Rotational energy harvesting for low power electronics

Energy harvesting is one of the key technologies for the realization of autonomous sensing. The aim of this thesis is to develop low-frequency broadband rotational energy harvesting solutions for self-powered sensing. As an example of rotational energy harvesting, an airflow energy harvester using a miniaturized turbine and piezoelectric transduction was first introduced. Rotation was converted from airflow by the turbine, and a piezoelectric beam was actuated by the turbine rotor using magnetic plucking. Issues, including high cut-in speed and low output power at high rotational frequencies, were discovered. In order to decrease the cut-in speed, a self-regulating mechanism was proposed and integrated. The magnetic plucking strength can be passively adjusted according to the rotational speed. This self-regulating harvester exhibited a lower cut-in speed. In order to understand the limited performance at high rotational frequencies and to optimize the design, a theoretical model was built. Different arrangements were investigated, showing that this harvester is ideal to operate at low excitation frequency far below the piezoelectric beam's resonant frequency. Bistable behaviour was also employed and studied to enhance the energy harvesting capability over a wide bandwidth at low frequency. Then, a complete self-powered condition monitoring system, including a bistable frequency up-converting harvester, a power management circuit and a wireless sensor node, was studied and developed to implement the concept of self-powered sensing. Finally, a fundamental study was conducted for three types of rotational energy harvesters, including electromagnetic, piezoelectric resonant, and piezoelectric non-resonant harvesters. Scaling laws for each type were established to study harvesters' performance for different operating frequencies and device dimensions. This study provides a guideline for selection and design of rotational energy harvesters with specific requirements of device dimension and operating frequency.Open Acces