In contrast to the conventional microphone with a moving diagram, this study explores the use of plasmas to create a diaphragmless ionic microphone. By performing FM demodulation of the shift in oscillating frequency of a high-temperature plasma, a useful audio signal was obtained. Increased output levels were observed with a decrease in the sound wave frequency. It was difficult to maintain consistent performance because the discharges in the air led to wearing of the electrode tip as well as adhesions of the discharge products. Results showed that the stability of the discharge corresponded to the nonuniform electric field, which was dependent on the formation shape of the high-temperature plasma, the shape of the discharge electrode, and the use of inert gas to protect the needle electrode. The authors review the experimental outcome of two ionic methods.
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