What is it about?

The 65 million years old acoustic arms race between bats and their insect prey has produced many fascinating adaptations. Using an array of innovative techniques, we show that the very thin scale layer on moth wings has evolved extraordinary ultrasound-absorptive properties that provide stealth camouflage against echolocating bats. We document its ability to absorb sound over a comprehensive frequency bandwidth despite its aerodynamically constrained deep-subwavelength thickness. This goes well beyond the limits attainable with classical porous absorbers. We reveal that the architecturally complex scale layer instead works as an array of finely tuned narrowband resonators, whose collective action creates its emergent acoustic properties. This confirms that moth wings are indeed the first known natural acoustic metamaterial.

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Why is it important?

Bats and moths are embroiled in an evolutionary arms race. Using ultrasonic biosonar, bats detect their insect prey, which in turn deploy diverse strategies to avoid predation. Here, we show that some moth species evolved wings covered with a canopy of scales that reduces ultrasonic echoes. Our empirical and mathematical analysis together show that moth wings exhibit key features of a desirable technological acoustic metamaterial. This work enriches our understanding of the structural and functional complexity of lepidopteran wings and reveals enticing new ways to design, using bioinspired metamaterial properties, high-performance acoustic panels and noise mitigation devices.

Perspectives

This discovery of a fascinating adaptation opens the opportunity to work towards better and thinner sound absorbers for our homes and offices.

Marc Holderied
University of Bristol Queen's Building Library

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This page is a summary of: Moth wings are acoustic metamaterials, Proceedings of the National Academy of Sciences, November 2020, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2014531117.
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