A ‘teeter-totter’ approach to microphone design

Human ears detect pressure fluctuations, which are translated into electric signals and then interpreted as sound. Most animals, however, respond to the motion of the surrounding medium in a sound field, capturing both sound and the direction of its propagation. Few have explored this natural acoustic sensing mechanism in the fabrication of microphones.

Karimi et al. set out to replicate acoustic flow sensing through developing prototypes of velocity-sensitive microphones.

“In our approach, computational modeling and detailed fabrication are replaced with the creation of physical models that are constructed by hand. This is highly unusual in engineering and requires great skill and effort,” said author Ronald N. Miles. “It can, however, provide results very quickly and can account for physical principles that might have been ignored altogether in a more conventional study.”

By assembling beams attached to a hinge inside a cavity, the authors represented the “teeter-tottering” feature of acoustic flow sensing, akin to the motions of spiderwebs and the viscous-driven hairs of insects.

Subsequent structural and material modifications revealed key design parameters of high-performance, low-noise acoustic particle velocity sensors. Their practical approach to constructing microphone prototypes minimizes design modifications in microfabrication processes, which can be costly.

Next, the authors aim to address the interpretation aspect of acoustic sensing, more specifically the transduction of the sound-driven motion into electronic signals. If realized, this work could lead to innovations such as next-generation hearing aids and underwater robots.

“This transduction is, unfortunately, perhaps the most difficult part of microphone design,” said Miles. “We suspect that some sort of optical scheme might prove to be very attractive and practical to provide this transduction for sensors such as ours.”

Source: “A micro bio-inspired teeter-totter velocity sensitive microphone structure,” by Morteza Karimi, Junpeng Lai, Zihan Liu, Weili Cui, Changhong Ke, and Ronald N. Miles, The Journal of the Acoustical Society of America (2025). The article can be accessed at https://doi.org/10.1121/10.0037234 .