A two-stage power conditioning circuit consisting of an AC-DC converter followed by a DC-DC converter is proposed for a vibration-based energy harvesting system. The power conditioning circuit intends to maximize the amount of power extracted from a piezoelectric energy harvester by matching the source impedance with the circuit by adaptively adjusting the duty cycle. An equivalent electrical circuit representation derived from a distributed-parameter piezoelectric energy harvester model is adapted to enable the impedance matching method proposed here. For a given piezoelectric energy harvester, there is a theoretical maximum power output that is determined by the mechanical damping, base acceleration, and the effective mass of the harvester structure under base excitation. Experimental results are given to validate the effectiveness of the proposed resistive impedance matching circuit around the first resonance frequency of a cantilevered piezoelectric energy harvester.

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The harvesting of ambient energy to power small electronic components has received tremendous attention over the last decade. The research goal in this field is to enable self-powered electronic components for use particularly in wireless sensing and measurement applications. Thermal energy due to temperature gradients, solar energy and ambient vibrations constitute some of the major sources of energy that can be harvested. Researchers have presented several papers focusing on each of these topics separately. This paper aims to develop a hybrid power generator and storage system using these three sources of energy in order to improve both structural multifunctionality and system-level robustness in energy harvesting. A multilayer structure with flexible solar, piezoceramic, thin-film battery and metallic substructure layers is developed (with the overhang dimensions of 93 mm × 25 mm × 1.5 mm in cantilevered configuration). Thermal energy is also used for charging the thin-film battery layers using a 30.5 mm × 33 mm × 4.1 mm generator. Performance results are presented for charging and discharging of the thin-film battery layers using each one of the harvesting methods. It is shown based on the extrapolation of a set of measurements that 1 mA h of a thin-film battery can be charged in 20 min using solar energy (for a solar irradiance level of 223 W m −2), in 40 min using thermal energy (for a temperature difference of 31 • C) and in 8 h using vibrational energy (for a harmonic base acceleration input of 0.5g at 56.4 Hz).

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