Even within a phylum so full of mean little creatures, the yellow-coloured Orima ochracea fly is distinguished among other arthropods for its cruelty – at least to crickets. Native to the south-eastern U.S. states and Central America, the fly is a most predatory sort of parasite. It swoops onto the back of a singing male cricket, deposits a smear of larvae, and leaves its wicked brood to invade, kill and consume the cricket from inside out.
None of this would be possible without the fly’s ability to find a cricket – the cornerstone of this parasitic lifestyle. The fly can pinpoint the location of a chirping cricket with remarkable accuracy because of its freakishly acute hearing, which relies upon a sophisticated sound processing mechanism that really sets it apart from all other known insects.
Now a team of researchers at the University of Texas at Austin has developed a tiny prototype device that mimics the parasitic fly’s hearing mechanism, which may be useful for a new generation of hypersensitive hearing aids. Described in the journal Applied Physics Letters, from AIP Publishing, the 2-millimeter-wide device uses piezoelectric signals. The use of these materials means that the device requires very little power.
“Synthesizing the special mechanism with piezoelectric readout is a big step forward towards commercialisation of the technology,” said Neal Hall, an assistant professor in the Cockrell School of Engineering at UT Austin. “Minimising power consumption is always an important consideration in hearing aid device technology.
There are military and defence applications as well, and Hall’s work was funded by the Defence Advanced Research Projects Agency (DARPA). In dark environments, for instance, where visual cues are not available, localising events using sound may be critical.
Super Evolved Hearing
Humans and other mammals have the ability to pinpoint sound because of the finite speed of sound combined with the separation between our ears. The spacing of several centimetres or more creates a slight difference in the time it takes sound waves to hit our ears, which the brain processes perceptually so that we can always experience our settings in surround sound.
Insects generally lack this ability because their bodies are so small that sound waves essentially hit both sides simultaneously. Many insects do detect sound vibrations, but they may rely instead on visual or chemical sensing to find their way through the fights, flights and forages of daily life.
O. ochracea is a notable exception. It can locate the direction of a cricket’s chirp even though its ears are less then 2mm apart – a separation so slight that the time of the arrival difference between its ears is only about four millionths of a second.
But the fly has evolved an unusual physiological mechanism to make the most of that tiny difference in time. What happens is the four millionths of a second between when the sound goes in one ear and when it goes in the other, the sound phase shifts slightly. The fly’s ear has a structure that resembles a tiny teeter-totter seesaw about 1.5mm long.
Teeter-totters by their nature, vibrate such that opposing ends have 180 degree phase difference, so even very small phase difference in incident pressure waves force a mechanical motion that is 180 degrees out of phase with the other end. This effectively amplifies the four millionths of a second time delay and allows the fly to locate its cricket prey with remarkable accuracy.
Such an ability is almost the equivalent of a human feeling an earthquake and being about to discern the direction of the epicentre by virtue of the difference in time between when the right and left foot fist felt the tremor – except the fly’s hearing is even more sensitive than that, said Hall.
Mimicking the Mechanism
The pioneering work is discovering the fly’s unusual hearing mechanism was done by Ronald Miles at Binghamton University and colleagues Ronald Hoy and Daniel Robert, who first described the phase amplification mechanism the fly uses to achieve its directional hearing some 20 years ago. In 2013, Miles, and his colleagues presented a microphone inspired by the fly’s ears.
Inspired by Miles’ prior work, Hall and his graduate students Michael Kuntzman and Donghwan Kim built a miniature pressure-sensitive teeter-totter in silicon that has a flexible beam and integrated piezoelectric materials. The use of piezoeletrical materials was their original innovation, and it allowed them to simultaneously measure the flexing and the rotation of the teeter totter beam. Simultaneously measuring these two vibration modes allowed them to replicate the fly’s ability to detect sound direction in a device essentially the same size of the fly’s physiology.
This technology may be a boon for many people in the future, since 2 percent of Americans wear hearing aids, but perhaps 10 percent of the population could benefit from wearing one, Hall said.
“Many believe that the major reason for this gap is patient dissatisfaction, he added. “Turning up the gain to hear someone across from you also amplifies all of the surrounding background noise — resembling the sound of a cocktail party.”
The new technology could enable a generation of hearing aids that have intelligent microphones that adaptively focus only on those conversations or sounds that are of interest to the wearer. But before the devices become part of the next generation of hearing aids or smartphones, more design and testing is needed.
“The delicate mechanism must be protected from consumer handling with surrounding packaging,” Hall said, “something the fly need not worry too much about.”
All information contained in the above article belongs to http://www.sciencedaily.com/releases/2014/07/140722111407.htm
