Manipulating the phase and group delay of a unit cell in metasurface via impedance engineering

Abstract

The emergence of metasurfaces that tailor the phase via carefully controlling each unit cell brings promising applications including wavefront manipulation, acoustic lenses and levitations. Although excellent phase engineering has been reported in the literature, most metasurface designs suffer from narrow operating bandwidth. To achieve consistent performance over a broad bandwidth, it is necessary to engineer the group delay, in addition to the phase delay, however, few studies have considered this. The majority of them realized specific group delay by true time delay via tuning the depth of a cavity or peculiar topology-optimized structures. No systematic method of unit cell design has been proposed which is a significant step to broadband design. In this work, we proposed a unit cell design process incorporated with transfer matrix method and equivalent LC-circuit fitting. The transfer matrix method is a semi-analytical model capable of predicting the phase response if parameter lists are given. The LC-fitting interprets targeted impedance profile of unit cell by the equivalent inductance and capacitance, assisting the parametric sweeps for geometry design. A numerical study presented showing the mapping of LC values with two physical parameters, leading to control of phase and group delay simultaneously.