Strain in Sound: Soft Corrugated Tube for Local Strain Sensing with Acoustic Resonance

A team from Stanford University, led by Michael Chun, Ananya Nukala, and Tae Myung Huh, has developed a novel sensor called 'Strain in Sound' that uses acoustic resonance within a soft corrugated tube to measure local strain with high precision. The core innovation is a tube with internal corrugated cavities (with periods of 3.1 mm and 4.18 mm). When air flows through, these cavities induce pressure oscillations that excite a standing wave resonance, generating a specific acoustic tone. Critically, stretching the tube changes both the overall resonance frequency and the relationship between frequency and flow speed, due to variations in cavity geometry.

By sweeping air flow rates under different stretch conditions, the team collected resonance frequency data and trained a machine learning model—a gradient boosting regressor—to interpret these acoustic signatures. The dual-period tube design achieved a remarkably low mean absolute error (MAE) of just 0.8 mm for strain estimation, while a simpler single-period version still delivered a 1 mm MAE. The sensor's practical utility was validated by testing it on a mannequin finger, where it successfully differentiated complex, multi-joint configurations, proving its ability to track non-uniform deformations in soft, flexible bodies.