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A tunable terahertz metamaterial sensor based on aluminum and silicon has been proposed in this paper. Two identical aluminum crosses are placed on either side of the silicon layer. Two substructures are formed by changing certain structural parameters, and two different resonant modes are enhanced directionally in these substructures, respectively. The refractive index sensing range for both resonant modes is 1.0–1.8. The sensitivity and figure of merit (FOM) of the electric dipole resonant mode which is centered at 2.333 THz are 117.67 and 1.07 GHz/RIU. As for the Fano mode which is centered at 3.381 THz, the calculated values are 81 and 2.53 GHz/RIU. Both resonant modes can achieve over 98% opacity. More significantly, an enhancement method of sensing capacity is realized based on perturbation theory. By placing polytetrafluoroethylene (PTFE) plates on the ends of the upper surface aluminum cross, the sensitivity of both resonant modes is improved. The optimized structure provides a sensitivity of 132.75 and 105.17 GHz/RIU for the two resonant modes, respectively. In addition, the effects of PTFE layer thickness on sensing performance are also discussed. This work opens up new prospects in the design of terahertz metamaterial sensors and provides a new method of enhancing sensing capacity. [ABSTRACT FROM AUTHOR]

An ultra-broadband, polarization-insensitive terahertz metamaterial absorber based on vanadium dioxide resonance structure is proposed in this paper. The device boasts advantages such as a straightforward design, broad absorption bandwidth, and substantial fractional bandwidth. Numerical simulations show that vanadium dioxide enables the absorber to achieve near-perfect absorption (with a rate greater than 95%) in its metallic state. It demonstrates an average absorption rate exceeding 96.5% across an ultra-broadband range (4.02 THz to 11.95 THz). The absorption bandwidth reaches 7.93 THz, with a relative bandwidth of 99.3%, representing a notable improvement over comparable absorbers. Furthermore, due to its highly symmetric pattern design, the device exhibits excellent polarization insensitivity and maintains stability even within a wide incident angle range. The operational mechanism of the absorber is elucidated through the application of impedance matching theory and near-field distribution analysis. The designed absorber structure makes vanadium dioxide materials more widely applicable in terahertz and ultra-broadband absorber devices, holding promising application prospects in fields such as security imaging, energy harvesting, and so on. • A novel terahertz absorber based on vanadium dioxide is proposed. • The ultra-broadband absorption from 4.02 to 11.95 THz can be achieved. • The relative absorption bandwidth reaches up to 99.3%. • The absorber excels in broad-angle absorption, polarization-insensitive. • Simple three-layer structure, facilitating easy manufacturing. [ABSTRACT FROM AUTHOR]