There’s a reason we fear—and respect—spiders: These arachnids use their nearly invisible, delicately woven webs to ensnare prey, trapping them in their sticky, ultra-strong silk. Spiders also use silk to create egg sacs, build protective shelters, and pick up air currents to sail in the sky.
Now, in a recent study in PNAS, researchers found out that spider silk can be used to detect sounds, and the science of this can potentially be applied to improving hearing aids and microphones.
For years, scientists have turned to animals to inspiration when making sensors. For example, some animals use hairs on their body to detect sounds, and researchers have tried to reproduce that. However, using spider silk had more significant effects and detected sound with high efficiency.
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Researchers from Binghamton University wanted to detect small air motions and were looking for a thin fiber material to capture this. The material would need to be thin, strong and lightweight, and the researchers tried to create artificial fibers using an electrospinning process.
Then, inspired by a spider web, Jian Zhou, a fourth-year Ph.D. candidate in mechanical engineering and co-author of the study, suggested they could use spider silk instead.
“I watched a spider spin its web,” Zhou said. “It’s very beautiful and holds in the wind. It must be very strong and I thought it would be ideal in our research.”
The diameter and thinness of spider silk were crucial to making it work for this study. The researchers coated spider silk with a thin layer of gold to allow it to conduct electricity. This way, when they put the fiber in a magnetic field, it could produce a detectable voltage.
“There are very few characteristics that are very important,” Ron Miles, mechanical engineering professor at Binghamton University and co-author of the study, said. “The most important is the diameter of the silk and how thin it is. The other properties like the strength and the stiffness of the silk is actually less important for making it work.”
Since the fibers were so thin, researchers were able to use the spider silk to detect tiny air motions in a sound field over a broad range of frequency, from infrasound to ultrasound. Not only that, it can also detect sound based on its direction. For example, the fiber won’t respond when the sound is coming from a direction parallel to it. But when the sound comes from a direction perpendicular to it, it moves.
“This fiber can be used to detect sound over an incredibly broad range of frequencies, and it can do that because it’s very thin,” Miles said. “Not only is it a flat response microphone but a directional microphone.”
This is helpful when applied to devices like hearing aids. For example, current hearing aids currently use a pair of microphones to get rid of unwanted noise around the user. Still, these microphones have limitations in a noisy environment.
However, thin fibers would be better at detecting noise coming from a certain direction. It’s possible that the results of this study can be used in creating small directional microphones that can process signals to eliminate unwanted sounds. These microphones could be used in portable electronics, cell phones, computers, hearing aids and more.
“People who use hearing aids have a hard time communicating in a noisy environment, so there’s technology in the hearing aids that help them get rid of unwanted sounds. One problem is when you use a pair of microphones, it depends on frequency. As you go down in frequency, the wavelength becomes longer and you get less signal,” Miles said.
Miles also suspects that since spider webs can move with the air, spiders may possibly be able to “hear” using the motion of their web. It’s not yet proven, but researchers are interested in investigating this.
For future research, Miles and Zhou are looking into commercialization. They’ve shown that a fine fiber can respond to sound flow, so now they have applied for a patent and are in discussions to continue developing the idea of using fibers as a high frequency sensor to detect sound.
However, Miles says, the main limitation of the study is to make it more practical. Using spider silk is not the most practical method.
“It may be difficult to have spider silk,” Zhou said. “In the future, maybe we’ll use nanotube materials and fibers. We will try to make it practical.”
They are currently looking into alternatives, such as carbon nanotubes or carbon yarns. And it’s feasible that in the future, we may have better hearing aids—thanks to thin fibers inspired by spiders and their delicately woven webs.
