Interforometry-Based Optical Fibe Microphone Using Graphene Diaphragm

MAE 546 Final Project Interferometric fiber microphones using graphene diaphragms Introduction Microphones and fiber optic microphones Introduction Microphones are devices that contain acoustic electronic sensors that convert sound into electrical signals. Conventional microphones use a mechanism of electromagnetic induction (dynamic microphone) or capacitance change (capacitive microphone). Microphones have many uses in our daily life, such as telephones, hearing aids, engineering, radio and television broadcasting, speech recognition, etc.

Recently, some companies are interested in using graphene film for speakers and microphones. In May 2017, Apple received a detailed new patent (submitted in 2015) on audio devices using diaphragms made of graphene reinforced composite material. Apple graphene film can be used for speaker, microphone, or headphone device.

Record sounds and music using the microphone. The most common type is a moving or moving microphone. A device with a diaphragm attaches a small movable induction coil within the magnetic field of the permanent magnet. When the sound enters the microphone, the diaphragm moves with the acoustic wave, which causes the coil to move in the magnetic field. This motion generates a current that changes to the coil, thereby converting the sound waves into electric pulses. The current from the microphone is recorded after being amplified. During playback, the process is reversed. The electrical signal is amplified from the recording medium and then played through the speaker. And it is a fairly large version of a microphone with a tapered moving coil

It is also possible to move the coil around the magnet with varying frequency and amplitude patterns to induce current in the coil. This is the basis of many devices, especially microphones. When the pressure wave changes, the sound moves the diaphragm outward. If the diaphragm is connected to a movable magnetic coil surrounding the core, it produces a changing current as well as incident sound waves. The electrical signal can then be amplified, recorded, or transmitted as required. Marsh told Live Science that small ultra rare earth magnets are currently being used to manufacture small microphones for mobile phones.

MEMS microphones usually consist of a fixed back plate and a movable diaphragm. When sound is generated, the movable diaphragm is deformed by the sound pressure, thereby changing the gap (and the capacitance) between the surface and the back plate. Next, the capacitance change is measured and converted to an electrical signal by the digital ASIC. This electrical signal represents sound. Since the gap between the diaphragm and the backplane is important for the operation of capacitive MEMS microphones, it can also lead to many failure modes. The following figure shows several failure modes. 1) normal, 2) dust / particle damage, 3) water intrusion, 4) static friction fracture