|Researchers at the University of Utah have developed a MEMS microphone
that can be implanted in the middle ear to restore hearing and requires
no clunky external electronics. The device improves upon conventional
cochlear implants, which require a microphone and related electronics to
be worn outside the head, creating reliability issues and social stigma.
Sound normally moves into the ear canal and makes the eardrum vibrate.
At a structure known as the umbo, the eardrum connects to a chain of
three tiny bones-the hammer, anvil and stirrup-that vibrate. The stirrup
touches the cochlea, the inner ear's fluid-filled chamber, and hair
cells on the cochlea's inner membrane move, triggering the release of a
neurotransmitter chemical that carries the sound signals to the brain.
In profoundly deaf people the hair cells don't work. So in a traditional
cochlear implant, the microphone, signal processor and transmitter coil,
which are worn outside the head, send signals to a receiver-stimulator
under the skin, which then sends the signals to electrodes implanted in
the cochlea and stimulates auditory nerves. The ear canal, eardrum and
hearing bones are bypassed.
The system developed in Utah moves all the external components inside
the body. Sound moves through the ear canal to the eardrum, which
vibrates as it does normally. An accelerometer is attached to the umbo
to detect the vibration. The accelerometer is also attached to a chip,
and together they serve as a microphone that picks up the sound
vibrations and converts them into electrical signals sent to the
electrodes in the cochlea.
The package is glued to the umbo so the accelerometer vibrates in
response to eardrum vibrations. The moving mass generates an electrical
signal that is amplified by the chip, which then connects to the a
speech processor and stimulator wired to the electrodes in the cochlea.