Why to harvest energy in Wireless Sensor Networks?
A wireless sensor network (WSN) is formed from a set of sensor nodes deployed over a geographic area to collect environmental data and to transmit the gathered data toward the base station typically through wireless channels, relaying by other nodes. The sensor nodes are capable of measuring ambient parameters, such as light level, pressure, temperature, and humidity, as well as detecting the presence of creatures and their movements. The more capabilities a sensor node owns, the more expensive it is. A sensor node contains a power storage, like a battery. However, such suppliers suffer from low capacity, lower than the required power by new applications. They will be depleted in a few months after the network deployment and need to be replaced. But sensor replacement is not cost-effective and usually impossible due to environmental obstacles. A good solution is to equip sensor nodes with energy harvesting devices, able to harvest energy from the environment to power the network nodes near-perpetually. Energy harvesting has been in use for a long time, for example solar panels in satellites, but building the miniaturized efficient harvesting devices that are able to satisfy the tiny sensor nodesâ€™ constraints in WSNs is new.
Wireless Sensor Network
What are the challenges?
Designing energy harvesting wireless sensor networks (EH-WSNs) faces several challenges, such as choosing an appropriate type of energy harvester and energy storage, and a good duty cycle that gives the best efficiency. The most difficulty in energy harvesting systems is unpredictability and uncertainty of produced power. The level of available power is low, variable and unpredictable. The metrics of interest for harvesting-powered systems are beyond the battery- powered ones. While the latter aims the maximum lifetime, the former seeks the maximum system availability as well. However, even if a harvesting system is able to provide unlimited energy in theory, the produced power is unpredictable. As a result, power storage elements, like rechargeable batteries and super-capacitors, are used to store energy for later use. When the available energy is high, the node stores the extra produced power in power storage. However, these power storages are finite and unable to provide perpetual power by themselves. Thus, power management techniques in WSNs must be adapted to EH-WSNs in order to make the system available even in long time lack of power. An in-depth understanding of these challenges is required to design an efficient EH-WSN, which is influenced by the interaction of numerous factors, like features of power generators, transducers, power storages, and also power management methods and application requirements
Solar and Thermal Energy Harvesting Sensor Nodes
What are the sources of energy?
In order to be cost effective, the sensor nodes are designed tiny to reach low cost and low power consumption. This presents challenges in terms of energy consumption, required memory size and power storage capacity in sensor nodes. Despite improvements in battery technology and declines in electronics power demands, many new applications in WSNs are taking into account increasing power requirements. Furthermore, since in WSNs it is frequently desirable to deploy nodes in unobtainable places, it might be impossible to provide large enough power for such applications given the fact that battery replacement is not practicable. This results in significant interests in designing sensor nodes with the capability of extracting electrical energy from surrounding ambient sources. These sources contain solar energy, thermal gradients, magnetic, electromagnetic, bio-chemical, vibration and other motion sources.
Papers and Posters
Journal paper: Satyajayant Misra, Nahid Majd and Hong Huang,
“Approximation Algorithms for Constrained Relay Node Placement in Energy Harvesting Wireless Sensor Networks” IEEE Transactions on Computers (ToC), accepted for publication.
Conference paper: Satyajayant Misra, Nahid Ebrahimi Majd, and Hong Huang,
“Constrained Relay Node Placement in Energy Harvesting Wireless Sensor Networks,” 8th IEEE International Conference on Mobile Ad Hoc and Sensor Systems (IEEE MASS), pp. 23–34, 2011.
Workshop poster: Satyajayant Misra, Nahid Ebrahimi Majd,
“Constrained Relay Node Placement in Energy Harvesting Wireless Sensor Networks,” NMSU 11th Annual URC Research and Creativity Activities Fair, 2011.
Satyajayant (Jay) Misra: He is an Assistant Professor of Computer Science at New Mexico State University. He received his MSc degrees (2003) in physics and computer science from BITS, Pilani, India and his PhD degree (2009) in computer science from the School of Computing and Informatics at Arizona State niversity. His research interests are in networks, namely wireless and social networks and include network security, optimization, and analysis. He has ver 30 publications in peer-reviewed international journals and conferences. He is currently serving as the TPC Vice-chair for Information Systems, IEEE INFOCOM 2012, and on the editorial boards of the IEEE Communications on Surveys and Tutorials and the IEEE Wireless Communications Magazine.
Nahid Ebrahimi Majd: She is currently a PhD candidate in Computer Science at New Mexico State University (NMSU), Las Cruces.She received her MS and BS degrees (2006 and 2003 respectively) in Computer Science from FUM and SBUK (respectively), Iran. Her research interests are in networks, namely wireless sensor networks, mobile ad hoc networks, wireless networks powered by ambient energy and information centric networks and include relay node placement, cooperative caching, security and optimization. She has published peer-reviewed international journal and conference papers in these research areas in collaboration with her advisor, Dr. Misra, and his network research group (NSOL). She was a faculty member in Iran for three years, teaching various undergraduate courses. She is a research/teaching assistant at NMSU computer science department, and received the NMSU Merit-based enhancement award, offered to outstanding graduate assistants at NMSU, in 2012-2013 academic year.
Hong Huang: He received his B.E. degree from Tsinghua University, Beijing, China, and M.S. and Ph.D. degrees from Georgia Institute of Technology in 2000 and 2002, respectively, all in electrical engineering. He is currently an associate professor with the Klipsch School of Electrical and Computer Engineering at the New Mexico State University. His current research interests include wireless sensor networks, mobile ad hoc networks, network security, and optical networks.