Binghamton University professor Ron Miles and graduate student Jian Zhou examined what we can learn from insects when it comes to hearing. Most insects have a completely different hearing system than our own. While we use our eardrums to detect the pressure from sound waves, insects typically use hairs on their body to detect the speed of the waves — in other words, they hear through hairs on their bodies.
As it turns out, spider silk is also thin enough to be moved by sound waves, even at very low frequencies. Researchers liken it to tectonic plates moving as a result of an earthquake.
“This can even happen with infrasound at frequencies as low as three hertz,” Miles said of the movement of spider silk.
Technically, any fiber thin enough could be used to detect sound, but its other properties make spider silk much more desirable. While the fiber senses the direction of incoming sound with great accuracy, it first needs to be translated into an electric signal to be of any use, so Miles and Zhou coated spider silk in gold and placed it inside a magnetic field to generate a very simple microphone.
“The microphone consists of super-thin fibers that move with the air in a sound field,” said Miles, a mechanical engineer at Binghamton University. “The fibers are driven by viscous forces in air, like those that cause tiny dust particles to float around in a slight breeze.”
However, this simple microphone proved to be much more effective than many existing commercial options, able to pick up sounds that are too quiet for regular microphones — with great precision.
“By modifying a spider silk to be conductive and transducing its motion using electromagnetic induction, we demonstrate a miniature, directional, broadband, passive, low-cost approach to detect airflow with full fidelity over a frequency bandwidth that easily spans the full range of human hearing, as well as that of many other mammals,” researchers write in the study.
With further sophistication (such as filtering out background noise and improving signal quality), the technology can improve even further. This could be a game changer not only for microphones and hearing aids but also for mobile phones, as well as any industry that requires picking up sounds better and with higher fidelity.
You can see a video comparing the waveform of the silk (the way it moves as a result of sound waves) to its spectrogram here.
Journal Reference: Jian Zhou and Ronald N. Miles. Sensing fluctuating airflow with spider silk. doi: 10.1073/pnas.1710559114