Nonlinear Acoustic Meta-Materials for Wave Propagation Management and Control

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The research explores nonlinear phononic behavior in periodic meta-materials, with the intent of enabling the development of low-power wave-based devices with novel functionality, enhanced performance, and adaptive tunability. Phononic meta-materials with periodic microstructures exhibit extraordinary wave properties such as band-gaps, response directionality, left-handedness, and negative acoustic refraction, all of which can be employed for the design of acoustic devices operating over a broad range of frequencies and length scales. As devices miniaturize, nonlinear behavior becomes the norm and not the exception, as witnessed in part by the complex potentials used to describe small-scale interactions. This research investigates the effects of nonlinearities on dispersion characteristics, band-gaps, and directionality and specifically explores nonlinearities as means to achieve novel functionalities that enrich the design space of periodic media. Stiffening and softening effects, normal versus shear modes of response, amplitude-dependent dispersion, and the presence of super- and sub-harmonics may in fact positively affect the wave guiding characteristics of a given medium and may be exploited to achieve tunability of the wave properties. Analytical and computational techniques will be formulated to investigate the nature of nonlinearities in nonlinear phononic systems, and to predict their wave mechanics effects.The developed tools will enable the design of tunable pass-band filters with controllable bandwidth and of acoustic meta-materials capable of directing and focusing the acoustic energy towards specific directions. The application of these concepts to filters, waveguides, logic ports, and ultrasonic transducer arrays which perform a variety of acoustics-based signal processing functions is very attractive particularly at frequencies where electronics suffer from severe power limitations. The project is expected to significantly advance knowledge and understanding in the general area of nonlinear meta-material wave mechanics, which will be important for the development of high-frequency, tunable devices for use in communication systems (mobile phones, GPS units, etc.), noise isolation, energy-directing materials, tunable ultrasound for medical devices, tunable acoustic microphones and receivers, and acoustic beamformers.