Piezoelectric energy harvesting from bridge vibrations has the potential to power wireless sensors used for bridge health monitoring. Often, it is necessary to store the harvested energy before it could be used to power the sensor intermittently. However, the behavior of the piezoelectric energy harvester (PEH) with nonlinear interface circuits for energy extraction and storage subject to realistic bridge vibrations has not been fully understood. This work performs a comprehensive analysis on the performance of the PEH subject to the measured railway bridge vibrations and compares the energy stored on a capacitor using four different interface circuits. Firstly, the dynamic characteristics of the railway bridge is analyzed. A cantilevered PEH is then designed and fabricated based on the dynamic characteristics of the bridge. Subsequently, four realistic energy extraction and storage interface circuits, namely, the standard energy harvesting (SEH), synchronized charge extraction (SCE), parallel synchronized switch harvesting on inductor (P-SSHI) and series SSHI (S-SSHI) circuits, are evaluated and compared when the PEH subject to the measured bridge vibrations. The influence of the storage capacitance and the 1st short-circuit natural frequency of the PEH on the stored energy with these four circuits is then discussed. An optimal storage capacitance exists in the systems based on SEH, P-SSHI and S-SSHI circuits. The system based on P-SSHI circuit has the highest efficiency on energy storage. This work provides a technical framework to develop the realistic energy harvesting and storage system for realization of self-powered bridge condition monitoring.

To enhance the efficiency of piezoelectric energy harvesting, various interface circuits have been developed, including standard energy harvesting (SEH), synchronized charge extraction (SCE), and both parallel and series synchronized switch harvesting on inductor (P-SSHI and S-SSHI) circuits. However, voltage drops in transistors and diodes prevent the synchronization switch from closing precisely when the output voltage of a piezoelectric energy harvester (PEH) reaches its peak, resulting in a switching delay. The impact of this delay on energy harvesting and storage remains insufficiently understood. This study models and compares the effects of voltage drops in transistors and diodes on energy harvesting and storage in self-powered SCE, P-SSHI, and S-SSHI circuits. Analytical solutions for the voltage variations on energy storage capacitors during each half-cycle are derived, and experimental tests are conducted to validate the theoretical results. A systematic comparison of the energy charging performance is conducted for PEHs under weak, medium, and strong coupling conditions, with a focus on the influence of threshold voltages across transistors and diodes. Results show that switching delays can reduce the energy charged into storage capacitors in systems with self-powered P-SSHI and S-SSHI circuits. The self-powered P-SSHI circuit is most effective for energy charging in PEHs with weak coupling, while the SEH circuit proves most efficient for PEHs with medium or strong coupling.

Harvesting energy from the environment to energize IoT nodes is a contemporary study focal point. Contemporary research fails to achieve wideband and high-efficiency energy harvesting concurrently, and the majority of studies neglect the stochastic characteristics of ambient vibrations, hence hindering the practical application of energy harvesters. We propose a graded E-shaped piezoelectric energy harvester array (GEEHA) to tackle this issue. In the theoretical part, the average voltage theory of 1-DOF piezoelectric energy harvester (PEH) excited by random vibration is extended to encompass 2-DOF E-shaped PEH, to guide the design of GEEHA. The simulation part examined the energy harvesting and storage capabilities of the GEEHA interfaced with the standard energy harvesting (SEH) circuit and self-powered synchronized switch harvesting on inductor (SP-SSHI) circuit under diverse vibrational conditions. Finally, all the results were validated by experiments. Studies demonstrate that the designed GEEHA achieves high power output across multiple discrete frequency bands within the range of 30–120 Hz, with a maximum output power exceeding 20 mW. And it was found that, the energy output performance of the series-connected PEH array surpasses that of the parallel circuit. For the energy storage capacity of circuits, under harmonic and Gaussian white vibrations, the energy storage capability of SP-SSHI circuit was around 4–8 times that of the SEH circuit. Nevertheless, under bridge vibration, the SP-SSHI circuit did not yield a significant advantage. Ultimately, the GEEHA was employed to power temperature and acceleration sensors. Activation of the wireless sensor nodes was successfully achieved under harmonic vibration, Gaussian white noise excitation, and measured bridge vibration, with activation periods of 19 s, 52.5 s, and 24 s, respectively. Overall, our research has achieved broadband and high-capacity energy harvesting and storage, facilitating the enhancement of green energy supply for IoT nodes.