Wireless power transfer analysis of circular and spherical coils under misalignment conditions for biomedical implants.

In this paper, a 3-coil inductive WPT system having circular shaped external coil and miniaturized spherical shaped implantable coil is designed and optimized at 13.56 MHz to overcome reduced PTE under misalignment conditions. The external coil is placed at a distance of 10 mm from the implantable coil. The proposed design is referred to as C-S WPT system. To evaluate the performance of the C-S WPT system, a 3-coil inductive WPT system having circular shaped external coil and circular shaped implantable coil is designed and is referred to as C-C WPT system. The impacts of perfect alignment, lateral and/or angular misalignments on the overall PTE of the systems are analyzed and compared. At perfect alignment, the PTE of C-C and C-S WPT systems are 59.8% and 52.6%, respectively. Though the PTE of C-C WPT system is slightly higher than C-S WPT system, there is a sharp decrease in PTE of C-C system for angles greater than 40°. At 90° of angular misalignment, the PTE's of C-C and C-S WPT systems are 0.4% and 5.6% respectively. When the coils are laterally displaced by a distance of 10 mm, the C-C and C-S WPT systems produce PTE of 33.4% and 27.1% respectively. The C-C and C-S WPT systems attain PTE of 1.6% and 5.5% respectively at 10 mm displacement and 50° rotation. The simulated systems are fabricated to analyze the result in real-environment. The measurement results show that the C-S WPT system provides better PTE when compared to C-C WPT system under angular and a combination of angular and lateral misalignments.