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Owls inspire more effective sound insulation

www.spektrum.de

Nanomaterial: Eulen sollen Autos leiser machen

cross-posted from: https://metawire.eu/post/176521

Nanomaterial: Eulen inspirieren zu wirksamerem Schallschutz

Die besondere Haut und die Federn an ihren Flügeln lassen Eulen fast lautlos fliegen. Ein Material, das die Flügel nachahmt, könnte für leisere Autos und Industrieanlagen sorgen.

4 comments

  • Lovely Boobook stock photo they chose. 🥰

    Tried to find a non-paywalled version of the full article without luck. The summary does give a quick look at the material layers.

    I hadn't heard anything referencing owl skin as part of the silence equation before, so I had to search that up right away. In this paper that is available free, it discussed the typical wing proportions and feather structures that break down the large turbulences, but also mentioned not a porous skin, but a velvet-like wing coating they hypothesized could dampen sound from feathers rubbing on each other during flight.

    So I'm not sure what we're losing in translation from Chinese to German to English here, but based on my non-expert opinion, I'd say after reading everything available the silicone nanofibers mimic that velvet skin cover and the aerogel is the structure made by interlocking feather barbules. This was interesting as it was the opposite of my first impression, as I'm used to the whispy leading and trailing wing edges being the focal point when discussing owl flight, but that would be nothing new. The paper I linked referenced studies of that nature back in the 70s.

    As an aside, the juvie Great Horn I've been working with is starting to fly but doesn't have all its adult feathers in, and when it flies next to me, it is certainly not what I'd call quiet! Its neighbor the Cooper's Hawk is about the same volume, though it is a sharper and snappier sound.

    To be fair though to the GHO, when it would be hunting, I think it is more dive and glide than flapping, which would greatly reduce the sound generated. Even though its flapping is not quiet, it's mainly just the sound of a large mass of air being moved than shall we say mechanical noise like with the hawk.

    My normal reference is to a CPU cooler fan. A larger fan is quieter for the same volume of air because it's able to do so at a lower rpm. Owls have big wings for their size so they can fly equally well while flapping less. The other micro-features surely enhance it further still, but being able to not flap near as much as other birds I feel is immensely helpful to staying quiet.

    Reminder I'm not a scientist or engineer, but I do read a ton on owls and have some basic hands on experience with my silent-ish feather friends, so don't take any of this as anything more than anecdotal experience. 😇

    Oh, and thank you so much for sharing!

  • What do you hear when an owl flies over you? Right: practically nothing. The fact that owls fly almost silently is due to the skin and feathers of their wings. The skin consists of microscopic cavities that suppress low-frequency sounds, while its fluffy feathers absorb high-frequency sound. This means that the animal is ahead of noise absorbers, such as we use today in cars or in production machines: They dampen sound over a wide frequency range. With conventional materials, on the other hand, you have to decide: should the high-frequency part of a noise source be damped, for example the sound of squeaking brakes, or low-frequency noises such as the deep rumble of a car engine. In practice, one helps oneself by laying several layers of different sound-absorbing material on top of each other, which often leads to unwanted additional weight.

    Researchers at Tiangong University in China have now been inspired by the owl to develop a broadband sound absorber that imitates the structures of its wing. For the first layer of the material – a so-called aerogel – they let droplets of hexane freeze. In doing so, they applied a special process whereby the material is arranged in a comb shape. On it, they applied a second layer of silicon nanofibers, which together produce a fibrous structure.

    As the researchers in the journal ACS Applied Materials & Interfaces report, the lightweight material on a conventional internal combustion engine of a car absorbs 58 percent of the sound waves that hit, reducing the noise from 87.5 to 78.6 decibels. According to the research team, no other noise absorber available today can do this.