Thermal Radiation

Thermal Radiation
Selective Emission

Black bodies radiate their energy over a wide range of wavelengths, with a distribution determined by temperature. No true black body exists but many objects emit in a similar pattern. The atmosphere is naturally transparent to radiation at certain wavelengths. In these "atmospheric windows," objects exchange their energy not with the surrounding atmosphere, but with the much colder reaches of space. Tuning a structure's emissive behavior to only emit in these windows allows for radiative cooling below the ambient temperature. This is a green and effective way to achieve cooling without any electrical input.

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Near-Field Effects

The black body limit is typically thought to be the maximum amount of energy two objects may exchange through thermal radiation. However, it has been shown experimentally that the black body limit can be exceeded when the two objects of interest are separated by a very small gap, on the order of the wavelength of light transmitting the energy. Near-field effects, such as the tunneling of surface waves across the gap, are the cause of the broken limit. Objects that support surface polaritons may exceed the limit by several orders of magnitude. We use dyadic Green's function solutions to the vector Helmholtz equation to quantify the near-field radiative transfer, working in both planar and spherical geometries.

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