Joint sensing methods to reconstruct acoustic fields over space

Optical interferometry makes it possible to measure acoustic fields, by exploiting the acousto-optic interaction, without using microphones or other electroacoustic transducers. Scanning interferometers can sample a sound field with high spatial resolution in an automated way. Therefore, optical interferometry is particularly suitable for measuring sound fields over space at mid and high frequencies, where sampling requirements make the use of microphones demanding and costly. However, optical methods are sensitive to vibrations of the equipment that biases the measurements, especially at low frequencies. In this study we propose a joint sensing approach that combines data acquired with conventional microphones as well as with an optical interferometer. The robustness and qualitative accuracy at low frequencies is improved due to the microphone data, whereas the sound field at higher frequencies is successfully captured over space with the scanning interferometer. In an experimental study, a three dimensional acoustic field is sampled combining the two sensing methods. The results show that the frequency range in which the reconstruction is correct is extended using the joint microphone-interferometer measurements.