Vibration‐Based Energy Harvesting From a Two‐Degree‐of‐Freedom Auxetic Beam Element With Variable Stiffness

ABSTRACT In this study, energy harvesting was carried out by creating a piezoelectric‐based two‐degree‐of‐freedom aeroelastic structure. It is aimed to obtain more energy by gluing the piezoelectric material on the auxetic region. In addition, a second degree of freedom was created by connecting three thin rods between the beam element and the flow disruptor geometry. By changing the number of these springs, the effects of different stiffness values on the harvest structure were examined. As a result of this design, a unique nonlinear harvester structure that can be adapted to different resonance frequencies with variable stiffness connection elements has been developed. Beam vibrations were measured with the image processing method, and its accuracy was determined by comparing them with the measurements taken with the laser sensor. The equations of motion of the two‐degree‐of‐freedom system were obtained using the Lagrange method, and the natural frequencies were determined. In addition, experimental measurements were taken, and the structure dynamics were confirmed by performing numerical modal analysis in the ANSYS environment. Model accuracy was ensured by comparing the open circuit voltage values measured on the harvesting structure with the voltage values obtained in the ANSYS environment. Finally, different resistance values were connected to the energy harvesting structure, and the load value that would provide optimum power output through this structure was determined.