Traditionally, vibration-based energy harvesters have been designed for specific base excitation frequencies by matching their natural frequencies. However, harvesting energy from common human motions is challenging because the low frequencies involved are incompatible with small, light-weight transducers, which have much higher natural frequencies. By using the frequency up-conversion method, a vibration-based, nonlinear, magnetically excited energy harvester exhibits efficient, broadband, frequency-independent performance.
A complete model is provided for an energy harvester utilizing the frequency up-conversion method that defines the relationship between the enclosure excitation, the base excitation and the stationary magnets, where the base of the beam is mounted elastically inside an enclosure. The average power output of a vibration-based energy harvester with frequency up-conversion is analyzed using artificial and naturally occurring base excitations such as sinusoidal and walking motions, respectively. Simulations are provided to demonstrate the broadband capabilities of vibration-based energy harvesters with frequency up-conversion, especially for driving frequencies lower than the fundamental frequency, where significant increase in power output are observed when utilizing frequency up-conversion. In addition, the advantages and limitations of approximating a range of natural base excitations with a set of orthogonal basis functions are explored, which provides motivation for Wavelets Analysis. Finally, a procedure is proposed to determine the maximum expected power output.