Credit: Nano. Energ. 104, 107902 (2022)

Waste polystyrene film has been converted into a tiny generator that can generate electricity from mechanical vibrations1. Human movements such as knocking, finger pressure and foot stamping produced a large output voltage.

This could be an alternative to batteries for wireless and self-sustaining devices, says a team at the University of Calcutta.

The scientists, led by Abhijit Mallik, prepared a flexible thin film using waste polystyrene and then pasted copper tape onto it to act as a positive triboelectric layer. A negative triboelectric layer was made by stretching a different polymer film onto an aluminium tape. The two layers were assembled with a gap left between them, producing a nanogenerator.

Applying external force caused the polystyrene film to come into contact with the other polymer film, inducing a positive charge on the former and a negative charge on the latter. After withdrawing force, the films separated and induced an output voltage between them, causing free electrons to flow through the external load during the separation process.

Fingers pressing on the nanogenerator produced a voltage that lit up 120 LEDs in a connected series. The device also powered a clock and a calculator without a battery.

It could potentially be used in a traffic surveillance system, with the self-powered sensor detecting vehicle speeds by generating a voltage signal when a vehicle crossed it.