Owls to make cars quieter

Spektrum der Wissenschaft

5.7.2025

Translation: machine translated

The special skin and feathers on their wings allow owls to fly almost silently. A material that mimics their wings could make cars and industrial plants quieter.

What do you hear when an owl flies overhead? That's right: nothing. The fact that owls fly almost silently is due to their skin and the feathers on their wings. The skin consists of microscopic cavities that suppress low-frequency sounds, while their fluffy feathers absorb high-frequency sound. This makes the animal superior to noise absorbers such as those we use today in cars or production machines: It dampens sound over a wide frequency range. With conventional materials, on the other hand, you have to make a decision: Should the high-frequency part of a noise source be dampened, for example the sound of squealing brakes, or low-frequency sounds such as the low rumble of a car engine. In practice, this is achieved by overlaying several layers of different sound-absorbing material, 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 mimics the structures of its wing. The first layer of the absorber consists of an aerogel. To produce the ultra-light and highly porous material, the researchers used droplets of hexane, which are evenly distributed in an aqueous solution. When frozen, they arrange themselves in honeycomb structures. As soon as they evaporate again, they leave cavities in the aerogel, which later serve as resonance structures. The researchers applied a second layer of flexible nanofibres to the aerogel. Similar to an owl's wing, the aerogel then absorbs the low frequencies and the fibres the high frequencies. According to the researchers, the material is dimensionally stable. Even after being compressed hundreds of times, the structure of the absorber remained intact.

As the researchers report in the journal «ACS Applied Materials & Interfaces», the lightweight material absorbs 58 per cent of the sound waves hitting a conventional car combustion engine, reducing the noise from 87.5 to 78.6 decibels. According to the research team, no other noise absorber available today can achieve this.

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