Design And Studies Of Band-stop Terahertz Filters Based On Metamaterials

Terahertz wave is between microwave and infrared,which has many characteristics that microwave and infrared wave do not have,such as transient,safety,penetrability and wide band property.Hence,terahertz wave can be widely used in terahertz imaging,terahertz time-domain spectroscopy,terahertz communication and other fields.In recent decade,the research of terahertz generators and detectors has been developed rapidly,but the scarcity of terahertz devices with good performance hinders the research and practical application of terahertz.Terahertz filters is one of the important terahertz devices.Therefore,among the research in terahertz devices,it is a hotspot to research terahertz filter which has the characteristics of polarization independent and tunable.Metamaterial is a kind of artificial medium which has attract researchers' attention in terahertz field wildly.Terahertz filter with excellent performance can be obtained by designed the structure,parameters and materials of the metamaterial.In This thesis,the research is carried out for the good performance terahertz filter which is badly needed in the terahertz system.Three kinds of band-stop terahertz filter are designed through optimize the material,structure and geometrical parameters of the filter.The main research work completed in this thesis is as follows:(1)A kind of Closed Ring-Cross Wire structure unit filter is designed.The Closed Ring and Cross Wire structure is combined to get wide bandwidth.A three-layers Closed Ring-Cross Wire Structure Unit THz filter with good performance is designed by adjusting line width,substrate's size,layer number and other factors.The filter's rising edge and falling edge can be up to 1313 dB/THz and 942 dB/THz,respectively.The average transmissivity in the stop band can be less than 5%(modulation depth below-25 dB),the filter's center frequency can be tuned range from 0.72 THz to 1.28 THz,and the filter is polarized independent.This terahertz filter has a significant advantage comparing with the current terahertz filter which universal bandwidth is less than 0.5 THz and modulation depth is-23 dB.(2)A kind of Wire Cut filter is designed.A new type of Wire Cut structure is designed based on cutting the Closed Ring structure.The filter with three-layers and four-layers structure perform very well.The three-layers structure filter works in the 0.1-4 THz,the resistance band bandwidth up to 1.3 THz.The filter's rising edge and falling edge up to 350 dB/THz and 592 dB/THz,respectively.The four-layers structure works in 0.1-4.3 THz,the resistance band is 1.04 THz,and the rising edge and falling edge can be up to 237 dB/THz and 207 dB/THz,respectively.The average transmissivity in the band is less than 2%.By changing the filter's substrate material,the filter can be tuned in large range.The three-layers structure filter's center frequency can be tuned in 1.8?3THz.Compared with the Closed Ring-Cross Wire structure,this kind of filter has wider bandwidth,better inhibition effect in the resistance band and wider tunable range.(3)A kind of Wire Cut-Cross Wire structure unit filter is designed.A new type of dual band characteristic filter is designed by combining the Wire Cut structure with the Cross structure.Three-layers,four-layers,five-layers structure filter is performance very well.The resistant band can be tuned precisely by adjusting the width of the cross line in the structure,and the resistance band can be tuned in a wide range by changing the material of the substrate.Taking five-layers structure as an example,the resistance band bandwidth at low frequency is 0.635 THz,the rising edge and falling edge can be up to 228.6 dB/THz and 170.1 dB/THz.The resistance band bandwidth at high frequency part is 1.1 THz,with transmissivity less than 1%.The rising edge and falling edge can be up to 307.1 dB/THz and 212.5 dB/THz.By changing substrate's material,resistance band at low-frequency and high-frequency partial tunable range can be up to 1.04 THz and 2.43 THz,respectively.Comparing with the single-band filter,filter with dual-band can has more selection in filtering.This kinds filter is better than some dual-band filter with maximum modulation depth is less than-40dB,band bandwidth is less than 0.2 THz,and the rising/falling edge slope is less than the 200 dB/THz.