A Measurement Methodology for the Characterization of a Compensated Nonlinear Energy Harvester for Vertical Operation

In this paper, a measurement methodology for the characterization of the mechanical and electrical behavior of a nonlinear vibrational harvester is discussed and demonstrated on a real case study. The harvester, here considered, takes advantage of a flexible beam in a snap-through-buckling configuration and a novel magnetic repulsion mechanism to compensate for the asymmetric behavior of the device, in the vertical direction, due to the effect of the proof mass load. A measurement protocol aimed at the device performance estimation in terms of the minimum acceleration, the number of switching events, the output voltage, the generated power, and the mechanical-to-electrical conversion efficiency of the system is discussed. The advantages of the proposed compensation strategy are highlighted by evaluating the device's performances in the range of frequency 0.5-12 Hz for different tilts applied to the device and compared to the performance of the same device without the repulsion mechanism. The harvester is capable of scavenging energy in the range 0.5-5 Hz with acceptable efficiency; it can, however, be exploited up to 12 Hz with an acceptable loss of efficiency. A power of about 412 μW with a root-mean-square acceleration of 10.22 m/s$²$ at 5 Hz and an efficiency of about 23.5% has been measured for the harvester, with the repulsive mechanism, operated in the vertical position. The power generated is suitable for powering wireless devices.