It’s not a secret that replicating what the human brain and senses do naturally still presents a substantial challenge in engineering. New advances in restoring and improving hearing are getting closer to the real thing by going mobile and taking cues from nature.
A little yellow fly that lays parasitic eggs is actually the inspiration for a next-gen hearing aid. Its complex “ear” near the base of the front legs responds to male cricket calls, and is the model for tiny microphones. Two or more microphones detecting the pressure changes in sound waves are better for hearing aids, but the smaller and closer the microphones, the harder it is to accurately detect those waves. The mechanics of the MEMS microphone design come directly from the fly, and new research scheduled to be presented at the International Congress of Acoustics in June shows that by tweaking certain parameters, the prototype hearing aid can be made much smaller than conventional ones, with a greater tolerance to noise.
Of more immediate impact are hearing aid apps for smartphones, which contain the microphone, processor, and headphones needed for a hearing aid at a fraction of the cost of a separate device. Hearing aid apps with diverse features and prices are available, but one recent app that stands out is BioAid, a free and open source hearing aid.
The difference with BioAid is that its algorithm performs compression and amplification selectively across different frequency bands, instead of a uniform gain across all frequencies, like turning up the volume. Since it was built by hearing researchers in the U.K., it has been lab tested with real hearing-impaired volunteers. With the app’s sliders, users can adjust and save filters for different background noise levels. Plus, the phone’s touchscreen and charger save users from the tiny-battery-fat-fingers dilemma.
On a regulatory note, the Food and Drug Administration is paying close attention to mobile health services, which may explain why some apps shun the “hearing aid” label or are plastered with heavy disclaimers. Congressional hearings in March were a prelude to upcoming new FDA guidelines on smartphone and mobile health apps; 75 apps have been approved so far.
The bulky cochlear implant, one of the great successes of sensory prosthetics, is also getting a makeover. Georgia Tech researchers, for example, have developed a thin film electrode array that flexes to fit the tiny, two-millimeter diameter cochlear surface to better stimulate the auditory nerve. This still needs to be connected to a battery, microphones, and processor; the externally visible part of conventional cochlear implants. A fully internal system, trialed by industry leader Cochlear in 2007, means users never have to remove it to swim, sleep, or shower. The downside with an internal microphone, apparently, is that you can really hear your chewing and heartbeat, but with signal processing this effect can be mitigated.
With the cost of conventional implants being reduced by upstarts like Nurotron thanks to cheap manufacturing and fast-tracked regulatory approval in China, and biotech providing new materials and designs, a true bionic ear (3D printed of course) may be arriving at the speed of sound.