Displacement Sensor Based on Quasi Bound States in the Continuum of Localized Spoof Surface Plasmons

Quasi bound states in the continuum (quasi-BICs) of localized spoof surface plasmons (LSSPs) have weak radiation loss and high quality factors (Q-factors). In this paper, a displacement sensor based on the quasi-BICs of the LSSPs is proposed. The unit cell of the metasurface contains a circular grating and a circular dielectric sheet, and a plane wave is normally incident on the metasurface. When the circular grating and the circular dielectric sheet are concentric, only TE
1,1
can be excited, TE
2,1
and above are BICs and cannot be excited; when the circular grating and the circular dielectric sheet are offset by a displacement, TE
2,1
and above transform into quasi-BICs and can be excited. The Q-factors of corresponding modes are related to the displacement, which is the principle of the sensor. Simulation is carried out and the feasibility of the sensor is verified. The sensor has the advantages of ultra-compact and high sensitivity.