Sound Attenuation by Glow Discharge Plasma

摘要

A unique method of blocking sound waves using a glow discharge plasma sheet was demonstrated experimentally. The main thrust of the investigation was the determination of the effectiveness of using glow discharge plasma as a sound barrier in aerospace applications. Experiments were conducted in an anechoic chamber where the attenuation of single-frequency (12.5-kHz) sound propagating through a plasma sheet formed between two electrodes was studied. The sound attenuation was measured at different locations inside the chamber with the discharge plane oriented normal to the direction of sound-wave propagation. Some measurements were also carried out with the plasma plane oriented 45 deg to the sound-wave propagation direction. The measurements clearly demonstrated that the plasma attenuates sound. The highest attenuation of about 23 dB was obtained when the plasma was oriented 45 deg to the sound propagation direction. In this configuration, sound reflection from the glow discharge region was also observed. The present results suggest that the dominant mechanism responsible for the sound attenuation is the change in the index of refraction caused by gas temperature gradient at the plasma boundaries.