High-performance metasurface sensors based on perturbation theory and boundary condition

Quasi-bound states in the continuum (quasi-BIC) with high quality factors and strong localized fields represent a highly competitive mechanism achieving high-performance sensors. Recently, metasurfaces with various meta-atom geometries have been designed to excite sharp quasi-BIC resonances for sensing applications. However, there is currently no systematic theory guiding the design of these structures. Perturbation theory was initially proposed to explain shifts in resonant modes of resonators due to changes in the external environment. We introduce this theory into the analysis of quasi-BIC modes, identify the parameter directly related to sensitivity (S), and demonstrate that optimizing the structure to ensure the excited mode field satisfies the boundary conditions can effectively enhance this parameter. Directed by perturbation theory and boundary conditions, we propose a high-performance metasurface sensor design method with significantly enhanced mode S. Specific cases are presented in this work, where the designed metasurfaces achieve significantly improved S of 805.97 nm/RIU and 1041.26 nm/RIU, exceeding the highest values reported in existing literature, and realizes an extremely high figure of merit. This approach can be applied to the analysis of different modes, providing a theoretical method and technical support for the development of high-performance sensors.