fantastic plastic

Takeo Someya and coworkers at the University of Tokyo have created a flexible sheet comprising organic TFTs that inductively charges electronic gadgets placed on its surface.

According to this Technology Review article, the

system is designed in a way that overcomes the limitations of common induction schemes. Traditional induction systems can only spread small amounts of power over a relatively large area, and fairly large amounts of power can only be supplied to precise locations (such as a toothbrush mount). Someya’s power sheets, in contrast, can be large, and they can still supply a large amount of power to gadgets placed near them.

This new capability, he says, is enabled by a novel design and by advances in the fabrication of flexible electronics. The power system actually consists of two types of sheets: one sheet senses the position of an object, and the other sheet supplies power to the object’s point of contact, but not to the rest of the sheet. “In this way, the system selectively feeds power as high as 30 watts to electronic objects placed upon it,” Someya says.

The position-sensing sheet relies on two types of flexible electronics. Using a technique similar to silk screening, the researchers printed an array of copper coils 10 millimeters in diameter. In addition, they used a modified inkjet printer to print an array of organic transistors. Both devices are thin and flexible enough to bend with a sheet of plastic.

Gadgets would need to be equipped with a coil and special power-harvesting circuitry to use the power pad. As the gadget gets closer to the pad, the electrical resistance of the pad’s coils decreases. The array of transistors detects the exact position of the change in resistance and effectively directs the subsequent power flow, which is provided by devices on the second sheet of plastic.

This second power-supplying sheet has an array of switches and copper coils. The switches, made of silver and plastic, turn the electric current on and off, mediating its flow to the adjacent copper coil.