Design and performance study of displacement-driven piezoelectric energy harvesters used in steel spring floating slab tracks

The deflection of track structures, which represents an abundant source of mechanical energy in railway systems, holds potential for powering monitoring devices. In this study, a kind of displacement-driven piezoelectric energy harvester specifically for steel spring floating slab tracks is developed, which boasts high power output and two notable advantages: (a) Its compact design seamlessly integrates the force transmission metal tube and the piezoelectric stack within the compression spring, significantly reducing the overall height of the device. This makes it ideal for applications where space within track structures is limited. (b) The inverted design of the force transmission metal tube facilitates easy assembly with the high-stiffness compression spring. This design effectively transmits more mechanical vibration energy to the piezoelectric stacks, resulting in substantially greater electrical outputs. Energy harvesting performance of the proposed harvester, including AC voltage and power under the harmonic displacement, has been assessed both experimentally and theoretically. Effects of displacement input, piezoelectric stack parameters and spring stiffness on the performance of the harvester are discussed. In laboratory tests, the fabricated prototype can achieve the maximum average power of up to 942.55 mW at an optimal resistance of 11 kΩ, under a displacement of 4 mm, and a frequency of 5 Hz. Furthermore, when exposed to the floating slab displacement of steel spring floating slab tracks, the prototyped device was able to harvest a maximum energy of approximately 742 mJ at an optimal resistance of 76 kΩ, over 10 cycles of floating slab displacement signals. This translates to a total energy of 15.14 J per day, which is sufficient to power the ViPSN2.0 wireless temperature Internet of Things (IoT) sensor node. The findings of this study offer valuable design guidelines for the development of the displacement-driven piezoelectric energy harvesters in railway systems.