Abstract
Micromachined fluid filled variable impedance waveguides intended to mimic the mechanics of the passive cochlea have been fabricated and experimentally examined. These devices consist of a fluid filled chamber of dimension 37 mm by 6.25 mm by 0.1 mm fabricated on a pyrex wafer. One side of this chamber is constrained by a 3-cm-long, exponentially tapered, 0.3-μm thick tensioned membrane made of low-pressure chemical vapor deposited (LPCVD) silicon nitride. The membranes vary in width from 170 μm to 1.9 mm, and are fabricated using deep reactive ion etching (DRIE). The devices are filled with silicone oil or de-ionized water. Experimental tests demonstrate acoustically excited traveling fluid-structure waves with wave numbers well below the free-plane wave wave number, and with phase accumulations as high as 25 rad (at 6.5 kHz) in the 3 cm length of the device. Comparison of experimental measurements with both numerical (finite-element) and asymptotic (Liouville–Green) models assist in understanding the results. A thin-layer finite-element approximation is developed to take advantage of the device aspect ratio and increase computational efficiency. Viscous fluid effects are included in the models to accurately capture damping phenomena. [Work supported by ONR and NSF.]
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