Multi-objective optimization of piezoelectric vibrational energy harvester orthogonal spirals for ore freight cars

Abstract

Heavy haul freight car cargo capacity and speed have both been increased over time, aiming to boost overall rail transportation efficiency. These trains are often long and operated by a single person, who may not notice failures, especially in the wagons located far from the main locomotive. Sensors to measure the in-train forces have emerged as a feasible solution to assist the driver, indicating possible failures, avoiding accidents and derailments. However, the vast majority of freight cars used in commodity transportation do not have any electric power source, requiring some kind of energy harvester. Vibration energy harvesters (VEH) present some advantages compared to batteries, which need to be charged or replaced periodically. Among VEH designs, the piezoelectric orthogonal spiral (OSo) multibeam has proven to be adequate in reducing environmental frequencies that are typical of these vehicles, for both the well-defined loaded and unloaded conditions. This paper searches for the best set of characteristics for an OSo device for freight car sensors, aiming to enhance the output power in both wagon conditions, as well as ensuring its safety against structural failures. For an aluminum structure and lead zirconate titanate (PZT) ceramics, the best configuration leads to an overall factor of safety of 1.51 and generates up to 2.73 mW (loaded) and 16 mW (unloaded), which is sufficient to feed most of the low power sensors.