MAE 546 Final Project
Interferometry-based optical fiber microphone using graphene diaphragm
Introduction of conventional microphones and optical fiber microphone
Microphone is a kind of device which includes an acoustic-to-electric sensor that converts sound into electrical signals. Conventional microphones use the mechanism of electromagnetic induction (dynamic microphone) or capacitance change (condenser microphone). Microphones have a great many of applications in our daily lives such as telephones, hearing aids, engineering, radio and television broadcasting, speech recognition and so on.
Instead of sensing changes in capacitance or magnetic field as with conventional microphones, optical fiber microphone converts acoustic waves into electrical signals by sensing changes in light intensity. It can achieve a large dynamic and frequency range, compared to high fidelity conventional microphones. A great advantage of optical fiber microphone is no reacting to or influenced by any electrical, magnetic, electrostatic or radioactive fields. Therefore it is ideal for use in areas where conventional microphones are ineffective or dangerous, such as industrial turbines or magnetic resonance environment.
Also optical fiber microphone is resistant to environmental changes in temperature and humidity, and can be fabricated for any directionality. The distance between the microphone's light source and photodetector can be several kilometers without using any preamplifier or other electrical device, which makes optical fiber microphones suitable for industrial acoustic monitoring.
Possessing those qualities, optical fiber microphones are used in some specific applications such as infrasound monitoring and noise-canceling. They have been proven especially useful in medical applications like normal communication among staff working under noisy magnetic field. Other applications include industrial equipment monitoring and sensing, audio calibration and measurement, high-fidelity recording and so on.
Sensors in microphones application
Microphones are generally consist of acoustic pressure sensors. They are fabricated for the measurement of very small variations of pressure around the atmosphere. Microphones convert acoustical waves into electrical signals. The most common microphone, condenser microphone, operates basing on a capacitive design. It uses basic transduction principles and converts the acoustic pressure to capacitance variations, which are then transformed to an electrical voltage. This is achieved by taking a small thin diaphragm and mounting it a small distance away from a stationary metal plate. A voltage is applied to the metal plate to form a capacitor. Under oscillating acoustic pressure, the diaphragm has a displacement which changes the gap between the diaphragm and the metal plate. This produces an oscillating voltage from the capacitor, proportional to the pressure oscillation.
Instrumentation microphones can operate...