The acoustic arms race between bats and moths has been going on for about 65 million years since bats developed ecolocation to find prey.
Moths have come under a lot of evolutionary pressure to evolve their survival defenses, and one of those adaptations — the small scales on the wings — could be the key to transforming future noise-removing technology.
according to a new study published in Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences.
“Sts will inspire the next generation of sound-absorbing materials,” says Marc Holderied, a professor of sensory biology at the University of Bristol’s School of Biological Sciences in the UK.
“New research has shown that one day it will be possible to decorate your home walls with ultra-thin absorbent wallpaper, using a design that copies the mechanisms that give the moth acoustic camouflage.”
The moth’s wings naturally absorb sound
Earlier, these researchers found that moth wings protect against the echolocation of bats by porous nanostructures that absorb sound from their surface.
The mite’s wing scales are only about 100-200 microns long and 1-2 microns thick (less than the wavelength of the highest frequency sound used by bats in echolocation). This means that they do not return sound waves to the bat, they vibrate and convert the sound into kinetic energy.
Now, scientists have studied whether this structure could be aware of the design of the sound absorber mounted, by examining the ability of moth wings stuck to a surface to absorb sound.
“The first thing we needed to know was how these moth scales would work if they were acoustically in front of a highly reflective surface, such as in front of a wall,” says Holderied. “We also needed to find out how the absorption mechanisms of scales could change when they interacted with this surface.”
They studied this by placing small parts of the wings of the sisal on an aluminum disk, and then tested how the orientation of the wing (in terms of the incoming sound) and the removal of the flake layers affected the sound absorption.
It is noteworthy that the wings absorbed 87% of the input sound energy when mounted on a solid surface, while absorbing a wide range of frequencies (broadband) from different angles (in all directions).
“It’s even more spectacular that the wings are doing this while they are incredibly thin, only 1/50 of the thickness of the wavelength of the sound being absorbed by the scale layer,” explains lead author Dr. Thomas Neil. Researcher at the University of Bristol School of Biological Sciences.
“This outstanding performance is classified as a natural metasurface that absorbs the moth’s wing, a material with special properties and capabilities that cannot be created using conventional materials.”
Implications for building and traveling
The creation of ultra-thin sound-absorbing panels has implications for both the construction industry and travel.
As cities get louder, the need for non-intrusive noise reduction grows, and lightweight sound-absorbing panels can also have a big impact on the travel industry, where any weight saved on planes, cars and trains increases their efficiency.
To date, the sound absorption studied has been at ultrasonic frequencies – above the range that humans can perceive – as the echolocation of bats uses sound waves in that range.
This is not practical to use to alleviate sound, as these technologies should reduce the noise pollution that humans hear.
Now, scientists plan to tackle the challenge of replicating the ability to absorb the sound of moth wings by designing and building prototypes that operate at lower frequencies in the field of human hearing.