Visualization of electrical discharge sound of the atmospheric pressure plasma with optical wave microphone on phenomenon clarification

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The novel method, which we call the "Optical Wave Microphone (OWM)" technique, is based on a Fraunhofer diffraction effect between sound wave and laser beam. This new method can realize high accuracy measurement of slight density change of atmosphere. In this work, coplanar dielectric barrier discharges in different gases was characterized via the OWM. The following results were obtained. (1) OWM picked up the ultrasonic wave, which condenser microphone could not detect, emitted from the discharge. (2) The change of the frequency components and intensity of discharge sound were investigated by the difference in atmosphere gas such as Air, Helium, Argon and Nitrogen. The intensity of discharge sound was increased as the molecular weight of atmosphere gas became large. (3) OWM could be applied for the visualization of sound field by Computerized Tomography (CT) method. Visualization of the two-dimensional sound field for the discharges showed quite different gas dependency.