Autonomous Energy-Harvesting Sensor for Building Health Monitoring

Buried, battery-free sensor nodes offer a promising solution for structural health monitoring, reducing maintenance and improving infrastructure sustainability by monitoring slow-varying parameters such as temperature and humidity, which do not require high sampling frequencies. This study shows the practical implementation of an autonomous LoRa node powered solely by RF energy harvested from a gateway using an 868 MHz rectenna and a custom energy management circuit charging a supercapacitor. Experimental characterization revealed that, with a single rectenna placed 40 cm from the gateway, communication intervals ranged from 58 min (+14 dBm) to 10 min (+20 dBm), clearly linking available RF power and energy management to achievable monitoring frequency. To further illustrate this, deploying a multi-element rectenna array enabled reliable node operation at distances greater than 10 m, demonstrating that the number of rectenna elements is the dominant factor governing harvested energy and the achievable operating range. Configuring the gateway as both a communication hub and an energy source further simplified deployment. These results highlight strategies for overcoming power delivery constraints in deeply embedded wireless sensing applications for civil structures.