Not yet reviewed by Pith; the record is open.

The dielectric layers surrounding a metasurface have a large impact on its frequency and angular response. The notion of effective permittivity captures this dependence by suggesting that a layered dielectric environment will perturb metasurface resonances in the same manner as an infinite environment of that effective permittivity. A model for effective permittivity is presented in this work. In contrast to previous empirically derived models, this multi-term model is a robust approximation based on the modal expansion of fields at the metasurface. A simple dipole metasurface array is simulated to demonstrate the accuracy of the model, which is shown to be improved over other models. Finally, we show that it is possible for dielectric layers to produce an effective permeability different than unity, which must be considered in conjunction with higher-order equivalent circuit modeling to effectively predict metasurface impedance variation.