This article presents the dynamic analytical solution of piezoelectric composite stack transducers under external harmonic mechanical loads, which is based on the linear theory of piezoelasticity. The solution is obtained by using the displacement method. The effects of the load frequency, the load amplitude, and the thickness of electrode on the dynamic characteristics of the transducers are discussed. Experimental results strongly verify the validity of the proposed theoretical analysis.

Capturing vibration energy of track structures using piezoelectric energy harvesters has attracted increasing attention for powering wireless sensor networks along railway line. To better use the vertical space below steel rail, a kind of piezoelectric tube stack energy harvesters is proposed in this paper, which can be placed at the bottom of the steel rail to harvest the vibration energy of the vertical displacement induced by the moving train. The harvester consists of a displacement transmission rod, a compression spring, a force transmission metal tube, a piezoelectric tube stack, a whole metal shell, screw bolts, and a wire hole. The advantage of this design is to fully combine the heights of the compression spring, the force transmission metal tube and the piezoelectric tube stack, which helps reduce the vertical height of the device and enables its wide application to a variety of tracks, including, ballast track, ballastless track, and steel-spring floating slab track. Energy harvesting performance of the developed piezoelectric tube stack energy harvester is investigated experimentally, which is consistent with the theoretical results of the simplified model of such a harvester reported. Effects of displacement amplitude, displacement frequency, spring stiffness, resistance, and key parameters of piezoelectric tube stack on the energy harvesting performance of the harvester are also discussed. The present study provides a new design concept for developing piezoelectric energy harvesters used in railway systems with the smaller vertical space below steel rail.

No abstract

In this paper, a flex-compressive piezoelectric energy harvesting cell (F-C PEHC) is proposed. This cell has a large load capacity and adjustable force transmission coefficient assembled from replaceable individual components. A statically indeterminate mechanical model for the cell is established and the theoretical force transmission coefficient is derived based on structural mechanics. An inverse correlation between the force transmission coefficient and the relative stiffness of Element 1's limbs is found. An experimental study is also conducted to verify the theoretical results. Both weakened and enhanced modes are achieved for this experiment. The maximum power output approaches 4.5 mW at 120 kΩ resistive load under a 4 Hz harmonic excitation with 600 N amplitude for the weakened mode, whereas the maximum power output approaches 17.8 mW at 120 kΩ under corresponding load for the enhanced mode. The experimental measurements of output voltages are compared with the theoretical ones in both weakened and enhanced modes. The experimental measurements of open-circuit voltages are slightly smaller for harmonic excitations with amplitudes that vary from 400 N to 800 N and the errors are within 14%. During the experiment, the maximum load approaches 2.8 kN which is quite large but not the ultimate bearing capacity of the present device. The mechanical model and theoretical transmission coefficient can be used in other flex-compressive mode energy transducers.

This paper presents the dynamic analytical solution of a piezoelectric stack utilized in an actuator and a generator based on the linear piezo-elasticity theory. The solutions for two different kinds of piezoelectric stacks under external load were obtained using the displacement method. The effects of load frequency and load amplitude on the dynamic characteristics of the stacks were discussed. The analytical solutions were validated using the available experimental results in special cases. The proposed model is able not only to predict the output properties of the devices, but also to reflect the inner electrical and mechanical components, which is helpful for designing piezoelectric actuators and generators in a comprehensive manner.