Self-powered flexible pressure sensors with vertically well-aligned piezoelectric nanowire arrays for monitoring vital signs

Human vital signs such as the heartbeat and respiration are important physiological parameters for public health care. Precisely monitoring these very minute and complex time-dependent signals in a simple, low-cost way is still a challenge. This study shows a novel fabrication of vertically well-aligned piezoelectric nanowire arrays with preferential polarization orientation as highly sensitive self-powered sensors for monitoring vital signs. The process realizes in situ poling of the P(VDF-TrFE) nanowires within the nanopores of the anodized aluminium oxide (AAO) template to yield a preferential alignment of both nanowires and the polymer chains required for superior sensitivity in one step. The resulting self-powered flexible sensor shows high sensitivity, good stability and strong power-generating performance. Under bending conditions, the device exhibits a maximum voltage of ∼4.8 V and a current density of ∼0.11 μA cm^-2. The fabricated self-powered sensor shows a linear relationship of output voltage versus compressive force with a high sensitivity, and the piezoelectric voltage of the P(VDF-TrFE) nanowire array is enhanced 9 times that of conventional spin-coated bulk films. Furthermore, the highly sensitive vertically well-aligned nanowire array can be applied as a self-powered sensor for detecting some tiny human activities including breath, heartbeat pulse, and finger movements, which may possibly serve for medical diagnostics as sensors, robotics and smart electronic devices.