Energy harvesting devices were the focus of the majority of papers at this year’s nanoPower Forum. Piezoelectric, thermoelectric, radio frequency (RF), and even multi-source energy harvesting were among the areas discussed in detail. The following is a brief summary of three of the over 20 papers presented on various aspects of energy harvesting.
Jeff Rogers, CTO with The Face Companies, presented a piezoelectric energy harvesting technology called "Lightning" that can generate 300 mJ of energy, or more with larger devices. Producing 300 mJ of energy is one or two orders of magnitude more energy than typically produced by earlier generations of piezoelectric materials.
Lightning elements are a few (typically 6 to 15) thousands of an inch thick. They consist of a PZT ceramic layer bonded to an aluminum substrate using a thermoplastic film. The substrate construction makes Lightning very rugged and contributes to its ability to be cycled millions of times without failure. The company recently entered volume production of Lightning in a factory in Taiwan.
"We make the PZT material in mainland China and assemble the Lightning elements at the factory in Taiwan," stated Rogers. "In the future, we expect to reduce the cost of Lightning elements to about a dollar, possibly less, in high volumes, depending on the size of the element."
Earlier the same morning, Jesse Goellner, Program Manager with Powercast discussed a field trail with the goal of "making wireless networks truly wireless using RF power." For purposes of this field trial, Powercast partnered with IntelliSensor and deployed radio frequency power harvesting to provide a continuous trickle charge for a rechargeable battery in a real environmental monitoring situation.
Powercast has integrated its Wireless Power Platform™ with IntelliSensor’s intelligent wireless temperature and humidity sensors. Powercast’s Wireless Power Platform™ ensured an uninterrupted stream of data by maintaining rechargeable batteries at their full charge level. To evaluate the technology, the IntelliSensor node utilizing Powercast technology was deployed next to an existing identical wireless temperature and humidity sensor powered by a conventional battery pack. The co-location provided a direct test comparison of the data response and reliability of the differently powered sensors and a comparison of their power consumptions.
"Approximately 103 days into the test, voltage in the conventional battery supply had dropped from its initial state of 3 volts to 2.4 volts. At 117 days into the test, the conventional battery supply failed," Goellner said. "Today , at almost 270 days into the test, the IntelliSensor node Powered by Powercast is still operational and in use, with the battery voltage remaining at 3 volts."
On the final morning of the nanoPower Form, John Langley, CTO of Ambient Micro, discussed "multi-source energy harvesting." The test bed included a custom-designed ferrite rod RF collector, a vibration transducer from Piezo Systems, a Plastecs photovoltaic cell, and a Melcor thermoelectric generator.
"Collecting energy from multiple ambient sources can yield a more constant energy supply," Langley stated. "Employing multi-source harvesting can reduce battery size, and cost requirements."
He also provided examples of specific applications that can benefit from multi-source energy harvesting. Solar combined with vibration sources can be effective for powering ID transponders on rail cars or for safety of life at sea (SOLAS) search tracking buoys. Thermal combined with vibration sources can be used to power UAV avionics power and for asset tracking tags on small equipment. Finally, he observed that solar combined with thermal energy sources can power intrusion sensor networks and for industrial process monitoring.
