Locating embedded iron bars for wireless power transmission through reinforced-concrete wall

We previously showed that using low-frequency magnetic waves is effective for wireless power transmission (WPT) through reinforced-concrete walls. When a magnetic wave below 400 Hz was used, it was confirmed that the temperature increase of iron objects inside concrete is very small by numerical calculation based on a non-steady heat conduction equation that included a one-dimensional heat conduction term and heat generation term. However, even if the frequency was lowered to 60 Hz, the power loss was still serious due to magnetic coupling impedance caused by iron bars, such as a rebar lattice, inside the concrete wall. This fact was confirmed from both experiments and numerical calculations. In this study, we propose an iron bar location system using a pair of patch antennas to detect iron bars embedded in the concrete and use this information to place WPT couplers away from embedded iron. Then, we show that the proposed system can be adapted to concrete walls up to 70 cm thick by numerical calculation with the finite-difference time-domain method. Our research results will contribute to WPT in cases where iron bars or pipes are present inside a wall.