Self-Powered Sleep Tracker: A Battery-Free Wearable Device Using Flexible Piezoelectric Nanogenerator

Piezoelectric nanogenerators have emerged as alternative power sources for various portable and wearable electronic devices and applications in self-powered sensors. In this study, barium titanate ceramics (Ba1–xCaxTiO3) were synthesized and doped with Ca by employing the solid-state reaction method with the doping of calcium as x = 0.03, x = 0.05, x = 0.07, and x = 0.10. The synthesized barium calcium titanate (BCT) piezoceramics were investigated for their piezoelectric properties and energy-harvesting performance. The structural characterizations show that Ca doping with x = 0.05 remains pure and maintains the tetragonal phase of BaTiO3, which exhibits a piezoelectric property. PENG device was fabricated using the prepared BCT/PDMS composite films that were fabricated using the x = 0.05 doping nanoparticles with the polymer to particle weight ratio of 5, 10, 15, 20, and 25 wt%. From the electrical response analysis, 20 wt% composite film generates a maximum electrical output of 80 V and 5.2 μA. The generated electrical response was validated by charging a commercially available capacitor and powering up LEDs. Finally, the fabricated PENG device was used for the real-time application of a self-powered sleep monitoring and sleep activity tracking system by placing the device in various positions in the human body, as well as on the bed. The system was designed with the support of the ESP 32 microcontroller and ThingSpeak cloud. The above analysis and real-time experiments prove that the fabricated PENG device paves the way toward self-powered smart sensors for smart health care applications and the artificial intelligence of things.