Y. C. Sutton

Looking Into a Plasma Loudspeaker

A 325-kHz atmospheric discharge can be modulated at audio frequencies so that it acts as a loudspeaker by direct electroacoustic coupling, without any electromechanical components. In exploring the details of the mechanism, it has been useful to visualize the heated gas within and around the discharge plume using Schlieren techniques. This has enabled a 2-D reconstruction of the translational temperature of the neutral gas (up to 2500 K) that complements spectroscopic measurements of rotational and vibrational temperatures (up to 2700 K) in the luminous region.

A numerical and experimental investigation of an axially symmetric RF plasma

The characteristics of an atmospheric pressure, RF discharge in air were determined and compared with a 2D numerical model adapted from that used for a dc glow discharge. For a 15 mm discharge, the RF plasmas electrical and optical characteristics show a close correlation to several equivalent dc plasmas and to the results calculated from the adapted model. For an rms conduction current range of 11–30 mA, the rotational temperature varies between 2800 and 3200 K; the vibrational temperature shows a change of 3500–4000 K with near equilibrium conditions to the rotational state occuring in the central region of the discharge. Spatial measurements and modelling of nitrogen emission spectra identify the changes in the temperatures and dimensions along the vertical z-axis as well as the spatial dependence on the atomic and molecular species generated in the discharge.