Piezoelectrically and Capacitively Integrated Wearable Device with Stretchable Ability for Monitoring Rapid Change in Gait and Precisely Step Counting

This paper presents a cost-effective and simple structured lead zirconate titanate (PZT) film-based wearable device for smartly monitoring gait and pace count. The device possesses the interconnected structures of serpentine-shaped strips and square nodes, which causes the large stress and strain gradients when the external force is applied to the terminal nodes of the device. The bimorph configuration of metal/PZT/metal thin-film makes the wearable device thinner than a regular paper. This device responses to the strain with simultaneously piezoelectric and capacitive signal outputs. By attaching this device to the skin around human knee joint with athletic tape laminate units, the information of step counting and rapid change in gait of the walking person could be precisely obtained by the capacitive and piezoelectric detections, respectively. The design, fabrication and characterization of the developed device are described in the text. A subject wears the device to walk on a treadmill with different speed settings of 3 km/h and 9 kmh are performed. The resulting signals successfully demonstrate the device functionality of monitoring gait and counting steps.