Difference analysis in terahertz wave propagation in thermochemical nonequilibrium plasma sheath under different hypersonic vehicle shapes

Research on terahertz communication under different vehicles has important guiding significance for the design of future hypersonic vehicle and Radio Frequency(RF) blackout. In this paper, a joint simulation model of plasma flow under thermochemical nonequilibrium state and terahertz transmission is developed to investigate the differences in terahertz wave transmission characteristics under different vehicle shapes and the related mechanisms. By comparing the plasma sheath characteristics and terahertz transmission among HIFIRE-5b(Hypersonic International Flight Research Experimentation-5b), RAM C(Radio Attenuation Measurement C) and ARD(Atmospheric Reentry Demonstrator) vehicles, it is found that the sheath thickness and electron density of ARD vehicles is significantly larger than that of HIFIRE-5b and RAM C vehicles, resulting in greater terahertz wave attenuation. Collision absorption plays a major role in the terahertz attenuation of vehicles, and the contribution of reflection effects is only observed in the ARD vehicle due to its larger plasma sheath thickness and spatial structure variation. Based on the above comparison results, a shape design scheme of reducing the vehicle head and tail for mitigating RF blackout is proposed, and the scheme is proved by further analyzing the effects of different vehicle heads and tails on the terahertz communication. With the decrease of the head radius and tail width of hypersonic vehicle, the wave attenuation at the same terahertz frequency decreases, and the contribution of reflection effect to wave attenuation gradually disappears. Therefore, the shape design scheme of reducing the vehicle head and tail can effectively alleviate the RF blackout problem, which provides an important reference value for future hypersonic vehicle design.