Application Of Hyperbolic Metamaterials In Near-Field Thermal Radiation

Near-field thermal radiation can theoretically break through the Planck blackbody radiation limit and achieve high heat transfer efficiency at the micro-nano scale.How to use surface plasmons or artificial structures to enhance the efficiency and large-area accurate measurement are important research in the near field thermal radiation.The thermophotovoltaic device(TPV)based on near-field thermal radiation is a thermoelectric conversion device with great prospects.We explore the application of hyperbolic metamaterials in near-field thermal radiation from three aspects:theoretical calculation,experimental measurement,and device.The theoretical calculation of near-field thermal radiation of doped silicon nanowire array and silicon/germanium multilayers hyperbolic structures are given,and the near-field thermal radiation of doped silicon nanowire array is experimentally measured,thus the validity of the characteristics of the high-dimensional metamaterials structure described by the homogenization method is verified.The TPV based on the W nanowire-InSb p-i-n radial core-shell nanowire is first proposed.The specific work is as follows:First,we give the theoretical calculation of the near-field heat flux of hyperbolic metamaterials.When calculating the near-field thermal radiation between semi-infinite plate structures,wave electrodynamics and Green's function-based methods are generally used.Based on the method,using the Drude model of highly doped silicon,combined with the effective medium theory,we calculate the transmission probability map of the silicon nanowire array and give the relationship between the filling ratio,silicon nanowire height,gap and the heat flux.In addition,the near-field heat flux of the silicon/germanium multilayers is also calculated and compared with that of the silicon plate.The results show that the hyperbolic metamaterials plays a strengthen role on heat flux,which provides a theoretical basis for the experimental measurement of near-field thermal radiation of the silicon nanowire.Second,we measured the near-field heat flux of highly doped silicon.In the near-field,in order to describe the light-matter interaction,it is essential to measure the near-field thermal radiation between high-quality,large-size samples with controllable losses.A self-assembled PS bead template was used to prepare the silicon nanowire array,and then the near-field and far-field heat flux were measured using a magnetically induced equipment.The sample area is 2×2 cm2,the gap is 500 nm and the temperature bias is 32 K.The measurement results are consistent with the theoretical results.The heat flux can reach 830 W/m-2,which is a significant increase of 4.7 times compared with the far field,verifying the effective medium theory(homogenization method)can be used in the near field to describe the the relative permittivity of silicon nanowire hyperbolic metamaterials and shows the significant enhancement effect of silicon nanowire on near-field thermal radiation.Third,the theoretical calculation of hyperbolic metamaterials can improve the performance of power and conversion efficiency of near-field TPV.At present,the cell of the near-field TPV is mainly a III-V semiconductor p-i-n layer,while the p-i-n radial core-shell structure has a large contribution to the current density due to its large p-n junction area,which can be compared with the device with W as the radiator and the InSb p-i-n layer as the cell.The result shows its thermoelectric power and conversion efficiency increased by 8.5 times and 4.5 times,the power can reach 1340 Wm-2,and the efficiency can reach 35.7%,which shows that due to the characteristics of hyperbolic metamaterials and the p-n junction large area,the heat flux and energy conversion efficiency of the thermophotovoltaic device can be significantly enhancedFinally,the theoretical calculation,experimental measurement and application of hyperbolic metamaterials in the near-field thermal radiation are summarized and prospected.