While some scientists are working at using photovoltaic, thermoelectric or piezoelectric technologies to harvest power and unyoke devices from batteries, MIT researchers are going a different route. They’re rolling all three technologies into one remarkable chip.
The university says this effort is going on in the lab of Department of Electrical Engineering and Computer Science professor Anantha Chandrakasan, with doctoral student Saurav Bandyopadhyay the man behind the new energy-combining circuit that’s capable of using the three power sources at virtually the same time.
What sort of devices might benefit from such a chip? Tiny biomedical devices. Remote sensors. Out-of-the-way gauges – those kinds of things. So imagine a heart or blood-sugar monitor, or a pipeline sensor that could warn of stress that might presage a break. These devices don’t take much energy to run, but then again, the ambient energy sources drawn upon – glances of light, body temperature differences, vibrations – are hardly big generators. Nor are they predicatable.
As the university tells it, the big advance here is the ability of the control circuits on the chip to switch smoothly and seamlessly between the various power sources.
Combining multiple power sources, Bandyopadhyay said, has been tried before, but not with great success. A problem was that the device would take advantage of whichever of the energy sources was putting out the most power at a particular time. This made for a lot of cumbersome and energy-stealing switching – from a heat source, to a light source to a mechanical stress harvester. All rather clumsy.
The MIT approach combines energy from multiple sources by switching rapidly between them. It doesn’t quite sound simultaneous, but Bandyopadhyay did say of the system, “we extract power from all the sources.”
The conquered another challenge, according to the university: driving down how much power the control circuit itself consumes.
The researchers made the system more efficient by using what the university called “an innovative dual-path architechture.” This means the system is able to build up a charge in an energy-storage device (a battery or supercapacitor), which is customary – or it can bypass energy storage and directly power the device.
According to the abstract for the paper that describes the MIT research, published in the IEEE Journal of Solid-State Circuits, this dual-path architecture “has a peak efficiency improvement of 11%–13% over the traditional two-stage approach.”
The abstract also reports: “A proposed time-based power monitor is used for achieving maximum power point tracking for the photovoltaic harvester. This has a peak tracking efficiency of 96%. The peak efficiencies achieved with inductor sharing are 83%, 58%, and 79% for photovoltaic boost, thermoelectric boost, and piezoelectric buck-boost converters, respectively.”
The work has been funded by the Interconnect Focus Center, a combined program of the Defense Advanced Research Projects Agency and companies in the defense and semiconductor industries.