A new ear implant could allow deaf people to hear without having to wear an inconvenient external microphone.
Researchers in the US have tested a proof-of-concept version of the 25mg microphone, which is designed to sit in the middle ear and work with electronic cochlear implants that have already restored basic hearing to hundreds of thousands of people.
Conventional cochlear devices use a head-mounted microphone behind the ear that transmits the sound as a radio signal to an implant that then converts it into electrical impulses that can be fed into the nervous system.
‘It’s a disadvantage having all these things attached to the outside [of the head],’ said Darrin Young, associate professor of electrical and computer engineering at Utah University and senior author of a study of the device.
‘Imagine a child wearing a microphone behind the ear. It causes problems for a lot of activities. Swimming is the main issue. And it’s not convenient to wear these things if they have to wear a helmet.’
The researchers tested the microphone in the ear canals of cadavers and their study, published in the journal Transactions on Biomedical Engineering, showed incoming sound is transmitted most efficiently if one of the three small bones in the ear (the incus or the anvil) is first removed.
Conventional microphones use a membrane that moves and generates an electrical signal change in response to sound, but these require a hole for the sound to enter that would get clogged by growing tissue if implanted.
The new device instead uses an accelerometer — a 2.5mg mass attached to a spring — placed in a sealed package with a low-power silicon chip to convert sound vibrations to outgoing electrical signals.
The current version of the microphone measures 2.5 x 6.2mm but Young said it would need to be reduced to 2 x 2mm and its ability to detect quieter, low-pitched sounds improved, meaning tests in living people would likely be around three years away.
Users would also need to wear a charger behind the ear while sleeping at night to recharge an implanted battery, which could last up to several days between charges.
Young said the microphone might also form part of an implant that could replace conventional hearing aids for a certain class of patients who have degraded hearing bones that are unable to adequately convey sounds from conventional hearing aids.