Battery-Free and Gateway-Free Cellular IoT Water Leak Detection System

TL;DR

The paper addresses the challenge of battery-free, gateway-free IoT water-leak monitoring by harvesting energy directly from water using a two-compartment electrochemical sensor to drive LTE-M transmissions. It introduces a dedicated power path with a PFM boost converter, a 1.5 F supercapacitor buffer, and a TLV431-based hysteretic load gate to ensure LTE-M activation only when energy is sufficient, enabling reliable direct-to-cloud uplinks on a Thingy:91 module with TLS protection. Experimental validation shows activation latencies around $23$ minutes, eight beacon transmissions per charge, and reliable operation across water depths down to $0.5$ mm, with a satellite-compatible configuration demonstrating NTN readiness. The work establishes a practical, maintenance-free foundation for remote, infrastructure-monitoring IoT networks leveraging event-driven hydroelectric energy harvesting and cellular connectivity.

Abstract

This paper presents a battery-free and gateway-free water leak detection system capable of direct communication over LTE-M (Cat-M1). The system operates solely on energy harvested through a hydroelectric mechanism driven by an electrochemical sensor, thereby removing the need for conventional batteries. To address the stringent startup and operational power demands of LTE-M transceivers, the architecture incorporates a compartmentalized sensing module and a dedicated power management subsystem, comprising a boost converter, supercapacitor based energy storage, and a hysteresis controlled load isolation circuit. This design enables autonomous, direct to cloud data transmission without reliance on local networking infrastructure. Experimental results demonstrate consistent LTE-M beacon transmissions triggered by water induced energy generation, underscoring the system's potential for sustainable, maintenance free, and globally scalable IoT leak detection applications in smart infrastructure.

Figures (14)

• Figure 1: Evolution of leak detection architectures. The legacy approach (left) relies on local gateways and batteries, limiting scalability and increasing maintenance overhead. The proposed battery-free system (right) eliminates local infrastructure by connecting directly to terrestrial LTE-M towers, with firmware-supported compatibility for LEO satellites (NTN), enabling autonomous global monitoring.
• Figure 2: System architecture of the battery-free LTE-M system, where harvested energy powers the nRF9160 modem to transmit leak data to the cloud via MQTT.
• Figure 3: CAD model of the sensor enclosure: (a) Isometric view showing the internal compartments designed to hold electrode and electrolyte materials; (b) Bottom view illustrating inlet channels that allow water to enter and trigger the electrochemical reaction for energy generation.
• Figure 4: Schematic of the DC-DC boost converter used to step up the sensor output voltage to 5 V, which gets stored in a supercapacitor for powering the LTE-M module.
• Figure 5: Load isolation circuit using a TLV431-based comparator and P-channel MOSFET. The resistor network ($R_1$, $R_2$, $R_4$) sets the hysteretic voltage thresholds, enabling the load when the supercapacitor voltage exceeds $V_{\text{on}}$ and disconnecting it below $V_{\text{off}}$.