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theses

This thesis describes a parabolic acoustic reflector with an inflatable reflecting surface, which has tunable gain and directivity. Conventional parabolic reflectors focus and amplify sound waves using metallic or plastic dishes with fixed geometries. This work presents a morphable reflecting surface that deforms into a concave structure to provide polar response and tunable gain considering the deformed geometry of the reflector. The deformable concave structure was a silicone elastomer (Ecoflex 00-10) with a coefficient of reflection approximately 0.9. This reflective coefficient suggests these silicone-based elastomers serve as reflective substrates for advanced morphable devices to manipulate sound. We experimentally determined the Youngs Modulus and the radial displacement achieved during pre-stressing the membrane over the aluminum reflector. For our parabolic reflector, acoustic gain and directionality depended on the level of vacuum applied to the elastomeric membranes, which affected the curvature of the paraboloid. Experiments performed in closed and open environments, along with simulations, demonstrate that the soft reflective surface was capable of transformation into a set of desired parabolic shapes between an initial planar geometry (neutral position) and configurations with varying curvature. The magnitude of the acoustic power gain obtained for vacuums below -1.7 kPa at frequencies greater than 7 kHz was comparable with gains of commercially available reflectors, and the directional response of the reflector was super hyper cardioid in nature. The maximum gain was also ~17 dB at 8.5 kHz. Simulations coupling mechanical deformation with acoustic shells agreed qualitatively with experimental results. These systems might find future uses for adjustable parabolic microphones, long-range communication devices, and tracking of sound sources.

ETD_8618

M.S.

Includes bibliographical references

by Saurabh Apte

doi:10.7282/T34M97RQ

ETD graduate

The author owns the copyright to this work.