Variable-curvature Piezoelectric Composite Energy Harvesters for Powering Wrist Wearables

Description

Energy harvesting is a nascent micro-energy technology developed to capture wasted ambient mechanical energy and convert it into electricity. Along with the development of the Internet of Things and wearable devices, piezoelectric energy harvesters (PEHs) have attracted much attention as promising long-lifespan power alternatives to batteries. However, most PEHs cannot generate adequate power for their potential applications. By closely analyzing the relevant literature on design and vibration theory, we find that PEH designs are largely limited to straight-beam structures, such as cantilevers, fixed-fixed beams, and buckling beams, and existing theories can only analyze straight-beam PEHs. However, not all applications can provide sufficient space for straight-beam harvesters, such as smartwatches and fitness trackers. The large size, poor environmental adaptability, and low output power hinder the practicability of piezoelectric energy harvesters. To improve energy harvester performance, this project proposes to establish a widely applicable comprehensive theoretical framework for curved PEHs. The framework will help to extend the design scope of energy harvesters from 2D straight beams with flat piezoelectric elements to a broader domain of 3D curved structures. Curved PEHs will yield more alternatives to address the space limitation of diverse applications, and further possess such characteristics as high bending stress, large deformation, and low resonance frequency, which are beneficial for the performance enhancement. For demonstration, we will develop high-performance curved PEHs and integrated them into self-powered smartwatches.To develop the theoretical framework, the following critical engineering challenges and scientific issues must be addressed: 1) mathematically describing the deeply curved piezoelectric composites with variable curvatures and the electromechanical coupling effect, which is much more complex than the existing theories for straight-beam PEHs; 2) modeling segmented curved piezoelectric composite harvesters and developing solution methods; 3) gaining insights into the stress concentration effect of curved structures and its enhancing effect on PEHs; 4) exploring the intricate nonlinearity of piezoceramics under high mechanical stress; and 5) developing effective fabrication and experimental procedures for curved piezoceramics and PEHs. Details of our methodologies to address these issues are presented in the proposal. The proposed research adds a new design dimension to PEHs and lays the foundation for developing new harvesters with curved piezoelectric composite laminates. The established theoretical and experimental framework will greatly advance the research fields of energy harvesting, composite structures, vibration, and sensors. Further, this work will promote the development of self-powered wearable devices, the Internet of Things, and other wireless devices.