Writing Dispersion Curves and Breaking Reciprocity with Nonlocal Acoustic Metamaterials

ABSTRACT

Metamaterials are engineered structures whose exotic effective properties arise from a repeated sub-wavelength unit cell. In acoustics, metamaterials have enabled novel methods for controlling sound and vibration, including the creation of band gaps for broadband vibration attenuation. However, most existing designs rely on locally interacting unit cells, in which the force exerted by a unit cell depends only on its own deformation and that of its immediate neighbors. This locality constrains metamaterials to frequency-dependent effective properties, limiting the ability to realize arbitrary dispersion relations. Moreover, breaking reciprocity in such systems requires nonlinearities or time-varying material properties, both of which introduce significant complexity. To overcome these limitations, this talk presents our recent work on nonlocal metamaterials, which incorporate interactions between distant unit cells. First, I will demonstrate how nonlocal interactions enable the inversion of arbitrary nonreciprocal dispersion curves, allowing us to “write” dispersion relations to match any desired specification. By regularizing the inversion, we can generate nonlocal lattice designs with reduced complexity, paving the way for customized, physically realizable (meta)material discovery. Second, I show how we can implement nonlocal interactions experimentally using piezoelectric transducers and nonlocal shunt circuitry. We show how hybridization between a nonreciprocal electrical lattice and the underlying elastic waveguide results in strong nonreciprocity in the coupled system, allowing us to achieve up to 62x nonreciprocity experimentally in an active, linear, time-invariant structure. This greatly simplifies implementation of nonreciprocal elastic devices, opening the path for elastic “circuits” and customized wave-based sensors.

BIOGRAPHY

Dr. Christopher Sugino is an Assistant Professor in the Department of Mechanical Engineering in the Schaefer School of Engineering and Science at Stevens Institute of Technology. His research focuses on the dynamics of smart structures and metamaterials, with an emphasis on using smart materials to investigate new physical phenomena. He is a recipient of the NSF CAREER Award (2024-2029) and 2021 Doak Award from the Journal of Sound and Vibration. He received his Ph.D. in Mechanical Engineering from the Georgia Institute of Technology in 2019 and his B.S. in Engineering from Harvey Mudd College in 2015.