Poling-Architected Graded Piezoelectric Energy Harvesters: On Exploiting Inevitable Rotational Speed Variability

Different components of rotating machines inevitably experience variations in angular speed due to intermittent activation of the driving power while controlling the speed at a target level. The effect of such fluctuation in high-speed rotating structural components is proposed to be exploited here for the dual purpose of energy harvesting and speed sensing through mounting piezoelectric elements. The voltage output is enhanced through the coupled effect of poling angle tuning and introducing functionally graded materials based on power and sigmoid laws. An efficient, yet insightful theoretical framework is developed on the basis of active Euler-Bernoulli beam theory and conservation of energy principles, which are further validated using separate finite element results and qualitative experimental characterization. We develop an effective computational mapping among the output open-circuit voltage, rotational speed, functional gradation and poling orientation, wherein the output voltage, voltage sensitivity, and charge sensitivity are used as critical metrics to quantify the performance of the energy harvesters. The concept of exploiting angular speed variation along with poling-architected piezoelectric functionally graded configurations will be crucial for designing selfpowered optimized electronic sensors and devices for a range of aerospace and mechanical applications such as helicopter blades, aircraft engines, wind turbines and other rotating machines.