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

我们称之为“光波麦克风（OWM）”技术的新方法是基于声波和激光束之间的夫琅和费衍射效应。该方法可实现对大气密度微小变化的高精度测量。在这项工作中，共面介质阻挡放电在不同的气体通过OWM的特点。获得了以下结果。(1)OWM拾取了从放电中发出的超声波，电容式麦克风无法检测到。(2)研究了不同气氛气体（空气、氦气、氩气和氮气）对放电声频率成分和强度的影响。随着气氛气体分子量的增大，放电声的强度增大。(3)OWM可用于计算机断层成像（CT）方法的声场可视化。放电的二维声场的可视化显示出完全不同的气体依赖性。

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.