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New research from Binghamton University, State University of New York shows that fine fibers like spider silk actually improve the quality of microphones for hearing aids. Source: Jian Zhou

An unconventional material could be the key to improving an important piece of assistive technology.

Researchers from Binghamton University found that fine fibers like spider silk could boost the quality of microphones built into hearing aids.

Hearing aids are built with three basic parts: a microphone, amplifier, and speaker. The device receives sound through a microphone transforms the sound waves to electrical signals and sends them to an amplifier. The amplifier boosts the power of the signals and then sends them to the ear through a speaker, according to the National Institute on Deafness and Other Communication Disorders.

Almost all of these devices have two microphones built into them, but users can encounter difficulties when they are in a crowded area since competing conversations can drown out the conversation they are trying to hear due to difficulties of processing different sounds.

However, this experiment could provide a way to solve that conundrum.

Ron Miles, a co-author of this study and mechanical engineering professor at the university specializing in vibrations, acoustics, and other areas, answered a few questions in an interview with R&D Magazine regarding the inspiration for this research and how it could lead to enhancements for these important medical devices.

R&D Magazine: Where did the idea for this experiment come from?

Miles: "The idea came from previous work studying hearing in small animals.  Many animals have ear drums like we do where they process sound based on pressure, but most animals, including lots of insects, can sense the motion of air in a sound field via very fine hairs. Using a fiber to sense sound is something I've been interested in for a very long time especially seeing how the fiber moves within a sound field."

R&D Magazine: Why did you explore how this silk could improve the microphones built into hearing aids?

Miles:  A significant issue with hearing aids is when the user is in a noisy place so competing conversations can drown out the conversation you are trying to hear. 

Virtually all hearing aids are built with two microphones. Both mics detect the difference between the pressures and the hearing aid processes that sound to get rid of unwanted noises.  However, the wavelength of sound depends on its frequency so at low frequencies (long wavelengths), the difference signal picked up by the two mics is much smaller than it is at higher frequencies.  As a result, the signal being processed sounds bad, making the hearing aid less effective at eliminating unwanted noises.

 

Basically, you need a directional microphone that can process these signals with really good fidelity to eliminate that background noise.

R&D Magazine:  Walk me through how the experiment was performed.

Miles: We used natural spider silk that came from a common spider that occurs in the northeast. It was the easiest material we could get. Originally, we tried thicker materials like wire as well as a PMMA material like plastic that was spun into a very fine fiber. It agreed with our analytical models and everything, but it was very easy to break.

The spider silk was coated in gold that was about 80 nanometers thick. We placed the fiber in an anechoic chamber, which is a very quiet room with no reflection from the walls. 

We had the fiber positioned three feet away or so from a loudspeaker placed in the chamber to create a sound field. The fiber was oriented perpendicular to the sound the speaker was creating.

A magnet was placed next to the fiber and we used an amplifier to measure voltage across the two ends of the wire. 

We also used a laser vibrometer to measure the small vibrations of the fiber which helped us verify our mathematical model. 

R&D Magazine:  What was the significance of these findings?

Miles: The silk was able to deliver an extremely broadband uniform response.  We showed it was directional even when picking up really low frequencies all the way down to 3 Hertz.

R&D Magazine:  What is the next step in this research?

Miles: The basic idea of this was to show that it is effective, but there's a lot of work that needs to be done. Engineering this application into future products would mean the fiber would need to be made out of a man-made fiber such as carbon nanotubes similar to graphene. The most important thing would be to have a fiber that is very thin. Less than a micron in diameter could be a really excellent sensor for sound.

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