Measurement of Pulsating Flow Using a Self-Attachable Flexible Strain Sensor Based on Adhesive PDMS and CNT

Accurate monitoring is needed for pulsating flow in many healthcare and bio applications. Specifically, real-time monitoring of pulsating blood flow provides rich information regarding a patient's health conditions. This paper proposes a flexible strain sensor capable of detecting the pulsating fluid flow by directly measuring the circumferential strain induced by a rapid change in the flow rate. The thin and flexible strain sensor consists of a polydimethylsiloxane (PDMS) with a Triton-X treatment to enhance the adhesive property and multi-walled carbon nanotubes (MWCNT) as the piezoresistive sensing layer. MWCNT integration implements a simple spray-coating method. The adhesive PDMS/CNT strain sensor exhibits a highly adhesive nature and can be attached to a silicone tube's curved surface. By analyzing the theoretical modeling based on fluid energy equation and solid mechanics, strains induced on the soft tube by the change in flow rate, viscosity, and fluid density can be predicted. We performed the flow rate measurement at varying fluid-flow rates and liquid viscosities, and the results match our prediction. The sensitivity and limit of detection of the presented strain sensor are about 0.55 %min/L and 0.4 L/min, respectively. Both the calculation and experiment confirm that the sensor resistance is most sensitive to the fluid-flow rate, thus, enabling the accurate tracking of pulsating fluids' flow rate, regardless of the viscosity or density.