Polarization-controlled PVDF-based hybrid nanogenerator for an effective vibrational energy harvesting from human foot

The effective conversion of vibrational energy from the motion of human body into electricity has been considered as one of the most promising technologies for charging portable electronic devices. Here, we report an electric polarization-controlled PVDF-based hybrid triboelectric-piezoelectric nanogenerator (TP-NG) as for an effective energy harvesting of various mechanical vibrations from human foot. The hybrid TP-NG simply consists of PVDF, Al, and acrylic, and the triboelectric NG component is vertically stacked on the piezoelectric NG component. We observed the strong electric-polarization-dependent electric power due to the modulated surface potential and negative piezoelectricity of PVDF. We also observed the in-phase power generation due to the vertical stacking of two flat NGs, irrespective of various loading rate, contact time, force, and frequency. Three hybrid TP-NGs were embedded at the forefoot, arch, and heel positions in a shoe insole. During normal walking, the shoe insole generated sufficient power to operate light-emitting diodes, which could be used in lightning at night. In addition, the insole operated a wireless pressure network, which could be used in monitoring and transmitting the pressure distribution on the foot to a cellular phone. This work provides an important step in the harvesting of random and irregular vibrational energy from the human foot, and in the realization of self powered lightning for safety and self-powered wireless pressure monitoring system for diagnostic healthcare.