Renewable energy dramatically reduces the consumption of conventional fossil energy and plays an important role in the reduction of greenhouse gases. In particular, thermophotovoltaic (TPV) energy conversion systems can convert thermal energy into electricity and these systems can be installed conveniently in many industrial environments to collect waste heat from engines, motors, or other high temperature sources of heat. A major challenge in increasing the conversion efficiency of TPV systems is to realize infrared absorbers with near-unity absorptivity and thermal emitters with high emissivity in the designed frequency range. Optical metamaterials are artificially structured materials to realize extraordinary properties and these materials can be used to realize high-performance infrared absorbers and thermal emitters. In this proposal, a new type of three-dimensional metamaterial infrared perfect absorbers and thermal emitters with advanced properties are designed and demonstrated to address the major challenge of TPV systems. This research will also benefit other applications in solar energy harvesting, thermal detection, and infrared sensing. The proposed research will be enhanced by outreach activities for high school students through summer research academy program and minority introduction to engineering program. The project also includes educational activities for training and mentoring graduate and undergraduate students especially underrepresented minorities and women.
Energy conversion and transport with electromagnetic waves is an exciting research area for renewable energy generation, including photovoltaic (PV) and thermophotovoltaic (TPV) energy conversion. In order to greatly enhance the conversion efficiency of TPV systems, broadband infrared perfect absorbers and selective tunable-band thermal emitters need to be designed to fit the required absorption or emission spectrum characteristics of TPV components. One new technology for developing TPVs is optical metamaterials. Although planar metamaterials have been studied to design infrared perfect absorbers, they still suffer disadvantages of narrow bandwidth, polarization dependence and limited incident angle, which limit the TPV device performance significantly. The goal of this proposal is to study and demonstrate a new type of three-dimensional metamaterial infrared perfect absorbers and thermal emitters based on metamaterial cavities, with the advantages of tunable and ultrabroad bandwidth, polarization independence, and wide incident angle, in order to address the research challenges in perfect absorbers. The optical properties of metamaterial cavities will be investigated in detail with theoretical analysis and numerical simulations. The light absorption induced heat generation and temperature variation inside the metamaterial absorbers will also be emphasized. The optimized metamaterial cavities will be fabricated and infrared perfect absorbers and thermal emitters with advanced properties will be demonstrated.
