristics of the liquid crystal materials to change the size of defects.The research result will provide reference for the fields of terahertz medical,communication,military and imaging.