Extraordinary focusing of sound above a soda can array without time reversal
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Maznev-2015-Extraordinary focusi.pdf
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Author(s)
Gu, Gen
Sun, Shu-yuan
Xu, Jun
Shen, Yong
Zhang, Shu-yi
Maznev, Alexei
Fang, Nicholas Xuanlai
Date Issued
April 2015
Journal
New Journal of Physics
Publisher
IOP Publishing
Citation
Maznev, A A, Gen Gu, Shu-yuan Sun, Jun Xu, Yong Shen, Nicholas Fang, and Shu-yi Zhang. “Extraordinary Focusing of Sound Above a Soda Can Array Without Time Reversal.” New J. Phys. 17, no. 4 (April 1, 2015): 042001. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Version
Final published version
Abstract
Recently, Lemoult et al (2011 Phys. Rev. Lett. 107 064301) used time reversal to focus sound above an array of soda cans into a spot much smaller than the acoustic wavelength in air. In this study, we show that equally sharp focusing can be achieved without time reversal, by arranging transducers around a nearly circular array of soda cans. The size of the focal spot at the center of the array is made progressively smaller as the frequency approaches the Helmholtz resonance frequency of a can from below, and, near the resonance, becomes smaller than the size of a single can. We show that the locally resonant metamaterial formed by soda cans supports a guided wave at frequencies below the Helmholtz resonance frequency. The small focal spot results from a small wavelength of this guided wave near the resonance in combination with a near field effect making the acoustic field concentrate at the opening of a can. The focusing is achieved with propagating rather than evanescent waves. No sub-diffraction-limited focusing is observed if the diffraction limit is defined with respect to the wavelength of the guided mode in the metamaterial medium rather than the wavelength of the bulk wave in air.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Massachusetts Institute of Technology. Department of Mechanical Engineering
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DOI of Published Version
https://doi.org/10.1088/1367-2630/17/4/042001
