Research On Tunable Terahertz Metamaterials Based On Shape Memory Alloys

With the development of terahertz applications gradually diversified,tuning terahertz metamaterial functional devices have attracted extensive attention.However,the tuning ability of the traditional active material-based tuning method obviously depends on the characteristics of the material,resulting in a limited tuning range.The structural reconfiguration of the unit cell geometry using microelectromechanical systems(MEMS)technology provides a more straightforward means of achieving resonance tunability in metamaterials.However,most of these MEMS metamaterials that are proposed for miniaturized solutions need metallic interconnects to provide the control signal,which greatly affects their production.In view of the above-mentioned shortcomings,this paper introduces shape memory alloy in the process of designing metamaterials,which can undergo martensitic transformation under the driving of an external field,which causes the geometrical shape and physical properties of the alloy changed before and after the martensitic transformation.Based on this,three SMAbased tunable terahertz metamaterial structures are proposed,and a variety of dynamically adjustable,simple structure and multifunctional terahertz metamaterial functional devices are realized.The specific research content is as follows:Propose a multifunctional metamaterial based on Ni Ti terahertz.The structural unit of the metamaterial is composed of a single-opening Ni Ti resonance ring,and the characteristics of the Ni Ti metamaterial that can undergo martensitic transformation under the drive of a thermal field are used to realize independently dynamic tuning the frequency and amplitude of transmission spectrum.Compared with the transmission curve before and after the phase change,the maximum modulation depth of frequency is 39%,and the maximum modulation depth of transmittance is as high as 89%.By analyzing the distribution of surface current and electric field,the mechanism of the above tuning process is revealed.On this basis,the switching effect and filtering performance of the tunable metamaterial are further analyzed.A tunable dual-band absorber based on Ni Ti terahertz metamaterial is designed.The absorber unit structure is composed of a cross-shaped titanium nickel metamaterial suspended on the top layer,a continuous metal copper plate and a polyimide stack in the middle.By thermally driving the change of the geometric configuration of the Ni Ti martensite transformation process,the resonance frequency of absorption spectrum shifts.The research results show that the cantilever deformation angle is increased from 0 degrees to 10 degrees,and the double absorption peak frequency shift ranges are 0.52 THz and 0.02 THz respectively and maintain perfect absorption.Among them,the ultra-narrowband has a sensitivity of0.87THz/RIU to external environment sensing.On this basis,the sensitivity of the absorber to the polarization and incident angle of the incident terahertz wave was studied.A tunable broadband absorber based on Ni Mn Sn terahertz metamaterials is constructed.The broadband absorber is composed of four independent metal discs,dielectric layers and planar metal ground plates.Utilizing the characteristics of Ni Mn Sn metamaterials that can undergo martensitic transformation under the driving of a magnetic field,the dynamic control of the bandwidth and operating frequency of the absorption spectrum is realized.By analyzing the distribution of surface electric field,the tuning mechanism of two active tuning methods is revealed.In addition,the dependence of the electromagnetic response on the polarization angle and incident angle of the incident terahertz wave in TE mode and TM mode was further studied.