Spectral and Directional Control of Thermal Emission with Nanophotonics

Enas S Sakr, Purdue University

Abstract

Thermal emission is a ubiquitous phenomenon required in many applications, including thermophotovoltaics (TPV), selective solar absorption, and infrared spectroscopy. Making it selective can greatly improve application performance. Here, selectivity is achieved using engineered photonic structures. Two specic design scenarios are discussed for different applications. The first scenario considers angular and spectral selectivity for TPV heat-to-electricity conversion. The second scenario excludes emission towards specic directions, with potential applications in daytime radiative cooling and sensitive IR detectors. In both scenarios, optical modeling is performed using rigorous coupled wave analysis, finite-difference time domain simulations, plus Kirchhoff's law of thermal radiation. In the first scenario, TPV efficiency is enhanced by matching the emitters photonic bandgap to the PV electronic bandgap. A rare earth-based spectrally selective emitter with integrated lter is proposed, where theoretical eciencies can approach 38%. To aid this goal, the proportion of emitted heat intercepted by the PV diode, or the view factor, should be maximized. Hence, symmetric sensitive metallic grating emitters are proposed to restrict directionality. Then, spectral and angular selectivity are combined using doped oxide thin lms and high contrast gratings. A relative enhancement of TPV system efficiency of 3.9x is expected using the proposed selective emitters at large separation distances. In the second scenario, directional emission exclusion is achieved using high contrast metasurfaces. A nearly-complete reduction of heat exchange by 99.77% is shown between an engineered emitter and a distant receiver, and by 77% between an emitter covered by sets of metasurfaces and a nearby target.

Degree

Ph.D.

Advisors

Bermel, Purdue University.

Subject Area

Electrical engineering|Electromagnetics|Optics

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