Can a Laser and Reflective Material Create a High-Frequency Microphone?

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A discussion on creating a high-frequency microphone using a laser and reflective material explores the potential of detecting frequencies up to 100 kHz. The idea involves bouncing a laser off reflective material, with methods including phase shift detection through pulse width modulation and Doppler shift analysis. Key considerations include the choice of material properties such as thickness, surface area, and tension, as well as the possibility of a resonant frequency. Participants share resources, including patents and examples of existing acoustic sensors and optical detectors. The feasibility of this approach for the desired frequency range remains a central question.
Raven Luni
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Greetings,

I've been looking for a way to create a microphone capable of picking up high frequencies (up to about 100kHz). Electrets don't tend to go that high and piezo crystals even detuned will only give a limited band.

I had the idea of bouncing a laser off a sheet of reflective material. The light can either be picked up directly, by pulsing the beam with a square wave and taking the phase shift as a form of pulse width modulation, or with a sine wave and using the doppler shift (I'll have fun experimenting with all these methods).

What I don't have any clue about is the material and what properties it should have. What kind of thickness, surface area, tension etc. would I need? Would there be a resonant frequency? Is it even possible for the frequency range in question?
 
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Raven Luni, Welcome to Physics Forums! 

You may see this patent, which detects acoustic frequencies up to 100 kHz:
http://www.google.com/patents/US5146083

Here is a ready-made acoustic sensor you may learn from:
http://www.digikey.com/us/en/techzone/sensors/resources/articles/ultrasonic-mems-sensor-spm0404ud5.html
 
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Excellent information - thanks :)
 

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