Novel terahertz metasurfaces based on complementary coupled split ring resonators

In this paper, we propose a terahertz metasurface unit cell based on an efficient coupling between two completely symmetric complementary split-ring resonators via a coupling slot. This coupling allows the excitation of a dark eigenmode resonance that is otherwise forbidden. In turn, the radiation losses are highly suppressed and the excited eigenmode features a quite large quality factor. Interestingly, this kind of coupling leads to the restoration of the symmetry of the unit cell of the coupled resonators with respect to the terahertz field illumination. More importantly, we show that the quality factor of this dark mode resonance can be tuned by modifying the coupling slot length and reach a high value of 67.4. Furthermore, a laser beam machining technique can be easily exploited during the fabrication process of this design. Besides using this design as a sharp bandpass filter, it can be utilized as an efficient biosensor. We show that a sensitivity level of 6.3 × 10⁴ nm/RIU is indeed doable using the proposed structure. This design may emerge as a potential candidate for future biosensors and hence utilized during the development of new cancer biomarkers.