Flavia Guarracino, Ph.D. Candidate 37th cycle, University of Trento, DICAM

The Ph.D. project aims at finding new ways of guiding waves or shielding from different frequencies through mechanical properties of micro-structured, hierarchically organized, and “architectured” materials, namely metamaterials, as well as conceiving ad hoc tools and strategies for predicting the characteristics they must own for this to happen.
In order to achieve the proposed aims some kinds of tunable metamaterials will be developed and investigated, which should react to changes in their environment, through zero-energy mechanisms or by changing their stiffness, and thus the frequency at which they disperse or enhance vibrations. These artificial materials should be able to respond mechanically as opposed to classical technological methods, which rely on electricity to change their properties.
The application possibilities are multifold, from industrial sectors, such as information and communication technologies, and space, to those involving health, energy and environmental areas.

The present research focus is on discrete structures of masses and springs, first in 1D and afterward as a 2D or 3D lattice, with nonlocal connections and nonlocal effects in dynamics. It is known from the classical Bloch theorem that the sole properties of the unit cell yield information for the dynamical behavior of the whole chain, through its dispersion relation, which relates the wavenumber of a wave to its frequency. The band diagrams will be tailored in order to obtain nontrivial dispersion relations and tune them to be able to respond to changes in its environment by closing or widening band gaps, specifically responding to dynamical perturbations at both the micro- and the macroscale.

The metamaterial design will be investigated at multiple scales to test the cross-properties that can emerge from single units and assembled large lattices with a unit cell with architectured properties, and by mingling more than one cell design with each other. In doing this, the possibility of gaining advantages from a design of specific hierarchical micro-architectures, including parts with higher deformability or capable to react to thermal and multi-physical stimuli, will be explored.

At the present state, a 1D analytical model is studied, in order to observe the fundamental properties of the unit cell of a chain with n springs between masses, from the nearest to farther ones, when varying the connections and their stiffness.  Both the dispersion relation of the unit cell and the frequency response to time-dependent stimuli of the chain are examined, and the variations in response due to tweaking masses and stiffness distributions in the model are interpreted.