Beam-based nonlinear springs can be used in energy harvesting from ambient vibrations, shock absorption for external loads, and passive control or suppression of mechanical instabilities involving targeted energy transfer from one component of a structure to another.
Mechanical energy harvesting is inefficient because of the uncertain character of the excitation (e.g. someone walking does not create uniform ambient vibrations). This is overcome by using a nonlinear 2 degrees-of-freedom system, which creates strongly nonlinear energy transfers between the modes of the system.
Traditional single degree of freedom (1DOF) linear vibration harvesters are efficient only when close to their resonant design point: that is, when the excitation frequency matches the harvester’s natural frequency. In contrast, this design has two degrees of freedom (2DOF) and a nonlinear spring. The system consists of cantilever beams and contact surfaces with carefully chosen distribution of curvature, which has minimal frictional losses and moving parts. This system behaves nonlinearly (i.e. does not a have a preferential linear frequency) because longer lengths of the cantilever contact the surface as more force is applied. This behavior results in a theoretically infinite spring force for a critical finite displacement which protects the spring from extreme loading conditions. For the purposes of energy harvesting, the proposed design was tested for walking, walking quickly, and running and nearly doubled the average harvested power compared to 1DOF systems or 2DOF linear systems.
High power conversion efficiency over different excitation
Ability to harvest vibrational energy