Scaling and Performance Analysis of MEMS Piezoelectric Energy Harvesters

Vibrational energy harvesters have been phenomenally adopted to absorb energy from mechanical vibrations and convert them into electrical energy. Power developed by such harvesters depends significantly on material properties and harvester geometry. Moreover, the power generated by micro-scale harvesters scales down rapidly. Hence, it is important to find scaling rules that ensure maximum power generation irrespective of the harvester size. In this paper, we derive an expression for the power generated by a piezoelectric harvester of a unimorph topology and show how this expression can be decomposed into five multiplicative factors representing size scaling, composition, inertia, material, and power factor (SCIMP). We present explicit expressions for each factor and show how these factors can be used for optimizing the performance of a harvester. The proposed factors provide an intuitive and insightful method for exploring an unwieldy multidimensional design space along five vectors that are particularly amenable to constraint-based choices a harvester designer has to make. The proposed method of analysis results in unique performance indices, enabling the comparison of harvester performance across different designs. We compute and compare the power developed by several MEMS harvesters reported in the literature using our method and show how this method can be used effectively for designing MEMS scale harvesters.