Posted On Wednesday, July 11, 2012 at 08:40:21 AM
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| PhD student Saurav Bandyopadhyay (left) and Professor Anantha Chandrakasan (right) showing the designed system |
Researchers at Massachusetts Institute of Technology have taken a step toward batteryfree monitoring systems — which could ultimately be used in biomedical devices, environmental sensors in remote locations and other applications.
Previous work from the lab of Anantha Chandrakasan has focused on the development of computer and wireless- communication chips that can operate at extremely low power levels, and on a variety of devices that can harness power from natural light, heat and vibrations.
The latest development, carried out with Saurav Bandyopadhyay, is a chip that could harness all three of these power sources at once, optimising power delivery. The energy-combining circuit is described in a paper published in the IEEE Journal of Solid-State Circuits.
“Energy harvesting is becoming a reality,” says Chandrakasan. Low-power chips that can collect data and relay it to a central facility are under development, as are systems to harness power from environmental sources.
But the new design achieves efficient use of multiple power sources in a single device, a big advantage since many of these sources are intermittent and unpredictable. “The key here is the circuit that efficiently combines many sources of energy into one,” Chandrakasan says.
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| An illustration showing the chip and the three sources of energy it combines — solar, vibrations and heat |
The individual devices needed to harness these tiny sources of energy — such as the difference between body temperature and outside air, or the motions and vibrations of anything from a person walking to a bridge vibrating as traffic passes over it — have already been made.
Most other efforts to harness multiple energy sources have simply switched among them, using whichever one is generating the most energy at the moment, Bandyopadhyay says, but that can waste the energy being delivered by other sources. “Instead of that, we extract power from all the sources,” he says.
It combines energy from its sources by switching rapidly between them. Another challenge for the researchers was to minimise the power consumed by the control circuit itself, to leave as much as possible for the actual devices it’s powering – such as sensors to monitor heartbeat, blood sugar, or the stresses on a bridge or a pipeline. The control circuits optimise the amount of energy extracted from each source. The system uses an innovative dualpath architecture.
Typically, power sources would be used to charge up a storage device, such as a battery or a supercapacitor, which would then power an actual sensor or other circuit. But in this control system, the sensor can either be powered from a storage device or directly from the source, bypassing the storage system altogether.
“That makes it more efficient,” Bandyopadhyay says. The chip uses a single time-shared inductor, a crucial component to support the multiple converters needed in this design, rather than separate ones for each source.
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08:23:44 AM