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A Batteryless Sensor Chip for the Internet of Things

A prototype sensor saves power by using transistors that never fully turn “on.”

The promise of the Internet of things is, in a sense, passivity. Our homes and offices will monitor us, and respond to our needs without instruction. But for tiny wireless sensors all over us and our things to really be feasible, we’ll have to replace today’s power-needy devices with more self-sufficient alternatives.

PsiKick’s first low-power chip
Low-power chip: PsiKick’s first low-power chip runs on harvested energy. It includes only a subset of components that the company plans to incorporate on its first commercially available chip.

A new kind of ultra-low-power microchip design could help make this possible.

Normally, the transistors in circuits are either on, with current flowing through them, or off, with no current flowing through them, depending on whether their voltage supply is above or below a certain threshold value. In reality, though, a small amount of current leaks through most transistors even when they are technically switched off. For certain tasks, chips can be designed to take advantage of this phenomenon and use this current, dramatically reducing their need to switch to a more power-intensive “on” state.

A Virginia-based startup called PsiKick is developing one such microchip for simple sensing tasks. Depending on the application, it consumes between 1 and 0.1 percent of the power of comparable chips on the market, says PsiKick cofounder David Wentzloff.

Wentzloff and cofounder Benton Calhoun did their graduate work together in Anantha Chandrakasan’s Energy-Efficient Circuits and Systemslab at MIT. The two went on to become professors at the University of Michigan and the University of Virginia, respectively, but continued their collaboration. The startup plans to sell its first chips in 2015.

Wentzloff and Calhoun aren’t the only ones developing what are known as “sub-threshold” microchips. Others exploring the concept include ARM Holdings, the British microchip company that licenses designs for many mobile processors, and IMEC, a microelectronic research center based in Belgium.

Requiring so little power means PsiKick’s chip can function even with the small amounts of power that can be scavenged without using a battery. Wentzloff and Calhoun have tested their chip design in a wearable EKG monitor that runs entirely on body heat. Thanks to other energy-saving techniques, the device required 0.1 percent of the power consumed by a typical EKG monitor, Wentzloff says.

In the future, the energy could come from a small solar panel; an antenna that collects ambient radio wave energy; a thermoelectric material that absorbs body heat; or piezoelectric devices that collect energy from movement.

Luis Ceze, an associate professor in computer science and engineering at the University of Washington, says he’s been following the work of Wentzloff and Calhoun and thinks their technology has promise.

“If you can actually pull off designing devices that work off of harvesting energy, it opens up an incredible number of applications,” Ceze says. “It’s pointing toward a trend that I think will be incredibly exciting.”

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