Abstract-In this paper, a method for estimating the mutual inductance between two planar printed circuit board inductors with straight tracks is presented. The thin copper tracks are first modeled as multiple straight line filaments. The Neumann formula, derived from the magnetic vector potential and Faraday's law of induction, gives an analytical solution of the mutual inductance. Unfortunately, due to the complexity of this formula, it can only be solved analytically for relatively simple geometries. However, by following the procedure presented in this paper, the mutual inductance between two arbitrary-positioned and orientated planar PCB inductors can be estimated with reduced computational effort by solving the Neumann formula using numerical integration. The proposed method is demonstrated at the hand of two experiments; and the measured and estimated mutual inductances show excellent agreement with a maximum absolute error of less than 5%.
In this paper, a method for locating and validating different load devices placed on a variable-phase CET desktop is presented. The CET desktop consists of multiple embedded primary coils, which have the ability to power small electronic devices, such as cellular phones, music players, and PDA's laying on its surface. Here, only the three primary coils closest to the load device are used to transfer power, and it is thus important for the system to correctly locate the positions of the load devices laying on the table. The presented method can detect the positions, and distinguish between three different types of objects placed on the table, namely, valid resonant load devices, conductive materials and ferrites. The objects are detected through the process of "scanning" which involves energizing each coil for a short duration of time, while measuring its impedance. Each object type influences the coil impedance in a different manner, which can be detected by the CET system. In this way, the object positions and types can be accurately estimated. The system is implemented, and various load detection experiments are performed on the prototype. The results show measurable and predictable changes in the coil impedances, and the system is able to correctly locate and identify all the objects placed on the CET desktop.
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