Planar metasurfaces and plasmonic resonators have shown great promise for sensing applications across the electromagnetic domain ranging from the microwaves to the optical frequencies. However, these sensors suffer from lower figure of merit and sensitivity due to the radiative and the non-radiative loss channels in the plasmonic metamaterial systems. We demonstrate a metamaterial absorber based ultrasensitive sensing scheme at the terahertz frequencies with significantly enhanced sensitivity and an order of magnitude higher figure of merit compared to planar metasurfaces. Magnetic and electric resonant field enhancement in the impedance matched absorber cavity enables stronger interaction with the dielectric analyte. This finding opens up opportunities for perfect metamaterial absorbers to be applied as efficient sensors in the finger print region of the electromagnetic spectrum with several organic, explosive, and bio-molecules that have unique spectral signature at the terahertz frequencies.
We report the simulation, fabrication, and experimental characterization of a multichannel metamaterial absorber with the aim to be used as a label-free sensing platform in the terahertz regime. The topology of the investigated resonators deposited on a thin flexible polymer by means of optical lithography is capable of supporting multiple resonances over a broad frequency range due to the individual contribution of each sub-element of the unit cell. In order to explore the performance of the chosen structure in terms of sensing phenomenon, the reflection feature is monitored upon variation of the refractive index and the thickness of the analyte. We achieve numerically maximum frequency sensitivity of about 139.2 GHz/refractive index unit. Measurements carried out using terahertz time-domain spectroscopy show good agreement with the numerical predictions. The results are very promising, suggesting a potential use of the metamaterial absorber in wide variety of multispectral terahertz sensing applications. V
The near and far field coupling behavior in plasmonic and metamaterial systems have been extensively studied over last few years. However, most of the coupling mechanisms reported in the past have been passive in nature which actually fail to control the coupling mechanism dynamically in the plasmonic metamaterial lattice array. Here, we demonstrate a dynamic mode coupling between resonators in a hybrid metal-semiconductor metamaterial comprised of metallic concentric rings that are physically connected with silicon bridges. The dielectric function of silicon can be instantaneously modified by photodoped carriers thus tailoring the coupling characteristics between the metallic resonators. Based on the experimental results, a theoretical model is developed, which shows that the optical responses depend on mode coupling that originates from the variation of the damping rate and coupling coefficient of the resonance modes. This particular scheme enables an in-depth understanding of the fundamental coupling mechanism and, therefore, the dynamic coupling enables functionalities and applications for designing on-demand reconfigurable metamaterial and plasmonic devices.
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