Flexible Resistive Strain Sensor Based on PDMS-Coated MWCNTs and MWCNTs/GNP for Wrist Pulse and Respiration Monitoring

This work presents a simple fabrication method for detecting human wrist pulse and respiration rate using a flexible resistive strain sensor. Two types of flexible strain sensors were fabricated, one based on polydimethylsiloxane (PDMS)-coated multiwall carbon nanotubes (MWCNTs) and the other MWCNTs/graphene nanoplatelets (GNPs) composite on a PDMS substrate. Both sensors exhibited high sensitivity, with gauge factors (GFs) of 35.37 for MWCNT-based sensors and 49.53 for MWCNTs/GNP-based sensors, and excellent stretchability, with detectable strain ranges of up to 236% and 164%, respectively. By detecting changes in resistance relative to applied mechanical strain, these sensors effectively captured weak wrist signals and breathing rates of 17 breaths/min for MWCNT-based sensors and 20 breaths/min for MWCNTs/GNP-based sensors. The fabricated sensors demonstrated high performance and applicability, making them suitable for use in wearable health monitoring devices.