Heat Transfer And Microwave Transmission Characteristics Of Biomimetic Structures Derived From Saharan Sliver Ants

Proper selections of suitable materials for thermal managements play key roles in orbit operations of space crafts.Currently,white paint and germanium-coated polyimide are common choices for thermal controls,which have poor temporal and spatial stability.And they have been extensively studied from the perspective of material compositions,leaving the effects of surface topographies at the micro-nano scale unaddressed.Inspired by Saharan silver ants relying on micro-nano structures of hairs for heat protection and dissipation,in this paper,based on the material with superior temporal and spatial stability and wave transmission characteristic,thermal control characteristics were obtained by adjusting its structure.Based on the method of finite element simulation and experiment,thermal characteristics(spectral characteristics and thermal conductive characteristics)and microwave transmission characteristics were studied and compared.For the study of spectral characteristics of the Saharan sliver ant biomimetic structures,in this paper,based on finite element simulation,spectral characteristics(e.g.,solar absorptance and infrared emissivity)of three types of biomimetic micro-nano structures(e.g.,including pyramid,tetrahedron,and triangular prism)were studied and compared.Simulation results revealed that spectral characteristics of these biomimetic micro-nano structures were mainly regulated by the tip height and the air gap where a decrease of the tip height and an increase of the air gap lead to a decrease in the solar absorptance and an increase in the infrared emissivity.When these biomimetic structures were compared with flat surfaces without micro-nano topographies,significant improvements in thermal managements(e.g.,a decrease of the solar absorptance to block the incidence of heat flow from the sun and an increase of the infrared emissivity to dissipate its own heat to the space)were located.For the study of thermal conductive characteristics of the Saharan sliver ant biomimetic structures,in this paper,numerical simulations of the glass/polyimide composite material were conducted to determine its effective thermal conductivity under the conduction condition with and without radiation.More specifically,unit cell models of polyimide matrix,glass-fiber yarns,and the composite materials were constructed sequentially to study the effects of the porosity and fiber volume fraction on the effective thermal conductivity of the composite materials.Simulation results revealed that an increase in porosity can reduce the effective thermal conductivity of the polyimide matrix with the maximal decreasing ratio of 39.5%.An increase in fiber volume fraction can increase the transverse effective thermal conductivity of the glass-fiber yarns with the maximal increasing ratio of 48.8%.Differences of 16.4%and 16.6% of the in-plane and out-of-plane effective thermal conductivities of the composite material were located under the conduction condition with and without radiation.For the study of microwave transmission characteristics of the Saharan sliver ant biomimetic structures,transmissivities of the glass fiber/polyimide composite material and the glass fabric were studied based on the finite element simulation method.The transmissivity curves of the glass fiber/polyimide composite material and the glass fabric were nearly identical in the frequency range of 1GHz-51 GHz.Therefore,the glass fiber cloth was used to replace the glass fiber/polyimide composite material in the experimental measurement,and its influence on the gain and the return loss of the antenna were measured.The experimental results showed that the glass fabric had little effect on the gain of the antenna and did not affect the transmission of microwave signals.The glass fabric and the polyimide film had little impact on the transmission efficiency of the horizontally polarized antenna.The influence of the polyimide film on the vertically polarized antenna was less than the glass fabric.The Saharan sliver ant biomimetic structures were tentatively deduced that there had little effect on the transmission of microwave detection system.In conclusion,this study provided guidance for further engineering and applications of the Saharan sliver ant biomimetic structures in the spacecraft with microwave detection equipment.This structure extended ranges of structures and materials for thermal control surface units of spacecrafts.It had potential benefits for the microwave transmission,the heat protection,the heat dissipation and the resistance to damage caused by radiation.