Experimental Investigation on Propagation Characteristics of Low-Frequency Electromagnetic Waves in Dynamic Slab Plasmas

Low-frequency (LF) electromagnetic (EM) wave has long been recognized as a potential solution to overcome communication blackout of near-space vehicles. In this letter, an experimental investigation on LF propagation in plasmas was conducted using a high-enthalpy shock tunnel. The study presents the first experimental observation of LF propagation in a dynamic slab shock-layer plasma, thereby validating the applicability of the equivalent transmission line theory under such plasma. The variation law of LF attenuation with plasma parameters and operating frequency was explained from the perspective of reflection loss. Using the radio attenuation measurement for communications (RAMC) vehicle flow field as a case, we analyzed LF operability relative to window placement locations. Results indicate that the cone's nose region, with its thinner plasma sheath and lower absorption loss, can serve as an effective antenna window for 7MHz and 14MHz. For 1MHz, the lower reflection and absorption losses permit antenna installation along the conical body section. This study provides theoretical and experimental foundations for designing emergency communication systems for blackout zones.