Normal vs tangential polarizations in metasurfaces

In this study we categorize metasurfaces with respect to the direction of their polarization currents i.e., either tangential or normal to the metasurface plane. We theoretically investigate whether or not normal polarization currents can add extra degrees of freedom in engineering the reflection and transmission characteristics of functional metasurfaces. We then present a general formalism in which two different metasurface design scenarios with distinct polarization directions perform equally in engineering desired reflection and/or transmission properties. The result of our study provides a valuable tool to choose the most convenient approach in the design of functional metasurfaces.