2-D Synthesized Magnetic Field Focusing Technology With Loop Coils Distributed in a Rectangular Formation

Abstract

In this paper, a novel loop coil structure for synthesized magnetic field focusing (SMF) technology and two current distribution calculating algorithms in the structure are proposed. The proposed structure enables field focusing in two-dimensional (2-D) space for the first time. The loop coil structure with a rectangular formation is adopted for a 2-D SMF system to minimize the volume and weight of the transmitting (Tx) coil array considering that conventional SMF systems inevitably have a volumetric design due to their dipole-based structure. Two algorithms to calculate the current distribution so as to focus the magnetic field at the target point are proposed. The first algorithm applies the Biot-Savart law to a loop-coil-based 2-D SMF system to calculate the distribution. The second algorithm utilizes a time-efficient synthesis method which reduces the matrix dimensions used in current distribution calculation. The second algorithm shows synthesis results with similar synthesis resolution compared with the first algorithm. Although the magnetic field distribution with the second algorithm has a little difference with that of first algorithm, its synthesis result focuses the magnetic field on the target point successfully, and it becomes more powerful as the number of coils increases. Synthesis results using two algorithms were compared with a finite-element method simulation with 100 Tx coils and 25 receiving (Rx) points. The synthesis resolution, as determined by -3 dB points, was enhanced by 4.45 times and 6.15 times for the first and the second algorithm, respectively, when compared to non-focused case. An experimental prototype with 36 Tx coils and 9 Rx points with each coil 10 x 10 cm in size was built to demonstrate field focusing with current distributions calculated by the second algorithm at a frequency of 145 kHz. The experimental results were in good agreement with the simulated results, including a case in which the magnetic field was focused at Rx point other than center.