Energy Harvesting: Power at Small Scale

Energy harvesting is a new promising research area for portable electronics. Portable electronic devices have been typically limited by the finite lifetime and size of the internal batteries. This has been a constant conflict and tradeoff between battery size and device capabilities. For instance, cardiac pacemaker lifespan is mostly limited by battery size, which occupies at least half the available volume. Energy harvesting or energy scavenging is an alternative that extracts energy from the surroundings in order to operate. Energy harvesting is also an interesting approach when battery replacement is not possible or is too costly, such as deployment of sensors in remote areas for surveillance or environmental monitoring. One of the best known examples is the self-winding wristwatch that started from being completely mechanical and operated by the wearer’s daily motion, to be nowadays a miniaturized electrical generator. Energy harvesting extracts energy from the surrounding by harnessing motion, vibrations, and temperature gradients among others. Kinetic energy generators extract energy by means of piezoelectric, electromagnetic, or electrostatic transduction techniques. Piezoelectricity is produced by materials with piezoelectric properties when subject to pressure, generating a voltage as a result. Electromagnetic transduction uses the relative motion of magnets and coils in order to induce a voltage. Electrostatic generators use the change of capacitance, by varying the separation between plates, to generate an electrical charge. Applications of the technology vary from consumer electronics, remote deployment of sensors to biomedical applications. This work presents the state-of-the-art on energy harvesting applications.