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Metamaterials assemble multiple subwavelength elements to create structures with extraordinary physical properties (1-4). Optical metamaterials are rare in nature and no natural acoustic metamaterials are known. Here, we reveal that the intricate scale layer on moth wings forms a metamaterial ultrasound absorber (peak absorption = 72% of sound intensity at 78 kHz) that is 111 times thinner than the longest absorbed wavelength. Individual scales act as resonant (5) unit cells that are linked via a shared wing membrane to form this metamaterial, and collectively they generate hard-to-attain broadband deep-subwavelength absorption. Their collective absorption exceeds the sum of their individual contributions. This sound absorber provides moth wings with acoustic camouflage (6) against echolocating bats. It combines broadband absorption of all frequencies used by bats with light and ultrathin structures that meet aerodynamic constraints on wing weight and thickness. The morphological implementation seen in this evolved acoustic metamaterial reveals enticing ways to design high-performance noise mitigation devices.
|31134 - 31141
|Number of pages
|Proceedings of the National Academy of Sciences of the United States of America
|Published - 8 Dec 2020
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We thank Christoph Rau, Shashi Marathe, and Kaz Wanelik from beamline I13 at Diamond Light Source for their invaluable assistance. We thank Aila Osborne and Alexander Quinn for help with measuring transmission coefficients. This study was supported by the Biotechnology and Biological Sciences Research Council (Grants BB/ N009991/1 and BB/I009671/1), the Engineering and Physical Sciences Research Council (Grant EP/T002654/1), and Diamond Light Source, beamline I13 (proposal MT17616).
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- Moth scale
- Natural metamaterial