Matt Reynolds, an assistant professor in the electrical and computer engineering department at Duke University, wears other hats, too — including that of co-founder of two companies. These days, his interest is in a real hat now in prototype: a hard hat with a tiny microprocessor and beeper that sound a warning when dangerous equipment is nearby on a construction site.
What’s unusual, however, is that the hat’s beeper and microprocessor work without batteries. They use so little power that they can harvest all they need from radio waves in the air.
The waves come from wireless network transmitters on backhoes and bulldozers, installed to keep track of their locations. The microprocessor monitors the strength and direction of the radio signal from the construction equipment to determine if the hat’s wearer is too close.
AMBIENT ENERGY
Reynolds designed this low-power hat, called the SmartHat, with Jochen Teizer, an assistant professor in the school of civil and environmental engineering at Georgia Tech. They are among several people devising devices and systems that consume so little power that it can be drawn from ambient radio waves, reducing or even eliminating the need for batteries. Their work has been financed in part by the National Science Foundation.
Powercast, based in Pittsburgh, sells radio wave transmitters and receivers that use those waves to power wireless sensors and other devices. The sensors, for example, monitor room temperature in automatic systems that control heating and air conditioning in office buildings, said Harry Ostaffe, director of marketing and business development.
The company recently introduced a receiver for charging battery-free wireless sensors, the P2110 Powerharvester Receiver, and demonstrated it in modules that sense temperature, light level and humidity data, he said. The modules include microcontrollers from Microchip Technology, in Chandler, Arizona.
UNTAPPED POWER
Until recently, the use of radio waves to power wireless electronic devices was largely untapped, because the waves dilute quickly as they spread, said Joshua Smith, a principal engineer at Intel’s research center in Seattle and an affiliate professor at the University of Washington.
“That’s changing,” said Smith, who explores the use of electromagnetic radiation. “Silicon technology has advanced to the point where even tiny amounts of energy can do useful work.”
Two types of research groups are extending the boundaries of low-power wireless devices, said Brian Otis, an assistant professor of electrical engineering at the University of Washington. Some researchers are working to reduce the power required by the devices; others are learning how to harvest power from the environment.
“One day,” Otis said, “those two camps will meet, and then we will have devices that can run indefinitely.”
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