Manufacture and characterisation of piezoelectric broadband energy harvesters based on asymmetrie bistable laminates

Piezoelectric energy harvesters that convert mechanical vibration into electrical energy are potential power sources for systems such as autonomous wireless sensor networks or safety monitoring devices. However, ambient vibrations generally exhibit multiple time-dependent frequencies, which can include components at relatively low frequencies. This can make typical linear systems inefficient or unsuitable; particularly if the resonant frequency of the device differs from the frequency range of the vibrations it is attempting to harvest. To broaden the frequency response of energy harvesters, a variety of researchers have introduced elastic non-linearity; for example by designing bistable harvesters with two energy wells. Researchers have considered inducing bistability through magnetic interactions, axial loading, and buckling of hinge-like components. An alternative method has been recently considered where a piezoelectric element is attached to bistable laminate plates with two plies of [0/90]T layup to induce large amplitude oscillations. Such harvesting structures have been shown to exhibit high levels of power extraction over a wide range of frequencies. In this paper we will manufacture and characterise the energy harvesting capability of bistable asymmetric laminates coupled to piezoelectric materials. Cantilever configurations will be explored and harvested power levels as a function of load impedance, vibration frequency and amplitude will be assessed. Harvested power levels, natural frequencies and mode shapes will be compared with linear cantilevers of similar geometry and stiffness to assess the benefits of using bistable configurations.