Performance Optimization of RF Energy Harvesting IoT Systems Operating Within Cast-Iron Box

Abstract

This study proposes a battery-less power system utilizing terrestrial digital television broadcast signals to address the power supply challenges for underground IoT devices. As a power-receiving structure, a slit configuration was integrated into the cover of a cast-iron meter box, transforming the radio-shielding enclosure into an antenna. Electromagnetic analysis and field experiments revealed that the adoption of an L-shaped slit maintains the structural integrity required for infrastructure while simultaneously achieving high radio-wave transmission performance and suppressing directional dependency in reception. Furthermore, an energy harvester circuit was designed using an eight-stage Cockcroft-Walton voltage multiplier, configured by considering the balance between boost performance and internal loss. In a field test conducted approximately 1.0 km from the transmission station, the system reached an operating voltage of 2.2 V in just over three minutes within the shielded enclosure and successfully performed five stable Bluetooth Low Energy (BLE) wireless transmissions over an eight-minute period. These results demonstrate that RF energy harvesting from television broadcast waves functions effectively as a power source for IoT devices, even in harsh underground shielded environments.