- Spider silk is a thin fiber that can sense sound with exceptional fidelity
- Researchers are exploring ways to use spider silk to enhance hearing aids
Sometime in the 1850s, a dour, alarmingly sideburned physicist named George Stokes slumped over a paper containing a crucial mathematical model. Stokes recognized that dust particles follow the direction of surrounding air, suggesting that extraordinarily thin cylinders styled after dust particles could move and respond to airflow in the same manner. The precise thinness necessary for this replication was nestled in Stokes’s model.
About 150 years later, Binghamton University Distinguished Professor Ron Miles and graduate student Jian Zhou were twiddling with Stokes’ model while studying how certain insects use tiny hairs to hear. As hairs qualify as thin cylinders, it was eventually determined that fibers less than a micron thick move through the air with exceptional fidelity.
A new question arose: If an ultrathin fiber could move with the air, could it also sense sound caused by movements of the air? Dr. Miles and his team began to experiment using spider silk with a half micron diameter to assess the sound-sensing ability of fine fibers.
The answer was “yes” — fine fibers can be utilized as sound sensors. Indeed, spider silk is the perfect research candidate as it qualifies in the two areas in which modern hearing aid microphones are limited: signal-to-noise ratio (SNR) and bandwidth.
To understand SNR, picture a crowded restaurant where you are talking to a friend. Modern hearing aids attempt to prioritize your conversation over other people’s chatter or the air conditioner murmuring in the corner. The signal from your friend compared to the unwanted signal from the air conditioner is SNR. One way to improve this sensitivity is to make the microphone directional, almost like equipping it with a personal compass to distinguish between wanted and unwanted stimuli. In this case, signals arriving perpendicularly from the front, where your friend is, would be accentuated over those coming from other directions.
The second limitation of modern hearing aid microphones is low bandwidth or range of detectable frequencies. However, more is not necessarily better since frequencies beyond the hearing aid microphone’s bandwidth are typically not produced in conversation. Kimberly Skinner, a PhD candidate in speech and hearing sciences at Indiana University, points out that even if present, receiving these outlier frequencies may not benefit a person who is hearing-impaired because of their individual biological incapability to process such sounds. In other words, even the broadest bandwidth cannot alter the fact that someone whose hearing range cuts off at 4,000 Hz cannot hear above 4,000 Hz. That is simply due to specific ear structure.
Naturally directional, remarkably robust, and of a low, ideal density for flat-response from 3 Hz to 50kHz—a bandwidth outreaching that of the human ear—spider silk has ideal qualities to be a sound sensor in microphones. If developed, such microphones may find themselves in smart speakers like Alexa or tucked tidily behind ears in a hearing aid.
While it appears promising, spider silk production is expensive and time-consuming, minimizing its practicality. Acknowledging this critical concern, Dr. Miles is now exploring commercial development of fine-fiber microphones to find a commercially viable spider silk replacement. Thinness—particularly the one-micron diameter limit demanded by Stokes’ model—is the primary requisite for a replacement candidate. Currently, Miles is considering manmade carbon nanotubes which need hefty research and development prior to confirming their potential.
Downsizing is another concern. In the research phase, fat and bulk were permissible—as long as the researcher could determine whether fine fibers could do the job. In commercial production, efficiency is key; thus, the developer is left furiously trimming down a model microphone so it can fit behind an ear. This weight loss program, like most, is a struggle: there are many organs and inner tubings, yet somehow the body is expected to shrink to a tidy, flat contraption.
“It takes a lot of work,” Miles admits. As he pursues commercialization, he is exploring patents, licensing arrangements, and contacts with a small Canadian start-up to make this product a reality. For now, spider silk microphones, complex technology modelled after a natural phenomenon, prove that there is nothing simple about Mother Nature.
Dr. Ronald N. Miles received his Ph.D. in Mechanical Engineering from the University of Washington. As a lecturer at UC Berkeley, Professor at the State University of New York Binghamton, and Associate Dean for Research at Binghamton University, he has received numerous acclamations for his teaching and research. Presently, his research seeks to develop sound sensors inspired by nature. In his free time, he visits his farm, in the warm company of goats, horses, chickens, and birds.
Kimberly Skinner, after 18 years as a passionate clinical audiologist, is currently a Ph.D. candidate in speech and hearing sciences at Indiana University. She works in the University’s Auditory Perception Lab where she researches speech perception, aging, and tinnitus. When away from her research, she enjoys spending time with her daughter.
- Caston, L. Email interview by the author. July 20, 2018.
- Clason, D. (January 16, 2018). Spider silk could offer a breakthrough in hearing aid microphones. The Healthy Hearing Report, Retrieved August 14, 2018, from https://www.healthyhearing.com/report/52826-Spider-silk-could-offer-breakthrough-in-hearing-aid-microphones
- Miles, N. R. Phone interview by the author. July 3, 2018.
- Raju, A. Skype interview by the author. July 21, 2018.
- Skinner, K. Phone interview by the author. July 21, 2018.
- Zhou, J., & Miles, N. R. (November 14, 2017). Sensing fluctuating airflow with spider silk. Proceedings of the National Academy of Sciences, 114(46), 12120-12125. doi:10.1073/pnas.1710559114
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