Piezoelectric and triboelectric nanogenerators can convert mechanical energy into electricity, which were invented in 2006 and 2012, respectively. The piezoelectric nanogenerator use piezoelectric polarization charges and the time-varying electric field to drive electrons in a circuit. While the triboelectric nanogenerator use surface electrostatic charges generated by contact electrification between two different materials and the time-varying electric field to drive the flow of electrons. Nanogenerators have demonstrated symmetry and complementarity with the traditional electromagnetic generator in governing equations and output characteristics. Nanogenerators have the advantages of light-weight, small-size, and low-cost. They can collect weak mechanical energy that is not easily obtained by electromagnetic generators, such as wave energy and mechanical vibration.
Nanogenerator as a new energy technology is another important way of power generation by mechanical energy, which could be parallel and equivalently important as the electromagnetic generator for power application. Nanogenerators are a field that uses Maxwell’s displacement current as the driving force for effectively converting mechanical energy into electric power/signal, which is another major application of Maxwell's displacement current in the field of energy and sensing after electromagnetic wave theory and technology. It will greatly promote the development of new energy and self-powered sensor technology, and will be widely used in internet of things, sensor networks, blue energy, big data and other important fields for human future development.