Abstract
In acoustics, wave tailoring refers to the manipulation of the propagation of waves or energy that are generated due to dynamic loading and is typically accomplished through the design of material properties. There are two approaches to designing materials for wave tailoring: the first is to develop new materials by tailoring their
atomic structure—for example metallic alloys, ceramic crystals and polymers. The second approach, adopted here, is to build “metamaterials” using the existing materials as building blocks and leveraging local architecture to develop new engineered materials with properties that often surpass the physical limits imposed
by the atomic structure of materials. Nonlinearity, especially strong nonlinearity, introduces additional dynamics that are not accessible in the linear dynamic regime such as frequency-amplitude dependence, sudden transitions (jumps), bifurcations, saturation effects, internal resonances and chaos. Here, several studies on the use of strongly nonlinear metamaterials to passively break acoustic reciprocity—a fundamental property of linear, time-invariant acoustic systems—are performed and nonreciprocity is successfully
demonstrated, both theoretically and experimentally. This is accomplished using two different schemes: first, a system involving nonlinearity and internal scale hierarchy in mass, and, second, a system consisting of two dissimilar coupled lattices. Both these systems contain the two main requirements for nonreciprocity:
nonlinearity and asymmetry. In the first system, nonreciprocity stems from the nonlinear energy sink – like behavior of one of the asymmetric small-scale masses leading to targeted resonance captures. In the second system, the mechanism of nonreciprocity is the intentional mismatch of the band structures of the lattice in
combination with the frequency-amplitude dependence that is characteristic of nonlinearity. In both cases, nonreciprocity is achieved in a controllable, predictable manner. We expand these design ideas into the nanoscale in which, due to scaling, there are many practical applications, e.g., NEMS/MEMS sensors and
communication devices such as filters, frequency synthesizers, and temperature-compensated MEMS resonators. As preliminary work, we consider two linear nanophononic waveguides connected by strongly nonlinear couplings. The band structures are highly tunable, and, either the nonlinear coupling, or the linear waveguides can introduce the asymmetry required for nonreciprocity. In this case the nonlinearity is due to electrostatic interactions that are readily accessible in the nanoscale.
About the Speaker
Dr. Jonathan Bunyan is a recent doctoral graduate of the department of Mechanical Engineering. He received his bachelor’s degree in Mechanical Engineering in 2013 from Purdue University and obtained his master’s and doctorate degrees in Theoretical and Applied Mechanics in 2016 and 2019 from the University of Illinois
at Urbana-Champaign. Following August 2013, he is a member of the Kinetic Materials Research Group where he researches nonlinear dynamics and acoustics of architectured materials.
Host: Professor Alex Vakakis
