Flies provide inspiration for hearing aids
Unless you’re an entomologist — or perhaps a six-year-old boy — you’re probably not a fan of bugs. And if a fly is buzzing around your head, you’re most likely shooing it away instead of thinking about its technological implications. But now some experts are looking to the insect world to perfect the next generation of hearing technology, and the results thus far have been positive.
Across the world, teams of engineers and scientist are in a race to develop the first directional microphone inspired by Ormia ochracea, a parasitic species of fly known for its acute directional hearing. The female Ormia ochracea uses its exceptional hearing, accurate to within two degrees, to locate the singing male cricket and deposit its larvae. The larvae then spend seven days feeding on the cricket’s interior before hatching, at which point the cricket dies.
But it is the structure of Ormia ochracea’s specialized hearing mechanism that is fascinating to scientists, as it is unlike any other insects; consisting of two membranes with a hinged center, the two parts move like a see-saw. Noise coming from one side, and not the other, will cause the nearer side to vibrate.
"The thing that makes it very special is that the fly ear is so small," said Neal Hall, an assistant professor of electrical and computer engineering at the University of Texas. Inspired by the ear of the Ormia ochracea, Hall and his team of engineers developed a prototype of a microphone that is about the size of a fingernail.
Man's large head features a significant space between the ears compared to that of the fly, causing sound to reach the ears at different times. It is that split second interval that allows us to determine the direction a sound is coming from. The small size of the fly’s head, however, with only one millimeter in between its ears, means sound reaches both ears at the same time. Fortunately for the fly (and unfortunately for the crickets) evolution has equipped the fly with the specially designed structure connecting the two eardrums and allowing it to hone in on its target with deadly accuracy.
"It's like having two microphones in one that are linked together by this teeter-totter," Hall said.
And it is the microphone structure in hearing aids that needs the most improvement. Hearing aid technology is constantly evolving and improving, but one thing that hasn’t changed in decades is the hearing aid’s microphone. Background noise is always a problem, and can sometimes be as loud as the speaker’s voice. While the ear itself can filter out unwanted sounds, a hearing aid cannot. And when the speaker is farther away than just a few feet, the sound pressure level reaching the microphone drops. Turning up the amplification is possible, but doesn’t really help as this just increases the level of the background noise as well. Directional technology is available, however thus far it is heavy, expensive and uses too much power to be a functioning solution. Now many are convinced that a microphone that mimics the directional hearing of the Ormia ochracea is the solution to those problems.
As a matter of fact, since the discovery of the fly’s unique hearing structure in the late 90s, scientists and engineers across the world have been working on tiny microphones that mimic the unique teeter-totter mechanism in the fly ear. Teams lead by Ronald Miles at SUNY Binghampton, Miao Yu at the University of Maryland and Neal Hall at the University of Texas have been making tremendous progress and are getting closer to integrating the tiny microphones into hearing aids. And a team at the University of Strathclyde in Glasgow and the MRC/CSO Institute for Hearing Research (IHR) has been awarded a £430,000 grant by the Engineering and Physical Sciences Research Council to build and test the hearing aid for three years, beginning in July 2015.
"Our research aims to create a hearing aid system that can reduce or control unwanted noises, focusing the hearing aid on only the sound arriving from in front of the user,” said Dr. James Windmill of the Centre for Ultrasonic Engineering at Strathclyde.
The hope is that the new microphone design will help better locate where the sound is coming from, reduce background noise and allow the user to focus only on the sound coming from in front of them instead of allowing it to get mixed up with all of the background noise. At Strathclyde, designing, building and testing in the form of human trials will come next.
"We are very excited about this collaboration, applying our hearing aid and hearing loss expertise to this project. These recent breakthroughs in microphones could revolutionize hearing aid design and could result in real advances in the quality of support offered to those affected by hearing loss,” said Dr. Bill Whitmer, scientist at MRC/CSO IHR.