Harvesting Energy from Bridge Vibration by Piezoelectric Structure with Magnets Tailoring Potential Energy

Bridges play an increasingly more important role in modern transportation, which is why many sensors are mounted on it in order to provide safety. However, supplying reliable power to these sensors has always been a great challenge. Scavenging energy from bridge vibration to power the wireless sensors has attracted more attention in recent years. Moreover, it has been proved that the linear energy harvester cannot always work efficiently since the vibration energy of the bridge distributes over a broad frequency band. In this paper, a nonlinear energy harvester is proposed to enhance the performance of harvesting bridge vibration energy. Analyses on potential energy, restoring force, and stiffness were carried out. By adjusting the separation distance between magnets, the harvester could own a low and flat potential energy, which could help the harvester oscillate on a high-energy orbit and generate high output. For validation, corresponding experiments were carried out. The results show that the output of the optimal configuration outperforms that of the linear one. Moreover, with the increase in vehicle speed, a component of extremely low frequency is gradually enhanced, which corresponds to the motion on the high-energy orbit. This study may give an effective method of harvesting energy from bridge vibration excited by moving vehicles with different moving speeds.

Power enhancement of a monostable energy harvester by orbit jumps

Energy harvesting has been regarded as a potential solution for power problems in wireless sensor network applications over batteries. Nonlinear configurations, as one of the most promising methods for broadening bandwidth, still make the system suffer from the coexistence of high-energy orbit and low-energy orbit, which significantly reduces output power. This paper proposes the electromagnetic kick method to enhance the output power of a monostable energy harvester through orbit jumps. The so-called electromagnetic kick is introduced by a solenoid consisting of a coil from the electromagnetic energy harvester and a three-volt button battery. The modeling and analysis demonstrate the excitation capability of the electromagnetic kick for orbit jumps. Inspired by a swing, two strategies are derived as the single kick and cycled kick. Based on an experimental setup, parameters for two strategies are first determined. The single kick and the cycled kick are then respectively employed to realize orbit jumps for the energy harvester under varying excitation and loading conditions. For each scenario, twenty trials are repeated to investigate the probability and capability. The system power output can be boosted from null to over 360 µW after orbit jumps, and the consumed energy can be resumed within 20 s. In addition, to evaluate different orbit jumping approaches in the literature, a figure of merit is developed, and the comprehensive advantages of the electromagnetic kick approach are demonstrated. The proposed effortless and efficient orbit jumping strategy expands the possibilities of realistic applications of nonlinear energy harvesters. The defined figure of merit not only makes it possible to compare different orbit jumping methods but also opens the door to new strategy development.

High-energy Orbit Sliding Mode Control for Nonlinear Energy Harvesting

Vibration energy harvesting has extensive application prospects in many significant occasions, such as mechanical structure health monitoring, vehicle tire pressure monitoring, IoT devices and human health monitoring. The nonlinearity is an effective method to improve the energy harvesting efficiency where there are low- and high-energy orbits in the multi-solution region of the system. The harvested power will be increased significantly when the system is guided from the low-energy orbit to the high-energy orbit. However, previous research mainly focuses on the theoretical and numerical investigation of controlling strategy, but the feasibility of control methods has not been verified experimentally. This paper proposes a high-energy sliding mode control method through rotatable magnets actuated by micro-motor. The electromechanical model of mono-stable and bi-stable systems with the identified nonlinear restoring force is established to design a sliding mode control algorithm for enhancing the energy harvesting performance. Simulation and experiment results demonstrate that the rotatable magnets with sliding mode control have a positive influence on reaching the high-energy orbit for both mono-stable and bi-stable systems within the multi-solution region. Moreover, the rotatable magnets method with a sliding mode control actuates the small magnets in the system for a short time with little consumption of energy. This research has provided a practical application of high-energy orbit control for improvement of the energy harvesting.