Investigating Vibration Energy Harvesting for Self Powered Sensors at Mine Sites

This project focussed on investigating vibration energy harvesting for self powered sensors at mine sites. Mine Internet of Things (MIoT) has gained considerable attention in recent years due to its potential to enhance safety and productivity in mining operations and pave the way for future digital mines. However, a major challenge in MIoT implementation is the limited availability of long lasting power sources for sensor nodes responsible for data perception and transmission. Since there are various vibration sources at the mine site, vibration energy harvesting (VEH) is a promising solution for developing self powered sensors, which aims to convert nearby vibration energy into electrical energy.

The principle of VEH was thoroughly studied in the project. After reviewing the existing commercial VEH devices, an electromagnetic energy harvester from ReVibe (model D) was procured for further investigation. To evaluate the performance of the purchased energy harvester, vibration energy harvesting tests were conducted based on the vibrations produced by a lab vibrator and an idling SUV automobile. Experimental results show that the ReVibe energy harvester (model D) can harvest vibration energy from operating machines. However, this energy harvester is designed to operate at its resonant frequency (50 Hz) to achieve maximum power output. Once the excitation frequency deviates from its resonant frequency, the power output of the energy harvester significantly decreases. Although the resonant frequency of the ReVibe energy harvester can be initially adjusted to 50-70 Hz, this energy harvester may not be well suited for capturing vibration energy from the vibration sources with extremely low dominant frequencies in mine site.

To take advantage of the VEH, the potential vibration sources in surface and underground mines were identified. Subsequently, both short term and long term vibration data were collected from various vibration sources, including five operating machines and a handrail, at a coal handling and preparation plant (CHPP) located in an open cut mine site. Vibration analysis was then conducted to determine the amplitude, dominant frequency, and consistency of the vibrations present in the CHPP. The results demonstrate that all identified vibration sources exhibit abundant and stable vibrations, characterised by substantial amplitudes (up to 5.55 g) and low dominant frequencies (ranging from 14 Hz to 25 Hz). These findings indicate that the vibrations generated by the operating machines at a CHPP are sufficient for vibration energy harvesting.

To effectively capture vibration from the vibration sources in the CHPP, a novel piezoelectric energy harvester with low operating frequencies was developed. The practicality of this energy harvester for mining applications was validated by experiments. In these experiments, the vibration applied to the energy harvester replicated the vibrations generated by the centrifuges in the CHPP, characterised by an RMS acceleration of 0.346 g and a dominant frequency of 25 Hz. Under such vibration excitation, the proposed energy harvester demonstrated its capability to successfully power a temperature and humidity sensor. Furthermore, the collected data can be transmitted to the computer via a Bluetooth Low Energy device at intervals of approximately 2 minutes and 40 seconds. Therefore, the proposed energy harvester shows great potential for developing self-powered sensors in mining environments.

This project demonstrates that there are numerous vibration sources at mine sites that are suitable for vibration energy harvesting. By developing vibration energy harvesters tailored to the characteristics of these vibration sources, self powered sensors can be effectively realised.