Single-Layer Transmitter Array Coil Pattern Evaluation toward a Uniform Vertical Magnetic Field Distribution

A uniform magnetic field distribution is a critical aspect in the transmitter array coil design process for achieving a homogenous vertical magnetic field distribution. The free position and orientation features can thus be implemented in the wireless power charging system. This paper presents vertical magnetic field distribution generated by a single-layer circular flat spiral air core transmitter array coil model analysis and evaluation using a numerical analysis method. This method is developed based on the off-symmetry axis magnetic field distribution due to a circular current loop derived from the Biot-Savart law. The proposed evaluation criteria are used to obtain the vertical magnetic field distribution characteristic of the evaluated array coil model. The vertical magnetic field distribution of several circular flat spiral air core coils, in both single and array coil models with different coil geometries were investigated to obtain the relation between the coil parameters and the distance between the adjoining coil centers to generate uniform vertical magnetic field distribution. A case study was also conducted to analyze and evaluate several array coil model patterns (1 × 2 array coil, 1 × 3 array coil, 2 × 2 array coil, 2 × 3 array coil) to meet uniform vertical magnetic field distribution. The array coil model is composed of an identical single circular flat spiral air-core coil. Every single coil has inner coil diameter (Di), outer coil diameter (Do), wire diameter (W), pitch (P) and a number of turns (N) at 25 mm, 47.8 mm, 0.643 mm, 0.03 mm, 17 respectively. The study and evaluation of several array coil pattern models show that the distance between the adjoining coil centers should be defined close to the half of coil outer diameter (1/2Do) to generate close to uniform vertical magnetic field distribution. The vertical magnetic field distribution average and magnetic field effective transmitting areas array coil model with the given coil parameters changing as the effect in variation in distances between the adjoining coil centers.