Experimental verification of a bridge-shaped, non-linear vibration energy harvesters

This paper reports the modeling and a first experimental characterization of a bridge-shaped doubly clamped nonlinear energy harvester. The doubly clamped beam at large deflection induces stretching strain in the layers in addition to the bending strain, which stiffens the beam as the beam deflects and transforms the dynamics to the nonlinear regime widening the frequency bandwidth. The sectional behavior of the bridge-beam has been studied through the Classical Lamination Theory (CLT) specifically modified to introduce the piezoelectric coupling and nonlinear Green-Lagrange strain tensor. A lumped parameter model has been built through separation of variables method, this results in coupled motion equations which include additional non-common terms originating from a correct analysis of piezoelectrics coupling in nonlinear strain context. The model has been validated through tests on a mesoscale prototype. The prototype consists of a Macro Fiber Composite (MFC, Smart-material) piezoelectric patch glued on a thin aluminum layer and a lead proof mass is attached at mid span. The beam is doubly clamped on an aluminum support. The device is tested in open circuit and the frequency response is measured at different acceleration amplitudes. Despite of the fact that the resulting high mechanical damping reduces the oscillation amplitude, the experimental data show a significant nonlinear behavior. These results are compared to the modeling showing good accordance.