Spatial and Temporal Modulation of Thermal Emission

5 years ago

Spatial and Temporal Modulation of Thermal Emission

Zachary J. Coppens, Jason G. Valentine

Precise control of a material's emissivity is critical for thermal-engineering applications. Metamaterials, which derive their optical properties from sub-wavelength structures, have emerged as a promising way to tune emissivity over a wide parameter space. However, metamaterial designs have not yet achieved simultaneous spatial and temporal control of emissivity, which is important for advanced engineering applications such as adaptive thermal management and reconfigurable infrared camouflage. Here, spatiotemporal emissivity control is demonstrated by designing and fabricating a large-area, infrared metamaterial that is modulated with ultraviolet (UV) light. The UV light generates free carriers in a photosensitive ZnO spacer layer, which changes the metamaterial optical properties and causes a localized increase in emissivity. Thermal imaging of the metamaterial during UV illumination reveals an apparent temperature increase as a result of the emissivity change. The imaged temperature fluctuation is recorded under exposure from a temporally modulated and spatially patterned UV illumination source to characterize both the temporal response and spatial resolution of the emissivity change. The results of this work demonstrate new capabilities for thermal metamaterials that could bring about the next generation of thermal-engineering devices. A dynamic metamaterial thermal emitter with spatially reconfigurable emissivity is demonstrated for the first time. The emissivity is modulated with ultraviolet illumination and the photoactivated carrier dynamics within the metamaterial are controlled to realize large-area modulation with a low-power, continuous-wave source. The capabilities demonstrated here can open new opportunities for advanced thermal-engineering devices.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201701275