To monitor the structural health of infrastructure, monitoring systems typically employ sensors embedded into concrete. These embedded sensors are connected to a central station by means of wires. The downside of such sensors is their installation, which is expensive, inefficient, labor-intensive, and difficult. In addition, the wires can corrode and thus the sensors become inoperative. Wireless sensors can decrease the cost of monitoring systems and reduce their installation time. Wireless embedded sensors need to operate for long periods of time, but sensor batteries only have a finite lifetime. Numerous wireless power transfer methods have already been proposed to overcome the power limitations of sensor batteries. At Florida International University, a new wireless power transfer method, known as strongly coupled magnetic resonance (SCMR), has been developed.

The researchers developed a receiver/transmitter system to support efficient air-to-concrete wireless power transfer at different humidity levels. They analyzed the performance of SCMR wireless power transfer systems by means of coupling simulations for concrete with different humidity levels and various depths. In addition, they designed a rectifying circuit to convert the wirelessly transferred RF power to DC power.

Although SCMR systems for air-to-air power transfer have been previously studied, the design must be modified for an air-to-concrete power transfer. A standard SCMR system consists of four magnetic loops. Simulations were performed while varying the height of the transmitting (TX) loop’s placement as well as the depth of the receiving (RX) loop’s placement in concrete.

The effects of humidity on the performance of the SCMR system were also examined, demonstrating that the efficiency of the SCMR system decreases as the humidity increases. An analysis of the SCMR system’s performance in reinforced concrete was performed, concluding that the SCMR approach can efficiently transfer power through reinforced concrete. A power rectification circuit was developed, and a comparison was made of the SCMR system’s efficiency before and after rectification. See “Wireless Power Transfer in Concrete via Strongly Coupled Magnetic Resonance,” IEEE Transactions On Antennas And Propagation, March 2013, p. 1378.