A novel 3D folded zigzag piezoelectric energy harvester; modeling and experiments

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Cantilever geometries have been widely used for vibration energy harvesting applications due to their simple geometries, frequency tune-ability, and obtainability of their closed form analytical solutions. Recent studies have focused on overcoming some of the drawbacks for this configuration, which include low power density and natural frequencies much higher than those available in the environment. Some investigate two-dimensional geometries, such as a zigzag shaped design, meandering and elephant design. The previously researched designs offer a higher flexibility that allows for much smaller fundamental natural frequencies and improved power densities. The presented work extends this idea by offering a three-dimensional (3D) design called ‘folded zigzag’ that provides much better flexibility than the aforementioned units, and aids significantly with natural frequency requirements despite a small footprint. Compared to a planar design the proposed 3D design of the same footprint offers a much lower resonating frequency with increased flexibility, and also results in improved strain node pattern by avoiding torsion in the fundamental modes of its operation. This significantly eases the fabrication as avoids the charge cancellations when mounting continuous electrodes. Power densities for the proposed design are presented and compared to the flex geometry, a planar symmetric design, and experimental validations are made for the folded unit. The results show that the new design can produce higher power density per layer compared to the planar symmetric zigzag (flex geometry). This comparison is made while keeping all the system parameters the same for both units such as the footprint, dimensions, and tip mass per layer. Additionally, the simulation results show that increasing the number of stories or the distance between the consecutive stories for this design can help significantly with the reduction in the number of strain nodes in the fundamental modes. This as well helps with the electrode geometry due to avoiding the charge cancellation. Finally, it is shown that the presence of the strain nodes can be avoided for smaller footprints compared to the planar symmetric zigzag before the torsional modes become dominant.