Hopping Harmonics and Entangled Wave Patterns: Adaptivity and Functionality Boosting in Metamaterial Architectures

Mechanical and Aerospace Engineering Department Seminar Series

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Stefano Gonella
Department of Civil, Environmental, and Geo- Engineering
University of Minnesota

Mechanical metamaterials and phononic crystals are examples of architected materials that owe their unique dynamic properties to an intelligent topogical arrangement of their internal network of constitutive elements. These material systems display a variety of exotic wave manipulation properties, which include the formation of bandgaps, frequency-dependent wave anisotropy, waveguiding and cloaking. One of the main challenges in the design of metamaterial systems is endowing them with tunable and adaptive capabilities. Tunability is the ability to modify a system's response through the control of some external parameters, in order to tune it to evolving operating conditions. A system displays adaptivity when it can spontaneously modify its response in reaction to sensed changes in the characteristics of the applied excitation. These properties provide versatility and grant the material the possibility to work far from the ideal design point. The opportunities are especially broad in the realm of wave control, in light of the inherent ability of metamaterial architectures to experience directional (anisotropic) wave propagation. In this context, tunability implies being able to switch on and off certain directional wave characteristics and to control the pattern of the wave paths along which the energy travels in the solid. It also allows augmenting the range of functionalities that it is possible to activate by exciting the system at a given frequency.
This presentation provides an overview of the wave manipulation capabilities of mechanical metamaterials and phononic crystals and introduces a strategy for tunability and adaptivity that exploits the nonlinearity is the system’s response as the main tuning mechanism. The idea is based on a new outlook on the phenomenon of higher harmonic generation, which is revisited in the context of periodic structures characterized by pronounced modal complexity. We show how, by simply, playing with the amplitude of excitation, it is possible to switch on new features in the nonlinear wave response, thus augmenting the wave directivity landscape and enhancing the overall functionalities of the medium.

Biosketch
Stefano Gonella received Ph.D. and M.S. degrees in aerospace engineering from the Georgia Institute of Technology in 2007 and 2005, respectively. Previously, he received a Laurea, also in aerospace engineering, from the Politecnico di Torino, Italy, in 2003. He joined the faculty of the Department of Civil, Environmental, and Geo- Engineering at the University of Minnesota in 2010, after 3 years of post-doctoral and teaching experience at Northwestern University. His main research interests revolve around the modeling and simulation of complex wave phenomena in unconventional structures and materials, with emphasis on cellular solids, phononic crystals and acoustic metamaterials. He is also interested in the development of new methodologies for structural and material diagnostics through the mechanistic adaptation of concepts of machine learning and computer vision.