RF Energy Harvesting System with a Mini Branch-Line Coupler for Monitoring Railway Conditions

The rail transportation system has been a cornerstone of the modern economy due to its low cost and environmental sustainability. However, the rapid expansion of railway mileage and the aging of existing infrastructure have posed challenges for efficient and widespread rail inspection systems. Existing approaches are hindered by their high costs and the occupation of tracks. In this study, we present a high-efficiency RF energy harvesting system using a mini-branch line coupler (Mini-BLC) for railway monitoring. The Mini-BLC effectively reduces the return loss caused by impedance mismatch and optimizes the high-efficiency region for high-power input. Using T-shape equivalent circuits, the size of mini-BLC is reduced by 30%. The wireless-powered sensor tag (WPST) exhibits an overall efficiency of 26.3% at the input power of 8 dBm, which is 33% higher than the efficiency of the conventional scheme at the same input power. The presented strategy is generalizable for developing multi-functional RF energy-powered systems with other frequency bands and power regions.