Scavenging energy from readily available sources offers the potential to power applications indefinitely without wires or batteries or, at minimum, extend the operating times of battery-powered systems. However, successfully implementing an energy harvesting solution requires a detailed understanding of the ambient energy source characteristics and harvester/transducer output power capabilities as well as the system power needs.
Ambient energy sources include light, heat differentials, mechanical vibration, transmitted RF signals, or any source that can produce an electrical charge through a transducer. These sources are all around us, and they can be converted into electrical energy by using a suitable transducer, such as a thermoelectric generator (TEG) for temperature differential, a piezoelectric element for vibration, a photovoltaic cell for sunlight (or indoor lighting), and even galvanic energy from moisture. These so called “free” energy sources can be used to autonomously power electronic components and systems.
A typical energy harvesting configuration or wireless sensor node (WSN) (see the figure) comprises four blocks: an ambient energy source, a transducer element and a power conversion circuit to power downstream electronics, a sensing component that links the node to the physical world and a computing component consisting of a microprocessor or microcontroller that processes measurement data and stores them in memory, and a communication component consisting of a short-range radio for wireless communication with neighboring nodes and the outside world.
Once the electrical energy has been produced, it then can be converted by an energy harvesting circuit and modified into a suitable form to power the downstream electronics. Thus, a microprocessor can wake up a sensor to take a reading or measurement, which then can be manipulated by an analog-to-digital converter (ADC) for transmission via an ultra-low-power wireless transceiver.
There are many existing energy harvesting deployments all around us. Examples include tire wear/pressure monitors, inductively coupled Smart Grid monitors, and HVAC and lighting control systems. On the short-term horizon are aircraft heath monitoring and asset tracking systems.