Review of Vibration Energy Harvester

This work presents a state-of-the-art on vibration energy harvesting that is one of the hottest topics addressed by a big part of the scientific community to minimize the requirement of external power source. A lot of transduction mechanisms have been investigated and designed by researchers, based on different mechanical systems and transduction principles, in order to recover energy coming from environmental vibrations. This dissertation is intended to illustrate and analyse the main findings in order to highlight the critical aspects of this technology and the key challenges for further developments. Firstly, a classification of vibration energy harvesters (VEHs) based on their "oscillating structures" and "transduction mechanisms" is provided, corresponding to the most widely used mathematical reference model and transduction devices, respectively. Then, the most common examples of application of such devices is presented to illustrate how vibrations of the surrounding environment can be converted into electrical energy exploited for different intended uses. Based on this survey, the limitations of the simplest devices are discussed, the most important of which is the ineffectiveness of VEHs when prompted by vibrations with a frequency even slightly different from the device resonance frequencies, (which is a common scenario, since environmental vibrations are often random and broadband). To solve this problem, researchers are currently focusing on developing efficient VEHs by adopting new materials and optimising the harvesting devices. The recent prototypal devices appear promising, but the achievement of robust solutions for real practical applications still seems a long-term goal, due to the limited capability of current technology to harvesting meaningful levels of electrical energy.