报告题目：Topologically Protected Wave Propagation in Acoustic Metamaterials
报告人：C.W. Lim 教授
报告摘要：Topological acoustic metamaterials have attracted enormous research attention in recent years. A significant hallmark of these structures is that they can support interface modes that are robust to structural disturbance and protected by topology. However, most of the studies are often limited to the passive structures that manifest wave propagation at fixed frequency ranges. In view of the shortage of non-passive topological acoustic metamaterials, this work has a primary motive to study the active control of topologically protected wave propagation in soft dielectric membrane-type metamaterials (MAM) based on quantum spin Hall effect (QSHE). The unit cell of the periodic structure is designed with symmetry. Then, the plane wave expansion method is adopted to analytically capture the system dispersion properties. A finite element model is further developed and excellent convergence with the analytical result is presented. By adjusting locations of spraying discs in the honeycomb unit cell, mode shape inversion is observed, separating the topologically trivial state from the nontrivial counterpart. Consequently, the topologically protected interface modes (TPIMs) are observed. Additionally, an electrical voltage that lies within the locking-up limit is applied to MAM to actively control the working frequency of the TPIM. Further, several waveguide paths are designed to control the robust wave propagation in the structure. Conclusively, a voltage-controlled topological metamaterial is designed to actively tune the working frequency range of the device.
专家简介：Currently a fellow of ASME, ASCE, EMI and HKIE, Ir Professor Lim received BEng from University of Technology of Malaysia, MEng and PhD from National University of Singapore and Nanyang Technological University, respectively. Prior to joining City University of Hong Kong, he was a post-doctoral research fellow at The University of Queensland and The University of Hong Kong. Professor Lim has expertise in theory of plates and shells, dynamics of smart piezoelectric structures, nonlinear dynamics, nanomechanics, symplectic elasticity and metamaterials. He is one of the editors for JoMMS, Assoc Editor for JVET, IJBC, JTS, Subject Editor for AMM, JSV, and on the editorial board of some top-ranked international journals. He has published one very well-selling title in Engineering Mechanics entitled “Symplectic Elasticity”, co-authored with W.A. Yao and W.X. Zhong, as recorded in April 2010 by the publisher, World Scientific. He has published more than 330 international journal papers, accumulated about 12,000 citations and has a Google Scholar H-index 56. One of his papers that generalizes two separate models, the nonlocal elasticity and strain gradients, to a generalized nonlocal strain gradient theory has been cited more than 800 times since it was first published in JMPS in 2015. It is also a highly cited paper in the journal. Another paper was granted the IJSS 2004-2008 most cited article award. He was also awarded Top Referees in 2009, Proc. A, The Royal Society. Professor Lim is a registered professional engineer in HK. He holds one registered finite element software and three patents. Recently Professor Lim was awarded the prestigious 2020 JN Reddy Medal as a recognition “for significant and original contributions to vibration of plates and shells, smart piezoelectric structures, nanomechanics, and symplectic elasticity”.