Ultramicro-sensing of terahertz metamaterials implemented by using sample traps

Abstract

A metamaterial sensor implemented by using sample traps based on terahertz electromagnetically-induced-transparency-like (EIT-like) effect is proposed. The basic unit structure of the sensor is composed of a metal wire and a pair of split ring resonators (SRRs), which are coupled to produce EIT-like effect. The full width at half maximum of transparency peak is 178 GHz obtained at 1.067 THz, and the maximum transmittance of the transparency peak is 89.71%. The sensing characteristics of the structure are studied, and the sensitivity per unit volume is <inline-formula><tex-math id="M3">\begin{document}$178\;{\rm{G}}{\rm{H}}{\rm{z}}/({\rm{R}}{\rm{I}}{\rm{U}}{\cdot} {{\rm{m}}{\rm{m}}}^{3})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20230080_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20230080_M3.png"/></alternatives></inline-formula>. The analysis of electric field distribution at the resonant frequency point of the metamaterial indicates that the electric field at the gap of the SRRs on both sides is strongest. Sample traps are constructed at the gap where the electric field is strongest. The photoresist is filled into the sample traps as the object to be measured, and 50 GHz frequency offset is successfully measured, verifying that the sample trap structure can be applied to sensing. With samples placed in the sample traps, the sample volume is reduced to the ultra-micro level, and the sensitivity per unit volume is increased to <inline-formula><tex-math id="M4">\begin{document}$5538\;{\rm{G}}{\rm{H}}{\rm{z}}/({\rm{R}}{\rm{I}}{\rm{U}}{\cdot} {{\rm{m}}{\rm{m}}}^{3})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20230080_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20230080_M4.png"/></alternatives></inline-formula>, which is 31 times higher than original one. The successful identification of water, human skin and rat skin samples show that the metamaterial sensor implemented by using sample traps has potential applications in the field of ultra-micro detection.