A two-way shape memory alloy-piezoelectric bimorph for thermal energy harvesting

We present an analytical model to analyze the bending of a bimorph beam comprising of piezoelectric material (PM) and shape memory alloy (SMA) thin layers. The model starts from the governing equations of the bending beam based on the Euler-Bernoulli beam theory. The PM and SMA layers are supposed to be perfectly bonded. The linear constitutive equations of PMs are used. Using this approach, we investigate thermal energy conversion into electricity by mean of the SMA-PM bimorph. Particularly, the model takes into account cyclic thermal energy harvesting by coupling the direct piezoelectric effect and the two-way shape memory effect. In this case, the SMA is assumed to be trained prior to assembling the bimorph so that it can deform in a cyclic way upon cyclic thermal loading without applying any external stress. The thermal-to-electrical conversion is achieved from the induced strain within the SMA layer upon heating which induces stress into the PM layer so that it produces an electrical potential.