Locally resonant sonic materials exhibit strong sound attenuation bands in the audible frequency range due to resonance scattering of elastic waves. We compare the results of a finite element modal analysis of a single resonant unit with sound attenuation spectra obtained from wave propagation simulations based on the local interaction simulation approach. The modal analysis yields a complete prediction of all resonance modes including information on node locations, mode degeneration, and modes that do not attenuate sound due to geometrical symmetries. Elliptical instead of circular inclusions break the geometric symmetry of the resonators, splitting the attenuation peak of degenerate modes into separate peaks. A small frequency shift is observed between the resonance frequencies and the frequencies of maximum sound attenuation, due to the asymmetric shape of the attenuation peaks and interference between resonance scattering and free propagating waves.
We have developed a new multifunctional structure battery material that replaces unifunctional structure in a micro-air vehicle (MAV) for the purposes of increasing the flight time endurance. Multiple layers of thin plastic lithiumion bicell battery material were combined with packaging and used as wing-skin in a developmental multifunctional MAV named WASP. This WASP vehicle has successfully demonstrated 107-minutes of continuous flight. Endurance flight time increases of ∼26% are predicted for multifunctional designs using the best available (highest specific energy) battery material as wing-skin.
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