Power Management, Energy Conversion and Energy Scavenging for Smart Systems

An integral part of the vision for ambient intelligence is the use of large numbers of wireless sensors in a “deploy and forget” manner. The long term provision of energy to wireless sensor nodes poses a challenge to this vision. Today the provision of power is almost exclusively by means of batteries. The trend in battery technology has been towards increasing energy densities; indeed small form factor batteries are available that have provided power to low power electronic systems (e.g. wristwatches) for years. However the power requirements for today’s wireless sensor nodes are considerably higher than the typical wristwatch, so the lifetime envisaged for many applications certainly exceeds the lifetime possible with today’s battery technology. In order to overcome the limitations on lifetime posed by the use of batteries as the energy source, the concept of energy harvesting has gained significant attention. This concept envisages the “harvesting” of energy from sources available in the environment to either directly power, or to augment the battery powering of, the wireless sensor node. Although many different sources of energy have been discussed, the sources for which practical results have been demonstrated are light, vibrations and thermal gradients. In this chapter the state of the art in each of these areas is reviewed, with respect to their potential for powering wireless sensor nodes, or motes.