Hello, all.
I'm a newbie here. The reason I joined is to gather feedback on the microphone design I've been working on. The new thing about it is that a moving stream of smoke or fog is used to replace the diaphragm or plate found in every other microphone. A laser beam penetrates the stream at a 90-degree angle and is received by a very fast PIN-type photocell (2 nanosecond rise time, 1.5 MHz bandwidth).
Sound pressure waves cause microscopic variations in the smoke stream, which scatter the laser beam. That scattering modulates the beam and the photocell's absorption to create an analog signal representing the original sound waves.
The U.S. patent, 7580533 can be downloaded for free from www.uspto.gov.
The audio quality of the first prototype is poor. I'm just happy it demonstrates the theory of operation. The next protos should be better. Since the smoke stream is very low mass and non-reactive, physically, this transducer has the potential to be sensitive and wide-band.
Cheers,
Dave
PS. Some very rudimentary models of the device are shown in YouTube clips. One of them is here:
Smoke n Laser Mic