Analysis of Wireless Power Transfer Between Near-Field Antennas Using the Bi-Characteristic-Impedance Transmission Line (BCITL) Model

Analysis of wireless power transfer (WPT) between near-field (NF) antennas is proposed by using a bi-characteristic- impedance transmission line (BCITL) model. In particular, misalignment between small near-field (NF) transmitting (TX) and receiving (RX) antennas degrades the power transfer efficiency (PTE). The proposed novel optimization procedure, based on the BCITL model, effectively maximizes WPT area, which is strongly influenced by antenna characteristics, the RX antenna's position, and the load reflection coefficient (Γ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i>) at each misaligned position. In such misalignment, (Γ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> ≠ 0), which is a crucial parameter in impedance matching to broaden the WPT area. This letter investigates the Γ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> impact on the PTE at misaligned positions based on BCITL parameters, providing a new optimization framework that adapts to varying degrees of misalignment. In simulation and measurement validation, it is demonstrated that this BCITL model may estimate an optimal Γ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> (Γ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ≠ 0) to produce WPT areas much broader than those using the conventional matching condition (Γ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> = 0).