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Monday, July 20, 2009

Energy harvesting made simple


Energy harvesting is a very interesting concept but hasn't yet made it into the mainstream. This is despite some quite compelling technology developments and key researchers such as TI's Gene Frantz looking closely at it.
Part of the problem as been putting together all the bits to make it work, to take the power modules that convert vibration or temperature differences into power for a sensor. Another problem is that this power source tends to be intermittent and a capacitor or other storage can be needed. Then you need very low power electronics to make it work properly.
All in all, a bit of a challenge, but now low power wireless microcontroller and module maker Jennic in Sheffield has developed a demonstration platform that solves all these issues.
This platform combines a sensor with a 32bit controller and standards-based low power wireless link to send signals without batteries, eliminating the potential maintenance overheads of conventional battery power by harvesting energy from sustainable sources.
This appeals to applications that don't usually take up new technology quickly such as Energy and Environmental Management, Building Management, Process Control, Condition Monitoring, Logistics and Asset Tracking, but having a ready-made platform allows sensors to be quickly and easily developed and deployed. Using energy harvesting means the sensors - usually temperature - can be easily deployed without wires and without having to have a costly maintenance schedule to go and replace the batteries.
“Harvesting energy from sustainable sources presents designers with the ultimate power challenge: the energy supplied is not necessarily continuous and is available at relatively low levels,” said Jimi Simpson, Jennic Product Marketing. “This means that every element of the design, from the sensor to the microcontroller, must be considered and managed to achieve the highest levels of power efficiency.”
For the platform, Jennic has worked with other technology suppliers:
- Micropelt for thermogeneration, converting temperature gradients into electrical energy;
- Cymbet, an expert in energy storage and solar power conversion;
- AdaptivEnergy, for harvesting mechanical energy, such as impulse, shock, vibration and footfall, using piezo-based DC power supplies and
- Powercast, for RF energy harvesting. 
Jennic has developed an ultra low power sensor solution based on its JN5139 and JN5148 wireless microcontrollers that interfaces to each harvesting source to obtain the power needed to make periodic sensor measurements and transmission of the same over the wireless network to a central controller.
The 32-bit RISC processor in Jennic’s wireless microcontrollers provides the processing capability to implement a software-controlled charge-and-fire energy management process, in which the microcontroller periodically wakes to measure energy levels, and then measures and transmits data when sufficient energy is available.
“The JN5148 wireless microcontroller undoubtedly sets the benchmark for ultra-low power IEEE802.15.4 based wireless in energy harvesting; featuring sleep current levels of <1µA, an active transmission current of 15mA and a receive current of 18mA,” said Simpson. “This ultra-low current consumption enables the JN5148 to use the smallest of energy stores including super capacitors and rechargeable cells to allow the lowest cost BOM.”


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