学术活动

Isotropic Transformation Acoustics, Phononic Stuctures and Applications
发布时间:2017-10-20 阅读次数:3774次

时间:2017年10月25日10:00-11:30

地点:土木工程楼520

报告人Andrew N. Norris   Department of Mechanical and Aerospace Engineering, School of Engineering, Rutgers University

Transformation acoustics (TA) offers the acoustical designer the potential to alter sound propagation in an exact manner that satisfies the wave equation regardless of frequency, high or low.  This is the reason why TA is the foundation for exotic effects such as acoustic cloaking, which requires material properties that are anisotropic but difficult to realize in practice. This talk will concentrate on the special case of isotropic TA and its applications.  The motivation for focusing on isotropic TA is that materials with the required properties can be readily realized by a wide variety of homogenized structures.  We concentrate on underwater acoustic devices and show that quasi-phononic structures with unit cells comprising circular, square and other shaped cylinders in water provide the range of required properties.  We first show that isotropic TA devices require only a change in effective bulk modulus, but not density.   Two implications are explored: first, the ability of conformal mappings to yield highly accurate focusing lenses is described.  These devices act, by reciprocity, as monopole to highly one-way-wave radiators.    Second, the fact that any TA device must match to the exterior fluid places constraints that are explored.  A class of focusing devices is described that are optimally matched in both impedance and focusing.   Numerical examples and data from experimental measurements will demonstrate these ideas.

 

 

CV: Andrew Norris is an internationally known expert in modeling of acoustic and elastic wave phenomena.  He has achieved wide recognition for work in acoustic metamaterials (AMM), a field devoted to making devices that can control sound waves in ways that at first glance  appear to violate physical principles.  With over 170 journal papers published, his current interests are in developing fundamental models for mechanical metamaterials that exhibit extraordinary wave bearing properties.  He is Distinguished Professor of Mechanical and Aerospace Engineering in the School of Engineering at Rutgers, editor in chief of the journal Wave Motion, and a member of the board of Editors of several journals including the Journal of the Acoustical Society of America.   Recent awards include the ASME Per Bruel Medal (2014) and the Rayleigh Lecture Award (2011), Fulbright Fellowship (2013) and the Daniel Gorenstein Award at Rutgers University (2017). 


发布人:王艳锋(力学系)