Application of Fiber-Optical Microphone for Thermo-Acoustic Measurements

Abstract

A high temperature resistant fiber-optical microphone (FOM) was developed and successfully applied in a combustion chamber at a thermal power of 8.4 kW to measure thermo-acoustic oscillations at a frequency of 85 Hz and a sound pressure level of 154 dB. The sensor head temperature was estimated to ∼1000 K. The core of the optical setup used for the FOM is a Fabry–Perot interferometer. To create an acoustical sensor based on this type of interferometer, a new method of generation and postprocessing of the interference signal was developed. The simple replaceability of the sensor membrane reduces the requirements concerning the sensor handling compared with conventional condenser microphones and allows the adaptation of the sensor sensitivity to its application case changing the membrane stiffness.