Chaunsali Rajesh, Li Feng, Yang Jinkyu
Aeronautics and Astronautics, University of Washington, Seattle, WA, 98195-2400, USA.
Department of Physics, South China University of Technology, Guangzhou, 510640, China.
Sci Rep. 2016 Aug 1;6:30662. doi: 10.1038/srep30662.
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.
我们展示了一种主动式、纯机械应力波隔离器，它由排列成螺旋结构的短圆柱形颗粒组成。这种声子结构使我们能够通过控制圆柱体的接触角来动态改变颗粒间的刚度。我们使用扭转行波来控制接触角，从而沿纵向方向对声子晶体施加所需的时空刚度变化。这种扭转激励是系统中一种参数泵浦形式，它导致了时间反演对称性的破坏。我们报告称，在准静态意义上，该系统呈现出拓扑非平凡带隙。然而，在泵浦效应显著的动态 regime 中，这些带隙在色散关系的频率和波数域方面变得不对称。通过数值模拟，我们表明这种不对称与系统的拓扑不变量即陈数有直接对应关系。我们提出，这种不对称伴随着选择性带间跃迁，可用于沿声子晶体传播的应力波的定向隔离。
