Investigation Of The Resonant Characteristics And Potential Applications For Metamaterial In Terahertz Wave Band

Since the first experimental observation of extraordinary optical transmission(EOT)phenomenon through two-dimensional hole arrays,the study of the transmission properties of subwavelength apertures has become a very active area of research in electromagnetism.Numerous models have been put forward to explain this phenomenon,but all of them have some limitations,and a general consensus has not emerged yet.Besides,terahertz metamaterial leads to a variety of applications including biological and chemical sensing,but it has also not been extensively studied.To solve these problems,we present a systematical study of the scattering and resonant characteristics of terahertz wave in subwavelength structures and its potential application in sensing.The main content is listed as follows:Firstly,we analyze the scattering and resonant properties of terahertz wave in subwavelength disk arrays.A new class of confined modes,which are named as disks scattering slab modes(DSSMs)originating from the interaction among the scattered fields,diffractions,and conventional slab modes,have been proposed when the incident terahertz wave incidents from the non-arrayed side of the sample.Based on the experimental data,we found that the disks scattering FP modes play a key role for the observed resonance dips.If the terahertz wave is incident from the array side,the dielectric losses will play an important role,which decreases the contributions of the conventional slab modes.As a result,we can observe a clear transition from DSSMs to disk scattering modes(DSMs)by increasing the substrate thickness.Besides,the influence of the geometric parameters on the resonance frequencies has also been investigated.A laconic theory model is developed,based on the dipole scattering approach,which can describe the main features of both DSSMs and DSMs,and the proposed phase matching conditions can predict the resonance frequencies very well.Secondly,the resonant properties of terahertz metamaterial absorbers have been studied.The substrate used in our experiment is the commercial Kapton film,which is very thin and ultra-flexible,and the top metallic patterns are cross,square ring and I-shaped structures.The effects of substrate thickness and incident angle on the absorption curve are systematically analyzed.A laconic multiple reflection interference model is developed to describe the absorption characteristics,and a very simple phase matching condition is proposed to predict the optimum thickness of each order.Finally,a very simple asymmetric cross-shaped absorber structure is proposed to achieve dual-band absorption.Two distinct absorption peaks are experimentally achieved with near unity absorbance,and the resonant frequency can be easily adjusted by changing the asymmetry of the structure.By applying the asymmetric cross-shaped absorber as a refractive index sensor,we can achieve very high sensitivity and FOM*values.Thirdly,the realization of an ultra-narrow band resonance in terahertz wave band has also been studied.The design concept is to suppress the radiative losses through electrically coupling two split ring dark mode resonators with a microstrip connecting line.The physical mechanism is explained by the resonance of the surface current distribution.Based on the design strategy of the JSRRs metasurface,a JSRRs absorber has been proposed which has much greater resonance strength,smaller resonant linewidth and higher Q factor.The influence of each geometric parameter on the resonant Q factor has been analyzed systematically,and an equivalent LC circuit model is introduced to qualitatively interpret the influence of structural parameters on the resonant frequency.Finally,the sensing performance of the JSRRs absorber has also been studied,the sensitivity is much higher than the general metamaterial absorber which might due to its high electric field enhancement factor.Finally,we have systematically analyzed the sensing performance of the metasurfaces and the metamaterial absorbers.The influence of the metallic pattern on the sensitivity has been studied.It is found that the asymmetric cross structure has a better sensing performance than the cross-shaped structure.We have verified that the lower the substrate refractive is,the higher sensitivity that could achieve.The metasurface has a much larger sensitivity than the metamaterial perfect absorber.Based on the analysis above,a novel structure has been proposed which has extremely high Q factor,high FS value and high sensitivity.Compared with many reported terahertz sensors,the proposed structure in this thesis also shows better sensing performance,and it may find application in bio-chemical sensing and material identification.