Research On Terahertz Metamaterial Filter

Terahertz technology including generation,detection,modulation and transmission of terahertz signal has developed rapidly in recent years due to its extensive applications in the fields of communications,security,etc.Filters play significant roles in the detection,modulation and transmission process of terahertz signal and hence the research on high-performance terahertz filters is valuable for practical applications.As a kind of artificial material structure with the unique electromagnetic properties which natural materials do not possess,metamaterials have been applied to terahertz devices in the rencent decades due to its simple structure and excellent performance.Concentrating on the enhancement of key performance parameters,such as attenuation depth,bandwidth and active tuning range,the work presented in the dissertation involves the design of terahertz metamaterial filters along and the analysis of their working mechanism,in order to widen the application range of terahertz filters.The main contents of the work in this dissertation are as follows.(1)A flexible terahertz metamaterial filter with a central frequency of 387 GHz is reported,in which the attenuation depth of-64 d B is realized by empolying two resonant metallic layers at a certain angle and the bandwidth is broadened in some extent.The filter exhibits a negative permittivity in the range of 374 GHz-400 GHz and a negative permeability in the range of 405 GHz –415 GHz.In addition,it has the characteristics of polarization insentivity,steep cut-off and transparency in the visible light region.The design is validated by the equivalent circuit theory and the equivalent LC parameters as well as the influence on the performance are obtained.The filter sample was fabricated using micromachining technology,while the frequency response was obtained by the free-space measurement.The fact that the measured results are in good agreement with the simulation results further demonstrates the reliability and robustness of the design.(2)A sandwiched terahertz filter with multi-layer structure is proposed based on the work in the part(1),in which the effect of multi-resonant-strucutre on the frequency response is explored.The simulation results reveal that the structure reduces the coupling of inter layers by introducing polymethacrylimide(PMI)with low permittivity,thereby improving the filtering performance.The relative bandwidth of the filter is up to 65% and the rectangle coefficient is 0.91.Moreover,the filter shows excellent polarization stability and angular stability within 30°.(3)A mechanically tunable terahertz metamaterial filter is designed,which consisting of two layers of slotted metallic pattern separated each other by a PMI layer and covered by a layer of zeonor,respectively.The effective permittivity and permeability of metamaterials change by applying a load on the surface of the structure and accordingly the transmission performance of the filter varies.Therefore,a larger tuning range and the conversion of single passband and double passband are realized.The variation of effective permittivity and effective permeability during the tuning process are studied and the filtering mechanism of different resonance frequencies is analyzed.