A nanogenerator for energy harvesting from a rotating tire and its application as a self-powered pressure/speed sensor.

Harvesting unexploited energy in the living environment to power small electronic devices and systems is attracting increasing massive attention. [ 1–7 ] As the size of the devices has shrunk to the nanoor microscale, the power consumption also decreased to a modest level, i.e., the microwatts to milliwatts range. It is entirely possible to drive such a device by directly scavenging energy from its working environment. This self-powered technology makes periodic battery replacement or recharging no longer necessary and it is thus attractive for portable or inaccessible devices. Mechanical energy is a very conventional energy source in our living environment, with sources including the vibration of a bridge, friction in mechanical transmission systems, deformation in the tires of moving automobiles, etc., all of which are normally wasted. This form of energy is particularly important when other sources of energy, such as sun light or thermal gradients, are not available. A nanogenerator (NG) is designed to transfer such energy into electric energy by the piezoelectric effect. [ 8–14 ] The fundamental mechanism of a NG is that, when it is dynamically strained under an extremely small force, a piezoelectric potential is generated in the nanowire and a transient fl ow of electrons is induced in an external load, as driven by the piezopotential to balance the Fermi levels at the two contacts. For bicycles, cars, trucks, and even airplanes, a self-powered monitoring system for measuring the inner tire pressure is not only important for the safe operation of the transportation tool, but also for saving energy. In this work, a NG was integrated onto the inner surface of a bicycle tire, demonstrating the possibility for energy harvesting from the motion of automobiles. A small liquid-crystal display (LCD) screen was lit directly using a NG that scavenges mechanical energy from deformation of the tire during its motion. The effective working area of the nanogenerator was about 1.5 cm × 0.5 cm and the maximum output power density approached 70 μ W cm − 3 . Integration of many nanogenerators is presented for scale-up. Furthermore, the NG showed the potential to work as a self-powered tire-pressure sensor and speed detector. This work provides a simple demonstration of the broad application prospects of NGs in the fi eld of energy harvesting and self-powered systems.