Now, charge your e-reader with a simple tap!

Researchers have developed new flexible paper generators that use simple rubbing or tapping to produce electricity that can light up LEDs and activate e-reader displays.
The new approach to energy harvesting uses electrets, materials with special electrical properties that already are used in microphones and in tiny MEMS devices.
The latest application, developed by researchers at Disney Research, Pittsburgh and at Carnegie Mellon University, could make possible new types of interactive applications involving books, posters and other printed materials that require no batteries or external power.
The design of a Paper Generator is simple: one approach is to sandwich a thin, flexible sheet of PTFE or Teflon between two conductive layers, such as sheets of metallised polyester, that serve as electrodes.

The prototype can produce 44 milliwatts of power, enough to run an array of LEDs or e-ink display, sound buzzers and infrared communication.
Electrical charge accumulates on the PTFE sheet when paper is rubbed against it.

Then, if the electrodes are made to move relative to each other against the PTFE, a tiny, alternating electrical current is generated.
"Though the fundamental principles of operation remain the same, it's possible to build Paper Generators that respond to a number of different gestures, such as tapping, touching, rubbing or sliding," said Ivan Poupyrev, director of Disney Research, Pittsburgh's Interaction Group.
"We can imagine any number of ways to use this to add sights, sounds and other interactivity to books and other printed materials inexpensively and without having to worry about power sources," said Poupyrev.