Audio reproduction with atmospheric pressure plasmas: Surface discharge device Hugh Potts, Declan...
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Transcript of Audio reproduction with atmospheric pressure plasmas: Surface discharge device Hugh Potts, Declan...
Audio reproduction with atmospheric pressure plasmas:
Surface discharge device
Hugh Potts, Declan Diver
University of Glasgow
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?
History
Demonstrated 1800’s
First patent 1924
First practical device 1946: Siegfried Klein
The IONOPHONE
History
Demonstrated 1800’s
First patent 1924
First practical device 1946: Siegfried Klein
The IONOPHONE
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. “
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/m2
Physics
• How much heating is required
• What amplitude is required?
• Imagine heating 0.1mm slab, scale by 1/r^2
• results
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
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…
100mmdiam
Planar discharge at 30kHz
Air 90% Argon
Performance
• Early prototype• 100mm diam• Excellent frequency
response <100Hz - >>20kHz
• Potentially efficient• Low temperature,
hence ozone production a problem