This paper proposes a novel energy harvesting floor structure using piezoelectric elements for converting energy from human steps into electricity. The piezoelectric energy harvesting structure was constructed by a force amplification mechanism and a double-layer squeezing structure in which piezoelectric beams were deployed. The generated electrical voltage and output power were investigated in practical conditions under different strokes and step frequencies. The maximum peak-to-peak voltage was found to be 51.2 V at a stroke of 5 mm and a step frequency of 1.81 Hz. In addition, the corresponding output power for a single piezoelectric beam was tested to be 134.2 μW, demonstrating the potential of harvesting energy from the pedestrians for powering low-power electronic devices.

Rotational energy harvesting technology has attracted more and more attention recently. This paper presents a piezoelectric rotational energy harvester that can be mounted with an offset distance from the rotation center. The piezoelectric energy harvester is designed to be dynamically excited by the force due to gravity, which causes the piezoelectric cantilever beams in the harvester to vibrate periodically as the harvester rotates. A novel design of the harvester structure with a hollow mass is proposed and analyzed in this paper. Experiments were performed to investigate the design and analysis. A power output of 106~2308 μW can be achieved at the rotating frequencies of 0.79~14 Hz with a piezoelectric cantilever beam in the prototyped energy harvester. Results showed that the prototyped harvester can be mounted on a rotating wheel hub and output sufficient power in a wide frequency range for wireless monitoring sensors.

Harvesting energy from human motions for powering portable or wearable electronic devices is attracting attentions in recent years. In this paper, an inertial energy harvester based on a piezoelectric cantilever beam is investigated for harvesting energy from a backpack. Vibration levels in the backpack during walking or jogging were tested and analyzed. Theoretical analysis was explored to determine parameters of the harvester. The generated power of the cantilever beam was experimentally studied. The experimental results show that the harvester can achieve a power output of 43.64 μW with a single piezoelectric element.

This paper presents a study of a piezoelectric energy harvesting circuit based on low-power-consumption synchronized switch technology. The proposed circuit includes a parallel synchronized switch harvesting on inductor interface circuit (P-SSHI) and a step-down DC-DC converter. The synchronized switch technology is applied to increase the conversion efficiency of the circuit. The DC-DC converter is used to accomplish the impedance matching for different loads. A low-power-consumption microcontroller and discrete components are used to build the P-SSHI interface circuit. The study starts with theoretical analysis and simulations of the P-SSHI interface circuit. Simulations and experiments were conducted to validate the theoretical analysis. The experimental results show that the maximum energy harvested by the system with a P-SSHI interface circuit is 231 μW, which is 2.89 times that of a system without the P-SSHI scheme. The power consumption of the P-SSHI interface circuit can be as low as 10.6 μW.

This paper presents a two-stage adaptive boost converter with low-voltage starter for low voltage piezoelectric energy harvester. The adaptive technique can deal with a range of input voltages from the piezoelectric generator for required output voltages. The parameters of the converter including inductance, switching frequency, duty cycles and the input/output voltage are studied for conversion efficiencies. The experiment results show that a two-stage adaptive boost converter can achieve a conversion efficiency of 84.3%∼91.3% for a piezoelectric harvester in the considered low voltage range to charge an 1.5 V energy storage device.

For ultra-low-frequency vibration applications, this study focuses on a piezoelectric energy harvesting system with a spring mass system, utilizing magnetic plucking to up-convert the frequency. The proposed spring mass system includes a spring, a magnet mass with a guide rail, and a fixed pulley. The spring mass system responds to external ultra-low-frequency excitation and transfers the vibration to the piezoelectric cantilever beam through the magnets, achieving frequency up-conversion. The theoretical model of the designed piezoelectric energy harvesting system is established, and the effects of magnetic forces and potential energy between the magnets are analyzed. Numerical analysis and experimental studies demonstrate that the proposed piezoelectric energy harvesting system can efficiently achieve frequency up-conversion and generate a higher output power under the conditions of sinusoidal excitation at a frequency of 1 Hz and an amplitude of 40 mm. The system exhibits its highest power output with a magnetic distance of 15 mm, resulting in a maximum output power of 57.35 μW. Finally, to verify the performance of the designed energy harvester in low-velocity water flow, a series of underwater experiments were carried out. The results show that the designed harvester can generate an output power of 23.73 μW with optimal resistance of 250 kΩ at a flow rate of 0.371 m/s. The designed structure is well suited for energy harvesting in flow-induced vibration in low-velocity water flow.