A parasitic fly has inspired scientists to create a new type of microphone that achieves better acoustical performance than what is currently available in hearing aids.
Scientists will be presenting results at the 21st annual International Congress on Acoustics in Montreal next week about how an unpresuming little fly called Ormia ochracea inspired their research. The house-fly-sized insect has eardrums that sense sound pressure and help them hear “quite well,” says Ronald Miles, Distinguished Professor of Mechanical Engineering at Binghamton University. He said the female flies use their directional hearing to locate singing male crickets, on which they then deposit their larvae.
The researchers first described the mechanism by which the fly achieves its directional hearing and then designed a new microphone inspired by its ears. The design uses a microelectromechanical microphone with a 1 mm by 3 mm diaphragm that rotates on a central pivot in response to sound pressure gradients. The motion of the diaphragm is detected using optical sensors.
In order to minimize the adverse effects of resonances on the response, the team used a feedback system to achieve “active Q control.”
“Q control basically is an electronic feedback control system to introduce electronic damping,” Miles explains. “You don’t want a microphone diaphragm to ring like a bell. It turns out that in order to achieve a very low noise floor – which is the quietest sound that can be detected without the signal being buried in the microphone’s noise – it is important to minimize any passive damping in these sensors. If you do that, the diaphragm will resonate at its natural frequency. We are the first group to show that you can use this sort of electronic damping in a microphone without adversely affecting the noise floor of the microphone.”
The noise floor of the fly-inspired microphone is about 17 decibels lower than what can be achieved using a pair of low-noise hearing aid microphones to create a directional hearing aid. The new design may be able to be used in applications ranging from hearing aids and cell phones to surveillance and acoustic noise control systems.
Fruit flies have a hearing mechanism that is remarkably similar to that of humans, and they have been used as research subjects to understand our own hearing. In January, researchers at the University of Iowa wrote in the journal Proceedings of the National Academy of Sciences about how fruit flies helped them understand how human hearing is similar to the operation of a car battery. The fly’s ear contains a cell that helps form a tight extra-cellular compartment around them known as scolopale space. This compartment is similar to compartments in a battery that need to be charged up to drive electrons through circuits.