Application of mechanical stretch to tune the resonance frequency of hyperelastic membrane-based energy harvesters

Vibration-based energy harvesting has been widely investigated as a means to generate low levels of electrical energy for applications such as wireless sensor networks. However, for optimal performance it is necessary to ensure that resonant frequencies of the device match the target ambient vibration frequencies for maximum energy harvested. Here a novel resonant frequency tuning approach is proposed where the application of membrane stresses generated by different stretch ratios applied to circular hyperelastic membranes is used to tune the vibration response. Specifically, tuning via mechanical stretch is described in terms of effective stiffness theory, where the mechanical stretch of the hyperelastic membrane induces membrane tuning stresses and a corresponding reduction in membrane thickness. A finite element model (FEM) using ANSYS agrees well with an analytical model of the tuned hyperelastic membrane. Lastly, using a mass-loaded circular membrane vibration model, the effective resonant frequency of the energy harvester can be determined as a function of changes in membrane tension due to the applied stretch. Preliminary experiments verify the resonant frequencies predicted from the analytical and FEM models as a function of different levels of mechanical stretch, centrally-loaded added mass, and membrane initial thicknesses. The proposed mechanical stretch tuning approach for hyperelastic membranes provides an alternative tuning strategy to enable energy harvesting from different ambient vibration sources in various environments.