Low-Cost Flexible Piezoelectric Sensors for Real-Time Tactile Monitoring and Energy Harvesting

This work presents a comprehensive investigation and demonstration of flexible piezoelectric tactile sensors for Internet of Things (IoT)-enabled electronic skin (E-skin) applications. These sensors were fabricated using a solution-processed thin film of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] sandwiched between low-cost copper (Cu)-cladded polyamide (PI) sheets, and exhibited extremely low response time <20 ms for ultrasoft finger touch. Excellent sensitivity of ~1.34 V/N was extracted by measuring the finger tapping force, with a high peak-to-peak output voltage ( $V_{\text {P- {P}}}\text {)}$ response of ~6.2 V for touch with force of ~4.5 N. E-skin functionality was investigated by attaching these sensors to various parts of the body, such as fingers, knee, hand, wrist, and neck. Maximum response for neck movement with $V_{\text {P- {P}}}$ value of 5.12 V was achieved. Real-time sensing of tactile activities was demonstrated through the array of sensors integrated with the IoT cloud. Moreover, the excellent energy harvesting capabilities of these devices were verified by charging a $22~\mu $ F capacitor through a bridge rectifier circuit using repeated finger tapping for 20 s to reach 1.2 V. Our investigations indicate that these solution-processed flexible tactile sensors can be useful for demonstration of IoT-enabled self-powered flexible E-skin for robotics applications.