Wirelessly Powered Embedded Sensor Nodes for Internal Structural Health Monitoring

Monitoring large civil structures during construction and over their entire lifetime is key to being able to predict structural weaknesses and provide predictive maintenance. Existing approaches to structural health monitoring typically rely on wired or wireless sensors placed on the exterior of the structure. Although these approaches, being easy to power and replace, provide useful information, they fall short of measuring what is happening deep within the structure itself, e.g. within foundations or within supporting beams. Wireless sensors embedded inside are particularly attractive for these applications, but lifetime is limited by the battery capacity. Charging these sensors has been the bottleneck. Existing wireless power transfer approaches based on electromagnetic propagation suffer heavy attenuation due to the high dielectric absorption of the dense concrete. To resolve the issue, the limitation of dielectric absorption is tackled with a novel physical layer. In this work, power transfer is built on the fact that nearly all concrete structures are reinforced with steel bars, to provide tensile strength. Instead of transferring power over a few centimetres of concrete with a large transmitter as previous work has attempted to do, the reinforcing steel can act as a conduit for extremely low-frequency magneto-inductive fields.