Studies on renewable energy harvesting have experienced significant growth due to the increasing demand of portable electronic devices and wireless sensor networks. We introduce the first time a beam energy harvester coupled with piezoelectric layers and stack actuators subjected to harmonic base excitation for achieving efficiency energy harvesting with a new developed self-frequency-tuning process. The self-frequency-tuning process of the harvester is realized by an adjustable axial force, which is generated by a piezoelectric stack actuator, through a feedback filtering electrical circuit. By the feedback filtering circuit, the value of axial force is determined by the amplitude of the output voltage generated on piezoelectric layers to tune the first natural frequency of the beam harvester close to the excitation frequency leading to a resonance of the harvester system. To describe and simulate the energy harvesting and the self-tuning process, a mathematical model is presented to calculate the dynamic response of the harvester as well as the output electric charge and voltage from piezoelectric layers for adjusting the axial force. It is noted that an iteration process is indispensable for the tuning process because of the transient nature of the vibrating system. A novel iteration numerical model is hence developed, and the whole energy harvesting process is divided into many short periods to represent the iteration steps and the self-tuning process. From numerical simulations, it shows that the self-tuning process helps increase the efficiency of the harvester, especially when the harvester is tuned close to its resonant state.

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