It is common to measure the response of devices and structures to sound due to an imposed sound source. Unfortunately, acoustic reflections from walls and/or instruments often contaminate the results. In this presentation, methods of acoustic characterization are described to minimize the influence of acoustic reflections. It is shown that this process results in clean and smooth data. A simple time-domain window is implemented for diminishing the contribution from reflection waves. Moreover, a single frequency curve fitting approach is employed for better parameter identification and noise reduction, compared to traditional fast Fourier Transform analysis. Results obtained from a theoretical acoustic model with a reflection source are compared with measured results. Different cases of data acquisition with time and frequency analysis are experimentally demonstrated and validated. All experimental measurements are performed in an anechoic chamber. Results show that the approach presented here significantly reduces noise and also the influences of reflection waves in experimental data acquisition outcomes.
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).
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