Moth wings are natural invisible acoustic metamaterials
Science and Technology Daily, Beijing, November 29thAccording to a recent report in the Proceedings of the National Academy of Sciences, British researchers have discovered the precise structure of moth wings. It is this structure that enables the species to Escape the most troublesome predator in the”evolutionary arms race” 65 million years ago.
The research team at the School of Biological Sciences at the University of Bristol uses airborne cross-sectional imaging, acoustics mechanics and refractive index A series of analysis techniques including the instrument found that the very thin scale layer on the moth’s wing has evolved extraordinary ultrasonic absorption characteristics, thereby providing an invisible acoustic camouflage for avoiding the echo detection of bats.
An even more striking discovery is that the researchers identified the first known naturally occurring acoustic metamaterial. Traditionally, metamaterials have been described as man-made composite materials that have been engineered to exhibit physical properties beyond those available in nature. Naturally occurring metamaterials are very rare and have never been described in the field of acoustics.
Earlier this year, behavioral acoustics and sensory ecology expert Dr. Mark Holderd and his co-researchers reported that deaf moths can develop ultrasonic-absorbing scales on their bodies, allowing them to Absorbing bats is used to detect 85%of their incoming sound energy.
The need to survive means that moths will evolve a 1.5 mm deep scale protective barrier, which can be used as a porous sound-absorbing material. However, this protective barrier cannot work on moth wings because the increase in thickness of the moth wings hinders the moth’s ability to fly. A key feature of acoustic metamaterials is that they are much smaller than the wavelength of the sound acting on them, making them much thinner than traditionally constructed sound absorbers.
By examining the complex cross-sectional images of sound captured using ultrasound tomography, the latest research from the University of Bristol found that moths have taken a further step toward saving lives, creating a resonance absorption The thickness of the bat is 100 times thinner than the wavelength of the sound it absorbs, so that the insect remains light while reducing the possibility of bats detecting the echo of their wings in flight.
The most surprising thing is that moth wings have also developed a way to make resonant absorbers absorb all bat frequencies by adding another amazing feature-they tune many of them individually to different frequencies. The resonator is assembled into a series of absorbers to jointly create a broadband absorber that can be used as an acoustic metamaterial. This is the first known acoustic metamaterial in nature.
The broadband absorption performance obtained by the ultra-thin moth wing structure is difficult to achieve, and its excellence lies in that it far exceeds the limit that can be achieved by the current traditional porous absorbers used in office environments to absorb sound. The resulting vision is that scientists may be able to design ultra-thin sound absorber”wallpaper” for homes and offices accordingly to replace the bulky sound absorber panels currently used. (Feng Weidong)
Source:Science and Technology Daily