| Terahertz technology has important application value in the fields of imaging,astronomical observation,biomedicine and broadband wireless communication.It is a cutting-edge technology that can have a significant impact on social and economic development.It is rated as one of the "top ten technologies to change the future world".In the future,6G communication will develop and use terahertz frequency band,which requires terahertz wave not only for data transmission,but also efficient and rapid regulation.However,it is difficult to find high-speed response materials to terahertz waves in nature,and the modulation methods that can be applied in microwave and light wave bands are not completely suitable for terahertz wave bands.Therefore,it is of great significance to develop terahertz active modulation devices with simple structure,low cost,high modulation depth and fast modulation speed.The main innovations of this paper have been proposed as follow:(1)Based on the reconfigurable metamaterial of micro-electro-mechanical systems(MEMS),the amplitude and frequency control device of terahertz wave is proposed by using time domain finite integral method.The device is driven by MEMS comb driver.And it has two passbands,the central resonant frequencies are located at 0.66 THz and 1.31 THz,respectively.When the comb driver applied DC voltage,the movable structure gradually approached the fixed structure,and the metamaterial structural units are reconfigured,leading to the amplitude modulation depth reaches 84.4% at the center frequency of the lowfrequency passband.At the same time,the resonant frequency of the high-frequency passband shows an obvious red shift,and the maximum frequency shift reaches 0.195 THz.The electromechanical performance of the comb driver is studied by the finite element method.The results show that the displacement of 4 μm is realized under the driving voltage of 120 V,and the switching time of the device is about 9 μs.Combined with the surface current distribution at the central frequencies of the two passbands,the corresponding equivalent circuit models and the expression of resonant frequency are established,and thus the dynamic regulation mechanism of the device is deeply analyzed.(2)A terahertz dual-mode amplitude modulation device by low voltage is designed and fabricated.The amplitude control of terahertz wave in orthogonal mode is realized by using vanadium dioxide hybrid metasurface.The sample is fabricated using a surface micromachining process and characterized by a terahertz time-domain-spectroscopy system.When the bias current is 0 m A,the device under transverse magnetic(TM)mode has a passband with a center frequency at 0.43 THz.When the bias current increases to 520 m A,the amplitude modulation depth reaches the maximum value of 68%.Under transverse electric(TE)mode,the device switches from transparent broadband to a new narrowband.The maximum modulation depth is 63%,and its saturation current is 500 m A.The switching speed of the device is characterized by dynamic experimental tests.It is found that the trigger time of vanadium dioxide phase transition is 2.1 s and the recovery time is 1.9 s.This work provides a new way for the miniaturization and integration of electronic controlled terahertz switches and amplitude modulators.(3)A broadband transmission terahertz phase modulator is proposed based on vanadium dioxide hybrid metasurface.By embedding vanadium dioxide between two metal resonant structures,the insulating-metallic phase transition property of vanadium dioxide are used to change the resonant mode of the unit cell and realize the reconfigurability of spectra characteristics.When the vanadium dioxide changes from insulating state to metallic state,the mechanism of large phase shift is explained by the changes of transmission amplitude and phase spectra.When the bias current is 290 m A,the experimental results show that a phase shift is achieved more than 90 degrees at 70 GHz bandwidth,and a phase shift of 102 degrees is obtained at 0.63 THz.The equivalent circuit models of metal resonance unit and vanadium dioxide structure are established,and the parameters of each circuit element are calculated by theoretical method.Using the circuit simulation method,the transmission amplitude and phase spectra of the device when vanadium dioxide is in different states are simulated,which are basically consistent with the full-wave simulation and experimental results,and thus the phase regulation mechanism of active control devices is intuitively analyzed.The three kinds of terahertz active modulation devices in this paper can realize the active control amplitude,frequency and phase of terahertz wave,and have potential application value in terahertz broadband wireless communication,phase-controlled antenna,beam control and other fields in the future.The research methods of this paper have important reference values for the research and development of new terahertz active control devices. |
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