Characterization of mechanically-equivalent amplifiers and frequency modulating concepts for energy harvesting devices

One of the major obstacles that are limiting the development of deployable integrated sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading in civil and mechanical structures is typically used as an alternative solution. Although, piezoelectric vibration harvesters have been widely used, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power. Most of the previously used methods focus only on modifying the transducer's properties and configurations. These techniques do little to modify the stimuli from the source. In contrast, this work proposes to focus on the input signal generated within the structure by inducing amplified response amplitude and a frequency up-conversion toward the harvesters' natural response spectrum. This paper introduces the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods will allow energy generation and conversion for loads within the unexplored quasi-static frequency range (<1 Hz). The post-buckling behavior of bilaterally restrained columns and bistable plates is used for frequency up-conversion. A bimorph cantilever PVDF piezoelectric beam, attached to the columns and plates, are used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept. The levels of extractable power are evaluated for different cases under varying input frequencies. Finally, numerical simulations provide insight into the scalability and performance of the developed concepts.