Quantification of Two-Dimensional Acoustic Field Generated by a Surface Barrier Discharge With Fiber-Type Optical Wave Microphone Computer Tomography

Abstract

An optical wave microphone, which is well designed based on Fraunhofer diffraction of a laser beam, is expected to be applied to various acoustic fields where conventional microphones cannot be used due to strong electric and/or magnetic field. The authors have developed this technique and applied it to detect discharge sounds emitted from plasmas such as micro plasma, gliding arc plasma and plasma jet. An improved optical wave microphone with regard to signal-to-noise ratio uses single mode optical fibers for laser transformation. In this study, detailed characteristics of the fiber-type optical wave microphone were evaluated according to the theory of the optical wave microphone. Furthermore, the fiber-type optical wave microphone was combined with computer tomography (CT). The fiber-type optical wave microphone CT succeeded to visualize and quantify 2-D acoustic field generated by an ultrasonic transducer, and the obtained sound pressure distribution showed good similarity to that measured with a condenser microphone. Furthermore, the technique was applied to surface barrier discharge with different applied voltage frequencies and the distribution of acoustic waves above the discharge was quantified.