Piezoelectric rubber films for autonomous physiological monitoring systems

We have successfully demonstrated the fabrication of piezoelectric rubber films and their applications in heartbeat sensing and human energy harvesting. To realize the desired stretchability and electromechanical sensitivity, cellular polydimethylsiloxane (PDMS) structures with micrometer-sized voids are internally implanted with bipolar charges, which function as dipoles and respond promptly to diverse electromechanical stimuli. The resulting composite structures behave like rubber (with an elastic modulus about 300 kPa) and show strong piezoelectricity (with a piezoelectric coefficient d33 higher than 1500 pC/N). In the prototype demonstration, an autonomous heartbeat monitoring system utilizing stacked piezoelectric PDMS films is demonstrated. While integrated with a 12-μA h solid-state energy storage device and a 552-nW nano-power charge amplifier, the energy harvested from human body is stored and employed to monitor heartbeat. With a working area of 10 cm2 and a compressive load of 10 kg, it is estimated that a charge of 0.1 μC/cycle can be collected using a single-layered piezoelectric rubber film. Furthermore, multiple layers can be stacked and connected in parallel to magnify the charge output. As such, the demonstrated piezoelectric rubber films, which function as both stretchable energy harvesters and highly-sensitive impact sensors, possess a great potential for the realization of wearable and implantable human physiological monitoring systems.