Scientists and Engineers Have Built a Flow-Sensing Microphone That Detects Tiny Gusts of Sound

Leveraging on their understanding of “spidey senses”, a group of scientists and engineers led by Ronald Miles have designed and created a flow-sensing microphone that can detect tiny gusts of sound. What exactly does this mean? Well, this microphone can beat even the modern-day studio-grade microphone in detecting and capturing the most minute sound source such as a proverbial pin drop.

Said flow-sensing microphone was designed by Miles, an engineer at Binghamton University in New York. Taking inspiration from spiders that use the vibrations of their webs to sense sound, Miles created a new type of acoustic microphone that can also detect tiny gusts of sound (viscous airflow) vis-a-vis, the flow-sensing microphone!

This new type of mic was presented earlier this month at the 18th meeting of the Acoustic Society of America in Ottawa, Canada. With such a great design and performance, this flow-sensing microphone is positioned to be a great blueprint for improving the signal in future small chip-based microphones.

This microphone came to be when Miles devised a theoretical model for the air movement associated with sound waves and calculated its effect on a spider thread. Putting this together along with his knowledge of how spider web threads can be sensitive to sound-induced air flows, Miles and his team were able to calculate how a silk thread can churn out a very broad frequency range.

“These spider silk studies showed that the velocity of the air is a great way to sense sound,” he says. With that, the team proceeded to fabricate 0.5-µm-thick silicon nitride microbeams with a variety of lengths and widths and laid them over a central hole on a silicon chip. The team then placed this microbeam array in an echo-free chamber that damps out all sounds and vibrations above 80 Hz.

After using laser motion-tracking techniques to measure how the microbeams’ displacement will respond to thermal noise and then measuring how it will respond to pure sound waves, they finally cracked the code.

“We ultimately found that if you design a microphone to sense flow, instead of pressure, you can make it small without sacrificing performance,” says Miles. “Large objects like telephone poles are not affected by the viscosity of these small-scale flows, but fine-scale things, like dust floating in the air, are”, he further adds.

While the flow-sensing microphone created by Miles and his team still has room for improvement, we can definitely say that such an invention and discovery is pivotal to the future of microphones.