Textured Metal Radiator For Direct Thermophotovoltaic Energy

IN THERMOPHOTOVOLTAICS, AN INCANDESCENT RADIATOR ILLUMINATES A PHOTOVOLTAIC CELL WHICH CONVERTS RADIANT HEAT TO ELECTRICAL ENERGY. THERMOPHOTOVOLTAIC SYSTEMS ARE ATTRACTIVE FOR SPACE POWER SINCE, IN PRINCIPLE, THEY CAN ACHIEVE CONVERSION EFFICIENCIES CONSIDERABLY HIGHER THAN THE 6% TO 8% CHARACTERISTIC OF CURRENT THERMOELECTRIC GENERATORS. THE CRUCIAL PROBLEM FOR THIS TECHNOLOGY IS MATCHING THE EMISSION SPECTRUM OF THE RADIATOR TO THE BANDGAP OF THE PHOTOCELL. CURRENT APPROACHES TO OVERCOMING THIS PROBLEM INCLUDE FABRICATING RADIATORS WITH STRONG EMISSION LINES AND PLACING FILTERS BETWEEN THE RADIATOR AND PHOTOCELL. WE PROPOSE AN ALTERNATIVE RADIATOR USING ION BEAM TEXTURED METAL SURFACE. IN EARLIER WORK, WE TAILORED METAL SURFACES TO HAVE VERY EMISSIVITY AT SHORT WAVELENGTHS AND MUCH LOWER EMISSIVITY AT LONGER WAVELENGTHS. ION BEAM TEXTURING OFFERS PRECISE CONTROL OVER THE SIZE AND SHAPE OF MICRONSCALE SURFACE TEXTURE FEATURES AND THESE, IN TURN, DETERMINE THE EMISSIVITY SPECTRUM OF THE METAL SURFACE. IN PHASE I, WE WILL TEXTURE THE SURFACE OF TITANIUM METAL TO PRODUCE AN EMISSIVITY CUT-OFF WAVELENGTH AROUND 2 UM. USING PHOTOCELLS ALREADY AVAILABLE AT SPIRE, WE WILL CONSTRUCT A PROOF-OF-CONCEPT THERMOPHOTOVOLTAIC CONVERTER SYSTEM AND USE THIS SYSTEM TO DETERMINE THE EFFICIENCY WHICH CAN BE ACHIEVED WITH TEXTURED METAL RADIATORS.