Battery-Free IoT Water Sensor Nodes: Design and Evaluation Across Different Radio Architectures

Abstract

Water-induced structural damage represents a significant challenge across residential, commercial, and industrial environments. Traditional water monitoring systems often rely on battery-powered nodes or wired infrastructure, posing recurring maintenance burdens and limiting large-scale or long-term deployments. This thesis presents a series of battery-free water sensor node architectures, each powered by water-activated electrochemical cells that use the presence of a leak as both the trigger and energy source for wireless communication.

The investigation spans multiple wireless protocols—Bluetooth Low Energy (BLE), RF-assisted BLE, LoRa, and LTE-M—each selected to address specific trade-offs in range, energy demand, and infrastructure dependency. The BLE-based system demonstrates the feasibility of low-power communication using only a brief energy burst generated upon leak detection. An RF-augmented variant integrates ambient RF harvesting to support periodic heartbeat pings, improving observability between leak events. To extend communication beyond localized zones, a LoRa-based design leverages a step-up converter and supercapacitor to meet higher transmission power demands. Finally, a gateway-independent LTE-M implementation is introduced, using a two-stage electrode configuration and comparator-controlled capacitor discharge to enable cellular uplinks directly to the cloud.

This thesis also presents the design and simulation of dual-mode helical antenna systems for hybrid terrestrial and satellite communication, ensuring global connectivity even in areas with limited cellular coverage. Two distinct antenna architectures are proposed: a PCB-based antenna that supports both broadside and end-fire radiation modes, and a 3D-printed geometry that combines quadrifilar and bifilar helices into a vertical structure. These antenna designs offer hardware-level compatibility for seamless integration into both LTE and satellite IoT networks.

Together, the contributions offer a modular and scalable approach to zero-maintenance leak detection. Experimental results validate the practical viability of BLE, LoRa, and LTE-M systems under energy-constrained conditions. While satellite integration remains simulation-based, the antenna designs provide an important step toward globally connected, infrastructure-independent sensing. This work charts a pathway for robust and sustainable water monitoring at scale.