Efficient computation of thermal radiation from biperiodic layered metasurfaces using the $T$-matrix method

Metasurfaces are becoming important tools for the control of thermal radiation. Understanding their functional possibilities on computational grounds requires evaluating the response of the biperiodic layered system for many degrees of freedom, including several radiation directions and polarizations, while varying lattice spacing, thicknesses, and/or materials of homogeneous layers, over a range of frequencies. The diverse set of cases that need to be considered in simulations prompts for efficient numerical tools to handle them. To respond to this need, we present a method for computing the thermal radiation from metasurfaces that combines the directional Kirchhoff's law with efficient 𝑇-matrix-based calculations. We show that such a method can accurately reproduce experimental data from a metasurface made of platinum square plates. Additionally, we predict highly circularly polarized emissivity from a chiral metasurface. When comparing CPU-times, the method outperforms other approaches such as rigorous coupled wave analysis already at the modest number of 61 cases per frequency.