Energy harvesting with piezoelectric materials for IoT – Review

The goal of this paper is to review up to date energy harvesting techniques, while focusing on energy harvesting with piezoelectric materials. A classification of various energy harvesting sources is provided in order to properly locate piezoelectricity. Piezoelectric energy harvesting uses the special material property that exists in many single crystalline materials: the direct piezoelectric effect. Those materials are generating electric potential when mechanical stress is applied. There are two types of mechanical stress suitable for piezoelectric energy harvesting: hitting and vibrating. The hitting method involves the direct transfer of energy to piezoelectric modules, so it generates more power than the vibrating method. This kind of energy harvesting is used to drive low energy consuming devices and is suitable for applications where replacement of battery or maintenance is unpractical, like sensors in the human body, for powering portable devices or it can be used for improvement of a smart building concept. If the piezoelectric transducers are placed in the floor of a crowded area or in shoes, it can theoretically generate 4.9 J/Step; therefore, this energy can be used to replace the chargeable batteries. This review is useful for a proper positioning of this type in the IoT broad context and mainly as an alternate energy source for wearables