Design Article
Self-powered systems -- can they eliminate the need for batteries?
John Marciszewski, Management Consultant, Advanced Cerametrics Inc.; Steve Leschin Managing Director of Business Development, Advanced Cerametrics Inc.
10/10/2005 11:08 PM EDT
Piezo power generation
Active fiber composites (AFC) open the door for an array of energy harvesting applications. The fiber can recover (harvest) waste energy from mechanical forces such as motion, vibration, and compression (strain). With simple, low-cost analog circuits, the piezo power can be converted, stored, and regulated as a direct replacement for batteries. A typical single, AFC can easily generate voltages in the range of 40 Vp-p from vibration. A typical single, AFCB (bimorph) can easily generate voltages in the range of 400 Vp-p with some forms reaching outputs of 4000Vp-p. Using a vibration frequency of 30 Hz, ACI’s piezo fibers have the proven the ability to produce 880 mJ of storable energy in a 13 second period…enough to operate a LCD clock that consumes 0.11 mJ/s for over 20 hours. Energy sufficient to power wireless systems for sensing and control of equipment, appliances, medical devices, buildings, and other infrastructure elements have been demonstrated.
Power output is scalable by combining two or more piezo elements in series or parallel, depending on the application. The composite fibers can be molded into unlimited user defined shapes and is both flexible and motion sensitive. The fibers are typically placed where there is a rich source of mechanical movement or waste energy.
Example application: Wireless sensor networks
Sensors that measure everything from process temperatures, to system pressures, to machine vibrations have been historically expensive to deploy in manufacturing and industrial environments. The sensors require expensive wiring and are expensive to service.
With the emergence of the new Zigbee standard, based on IEEE 802.15.4, the availability of large, low-cost, low-power wireless sensor networks (WSNs) that are self-managed is becoming a reality. Sensors, signal conditioners, controllers, and RF transceivers continue to become smaller, lower power, and more highly integrated. The combination of wireless networking, intelligent sensors, and distributed computing has created a new paradigm for monitoring the health of machines, buildings, and environments.
A low-cost, renewable energy source is critical to ubiquitous deployment of WSNs. After all who wants to have to change thousands of batteries? New piezo-electric fiber based energy harvesters, will in some cases, obviate the need for batteries in the WSNs. In other cases the harvesting technology can be used to recharge batteries to enhance service life. The power comes from the vibration of the system being monitored. Piezo fiber-based products will require no maintenance, significantly reduce the life cycle costs, and improve the overall quality of industrial and machine control systems.
Figure 1 shows an example of the PZT fiber acting as an energy harvester to convert waste mechanical energy into a self-sustaining power source for a Zigbee wireless sensor node. The piezoelectric fiber captures the energy generated by the structure’s vibration, compression, or flexure. The resulting energy (current) is used to charge up a storage circuit that then provides the necessary power level for the sensor node electronics. In this example, energy is harvested by the vibration of PZT fiber composites. The energy is converted and stored in a low-leakage charge circuit until a certain threshold voltage is reached. Once the threshold is reached, the regulated power is allowed to flow for a sufficient period to power the Zigbee controller and RF transceiver.
Figure 1. PZT fiber acting as an energy harvester
Next: Applications
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