Broadband Bidirectional Thermal Emission Supported by Localized Surface Plasmons and Magnetic Polaritons

Achieving broadband directive (BBD) thermal emission is of fundamental importance for high-performance thermal antennas, stealth, and energy harvesting. However, previous BBD emitters lack consideration of azimuth dependence, and the waveband is limited. Herein, we design a metal-insulator-insulator-metal (MIIM) thermal emitter for achieving polar-azimuthal selective emission within the 8-14 μm atmospheric window, namely, broadband bidirectional thermal emission. The proposed MIIM structure consists of aluminum (Al) stripes on the top, beneath aluminum oxide (Al₂O₃) and silicon oxide (SiO) films, and an Al substrate. We explicitly present the design procedure of the MIIM structure to achieve broadband bidirectional emission and reveal the underlying mechanisms. Results indicate that the intrinsic absorption of the dielectric layers, localized surface plasmons (LSPs), and magnetic polaritons (MPs) synergistically promote the broadband bidirectional emission of the MIIM structure, resulting in bidirectional thermal emission within two well-constrained solid angles with marginal angular dispersion. This work reports a high-performance broadband bidirectional emitter and provides new insights into controlling polar-azimuth emissivity through the superposition and coupling effects of LSPs and MPs, with potential applications in thermal imaging and camouflage.