Here's a fun fact you probably don't know: Whenever a sound goes into your ear, a much quieter sound comes back out - and if a device picks it up and analyzes it, audiologists can figure out if you have hearing problems.
The cochlea - a spiral-shaped cavity where sensory hairs pick up sound waves - generates those otoacoustic emissions (OAEs) in response to auditory stimuli. Studies have shown that OAEs disappear after the inner ear has been damaged.
Binghamton University Assistant Professor Jian Zhou, PhD '18, will lead a five-year, $1.84 million project funded by the National Institutes of Health to create a dual-sensing ear canal probe that will more accurately and reliably detect those OAEs.
Zhou will collaborate with co-investigators Distinguished Professor Ronald Miles at Binghamton University and Professor Christopher Shera at the University of Southern California's Keck School of Medicine. The team hopes to build a prototype during the first three years and then refine its performance through participant testing.
"Flow microphones have so many potential uses," Zhou said. "Rethinking it as a medical device could help millions of people with hearing impairment around the world receive better diagnosis and provide valuable feedback for treatment."
Conventional microphones detect sound pressure, but sound also causes air movement, and that's what particle velocity detects.
"One of my obsessions has been that you don't need to hear pressure in order to detect sound. You could detect the motion of the air," Miles said. "Both things are the sound, but the microphones that we make and use now are all modeled after human ears, because humans are arrogant animals and we make everything work like us. The truth is, most animals don't hear sound that way at all - they hear the motion of the air. That includes all the insects that can hear. They have mosquito antennae and hairs and other things that move back and forth."
The probe will build on technologies developed by Miles and Zhou - both faculty members at the Thomas J. Watson College of Engineering and Applied Science's Department of Mechanical Engineering - including patented sensing technology inspired by how spiders hear sound through their webs.
While earning his doctorate at Binghamton, Zhou went for a walk through the University's Nature Preserve and saw a spiderweb blowing in the breeze. He returned to Miles' lab with an idea: Could something strong but thin like spider silk be used in a microphone to detect particle velocity?
After some experimentation, the researchers found that it could respond to sound with perfect fidelity from 1 hertz up to 50 kilohertz, a broader frequency range and flatter frequency response than conventional pressure-based microphones.
Although the technology no longer relies on harvesting silk from spiders, Zhou remains grateful for the flash of insight.
"I won't say we can do better, but we can make smaller structures than the insects do using nanotechnology," he said. "We can fabricate structures with dimensions below 10 nanometers, up to 100 times thinner than spider silk."
The bio-inspired flow microphone has been commercialized by the Canadian venture firm TandemLaunch and its spin-off company Soundskrit. For the ear probe, the Binghamton team plans to shrink it down, integrate a laser for more precision, and include a more traditional acoustic-pressure microphone - all while making sure it remains safe for patients.
The smallness of the ear canal and the even tinier human hearing system make it complicated to study, but Miles is looking forward to helping with the design: "This project will require some crazy advances in technology, which is what we're doing because we're engineers who make stuff."
"If we are successful with this project, we will introduce a new instrument that can help us better understand how the ear works, and detect hearing loss earlier and more precisely," Zhou said.
