A team of researchers at Ecole Polytechnique Federale de Lausanne (EPFL) and the University of Tokyo have created a device made with everyday materials that can produce enough electricity to power several diodes, a small LCD screen or other small electronics and could be used in developing countries with low-power medical diagnostic tools.
Using card stock paper, Teflon tape and a pencil, they made the 8-cm2 device that can generate more than 3 Volts of power -- the same as two AA batteries or enough to power a remote control.
Essentially, the device produces static electricity. Two pieces of card stock paper are covered with pencil on one side and the carbon from the graphite acts as an electrode. The Teflon tape covers is applied to the other side of one of the cards. The paper and Teflon both act as insulators.
When brought together, they make a sandwich: two layers of carbon on the outside, then two layers of paper, and one layer of Teflon in the middle. They are then taped together in such a way that cannot touch, giving the system a configuration that makes it electrically neutral.
By pressing down with your finger on the system, the two insulators come into contact. This creates a charge differential: positive for the paper, negative for the Teflon. When you release your finger and the cards separate, the charge passes to the carbon layers, which act as electrodes. A capacitor placed on the circuit absorbs the weak current that is generated.
The researchers were able to boost the electricity output by pressing sandpaper against the cards, giving them a rough surface. This increased the contact area and lead to a six time increase in output.
Tapping the cards 1.5 times per second for a short burst of time releases the same voltage as two AA batteries, which could power small low-power sensors.
The TENG device (triboelectric nanogenerator), could be a natural fit for low-cost sensors made from paper that are already being tested in the medical field in developing countries. These devices could replace conventional batteries in those types of applications and the materials could be composted at the end of their use.
You can see the tiny generator in action below.