Propagation Characteristics of the THz Wave in Plasma Sheath Under the Conditions of Ablation of Thermal Protection Materials

Abstract

The ablation of thermal protection materials during the re-entry of a hypersonic vehicle alters plasma sheath characteristics, significantly affecting the vehicle’s communication performance. Terahertz (THz) technology emerges as one of the effective potential solutions for overcoming the high electron density encountered during the traditional re-entry blackout period. This article investigates the transmission characteristics of THz waves in the plasma sheath under two typical ablation conditions: phenolic graphite and Teflon, considering the effects of alkali metal impurities and the mass fraction of ablation products. Our results show that the total alkali metal content significantly increases the electron number density, with peak electron densities about an order of magnitude higher than those of Teflon. The collision frequency in phenolic graphite material varies nonlinearly due to differences in ablation product mass fractions and exhibits trends opposite to those of Teflon with altitude, with maximum deviations exceeding 50 GHz. Propagation attenuation analysis indicates that the minimum frequency of EM waves should be above 0.13 THz to mitigate the impact of alkali metal content on communication quality. In practical applications, selecting materials with low alkali metal content proves effective, allowing communication frequencies to be reduced to as low as 0.03 THz with Teflon to meet communication demands.