A Research On Terahertz Fingerprint Sensor Based On Metamaterial

Special recognition to molecules is essential for many biochemical processes,thus highly sensitive sensing methods for molecule recognition are strongly demanded.In particular,the inter-or intra-molecular vibrations of biochemical molecules are located in the THz region,making this regime have the advantage of fingerprint detection.But at present,the sensitivity of fingerprint detection needs to be further improved.The emergence of various artificial materials raises the possibility of molecular fingerprint detection with a high sensitivity using THz spectroscopy.So in this thesis,we explore the method based on the design of ultra-sensitivie teraehrtz metamaterial sensors to achieve fingerprint detection of trace samples.The main work of this thesis is described as follows:(1)We proposed a metamaterial sensor for enhanced fingerprint detection of lactose based on split-ring resonators(SRRs).It is based on the resonant coupling of plasmonic modes of SRRs and terahertz characteristic modes of lactose.Large electric field enhancement(about 120 times)at the gap of SRRs allows for the highly sensitive detection.A narrow transmittance peak in the broader transmittance dip was observed.The occurance of this transmittance peak is due to the interaction between lactose and SRRs.Besides,the transmittance peak exactly locates around the characteristic frequency of lactose.Therefore,the transmittance peak can be regarded as the fingerprint of lactose.Moreover,the differential transmittance enhanced as the lactose concentration increased.The selectivity of this SRRs sensor for the target molecule was also verified by using fructose.A low amount of lactose,as small as 20mg/mL was successfully detected in the experiment.The experimental results agreed well with the theoretical analysis.Our study opens a new avenue to exploit new materials or devices for molecule sensing with high sensitivity and selectivity.(2)We theoretically design a terahertz metallic nano-slits structure,which has the capability to enhance the electric field by over 6×10~5 times at 0.529 THz in the slits and could hence serve as a powerful biochemical sensor.Such a structure can be designed to exhibit high transmittance over an extra wide frequency range,which covers the characteristic frequencies of many molecules.Molecular fingerprint detection of lactose and maltose is demonstrated.It is found that this sensor can detect different saccharides without changing its geometry parameters.The absorption signal strengths of lactose and maltose are strongly enhanced by a factor of 44.45 and 31.59,respectively.In addition,the absorption signal strength of lactose is dependent on the its thickness,which provides an effective way to predict the thickness of lactose.Our sensor can open up possibilities for identifying different biochemical molecules in complex mixtures in ultrasmall quantities.