Owls’ silent flight inspires new noise reduction technology

If you’ve seen an owl fly, you probably didn’t hear a thing. That’s because their skin and feathers dampen sound by absorbing high- and low-frequency flight noise.

Inspired by this natural soundproofing, researchers publishing in ACS Applied Materials & Interfaces have developed a two-layer aerogel that mimics the structures inside owl feathers and skin to mitigate sound pollution. This new material could be used in cars and manufacturing facilities to reduce traffic and industrial noise.

Noise pollution is more than a nuisance; excessive noise can cause hearing loss and can worsen health conditions such as cardiovascular disease and type 2 diabetes. When eliminating the source of noise pollution isn’t feasible, soundproofing materials help dampen it. However, traditional materials absorb either high-frequency sounds, like squealing brakes, or low-frequency sounds, like the deep rumbling from a car engine. This means engineers often layer multiple types of soundproofing materials to achieve full-spectrum noise control, which adds weight and bulk.

To overcome this, Dingding Zong and colleagues turned to an unlikely acoustic expert: the owl. The owl uses its soft feathers and porous skin to remain whisper-quiet during flight. The researchers’ goal was to engineer a similarly versatile broadband sound absorber.

The researchers froze droplets of hexane into a layer of soft material, using a technique called emulsion-templated freeze-reconstruction. Removing the frozen hexane revealed a honeycomb-like pattern in the material. They added a second layer with silicon nanofibers instead of hexane droplets to create a fibrous pattern.

The resulting light, porous, two-layer aerogel mimics the structures in owl skin and feathers: The bottom porous layer resembles the bird’s skin with microscopic cavities that cancel out low-frequency noise; and the top feather-inspired layer, made of fluffy nanofibers, dampens high-frequency sounds.

Notably, the researchers found that their owl-inspired aerogels can:

• Absorb 58% of soundwaves that strike it, surpassing the threshold for effective noise control materials.
• Reduce 87.5 decibels of automobile engine noise to a safe level of 78.6 decibels, which is a better reduction than existing high-end noise absorbers.
• Maintain structural integrity through 100 compression cycles, with only 5% deformation.

The researchers believe this study paves the way for high-performance, lightweight and durable sound-absorbing materials that can significantly alleviate noise pollution from industrial equipment and traffic.