H-type All-metal Superstructure Terahertz Continuum Bound State And Its Application In Sensing

In the terahertz frequencies,resonant modes based on two-dimensional metasurfaces have been studied extensively in theory and experiment.However,most metasurfaces are affected by radiation loss and material loss,and their resonant Qfactor is only a few tens or even lower,which greatly limits their applications in terahertz fields such as ultra-narrow bandwidth and high Q-factor sensing.Bound states in the Continuum(BIC)are resonant modes with theoretically infinite Q.The introduction of BIC provides a new idea to improve the Q factor of metasurfaces.By breaking the structural symmetry,the coupling between BIC and incident wave can be realized,and the quasi-BIC resonance with high Q factor can be obtained.Therefore,in this paper,a terahertz metallic metasurface based on H-shaped array is designed.By introducing BIC,a resonant mode with high Q-factor is obtained.The metasurface designed in this paper is applied to terahertz film sensing.The specific studies are as follows.(1)By changing the structure parameters,the mirror symmetry of the structure is broken.The quasi-BIC mode is excited,whose Q-factor is related to the asymmetry parameter.The simulation results show that the proposed structure can obtain a simulated Q-factor of 180.The experimental Q-factor is 79 due to the errors and resolution of the test system,which is higher than the reported Q-factor of the metasurfaces.(2)The effects of different structural parameters on the quasi-BIC frequency and Q-factor are investigated in depth.The results show that the metasurfaces with smaller thickness can obtain a higher Q factor due to the strong coupling of SPPs between the upper and lower surfaces of the metal.At the same time,the resonance peak shifts toward the high frequency with the increase of its structural gap width when changing the width of the structure.Therefore,by controlling the width of the structure,the resonant frequency of the quasi-BIC can be controlled.For all-metal resonators,a higher Q-factor can also be achieved by using a material with higher conductivity.(3)The sensing performance of the metasurfaces with two different structural parameters is further investigated by attaching a dielectric film to the metasurfaces surface and varying the dielectric film thickness and refractive index.When the thickness of the dielectric film is 25 ?m,the experimentally measured sensitivity is63.01 GHz/RIU,which is lower than the value of 151.02 GHz/RIU and the high sensitivity and performance factor of 18.77 obtained on the simulation.When the thickness is 50 ?m,the experimentally measured sensitivity is 143.02 GHz/RIU and the simulated sensitivity is 205.57 GHz/RIU.(4)The sensing response of quasi-BIC to graphene was investigated.The electrochemical bubbling method for separating graphene and its considerations are discussed.It is found that graphene can eliminate the quasi-BIC with high Q-factor.The results show that the sample has a very sensitive response to the ultrathin monolayer graphene,and the vanishing quasi-BIC dip should prove the sensitive sensing property of the designed metasurface.The results of this paper suggest that this metallic metasurface has great potential for practical applications in the field of chemistry and biomolecules.