MMAE Seminar - Dr. Andrew N. Norris - Transformation Acoustics and Elasticity, Phononic Structures and Applications

Armour College of Engineering's Mechanical, Materials, and Aerospace Engineering Department will welcome Dr. Andrew N. Norris, Distinguished Professor of Mechanical and Aerospace Engineering at the Rutgers University, on Wednesday, February 6th, to present his lecture, Transformation Acoustics and Elasticity, Phononic Structures and Applications. This seminar is a part of Midwest Mechanics Seminar Series.

Abstract

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 often difficult to realize in practice. The talk will first explain how TA is essentially materials modeling using geometry. It will then 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 a wide range of effective properties can be obtained using quite distinct quasi-phononic structures. One approach uses metal lattices with hexagonal (2D) or diamand-like (3D) unit cells. Another 2D approach is based on a water matrix with unit cells comprising cylindrical tubes. Implications are explored: including the ability of conformal mappings to yield highly accurate focusing lenses. Numerical examples and experimental measurements will demonstrate these ideas. The extension of TA to linear elasticity presents challenges because of the multiple wave types, but some progress can be made using hyperelastic materials.

Biography

As an undergraduate in Ireland, Andrew Norris aimed for a future in physics but changed course after moving to the USA where he did his PhD in Engineering Sciences and Applied Mathematics at Northwestern University. After a few years working with Exxon he moved to Rutgers University where he is now distinguished professor of Mechanical and Aerospace Engineering. The common theme all along has been an intense interest in acoustic and elastic waves, which share the same characteristic qualities. He found that learning about seismic waves provides better understanding of acoustic phenomena, and vice versa. His current research is in acoustic and elastic metamaterials, focused on underwater applications. Acoustic metamaterials use concepts that at first sight might appear to be pushing the limits of physics, but are still feasible. A prominent example is transformation acoustics, which can lead to exotic effects such as cloaking, but is also the basis for designing accurate acoustic lenses. Dr. Norris has recently used these ideas to design and demonstrate underwater acoustic focusing devices, with help from collaborators. Dr. Norris is a Fellow of ASA, and recipient of ASME's Per Bruel Medal and the Rayleigh Lecture Award.