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Researchers at MIT’s Microsystems Technology Laboratory, Harvard Medical School and the Massachusetts Eye and Ear Infirmary have developed a hearing aid that lacks any external parts.

Cochlear Implants as Hearing Aids

Cochlear implants have been in use for over 30 years and have benefited hundreds of thousands of hearing-impaired individuals. However, they require external components in order to remain powered, which may often prove uncomfortable for the user.

The MIT group in charge of modifying implants, led by Professor Anantha Chandrakasan, set out to develop a new kind of hearing aid that wouldn’t require extensive parts to function, making maintenance much easier. The researchers combined a typical microchip with a specialized sensor, using an artificial human ear as a test subject.

This particular hearing aid uses a sensor that is piezoelectric, meaning it generates an electric charge when placed under pressure. Piezoelectricity is effective in stimulating the auditory nerve fibers of the ear. Discovered in the 1880’s, the phenomenon was used in early microphones.

The piezoelectric sensor absorbs sound waves while it is present in the middle ear, and in this latest project the MIT group redesigned the hearing aid so that it no longer uses a microphone. Rather, the implant utilizes the natural structure of the middle ear to help communicate sound. The hearing aid is similar in function to the common middle-ear implant, which interacts with the fragile bones, or ossicles, present in the middle ear. Two years before this new innovation, Professor Chandrakasan led a hearing aid-related project on collecting usable energy from the middle ear.

Hearing Aid Efficiency

The hearing aid acts as a relay system throughout the ear. The sensor absorbs sound and transmits the signal to a microchip, located at a different part of the ear. The sound is then changed to an electric signal and transmitted to electrodes in the cochlea, where the user can interpret the signal as sound. The cochlear implant can be charged wirelessly in as little as 2 minutes. The implant can function uncharged for approximately 8 hours, and the new circuit ensures that its power consumption is reduced by an extra 20 to 30 percent.

Older editions of hearing aid implants require bulky, external pieces including a processor, microphone, transmitting coil and power source. However, this new hearing aid’s characteristic wireless charging via smartphone allows for extended periods of comfortable usage and a less conspicuous device.

Alternatives to electric cochlear implants include bone-anchored hearing aids and hearing aid microsystems. Other recent innovations for cochlear implants include Darrin Young’s middle ear microphone at the University of Utah, a hearing aid piece that modifies the original, external components of cochlear implants so that they can be implanted inside the ear. The piezoelectric sensor needs to be modified before the hearing aid can be put on the market for human use, but this new development by Professor Chandrakasan’s group promises yet another useful innovation for the advancement of hearing aid technology.

by Aaron Rodriques