Performance and Degradation of a Battery-Free Water Leak Detection Device

Water waste is one of the major causes of water scarcity, and it has become an alarming issue these days. According to the reports from UNICEF, it is estimated that by early 2025, half of the world's population may be residing in regions facing water scarcity [1]. The main reason for water waste is water leakage which also leads to significant property damage and heavy restoration costs if the leak is not detected at early stages. Currently, one of the solutions to these problems, is to detect the leak before it causes significant damage and water waste. The existing market provide solutions through water leak detectors which can identify leaks immediately after the incident. However, these devices are constrained by their dependency on batteries that contains hazardous chemicals, require high maintenance, and are difficult to access in remote areas. To address these issues, our team has launched the world’s first IoT-based Battery-Free Water Leak Detection device in which wireless signal transmission (via BLE) is powered by the energy harvested from the sensor-water reaction. One example of this type of sensor is the Mg-CNF (carbon nano fiber) system that converts the chemical energy to the electrical energy upon reaction with water [2]. The device made by our research group uses a magnesium-graphite couple that undergoes an electrical change as a sensing mechanism, in the presence of water. This electrical energy is stored and utilized to power the Bluetooth low energy (BLE) module that transmits the signal (sensing) generated by the sensor after contacting water. Although, the prototype has previously been built successfully, further tasks are needed to improve the performance, find failure modes and reduce the cost of the device. Therefore, this thesis focuses on the electrical performance, degradation on repeated uses, and reasons behind the failure of the sensor device. The thesis will describe the I-V characteristics of the sensor under various conditions. It also discusses the electrical performance of the sensor with respect to charge capacity and internal resistance under variable load applications. Clear demonstration of the number of repeatability of the device under specific parameters is given, and the changes in the behavior of the device in terms of power production and beacon activation is also indicated. The reasons behind the degradation of the device are addressed by using various tools such as SEM/EDX, XPS, XRD and FTIR. Moreover, the