UC Irvine

While selective emitter designs can enable passive thermal solutions for cooling and heating, many selective emitters depend on complex structures, multiple layers, and/or limited application materials. Here we present a general algorithmic optimization framework for the design of single-material 3-dimensional anti-reflective surfaces for radiative thermal management. We use Finite-difference Time-domain simulations in conjunction with a minimization algorithm to computationally investigate optimum passive heating and cooling designs. Based upon a pyramidal topography and depending upon the selected material, our analysis yields that geometric optimization can result in broad set of solutions that significantly enhance spectral absorptivity and/or emissivity. Our findings show that the key mechanism driving the enhancement is the formation of spectrally selective anti-reflective behavior that results from light confinement and localized resonance. This behavior is strongly dependent upon the aspect ratio of the surface features, with higher aspect ratio structures generally leading to a higher spectral emissivity. Applying an optimized surface topology to nickel reduces the normally high metallic visible/near-infrared (IR) reflectivity to the point that it demonstrates a near perfect absorption spectra that ranges from 0.95 – 0.99. Simultaneously, the same geometry maintains an IR-reflectivity below 0.2-0.3, leading to almost ideal thermal passive heating. Conversely, structuring classically emissive materials such as alumina and Polydimethylsiloxane (PDMS) can further minimize reflection in the IR. This results in a significant enhancement to the IR-emissivity and, subsequently, the cooling performance. These findings will both guide future designs for robust and easily adaptable selective emitter designs and provide a general algorithmic framework for the thermal optimization of geometrically derived optical materials for radiative thermal management.