Optimizing Power Transfer Efficiency and Bandwidth for Near Field Communication Systems

Near-field communication (NFC) is a specification for short-range wireless links operating at 13.56 MHz in the high-frequency (HF) band. The achievable bandwidth, efficiency, and range of lightweight, size-constrained, low-power NFC systems are limited by fundamental theorems of small antenna theory. We develop a relationship between near field power transfer and radiation efficiency for dipole-type antennas, which is applicable to both communications and wireless power transfer applications, and present modeled and experimentally measured results for the bandwidth efficiency product of two ferrite loop antenna designs. The model is used to determine the optimal geometrical parameters that maximize this figure of merit for a given antenna size. Modeled and measured results show that ferrite loops can approach theoretical limits on performance for the bandwidth efficiency product of an antenna with a given size.