1. Audio reproduction with atmospheric pressure plasmas: Surface discharge device Hugh Potts, Declan Diver University of Glasgow

2. Why plasma? No moving mass –No resonances, smooth response –No upper frequency limit (CD 20kHz, SACD 100kHz) Looks nice Inefficient for low frequencies Complex, dangerous Ozone! *Although inaudible, has a significant effect on the perception of sound – shown in EEG brain measures (26-60kHz) Why not?

3. History Demonstrated 1800’s First patent 1924 First practical device 1946: Siegfried Klein The IONOPHONE

4. History Demonstrated 1800’s First patent 1924 First practical device 1946: Siegfried Klein The IONOPHONE

5. History Demonstrated 1800’s First patent 1924 First practical device “…after prolonged music-listening we felt some slight irritation of the skin in the auditory canal affected by the partially ionized air. “

6. Why does it work? Two main methods of sound production –Ion-wind coupling to neutral gas Poor efficiency, quantify –Heating Thermal expansion drives pressure waves Tiny amplitued required: Normal speech 0.002- 0.02 Pa pressure amplitude - only 4nm amplitude! Heat a 0.1mm slab of air: 0.01K, 0.4 W/m 2

7. Physics How much heating is required What amplitude is required? Imagine heating 0.1mm slab, scale by 1/r^2 results

8. Modern developments Atmospheric pressure plasma arc 317 kHz resonant frequency (drawing ~1.2A) 2D isotropic acoustic radiator measured acoustically over the frequency range 1-10 kHz N.S. Braithwaite, Y.Sutton, Open University

9. Planar discharge Surface DBD discharge Electrode configuration optimised using 3D finite difference iterative solver to produce the most even discharge possible. Praps a picture of the discharge in Argon OZONE! Oh dear oh dear…

10. 100mm diam Planar discharge at 30kHz Air 90% Argon

11. Performance Early prototype 100mm diam Excellent frequency response >20kHz Potentially efficient Low temperature, hence ozone production a problem