The growing need of creating a network of sensors in critical environment to monitor, sense and alert an operator about the environment gives rise to the research work carried out in the area of power supply to these sensors.
Wireless sensors are usually designed to run on batteries. However, as the number of sensors increases and the devices decrease in size, there is clearly a need to explore alternatives to battery power for wireless sensors. Reliable, efficient and environmentally friendly energy harvesting methods could be adopted to design and build a new electronic device that could be used to replace or supplement batteries in wireless sensors.
This thesis focuses on potential ambient sources of power that can be harvested to run low power wireless sensors in mining environments. It discusses several techniques for converting energy from such sources into useful electrical power. In particular, piezoelectric power conversion technique is described in detail.
Wireless sensor or sensor networks hold significant potential in the mining environment. The need for deployment of such sensor networks is increasing daily as mining companies are looking to adopt the system developed in the “Intelligent Mine – Technology Program (IMTP)”. The objectives of the IMTP are to increase the mine’s productivity, decrease the total costs and to improve the working conditions. To complement these objectives, there have to be improved methods for powering sensor devices to deploy them in large numbers.
Drilling is a crucial component in both underground and surface mining. Water jet assisted drilling is an example of a new drilling technology employing wireless sensors. There are various forms of energy that could potentially be used to power wireless electronic sensors provided the waste energy can be tapped in an intrinsically safe way. In this particular project, the required power to run sensors could be generated by converting mechanical vibration produced from water jet assisted drilling into electrical energy with an intrinsically safe circuit. Various power scavenging methods were researched, but vibration-to-electricity conversion using piezo-ceramic material was selected as the most promising method for this project.
Piezo-based energy conversion is not normally good for mining applications because of intrinsic safety issues. In the case of water jet assisted drilling, however, the environment is much more suitable for piezo-electric conversion. A detailed computer model for this type of power conversion has been developed. The mechanical model of the vibration spectrum is based on test data from the Contents 2 CRC-Mining group. A power conversion circuit has been built, detailed circuit simulations studied and the experimental results are demonstrated.
An example vibration scenario consisting of (20×10^-6)rms strain is considered. Based on this, and a detailed model of a 70mmx25mm PZT piezoelectric patch with 0:2mm thickness, our computer simulation studies and experiments demonstrate the ability to harvest up to 210mW of power.
Source: The University of Newcastle
Author: Upendra K. Singh