A Study of 13.5-MHz Coupled-Loop Wireless Power Transfer Under Concrete and Near Metal

This paper presents a study of near-field wireless power transfer to embedded sensors under concrete under a variety of scenarios, e.g., dry concrete, freshly made concrete, and power transfer near a metal rod. It is demonstrated that with a 1-W RF transmitter operating at around 13-MHz embedded sensor batteries under 20-mm-thick concrete can be wirelessly charged with dc currents such as 16 mA. Wireless power transfer experiments for an antenna under freshly made concrete exhibit 5 mA of dc current which increases to 10 mA after the natural drying of the concrete for 4.5 h. Finally, it is shown that with the help of ultra-thin sheets (1.2-mm total thickness) of high permeability (relative permeability = 350) magnetic materials wireless power transfer under concrete to a sensor wrapped around a steel rod could be significantly increased (as much as 12 dB).