Optical Wave Microphone Measurements for Understanding the Mechanism of Acoustic Emission From Atmospheric Plasma Jet

The author has developed and utilized a unique optical technique called an optical wave microphone to detect pressure waves including acoustic waves emitted from a plasma jet. In previous studies regarding a dielectric barrier plasma jet, acoustic waves were successfully detected with the optical wave microphone and their spatial distribution and frequency property were reported. In this paper, the author aimed to reveal the mechanism of the acoustic wave formation. To achieve the purpose, the helium plasma jet was operated by a single pulse of sinusoidal applied voltage to distinguish acoustic waves originated from each pulsed discharge and evaluate frequency and polarity dependencies. The mechanism of shockwaves formation at the moment of plasma generation was analyzed by changing the frequency of the applied voltage. The gas flow rate and measurement position dependence on the frequency property of detected optical wave microphone waveforms were investigated. Finally, a continuous acoustic emission was realized by synchronizing the specific frequency of the acoustic waves and the applied voltage frequency.