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.