Hearing aids, as those who wear them know, have some flaws. Whistling, echoing and feedback often frustrate even the most intrepid user. Biomedical engineering graduate student Peyton Paulick seeks to give those with hearing loss a better option, and if the first human clinical trial of her research device is any indication, she may well succeed.
The device, a small voice coil actuator placed deep within the ear canal, responds to an electronic signal by moving the eardrum mechanically – just the right amount – to allow sound waves to enter. This eliminates the problems that occur when sound waves are amplified, as in hearing aids.
Currently, options available for the hearing impaired are limited. Cochlear implants require major surgery and can cost upwards of $30,000. Traditional hearing aids have advanced technologically but still present those little annoyances.
“Satisfaction rates are pretty low,” Paulick said. “A lot of people with traditional hearing aids don’t use them.”
Additionally, of the more than 34 million hearing-impaired people in the United States, only 25 percent use hearing aids, leaving approximately 25 million patients untreated.
Paulick’s device is inserted – by a physician in an outpatient setting – deep enough within the ear canal to touch the eardrum. It uses a digital processing unit to convert sound to an electronic signal, which causes the device to vibrate at specific frequencies. The vibration moves the eardrum a predetermined distance, allowing the sound waves in and translating to a perceived sound by the patient.
“The small vibrating unit that couples directly to the eardrum knows exactly how much to make the eardrum move at any range and frequency to interpret that sound,” she says.
The small voice coil actuator is three millimeters wide and six millimeters long. It is inserted by a physician
in an outpatient setting. The team hopes it can be manufactured for about the same price as a hearing aid.
In many people with hearing loss, the eardrum may still move but sensitivity to sound has decreased. “So we make that movement bigger so they can hear it. We make sound louder by driving the eardrum to move more,” she explains.
The device – a small cylinder about three millimeters wide and six millimeters long – passed bench tests and cadaver tests earlier this year with flying colors. (In cadaver testing, a laser Doppler vibrometer measured how much the bones of the middle ear moved in response to sound.)
But the true test was the human trial in late September. The device was inserted into the right ear of volunteer Mark Bachman, assistant professor of electrical engineering and computer science, and a member of the research team.
Bachman also wore an external earphone on his left ear. Sounds were played through both devices at different decibel and frequency levels until the sounds matched, giving researchers insight into the settings necessary for the device to achieve comparable sound.
The process is subjective, but “that’s how hearing aids work too,” Paulick says. “The device will be tailored to a specific person, depending on how severe his/her hearing loss is. But just making those movements larger will achieve that. This was a proof of concept.”
Additionally, the trial tested the device’s capability to transmit complex audio waveforms – in this case, music. By all accounts, the experiment was a success. Bachman said the music sounded clear and pure, like it originated “inside his head.”
It was a big moment for the research team. “These complex audio waveforms are quite a bit more complicated than just regular sounds,” Paulick said, adding that hearing-aid users and those with hearing loss often miss fine pieces of sound – classical music and conversation in noisy environments, for example. “By playing this type of waveform with very different sound elements we know now we can transmit that information successfully.”
Bachman was pleased with the results as well. “It works. It does produce sound and it uses a lot less power than our original measurements were suggesting it might use,” he said. “As a proof of concept, it was fantastic; it was a big success.”
-- Anna Lynn Spitzer