Mechanism Of Piezoelectric Energy Harvesting From Road Pavement Deformation Induced By Moving Vehicular Loading

New type of green energy has long been a hot topic to solve the energy problem that is induced by vast consumption of traditional energy. An alternative efficient way is to use piezoelectric materials to capture mechanical energy from environment. This thesis focuses mainly on harvesting mechanical energy from the deformation of road pavement under the action of traffic load from both the experimental and theoretical aspects. Basic lab experiments will be performed to examine the effectiveness of using embedded piezoelectric bimorphs for energy harvesting from asphalt pavement when subject to periodic loading, while theoretical models will be established to reveal qualitatively the associated underlying physical mechanism of this type of energy harvesting.As a preliminary examination, a laminated beam model of plane strain state is proposed wherein a piezoelectric layer is embedded between two asphalt layers. Differential equations governing the full coupling electromechanical behavior of the system are derived and solved using the method of separation of variables. The harvested electric power under harmonic motion is found to depend on various material and geometrical parameters, as well as on the electric resistive in the harvesting circuit. A simple scaling law is obtained to reveal the underlying relationship between the normalized output power, normalized electric resistive, and the electromechanical coupling parameter.To consider a more practical situation of using distributed piezoelectric materials for energy harvesting in road pavement, a Timoshenko asphalt beam model with embedded piezoelectric patches is proposed and solved analytically using the state space method. Numerical results for the natural frequencies of the system with a closed energy harvesting circuit are validated by comparisons with existing results in literature. The dependence of electric outputs on various material, geometrical, and circuit parameters are also investigated.To account for the effects of the under beneath stable and subgrade layers of a practical road pavement, the Winkler foundation model is introduced into the above two beam models. Qualitative influences of the foundation on the efficiency of energy harvesting are investigated comprehensively.hi order to provide a solid demonstration on the possibility of using piezoelectric materials for energy harvesting from the deformation of road pavement, a series lab experiments are performed to measure the electric outputs when the pavement is subject to a dynamic load. Specifically, wheel tracking tests are proposed wherein piezoelectric bimorphs are embedded in a square asphalt specimen that is further loaded using a back-and-forth rolling wheel which is used to simulate the moving traffic load. The recorded output electric voltage exhibits a periodic feature that has a close correlation with the rolling wheel. This suggests that the moving loading on a road pavement may generate a typical AC current in the energy harvesting circuit.Accordingly, a simple compression model is proposed to study the physical mechanism of the wheel tracking test. Numerical results for the output voltage exhibits excellent agreement with the experimental measurements. A simple scaling is established which suggests that the normalized output power of the energy harvesting device depend only on the normalized period of the rolling wheel, the location and the size of the device. It is also shown that the output power may be optimized by tuning various system parameters especially the electric resistance of the energy harvesting circuits.Finally, the scaling law is extended to the practical road pavement according to the analogy between the wheel tracking test parameters and a practical road pavement under the ideal traffic flow condition. That is, the normalized output power is found to depend on the normalized vehicle speed and the normalized vehicle space (or the normalized safe time). The scaling laws presented in this thesis may provide a useful tool for guideline the design of energy harvesting using embedded piezoelectric patches from the deformation of road pavement under traffic load.