Following lunch in the exhibit area on Tuesday, the second annual nanoPower Forum focused on the issues surrounding the integration of energy harvesting into wireless networks. Pierre Mars, VP of Applications Engineering with Cap-XX in Australia and John Parker, Senior Engineer with Perpetuum in the U.K. lead off the afternoon with a "Vibrational Energy Harvesting Case Study."
Mars and Parker described how Perpetuum’s PMG17 vibration energy-harvesting micro-generator, together with a CAP-XX supercapacitor, allow wireless sensor system manufacturers to design battery-free condition monitoring systems that collect and report data on machinery for improved asset management.
They presented the results of a field trial at the Nyhamna gas plant in Norway to evaluate the system in a challenging industrial environment. Plants and refineries monitor pumps, machines and processes to ensure optimum safety, up-time and efficiency.
The Cap-XX supercapacitor stores the energy harvested by the Perpetuum PMG17 micro-generator (a low but steady source of between 0.5 and 50mW) and then delivers the peak power needed to transmit sensor condition data over wireless networks such as IEEE 802.15.4 (Zigbee) and 802.11 (WLAN).
The output of the micro-generator can easily cover the power needs of intermittent radio sensor systems such as Wireless HART, SP-100 and Wi-Fi in industrial applications, but its output impedance is too high to supply the 10s to 100s of milliwatts required by sensor nodes during data collection and transmission. The high capacitance and low equivalent series resistance (ESR) of the supercapacitor provides approximately one second of peak power to transmit data.
In another application of supercapacitors, Leo Estevez, Technology Strategist for Wireless Emerging Markets with Texas Instruments discussed, "Zigbee Energy Harvesting for Connected Health." In this case study, the supercapacitors were combined with small solar cells and a small rechargeable battery to product a complete energy harvesting power system.
Comprehensive energy management is a key element in the architecture of this health monitoring system. The discussion reviewed numerous areas including; processor energy management, memory energy management, RF energy management, location-based energy management, and even activity-based energy management.
Returning to harvesting vibrational energy, Stephen Burrow with the University of Bristol in the U.K. discussed, "Wireless sensors and energy harvesting for rotary wing aircraft health and usage monitoring systems." In this case, energy storage is not a significant issue since large amounts of vibrational energy are available continuously whenever the helicopter is operating.
Dr. Burrow observed, "The helicopter environment provides considerable scope for energy harvesting from vibrations. Typically 1-2g of acceleration can be found if the harvesting device is located favorably. The development of the power harvester as part of the project represents the most ‘blue sky’ activity within the project, and therefore the goal was to successfully demonstrate an energy harvester.
"The location of the device in the target application makes it impossible to access the energy harvester to adjust or set-up during operation; however, the space available for the harvester does not place particularly onerous constraints upon the design and the approximate power consumption of the sensing module (100-150mW) can be met by a harvester using conventional meso-scale techniques," Dr. Borrow concluded.