Ultrasound generated by alternating current dielectric barrier discharge plasma in quiescent air

Dielectric barrier discharge (DBD) driven by Alternating Current (AC) high-voltage power supply, also called silent discharge, has been known for more than a century since Siemens first proposed the term DBD in 1857, and penetrates into our daily lives. In our traditional view, AC-DBD is considered as an ozone generator for disinfection, an electronic emitter for depollution of gas streams, a jet actuator for flow control, and so on. However, the acoustic effect of AC-DBD is always neglected. Here, we demonstrate that an asymmetrical DBD plasma actuator which was powered by sinusoidal AC waveforms with an AC voltage of 16 kVp-p at a high voltage frequency of a few kHz can generate ultrasound in quiescent air by using a pressure-field microphone and a high accuracy phase-lock image Schlieren technique. The frequency of this induced ultrasound is approximately 100 kHz which is much higher than the sin high voltage frequency of a few kHz. It is the first time that ultrasound created by the AC-DBD is observed. This finding provides a comprehensive understanding of AC-DBD and might open up possibilities for novel industrial applications of AC-DBD by using the induced ultrasonic energy. In addition, according to the experimental results, a hypothesis is proposed on the formation mechanism of ultrasound generated by the AC-DBD.