title: Stress Wave Isolation by Purely Mechanical Topological Phononic Crystals.
abstract: We present an active, purely mechanical stress wave isolator that consists of short cylindrical particles arranged in a helical architecture. This phononic structure allows us to change inter-particle stiffness dynamically by controlling the contact angles of the cylinders. We use torsional travelling waves to control the contact angles, thereby imposing a desired spatio-temporal stiffness variation to the phononic crystal along the longitudinal direction. Such torsional excitation is a form of parametric pumping in the system, which results in the breakage of the time-reversal symmetry. We report that, in quasi-static sense, the system shows topologically non-trivial band-gaps. However, in a dynamic regime where the pumping effect is significant, these band-gaps become asymmetric with respect to the frequency and wavenumber domains in the dispersion relationship. By using numerical simulations, we show that such asymmetry has a direct correspondence to the topological invariant, i.e., Chern number, of the system. We propose that this asymmetry, accompanied by selective inter-band transition, can be utilized for directional isolation of the stress wave propagating along the phononic crystal.
authors.affiliation: Aeronautics and Astronautics, University of Washington, Seattle, WA, 98195-2400, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Chaunsali
authors.affiliation: Aeronautics and Astronautics, University of Washington, Seattle, WA, 98195-2400, USA.|Department of Physics, South China University of Technology, Guangzhou, 510640, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.affiliation: Aeronautics and Astronautics, University of Washington, Seattle, WA, 98195-2400, USA.
authors.forename: Jinkyu
authors.initials: J
authors.lastname: Yang