Rotational energy harvesting using bi-stability and frequency up-conversion for low-power sensing applications: Theoretical modelling and experimental validation

• Published in: Mechanical systems and signal processing 2019-06, Vol.125, p.229-244
• Main Authors: Fu, Hailing, Yeatman, Eric M.
• Format: Article
• Language: English
• Subjects: Bistability; Broadband; Conversion; Design factors; Electric power distribution; Energy; Energy harvesting; Frequency stability; Frequency up-conversion; Kinetic energy; Magnetic fields; Magnetic plucking; Modelling; Piezoelectric; Piezoelectricity; Plucking; Rotational energy harvesting; Upconversion
• ISSN: 0888-3270; 1096-1216
• DOI: 10.1016/j.ymssp.2018.04.043

•A topology to harvest low-frequency broadband rotational energy is studied.•Theoretical model is established for this bistable frequency up-converting harvester.•Asymmetrical potential wells were studied, showing benefits in stabilizing output.•Different operating modes were investigated; the double-well mode is the best.•Key factors determining operating modes were studied, providing design guidelines.•Experimental results verify the theory, showing a wide bandwidth at low frequencies. Kinetic energy harvesting has drawn great attention in the past decade, but low-frequency and broadband operation is still a big issue which impedes this technology to be widely deployed in low-power Internet of Things applications. In this paper, theoretical modelling and experimental validation of a rotational harvester with bi-stability and frequency up-conversion is presented for harnessing low-frequency kinetic energy with a wide bandwidth. Piezoelectric transduction was adopted to convert the rotational kinetic energy into electricity. Distributed-parameter modelling was employed for analyzing the electromechanical dynamics of the bistable piezoelectric beam. Bistable and frequency up-converting behaviours were considered in the theoretical model by introducing two external input magnetic forces. Different oscillating modes were analyzed, showing the variation of power generation capability under different modes, and the advantage of operating in the periodic double-well mode. From the potential well study, we got a conclusion that for the same input magnetic force, periodic double-well mode is capable of achieving a larger vibration amplitude compared to a harvester without bi-stability. Asymmetric potential well shapes were investigated. This asymmetric shape provides a way to stabilize the initiation position of the beam for each plucking cycle, and eventually to stabilized the output. Key design factors to control the oscillating modes were studied, providing a guideline for future design. An experimental study was conducted to verify the theoretical results. A close match was achieved. This bistable harvester demonstrated a significant improvement (up to 2×) compared to a harvester without bi-stability over a wide bandwidth (from 1 to 11 Hz) at low frequencies, when operating in the periodic double-well mode. This paper presents a detailed theoretical model and in-depth analysis of a bistable frequency up-converting harvester, providing a fundamental understandi