Research On Terahertz Metamaterial Sensor Based On Narrow-band Absorber

Terahertz wave has the characteristics of low energy,non-ionization and fingerprint spectrum,which makes terahertz spectroscopy technology more advantageous than conventional sensing technology in the field of non-destructive detection.However,terahertz spectroscopy technology exists outstanding problems such as weak detection ability and poor efficiency in sensing applications,which seriously hinder its wide application.With the rapid development of metamaterial research and micro-nano structure processing technology,the metamaterials working in the terahertz frequency band are increasingly used in the sensing field.As a free-label affinity optical sensor,the terahertz metamaterial sensor achieves detection of extremely small amounts of substances with high sensitivity,and its detection method is simple and high-efficiency.The narrow-band absorber utilizes the strong interaction between the triple-layer structure and the electromagnetic wave to produce the localized enhanced electromagnetic field and the ultra-narrow-band absorption peaks with high-quality factors,and it exhibits a promising potential in the sensing field.Therefore,this paper proposes a research on the terahertz metamaterial sensor based on a narrow-band absorber.The main contents of this thesis are listed as follows:1.To solve the problems of the low sensitivity and the non-tunability of the conventional metamaterial absorbers in the sensing application,the terahertz metamaterial microfluidic sensor based on dual-band absorber and the tunable terahertz metamaterial sensor based on graphene absorber are designed in this paper.The microfluidic sensor and the graphene sensor generated dual-band and triple-band resonance peaks with high absorption coefficients due to the strong interaction with terahertz waves,respectively.The resonance mechanism of the sensor is discussed by analyzing the distribution of the electric field and the surface current at the resonance frequency.Meanwhile,the absorption mechanism of the sensors is explained reasonably through studying the equivalent circuit model and impedance matching theory.Besides,the polarization-insensitive and wide-angle of incident-angle-insensitive of the sensors are obtained thanks to the four-fold rotational symmetrical structure of the unit cell,so that the sensors show excellent isotropic characteristics.2.By introducing the microfluidics technology,the microfluidic sensor effectively solves the problem of limited sensitivity due to the poor interaction between analytes and the localized enhanced electromagnetic field of the conventional metamaterial absorbers.The interaction between the analytes and the microfluidic sensor is improved dramatically by integrating the microfluidic channel.The results show that the microfluidic sensor can reach the sensitivity of 537 GHz/RIU,the normalized sensitivity of 0.525 RIU^-1,the quality factor(Q value)of 34.4,and the figure of merit(FoM)of 22 RIU^-1.Compared with the ordinary metamaterial absorber which is contacted with the analytes on the surface,the sensitivity and the normalized sensitivity of the microfluidic sensor are improved and the maximum sensitivity,normalized sensitivity and FoM increased by 100%,109%and147%,respectively.3.By bringing the graphene material,the graphene sensor effectively solves the problem of the lack of tunability caused by the conventional metamaterial absorbers are made of metal materials.The results show that the graphene sensor can be used to manipulate the resonance peaks by adjusting the Fermi energy of graphene and the tuning sensitivity of the sensor reaches 11.26 THz/eV.At the same time,the addition of graphene reduces the ohmic loss of the sensor and improves the resonance strength between the sensor and the terahertz wave,and the sensor obtains an outstanding sensing performance.The graphene sensor achieves the maximum sensitivity of 3.701 THz/RIU,the normalized sensitivity of 0.635 RIU^-1,the Q value of 170,and the FoM of 169 RIU^-1,respectively.Finally,the graphene sensor adds a medium groove under the graphene structure,which brings the larger area about the interaction between the analyte and the localized enhanced electromagnetic field and improves the performance.Compared with the graphene sensor,the maximum sensitivity,normalized sensitivity and FoM of the optimized sensor are improved by 29%,55%and 69%,respectively.