Study On Terahertz Narrowband Filter With Composite Structure

The frequency of terahertz wave is between the infrared and microwave,and has many important applications in imaging,non-destructive testing,communication,spectral biochemical sensing,safety check and so on.Terahertz communication,detection and other applications urgently need low loss and integratable devices such as terahertz narrowband filtering and frequency division multiplexing etc.The terahertz filter can filter out environmental noise and unwanted frequency components in the terahertz system,effectively improving productivity and system performance.In recent years,many researchers dedicated to the study of terahertz filters,proposed various kinds of terahertz filters.The waveguide type terahertz filter has the advantages of simple structure and easy realization of system integration.In this thesis,a small-sized composite structure narrow-band filter based on the periodic structure waveguide and the theory of interface is designed.Compared with other types of filters,it has larger power capacity,lower production cost.It can avoid electromagnetic radiation.The contents of the thesis are as follows:The basic theory of composite structure terahertz narrowband filter is expounded.From the Maxwell equation,the propagation characteristics of electromagnetic waves in the periodic structure waveguide are theoretically studied.The finite element method and the finite element software COMSOL Multiphysics are introduced.We have given the simulation process and the data analysis method of the variable cross-section periodic structure waveguide.Here,three composite terahertz narrowband filters are designed,which have different filtering characteristics.They are temperature tunable characteristics,mechanical tunable characteristics and multi-channel filtering characteristics.The structural parameters of the two periodic waveguides are designed,which make up composite structure.The filter mechanism of the composite structure is studied.The transmission peaks generated in the same frequency gap of the two waveguides are due to the local resonance at the junction,resulting in resulting in an interface state.The original band-gap appears the abnormal transmission phenomenon,to achieve the filtering function.They are studied of the temperature tunable terahertz narrowband filter,those are the influence of the number of waveguides and the temperature characteristics.We get the narrowest bandwidth of this structure is 0.29 MHz and the Q-factor is 3.5×10~6,which can be used as an ultra-narrowband terahertz filter.We have discussed influence of additive defects of mechanical tunable terahertz filter.And we have introduced two kinds of mechanical control structures with maximum tuning range of 175 GHz and narrowest bandwidth of 0.191 GHz is obtained.A multi-channel terahertz filter with“sandwich”composite structure is studied.The research shows that it can achieve multi-channel narrowband filtering,and the narrowest bandwidth of only 0.5 MHz.In this paper,three kinds of terahertz narrowband filters with different kinds of composite structures are designed by using the anomalous transmission phenomena in the band gap.The mechanism of anomalous transmission is analyzed.The characteristics of the narrowband filter are studied.The numerical simulation shows that the narrowest bandwidth of the anomalous transmission peak in the forbidden band can reach 0.29 MHz.Through the design of the filter material and structure,the composite structure terahertz narrowband filter achieves the functions of temperature tuning,mechanical tuning and multi-channel filtering,respectively.This has referential significance of terahertz devices and technologies to the further study.