Research On Nonreciprocal And Reconfigurable Devices Based On Spoof Surface Plasmon

Spoof surface plasmon polaritons(SSPPs)(or surface plasmon metamaterials)have imitated natural surface plasmon polaritons(SPPs)at low frequency by artificially constructing subwavelength structure.Since SSPPs can strengthen the binding of electromagnetic(EM)waves,SSPP transmission lines and devices have the advantages of low crosstalk and miniaturization.Moreover,the dispersion properties of SSPPs can be engineered by adjusting the parameters of the structure(s)or adding active device(s),providing flexibility in the design of devices.The proposal of the conformal ultrathin SSPP structure make the corresponding transmission lines and devices perfectly compatible with the process technology of traditional integrated circuits,which greatly expands the application space of SSPPs.In recent years,many important progresses have been made in the research of SSPPs.However,the research on nonreciprocal and reconfigurable SSPPs is relatively limited.To further promote the application of SSPPs in modern communication systems,it is urgent to construct miniaturized,multi-frequency,switchable,and nonreciprocal devices to meet the needs of different complex application scenarios.Based on the above application background mentioned above,the transmission regulation mechanism of SSPPs is studied in this paper.By introducing the spoof localized surface plasmon(SLSP)resonance structure with deep subwavelength characteristics and using the coupling effect between the SSPP transmission line(s)and SLSP resonator(s),miniaturized and multi-frequency isolator,circulator,reconfigurable filter,and reconfigurable coupler have been designed.The main research contents and innovations are summarized as follows:1.A miniaturized SSPP isolator is proposed and experimentally demonstrated.The coupling between the SSPP transmission line and SLSP resonator can concentrate EM energy on the resonator and enhance the interaction with the ferrite to improve the isolation of the isolator.By adjusting the field intensity of the bias magnetic field,the operating frequency of the isolator can be dynamically controlled.This design scheme is extended to realize a four-port circulator that allows one-way transmission in opposite directions in two separate frequency bands.2.A reconfigurable SSPP filter is proposed.By changing the bias voltage applied on the varactor loaded in the SLSP resonator constituting the filter,the resonant frequency of the SLSP resonator can be changed,and then the operating frequency of the reconfigurable filter can be dynamically controlled.3.A reconfigurable SSPP coupler is proposed and experimentally demonstrated.By dynamically controlling the dispersion characteristics of the SSPP structure,the direction of the group velocity of the SSPP wave can be changed,resulting in flexible switching between forward coupling and reverse coupling in the same frequency.By introducing active components into the SLSP resonator constituting the coupler,the tunability of the device can be further expanded,and forward/reverse coupling effects can be achieved at multi frequencies.