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Re: Speech sensors?



I have done a 'squealing wall' demo that reflects a laser beam from a wall
mounted mirror ALMOST directly back to the laser. Next toi the laser is a
photovoltaic cell, covered by a microscope slide, which reflects the beam back
to the wall mounted mirror and hence back into the laser cavity. (whew!)

Small motions of the wall create changing constructive and destructive
interference standing waves which produce a correspondingly changing current
produced by the solar cell. A small amplifier changes the solarcell output
into a squaeling sound.

Maybe this setup could be the 'eavesdropping' scheme referd to??