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Spider Silk Could Offer Breakthrough in Hearing Aid Microphones

A recent study on spider silk is providing promising possibilities for the way hearing aid microphones will be able to manage background noise — and may even change the way you look at the eight-legged creatures the next time you encounter one. The fiber they spin could be the future of directional microphone technology in hearing aids, improving the quality of sound wearers experience across all frequencies.

The study by Binghamton University distinguished professor Dr. Ron Miles and graduate student Jian Zhou was published in the Proceedings of the National Academy of Sciences of the United States(PNAS) in October, 2017.

Miles has been studying hearing in small animals, especially those which don’t have eardrums such as spiders, mosquitos and crickets, for years. His research focuses on ways to implement the basic way these animals hear into ideas which will create better directional microphones for hearing aids.

Hearing aid performance in noise

One of the biggest complaints among hearing aid wearers is trouble understanding speech in background noise. This is especially difficult when that background noise is more speech from multiple talkers, such as large meetings, cocktail parties or in busy restaurants. Speech includes a combination of high and low frequency sounds. A person with normal hearing can detect frequencies between 20-20,000 hertz (Hz). Vowel sounds, like a short “o” have low frequencies (250-1,000 Hz), while consonants like “s,” “h” and “f” have higher frequencies (1,500-6,000 Hz).

Although today’s directional microphones currently help hearing aid users with speech discrimination, the technology requires two microphones which must be spaced properly within each hearing device in order for them to correctly measure the difference in the frequencies and timing of sound they detect. Because of space limitations, directional microphones are only available in behind-the-ear (BTE) models and larger custom hearing aids — and detecting low frequencies is still problematic.

Solutions inspired by nature

Conversely, the fiber used in the study’s experimental microphone detects the directionally-dependent signal itself, eliminating microphone separation requirements and results in a hearing experience that sounds good at all frequencies, from three Hz all the way up to 50 kilohertz (kHz).

“This provides a very different way of obtaining a different signal that is not done now,” Miles said. “The ability to get rid of unwanted sound all the way across the audible band and to detect that different signal with high fidelity across the audible band seems like it will provide an advantage.”

“Our hope is that this will provide a new way of solving this hearing aid problem.”

Miles acknowledges the quest to replicate hair sensors isn’t new. “Other folks have tried to make flow sensors that work like hairs on small animals, but they don’t move very well,” he explained. “The basic reason is because they are too heavy. If we could make a sensor that was really thin, really light and would respond really well to the tiny bits of air flow that occur in a sound field, they could be used as a directional microphone.”

Since uber-thin fibers aren’t rigid enough to stand on their own and detect airflow, Miles opted to suspend the fiber between two points, much like a clothesline. The idea to use spider silk was an accidental one, he said. Man-made nanofibers, which can be electrospun to 20 nanometers in diameter, weren’t strong enough and are difficult to handle — that’s when Zhou made a game-changing observation during a walk on the campus nature preserve.

“He noticed spider webs could blow around in the wind and are very, very strong,” Miles said. “He said ‘why don’t we just use that?’ Tiny spiders spin very, very fine silk just the diameter that we needed — and it was easier than making our own.”

Practical considerations

Today the lab is home to a colony of well-kept spiders, who happily spin silk for Miles and Zhou to use in their research. But don’t wait to buy hearing aids until this technology is available. In addition to his study of animals and the ways in which they hear, Miles aid he’ll also be working to make their current discovery practical for mass production, something he doesn’t see happening for many years.

“I think it can be made very cheaply, but there’s a lot of development that has to go on,” he cautioned, “and that’s always really hard. That’s actually harder than coming up with the idea in the first place.” The most obvious challenge Miles acknowledges is the size of the microphone. The microphone used in their research is large, but hearing aid technology needs to be small in order for consumers to accept it. Getting the microphone to a size small enough for manufacturers to use in their smartly designed devices could take many years.

What will they think of next?!

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