EFFECTIVENESS OF SURFACE POLARITONS IN PERFORMANCE IMPROVEMENT OF THE NEAR-FIELD THERMOPHOTOVOLTAIC SYSTEM WITH A METAMATERIAL RADIATOR

A model of a near-field thermophotovoltaic (TPV) system with a metamaterial radiator comprising thin wires and split-ring resonators (SRRs) is constructed. Based on the fluctuation-dissipation theorem, the effective medium theory for the metamaterial and cells is applied in this work In this TPV system, the influences of the effective plasma frequency, the filling ratio, and the scattering rate of the metamaterial on the net spectral heat flux and the system output performances are analyzed. It is verified that the peak location of surface polaritons (SPs) in the net spectral heat flux is shifted to the shorter wavelength when the effective plasma frequency changes, causing the spectral efficiency to first increase and then decrease during the shifting process. The maximum output power densities for In0.18Ga0.82Sb, GaSb, and InSb cells are 30.1 W/cm(2), 7.4 W/cm(2), and 117.5 W/cm(2), respectively. The maximum system efficiencies can reach 13.3%, 25.1%, and 63.2%. It is demonstrated that the influence of the filling ratio on the SPs property is negligible, so the output performances of the TPV system are also independent of the filling ratio. It is beneficial to enhance the maximum output power density by increasing the scattering rate of the metamaterial because of the increased excitation energy of the SPs. Interestingly, the system efficiencies for different cells approach stable values with increased scattering rates.