Investigation On Characteristics Of Babinet Structure Metasurface

Metasurface,a two-dimensional planar structure,has been widely concerned because of its ability to tailor phase,amplitude,polarization,spectrum,propagation direction of electromagnetic wave in the plane.Firstly,the structure of trimeric Babinet metasurface array and asymmetric trimeric Babinet array structure are designed.The effects with regard to the structural parameters of abovementioned two models on Fano resonance and dual Fano resonance are studied,afterwards,physical mechanism on tuning characteristics of above resonances is analyzed.On grounds of aforementioned studies,we proposed trilayered Babinet polarization conversion metasurface structure with double-L-shaped slits by employing above structures,the influence of structural parameters on polarization conversion characteristics is explored,and the physical mechanism underlying the influence is analyzed.Finally,the surface current is introduced above the trimeric metasurface,the basic properties of Smith-Purcell emission generated by the ideal current model on slits metasurface are studied.The main research results are as follows:1.Babinet metasurface array structure with three same rectangular slits is proposed.The influence with regard to the structural parameters on Fano resonance appearing when electromagnetic wave incident on the metasurface is analyzed,through study we discover that the frequency of dark mode in Fano resonance keeps unchanged,while bright mode has a slight blueshift when the width of the slit changes in a certain range,so properly tuning bright and dark modes is realized by adjusting the width of slit;and when the slit length increases,both dark mode and bright mode for Fano resonance have different degrees of redshift simultaneously;when the spacing between the slits increased,the dark mode has redshift while the bright mode shows the trend of blueshift.The influence of the above three parameters on the quality factor of Fano resonance is analyzed.2.Asymmetric trimeric Babinet metasurface array structure is studied,and the influence of its structural parameters on the phenomenon of dual Fano resonance is analyzed.Dual Fano resonance originates from the interferences between radiative bright and Toroidal mode,dark mode,respectively.The results show that when the ratio of the length of a special rectangular slit to that of other slits increases,both low order dark mode and the bright mode have redshift,while high order Toroidal mode remains unchanged;when the length of the slits increases,we obtain the same conclusion as that of increasing the slits length ratio,there exists increasing slightly minimum value and peak value corresponding to low order dark mode and bright mode in the transmission spectrum;when special slit keeps away from two same-in-size slits gradually,it is found that low order dark mode has redshift,while the other two modes keep fixed;an increase in the thickness of the FR4 substrate in this structure causes a redshift in the entire dual Fano resonance.3.On grounds of above studies,we make up a polarization conversion device by employing Fano-resonant structure,it consists of two layers of 90°-twisted trimeric metasurfaces and one-layer metasurface with double-L-shaped slits.Optimal structural parameters for realizing narrow band asymmetric transmission are obtained after a series of parametric analysis,finally,the genetic mechanism underlying narrowband transmission phenomenon is given by piercing electric field,magnetic field,current density distributions.4.The far-field radiation of trimeric metasurface when introduced surface current is explored by parametric analysis with regard to the velocity of charged particles.We analyzed the orientation of Smith-Purcell emission under circumstance of various velocity of electrons,this research provides simulation foundation for realizing steerable the direction of electron beam in Smith-Purcell emission.