About 65 million years ago, right around the time dinosaurs went extinct, bats evolved the ability to echolocate. They would produce clicks with their mouth or nose and listen for echoes of those clicks bouncing off surfaces and animals in the dark. Bats were major predators of moths, so many moths evolved ears that are sensitive to that echolocation—but not all of them.
Some species, like furry silk moths, never grew ears. Instead, they used another defense mechanism that was already at their disposal: sound-absorbent wings.
Now a new study from the same team suggests that these moth wings could inspire a new type of ultrathin acoustic material that would work as wallpaper and be 10 times thinner than what’s currently on the market.
This isn’t the first time humans have turned to nature for solutions. While groundbreaking, the design of the wallpaper is part of an existing field known as biomimicry, or the act of imitating nature’s design and processes in man-made systems. Examples include bird-safe glass inspired by the UV-reflective strands in spider webs; cooling vents inspired by termite mounds; and, of course, plane wings modeled after birds.
Moths evolved 250 million ago, or about 200 million years before bats. According to Marc Holderied, a professor of sensory biology at the University of Bristol and coauthor of the new study with Thomas Neil, deaf furry moths had scales on their wings even before the bats arrived—perhaps to protect themselves from sticky spider webs. So all they had to do was adapt their function.
Under a microscope, that dust looks like a collection of tiny overlapping scales akin to a complex roof tile pattern. When a sound hits those scales at the right frequency (more on that in a bit), the scales start to vibrate. By vibrating, they take the sound energy out of the air and transform it into mechanical energy that will eventually be damped down and turned into heat. This process is known as resonant absorption.
The new material could work a bit like an ultrathin wallpaper fabric applied to a variety of surfaces, from office walls to the seats of an airplane.
“We’re talking about something that measures millimeters rather than centimeters,” Holderied says, noting that resonant materials would be much more efficient than the porous materials used in traditional acoustics. And when a material is thinner, he says, it would also be lighter, which could, for example, help reduce the overall weight of the plane and save on fuel.
The challenge now is to translate the concept so it works for the human audible range. In this particular study, the scientists used ultrasound signals that are above the range that can be heard by humans, but Holderied says the size of each scale on the metamaterial could help dictate the kind of sounds it can absorb.
It will likely be a few years before any new material hits the market, but if and when it does, it will be the culmination of 250 million years of work.