Bio-inspired ultra-sensitive directional acoustic flow sensing using electro-spun nanofiber mesh over a close-back cavity

Nearly two decades ago, it is shown that the mechanically coupled tympanic membrane ear of the Ormia fly can detect directional sound from a distance [1]. It achieves that by sensing the pressure gradient across the two coupled membranes. The recently discovered acoustic flow sensing using spider silk [2], opens new perspectives in acoustic sensing of particle velocity. Here we demonstrate an ultra-sensitive directional sensing scheme using a nanofiber mesh that is uniformly placed over the surface of a close back micro cavity. The nanofiber mesh can capture sound-induced velocity fluctuation well enough to represent the acoustic air particle velocity. Our result shows that the uniform sound field, which travels parallel to the fiber mesh plane, can drive the fiber mesh in and out of the cavity underneath. Since the small size of the cavity makes the air inside incompressible, the front and rear sides of the fiber mesh will move out of phase, much like the directional ear of the Ormia fly. By sensing acoustic air particle velocity and adopting the practical design of a back volume, this work provides a new approach for ultra-sensitive directional acoustic sensing. [1] R. N. Miles, D. Robert, and R. R. Hoy, “Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea,” JASA, 98(6), 3059–3070 (1995). [2] J. Zhou and R. N. Miles, “Sensing fluctuating airflow with spider silk,” Proc. Natl. Acad. Sci. U. S. A. 114(46), 12120–12125 (2017).