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Acoustic Metamaterials
length spatial filter known as the human cochlea springs to mind. Although these examples are not usually referred to in the context of AMMs, they exploit the same physical prin- ciples as individual AMM elements and can easily be con- sidered precursors to AMMs. Indeed, one can comfortably state that many AMM concepts have been hiding in plain sight waiting for us to stumble on them. We are fortunate to have finally come to appreciate and realize what properly designed subwavelength structures can provide to the field of acoustics.
In the span of just over a decade, AMMs have developed from several disconnected research efforts into a well-estab- lished, wide-ranging, and expanding field that encompasses ideas like negative refraction, super resolution, cloaking, enhanced absorption, nonreciprocity, active control, and material tunability. Concepts introduced in AMM research challenge acousticians to rethink what is possible and offer potential solutions to long-standing problems in acoustics. We are confident that new ideas hatched in AMM research, coupled with the expanding technologies of computational simulation and additive manufacturing, will produce the next generation of acoustical materials and devices.
Acknowledgments
We are grateful to Arthur Popper for suggesting this timely article and to Xiaoshi Su for graphical assistance. We thank all of our colleagues for their ideas, suggestions, and pa- tience in helping us come to understand acoustic metamate- rials. This work was supported by Office of Naval Research Multidisciplinary University Research Initiatives Grant N000141310631.
Biosketches
Michael Haberman is a Research Sci- entist at the Applied Research Labora- tories and Department of Mechanical Engineering at The University of Texas at Austin. He received a BS in mechani- cal engineering from the University of Idaho in 2000, MS and PhD degrees
from the Georgia Institute of Technology in 2001 and 2007, respectively, and a Diplôme de Doctorat in engineering me- chanics from the Université de la Lorraine in Metz, France, in 2006. His research interests include wave phenomena in
complex acoustic and elastic media, acoustical materials de- sign, ultrasonic nondestructive testing, and acoustic trans- ducers. He serves as an Associate Editor of The Journal of the Acoustical Society of America.
Andrew Norris received a BSc and MSc in mathematical physics from University College Dublin and a PhD from North- western University in 1981. After a post- doc at Exxon Research and Engineering Corporate Laboratories, he joined Rut- gers University where he is Professor
of Mechanical and Aerospace Engineering. He has worked on geophysical, structural, and ultrasonic nondestructive evaluation wave problems. His current interests are in meta- materials that exhibit extraordinary wave-bearing proper- ties. He is editor of Wave Motion, an Associate Editor of The Journal of the Acoustical Society of America, and a Fellow of the Acoustical Society of America. In his off time, he enjoys reading, running, and the great outdoors.
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