Highly sensitive strain sensors with minimal hysteresis using laser-induced graphene

Abstract

This study optimises the fabrication of piezoresistive strain sensors using direct laser writing to minimise hysteresis. Fine-tuning the fabrication process created highly sensitive, linear, and repeatable sensors. The most sensitive sensor, fabricated with 32% laser power and 325 pulses per inch, achieved a gauge factor of approximately 100. This is significantly higher than commercially available metal foil strain gauges, which typically have gauge factors ranging from 2 to 5. The resistance of these sensors can be adjusted across a broad range, from tens of ohms to several kilohms. This sensor element exhibits remarkable sensitivity, demonstrated by a greater than 4500% increase in resistance during each loading cycle at 40% strain. This substantial resistance change is a powerful signal amplifier, enhancing the signal-to-noise ratio and enabling operation across a wider strain range. The sensor's performance is optimised through laser machining, with electrical resistance inversely related to laser power. Notably, sensors fabricated with varying machining parameters consistently display excellent linearity, reaching up to 99.9% in some cases by adjusting the laser power between 36 and 40%. Ultimately, the optimised sensors achieve near-perfect linearity (0.999) across a 0–40% strain range (and beyond), coupled with a high gauge factor (approximately 100) and an exceptionally low limit of detection (0.027%). This combination ensures both high sensitivity and precision, providing a reliable tool for strain-sensing applications.