Cantilever-based acoustic velocity sensors

This paper discusses progress made on the design of an acoustic velocity sensor. An analytic model was developed for the frequency response of a slender cantilever rod forced by the pressure gradient and particle velocity associated with an acoustic wave propagating in a fluid. The model, validated with acoustic response measurements in air, was used to design cantilever sensors, which respond predominately to acoustic particle velocity. One such design utilizes a short cantilever formed from a 125 μm silica glass fiber immersed in a viscous fill fluid whose lateral tip displacement is detected using a multi-fiber optical probe. This velocity sensor is predicted to be able to detect fairly low acoustic sound levels in water. Progress has been made in instrumenting a large pool at NRL to allow accurate propagating acoustic wave response measurements in water of these new velocity sensors down to frequencies below 5 Hz. Measurements made in this facility on various cantilever sensors will be presented and discussed. [Work supported by ONR.]