Analysis and Numerical Modeling of Inductively Coupled Antenna Systems

Abstract

This work focuses on the analysis and design of Inductive Power Transfer (IPT) antenna systems. Practical applications for IPT systems include a wireless powering of mobile devices in consumer electronics or Radio Frequency Identification (RFID) systems in logistics. The physical relevant properties of the antenna systems such as an accurate inductance computation or a precise modeling of skin and proximity effects are extracted by means of numerical techniques. At the same time, an equivalent network description based on the transformer concept is enabled by representing the antennas via reduced circuit models, which are obtained by specialized parameter fitting techniques. The numerical simulations used in this thesis are based on the Partial Element Equivalent Circuit (PEEC) method. The PEEC method is especially appropriate for IPT antenna systems, because it allows efficient meshing techniques in case of long and thin conductors and provides a transformation of the electromagnetic coupling effects to the network domain. Furthermore, neglecting the retardation effects is traditionally fulfilled by the PEEC method when quasi-stationary assumptions of the Maxwell’s equations are used. This is beneficial for IPT systems, since the simulation time is reduced while the errors are kept sufficiently small. First, some fundamental concepts of electrodynamic effects are reviewed in this work. A new Lorenz-Quasi-Static (LQS) formulation is derived while its integration into well established techniques is shown. After presenting the fundamental concepts of IPT systems, the PEEC method is derived in a slightly modified way compared to the standard formulation in order to handle the different approximation techniques in a unified notation. Afterwards, the influence of parameter tolerances on the system behavior is analyzed by applying the adjoint sensitivity analysis to the PEEC method with a special focus on skin-effect problems. The presented system modeling approach is confirmed via measurements and Finite Element Method (FEM) simulations for a Printed Spiral Coil (PSC) system often used in RFID applications. By means of the optimized PEEC method, a remarkable speedup can be gained when compared with FEM simulations whereas the obtained errors typically do not exceed a few percent.