ABSTRACT
Terahertz (THz) absorption spectroscopy is widely used for molecular label-free fingerprinting detection, but it is not capable of efficiently analyzing trace-amount sample materials. For improving the efficiency of terahertz absorptance spectroscopy detection, we propose a sensing strategy by treating the geometry sweeping spoof surface plasmon polariton (SSP) of the stretchable metasurface. For the first time, the geometry sweeping can be realized by dynamically stretching the polydimethylsiloxane (PDMS) flexible substrate, leading to the resonant frequency variation of the unit cell. This design provides a significant absorption enhancement factor about 270 times for a 0.1 µm lactose film in a broad terahertz band, enabling the unambiguous identification of different trace-amount samples. The designed method exhibits a novel solution for the enhancement of broad-band terahertz absorption spectroscopy and great application potential in the field of detecting trace-amount samples.
Subject(s)
Motion Pictures , Terahertz SpectroscopyABSTRACT
A multifunctional design based on vanadium dioxide (VO2) metamaterial structure is proposed. Broadband absorption, linear-to-linear (LTL) polarization conversion, linear-to-circular (LTC) polarization conversion, and total reflection can be achieved based on the insulator-to-metal transition (IMT) of VO2. When the VO2 is in the metallic state, the multifunctional structure can be used as a broadband absorber. The results show that the absorption rate exceeds 90% in the frequency band of 2.17 - 4.94 THz, and the bandwidth ratio is 77.8%. When VO2 is in the insulator state, for the incident terahertz waves with a polarization angle of 45°, the structure works as a polarization converter. In this case, LTC polarization conversion can be obtained in the frequency band of 0.1 - 3.5 THz, and LTL polarization conversion also can be obtained in the frequency band of 3.5 - 6 THz, especially in the 3.755 - 4.856 THz band that the polarization conversion rate is over 90%. For the incident terahertz waves with a polarization angle of 0°, the metamaterial structure can be used as a total reflector. Additionally, impacts of geometrical parameters, incidence angle and polarization angle on the operating characteristics have also been investigated. The designed switchable multifunctional metasurfaces are promising for a wide range of applications in advanced terahertz research and smart applications.
ABSTRACT
In this paper, a hybrid vanadium dioxide (VO2)-graphene-based bifunctional metamaterial is proposed. The realization of the different functions of perfect transmission and high absorption is based on the insulator-metal phase transition of VO2 material. The Fermi energy level of graphene can be treated to dynamically tune the absorption and transmission rates of the metamaterial structure. As a result, when VO2 is in the insulating state, the designed metamaterial can be used as a filter providing three adjustable passbands with center frequencies of 1.892 THz, 1.124 THz, and 0.94 THz, and the corresponding transmittances reach 93.11%, 98.62%, and 90.01%, respectively. The filter also shows good stopband characteristics and exhibits good sensing performance at the resonant frequencies of 1.992 THz and 2.276 THz. When VO2 is in metal state, the metamaterial structure acts as a double-band absorber, with three absorption peaks (>90%) in the range of 0.684 THz to 0.924 THz, 2.86 THz to 3.04 THz, and 3.28 THz to 3.372 THz, respectively. The designed structure is insensitive to the polarization of vertically incident terahertz waves and still maintains good absorption performances over a large range of incidence angles. Finally, the effects of geometric parameters on the absorption and transmission properties of the hybrid bifunctional metamaterials have also been discussed. The switchable metamaterial structures proposed in this paper provide great potential in terahertz application fields, such as filtering, smart sensing, switching, tunable absorbers, and so on.
