Moths as Precursors for Future Bio-Inspired Noise Cancellation Devices

The technology has been undoubtedly evolving at a very fast pace. The evolution owes to the work of scientists and engineers who come up with innovative out-of-the-box ideas that efficiently solve many complex problems. As a main source of inspiration, nature consists of the main reference where God’s creations are meticulously studied to transfer their operational mechanisms into products which can be later used by individuals. Lately, bio-inspired approaches have been investigated to develop sound absorption paradigms that rely on a structure that absorbs sounds, in a similar fashion to the wings of moths. These tiny creatures have advanced innate mechanisms that could be precursors for future bio-inspired noise cancellation devices.

What is Noise Cancellation Technology?

Noise cancellation technology encompasses the group of approaches that aim at reducing outside noise that could interfere with the audio the users is listening to. These technologies have gaining further interest with the compulsory remote working that accompanied the coronavirus pandemic. To isolate the user from the outside world, two main approaches arise, passive and active noise cancellation. These techniques are in particular employed for headphone and earphone designs.

Passive Noise Cancellation

Passive noise cancellation includes designing ear cups with special material that will simply block outside noise signals from reaching the ears. The main problem with such systems is that the quality of the cancellation depends on the properties of the material itself, including its thickness. Moreover, the perceived experience highly depends on the user as human beings don’t share the same traits in terms of their ear’s responsiveness to different frequencies.

Active Noise Cancellation

Active noise cancellation tries to adapt to the surrounding noise characteristics by generating a signal that has opposing properties, in the aim of nullifying the unwanted disturbance. To achieve this feast, a set of microphones and speakers are used to listen to the environment then output the signal that is “hopefully” opposite to the noisy one. A good active cancellation is one that removes all the noise. The costly setup involves microphones inside and outside the earcup, a process known as hybrid active noise cancellation.

Other noise cancellation techniques exist. In its latest iPhone 13 lineup, calming background music are used to mask unwanted noise.

Moth Wings for a High-Quality Passive Noise Cancellation?

A recent article published in the proceedings of the Royal Society provides high hopes for the future of noise cancellation devices. The research team from the University of Bristol in the United Kingdom has demonstrated the efficiency of moth as sound absorbers. In particular, 87 percent of sound waves can be absorbed as reported in the published article.

A New Metamaterial?

The secrets to the new discovery lie in the scales and their arrangement on the moth wings. These small insects have had their structure refined through millions of years of biological evolution. Moths have had to strengthen their defense against bats that use a radar-like system where they send high-frequency signals and wait for the reflection to locate their prey.  As reported by one of the authors for a previous article in the Conversation journal, moths normally relied on their ears that are sensitive to the bats echolocation signals to take evasive actions. However, the interesting part is when these insects do not have ears. The answer is in the array of scales on their wings. These scales are sensitive to different frequencies of the sound waves. The synergy in the operation of all scales allows the moth to practically absorb frequencies up to 212 kilohertz. As a reminder, the human audible range is between 20 hertz and 20 kilohertz. Therefore, the operational mechanism of a moth’s wing can be used to eliminate most frequencies a human ear is sensitive to.

The paper also demonstrates the improvement in the addition of the wing structure to acoustic surfaces. What is promising is that the results are obtained for in-lab experiments with limited knowledge on how the sound absorption is actually taking place. However, the future proper understanding of the detailed mechanisms should allow the development of new improved metamaterials with notable sound absorption properties.

Towards Novel Passive Noise Cancellation Devices?

Noise cancellation is required for many applications including sound isolation in buildings, airplanes, cars, among others. The possibility of adding an extremely thin layer like the moth wings will allow to have a sound isolation layer than is not bulky to be noticeable. Such inventions, like solar skins which are similarly thin layers that can be used for renewable energy, represent the future trend in functional designs.

Passive noise cancellation headsets can re-emerge as the favorites compared to the popular active cancellation ones. The size reduction in the added material and the improved performance from a similar structure to the one seen on the moth wing should make it a cheaper alternative to the active mode of operation, yet with similar performance guarantees.

Summary

Biomimetics will continue to drive technology forward. When the problems become much more complex to solve, and when existing technologies have reached their end-of-line in terms of development, nature is here to reinvigorate the innovation path as fauna and flora has evolved throughout millions of years to adapt to different conditions that surrounded them. The bio-inspiration from the moth wings should drive sound isolation to new heights and disrupt several technologies including the widely used passive noise cancellation headsets.

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