Geometry-engineered hourglass-shaped cracks enable wide-linearity wearable strain sensors

Area of Science:

• Materials Science
• Mechanical Engineering
• Biomedical Engineering

Background:

• Flexible and stretchable strain sensors are crucial for health monitoring and human-machine interfaces.
• Conventional crack-based sensors suffer from performance degradation due to uncontrolled crack evolution.
• A need exists for reliable strain sensors with high sensitivity and large strain ranges.

Purpose of the Study:

• To develop a novel resistive strain sensor with enhanced reliability and predictable performance.
• To precisely control resistance variations using predefined hourglass-shaped cracks.
• To demonstrate the sensor's utility in wearable applications and athlete monitoring.

Main Methods:

• Laser-cutting a serpentine array of hourglass-shaped cracks into a 3D-printed conductive TPU film.
• Utilizing a pre-stretched elastomer substrate to close crack gaps and control crack evolution.
• Employing geometric design to ensure stable and symmetric crack opening under tensile strain.

Main Results:

• Achieved predictable and linear resistance changes over a broad operating range.
• Demonstrated high sensitivity, excellent recoverability after overstretching, and robustness against bending.
• Successfully integrated the sensor for athlete motion analysis and over-exercise warnings using machine learning.

Conclusions:

• The novel hourglass-shaped crack design offers superior reliability and performance for flexible strain sensors.
• The sensor is well-suited for robust wearable applications, including health monitoring and human-machine interfaces.
• This technology holds significant potential for real-time load adjustment and fatigue-risk management in athletes.