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 ...
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...)/(3r^4 (1-σ^2 )D(∂I/∂X))
The fundamental resonance frequency f of the graphene diaphragm can be expressed as
f=t/(2πr^2 ) √(E/(12ρ(1-σ^2)))
The microphone sensitivity is given by ∂X/∂P×∂I/∂X and the unit is W/Pa. The displacement sensitivity ∂I/∂X could be determined by the optical properties of fibers and need to be measured. From previous research, the measurement can be done by mounting fibers on a manually controlled micrometer translator and then placed close to a mirror mounted on a piezoelectric transducer.
Advantages and Discussion
The ultra-small thickness of graphene could significantly improve the pressure sensitivity of the FPI sensors. In addition, graphene has much better mechanical strength than other thin film materials including metal and silica and could bear a static pressure up to MPa.
Shadowing effects of the microphone.
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