Non-linear flexoelectricity in energy harvesting

Efficiently converting vibration energy from surrounding environment to electric energy for powering micro/nano-electromechanical systems (MEMS/NEMS), without using batteries, is an interesting research subject. One of the most important applications of flexoelectricity is in the field of transducers in energy harvesters where flexoelectric effect is significant at micro/nano-scale. In this paper, a theoretical model incorporating flexoelectricity and piezoelectricity for energy harvesting is developed. The model includes geometric nonlinearity deformation and damping effect so that it can more accurately predict the electromechanical behavior of energy harvesters. A special case study for a cantilever beam (which is the most common configuration of vibration energy harvesters) is carried out. Two types of commonly-used cantilevered energy harvesters, a single layer and a unimorph energy harvester, are derived. It is found that, in some cases, voltage output contributed by flexoelectric effect is extremely (e.g., five times) higher than that solely contributed by piezoelectric effect.