In sci.physics Helpful person wrote:
On Apr 21, 10:10Â*am, Helpful person wrote:
On Apr 20, 7:48Â*pm, RichD wrote:
Acoustic imagery is exactly analogous to light imagery except that
having longitudinal waves there is no polarization affect.
The long wavelength makes diffraction much more dominant that for
light. Â*Materials also have much greater dispersion over audible
frequencies.
Lenses tend to be difficult to demonstrate compared to mirrors due to
the large impedance mismatch to air. Â*However, for a very limited
bandwidth an interested demonstrator could easily be made using layers
of less dense materials to build up an anti reflection coating. Â*This
should not be too difficult due to the long wavelengths involved.
This is a demonstration I've always wanted to make but never had the
time.
http://richardfisher.com/
This thread has got me interested again about acoustic lenses. Does
anyone here have a source for speed and dispersion of sound in common
materials? It seems to me that liquids (and metals) are of most
interest as neither are very lossy. (Hardwood may also be a cool
material to use.)
By the way, the intensity (or volume) of imaged sound is solely
dependent on the NA, just as in light.
http://richardfisher.com/
One little problem in all this is the human body doesn't have a senor that
can process imaged sound, only imaged light.
Nor is there anything that I know of analogous to photographic film for an
audio image.
Which leaves building something like a solid state video camera for audio.
One could build a 32X32 pixel audio imager with 1,024 cheap microphones
like these for $0.27 in quanties of 1,000:
http://www.mouser.com/catalog/specsheets/KT-400332.pdf
Follow those with a little amplification/buffering, a switch matrix, and
dump the output into a PC sound card with appropriate software.
And voila, you have an audio imager.
--
Jim Pennino
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