Paper Generators – low-tech and inexpensive way to harvest energy from friction

Researchers at Disney Research, Pittsburgh and at Carnegie Mellon University recently presented a simple system that could be used to harvest power of different gestures performed onto a paper surface. Named Paper Generator, the system exploits gestures such as tapping, touching, rubbing or sliding friction in order to run simple interactive applications involving books, posters and other printed materials without any other source of power.

This new approach to energy harvesting uses electrets – materials with special electrical properties that already are used in microphones and in devices with Micro-Electro-Mechanical Systems (MEMS). Electrets are the electrostatic equivalents of permanent magnets, carrying a quasi-permanent electric charge. These dielectric materials include natural materials such as quartz as well as man-made materials such as polytetrafluoroethylene (PTFE) which is best known by the brand name Teflon.

The design involves sandwiching a thin, flexible sheet of between two conductive layers, such as sheets of metallized polyester, that serve as electrodes. 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 small amount of alternating electrical current is generated. This electrical current can be used to power low power electronics or be used to produce signals for communication devices.

“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.”

Although use of electrets to convert finger tapping into power isn’t groundbreaking, the Paper Generators present a far more low-tech and less expensive. Although the current produced by the devices is low – measured in hundreds of microamperes – the voltage is high, up to 1000 volts. That is ideal for triggering e-paper displays.

Running the alternating current through a small rectifier converts the power to DC to operate LEDs. The power can also be fed into store-and-release circuitry, enabling a buzzer to sound when enough power is stored, or to send an infrared signal to trigger action by a computer. Transmitting the current to an analog voltmeter produces mechanical motion of the needle.

“It’s very simple, it’s flexible and it’s printable using conventional printers”, said Mustafa Emre Karagozler, Disney Research, Pittsburg. “It’s a technology with potential applications we’ve only begun to explore.”

For more information, you can read the following research paper: “Paper Generators: Harvesting Energy from Touching, Rubbing and Sliding” [6.3MB PDF].