Abstract: Mechanical metamaterials derive their properties from an engineered
small-scale structure. By careful design of their microstructure, mechanical properties
can be engineered that are out of reach of natural materials, such as the ability to
guide, focus, and forbid elastic waves. This talk presents a framework for multiscale
modeling and inverse design of spatially graded metamaterials to manipulate elastic
waves. While metamaterials with periodic microstructures have been well studied,
spatial grading (which allows unit cells to smoothly vary in space) opens a vast but
largely unexplored design space. To explore this design space, ray theory is developed
for efficient modeling of dispersive elastic wave propagation, taking inspiration from
ray tracing formulations in optics and seismology. Based on ray tracing, two strategies
for inverse design are then presented. The first method utilizes conformal mappings to
create metamaterials with self-similar unit cells, which are shown to enable low-pass
filtering of elastic waves. The second method is an optimization framework that
enables steering and focusing of elastic waves. This work lays a foundation for the
design of functional metamaterials capable of vibration suppression, signal processing,
and energy harvesting.

BIO: Dr. Charlie Dorn is a postdoctoral fellow in the Department of Mechanical and Process
Engineering at ETH Zurich, where he researches elastic wave motion in mechanical
metamaterials. In 2021, he received his PhD in space engineering from the California Institute of
Technology, which focused on the mechanics and geometric design of origami-inspired
structures. He holds master’s degrees from Ecole Polytechnique and Caltech as well as a
bachelor’s degree from the University of Wisconsin-Madison.