How to realize arbitrary control over the velocity at which wave propagates is of interests to a lot of applications in electronic, photonic, mechanical and acoustic systems. However, this matter remains unsolved despite a great deal of proposals during the last decade. For acoustic wave, current techniques to decelerate sound wave are all associate with strong dispersion induced by near field coupling between resonators, which suffers from narrow bandwidth and distorted signal.
A new study has taken a big step toward answering that challenge. As recently reported online in Nature Communications titled “Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials” (http://www.nature.com/ncomms/2016/160520/ncomms11731
/full/ncomms11731.html), the corresponding author, Dr. Jie Zhu, Assistant Professor of Department of Mechanical Engineering, worked together with his collaborators at Heilongjiang University, Huazhong University of Science and Technology, Chinese Academy of Sciences and University of Michigan. They developed a helical-structured acoustic metamaterial. The specialty of this helical-structured metamaterial is its dispersion free high effective refractive index that is tunable through helicity adjustment.
Dr. Zhu and his colleagues conducted theoretical analysis, numerical simulation and experiments to thoroughly examine the new metamaterial and verify the phase modulation capability. The development of this new metamaterial is not only important to fundamental slow wave physics, but also able to provide a new passive way to acoustic wave phase engineering.