22.10.13

Tapping can power lights and trigger devices

Scientists at Disney Research have developed flexible generators made of paper and plastic that could be used in new types of interactive applications involving books, posters and other printed materials that need no batteries or external power. This approach to energy harvesting uses electrets, materials with special electrical properties that already are used in microphones and in tiny MEMS devices, which can power a string of LEDs or trigger infrared 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.”

Researchers created the Paper Generator by sandwiching a thin, flexible sheet of Teflon between two conductive layers, such as sheets of metallised 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 tiny, alternating electrical current is generated.

This electrical current can be used to power a broad variety of devices such as LED arrays, e­ink
displays, sound buzzers or trigger action by a computer.

Electrets are the electrostatic equivalents of permanent magnets, carrying a quasi-permanent electric charge. These dialectic materials include natural materials such as quartz as well as man-made materials such as PTFE (known by the brand name Teflon).

The researchers also printed Paper Generators using conventional ink-jet printers equipped with cartridges with conductive ink. Though the current produced by the devices is low –measured in hundreds of microamperes – the voltage is high, up to 1,000 volts.

The power also can 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,” Karagozler said. “It’s a technology with applications that we’ve only begun to explore.”