Numerical analysis and parametric study of the piezoelectric harvester design

Energy harvesting is a growing technological field also known as power harvesting or energy scavenging. The process concerns converting energy from external sources, such as the mechanical energy (or vibration energy), into useful electricity at small scale. Different transduction materials and mechanisms can be used in this harvesting process, such as piezoelectric, electromagnetic and electrostatic generators. Among these generator technologies, piezoelectric (bimorph and unimorph) harvesters can provide powers ranging from μW/cm3 to mW/cm3. Better output power is given when the vibrations are very high. To predict the electrical outputs (voltage, current and power energy) of piezoelectric harvesters, many analytical models are proposed in the literature. This paper discusses the numerical analysis of piezoelectric harvester devices, where two analytical models are compared. On one hand, the Erturk and Inman model is used as a basis for the most of linear energy harvester models. On the other hand, the transfer matrix method (TMM) has proven to be advantageous for analysing complex structures because the size of the transfer matrix does not grow with increasing number of components (segments) in cantilever beam harvesters. In this paper, both the mechanical response (relative displacement) and the electrical outputs are considered. A study of the piezoelectric harvester design is carried out in order to reach higher efficiency (bimorph or unimorph configuration, tip mass, electrical resistance, etc.) It is shown that for given mechanical properties of a piezoelectric beam, it is possible to find optimal geometric parameters leading to optimum electrical outputs at a desired excitation frequency. For example, the use of the bimorph piezoelectric configuration with a tuned frequency (using a tip mass) as an improvement technique, leads to both peak voltage and peak tip displacement increase in comparison to a piezoelectric configuration without a tip mass.