Design of travel limits for bistable vibration energy harvesting

Abstract

Energy harvesting from renewable energy sources has become more popular in the last decades than ever before. New energy sources consisting of human input vibrations are hopeful alternatives for powering wearable low power electronics. These sensors currently rely on the lifetime of the battery and come along with high maintenance costs in case of a replacement. Many designs found within literature are based on the working principles of linear resonant energy harvesters, consisting of high output generation when they are exited on their resonance frequency. However, if the vibration energy harvester is not accurately tuned to the input signal of the real world, poor output performance can be expected. Bistability, consisting of a unique double well potential energy curve is an interesting alternative. The oscillation between the two potential wells contribute to higher output performance in comparison with resonant configurations. However, these potential wells are segregated by an energy barrier and the motion between the two wells will not always occur during excitation. A solution is found to reduce the energy barrier by means of mechanical end-stops. A mechanical model based upon beam theory is created in ANSYS and their stiffness characteristics are used as an input parameter for the dynamical model. To confirm this model a prototype is constructed and investigated. A mechanical analysis is carried out using a quasistatic forcedeflection measurement and the dynamical analysis is performed on a linear air bearing stage, consisting of a maximum stroke of half a meter being able to reproduce low frequency input excitations. It could be observed that participation of the desired trajectory between the two potential wells is enhanced and occur at lower input accelerations, as the oscillators motion is confined by means of hard mechanical end-stops. Therefore, the integration of mechanical end-stops as a design parameter for bistable energy harvesters can be considered as a viable solution to capture the kinetic energy induced by human input motion with the use of bistable mechanisms.