| Summary: | A novel design of a nearly perfect metamaterial absorber based on square split-ring resonators for terahertz sensing applications is proposed and analyzed. The design in this report is simulated and analyzed by using standard numerical simulation software. Magnetic and electric resonant field enhancement in the impedance matched absorber cavity enables stronger interaction with the dielectric analyte. The proposed structure is based on the simultaneous increase in the electromagnetic field and the surface current distribution at the resonance frequency. An absorptivity of 99% is achieved at 0.53 THz with a narrow resonance peak and a Q-factor of 44.17. At a fixed analyte thickness, the resonance frequency is sensitive to the refractive index of the surrounding medium. The influence of the thickness of the covering sample on the sensitivity and absorption coefficient of the absorber is comprehensively analyzed, and the reported design can be used as a refractive index sensor with a high sensitivity of 126.0 GHz/RIU and a figure of merit of 10.5 in the refractive index range from 1.0 to 2.0 at an analyte thickness of <inline-formula> <tex-math notation="LaTeX">$15.0~\mu \text{m}$ </tex-math></inline-formula>. The results show that the sensor has high sensitivity to the analyte covering it. The sensor not only exhibits good sensitivity to thin analytes but also shows high sensitivity to analytes more than <inline-formula> <tex-math notation="LaTeX">$10~\mu \text{m}$ </tex-math></inline-formula> thick in the terahertz low frequency band. Specifically, the sensitivity changes rapidly when the thickness of the sample changes in the range of 0-<inline-formula> <tex-math notation="LaTeX">$6~\mu \text{m}$ </tex-math></inline-formula>, but slowly in the range of 6-<inline-formula> <tex-math notation="LaTeX">$16~\mu \text{m}$ </tex-math></inline-formula>. In general, the response of the resonance frequency to changes in the refractive index of the sample becomes more sensitive as the thickness of the sample is increased from 0 to <inline-formula> <tex-math notation="LaTeX">$16~\mu \text{m}$ </tex-math></inline-formula>. The reported terahertz sensor of a metamaterial absorber has potential applications in biomedical sensing and trace detection of substances.
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