An axially-suspended vibration energy harvesting beam for broadband performance and high versatility

It has recently been shown that negligible linear stiffness or very small negative stiffness may be the most beneficial stiffness nonlinearities for vibrational energy harvesters due to the broadband, amplified responses which result from such designs. These stiffness characteristics are often achieved by providing axial compression along the length of a harvester beam. Axial compressive forces induced using magnetic or electrostatic effects are often easily tuned; however, electrostatic energy harvesters are practically limited to microscale realizations and magnets are not amenable in a variety of applications, e.g. self-powered biomedical implants or when the harvesters are packaged with particular circuits. On the other hand, mechanically-induced pre-compression methods considered to date are less able to achieve fine control of the applied force which is typically governed by a pre-compression distance that has practical constraints such as resolution and tolerance. This notably limits the harvester's ability to precisely obtain the desired near-zero or small negative linear stiffness and thus inhibits the favorable dynamical phenomena that lead to high energy conversion performance. Inspired by the wing motor structure of the common diptera (fly), this research explores an alternative energy harvester design and configuration that considerably improves control over precompression factors and their influence upon performanceimproving dynamics. A pre-compressed harvester beam having an axial suspension on an end is investigated through theoretical and numerical studies and experimental efforts. Suspension and pre-loading adjustments are found to enable comprehensive variation over the resulting dynamics. It is shown that the incorporation of adjustable axial suspension into the design of pre-compressed energy harvester beams is therefore a versatile, all-mechanical means to enhance the performance of such devices and ensure favorable dynamics are retained across a wide range of excitation conditions.