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 a circular shaped external and miniaturized spherical shaped implantable coils are designed and optimized at 13.56 MHz frequency 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 proposed C-S WPT system, we have also designed a 3-coil inductive WPT system with circular shaped external and implantable coils and the design 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 was a sharp decrease in PTE of C-C system for angles greater than 40°. At 90° of angular misalignment, the PTEs of C-C and C-S WPT systems are 0.4% and 5.6% respectively. When the coils were laterally displaced by a distance of 10 mm, the C-C and C-S WPT systems produced PTE of 33.42% and 27.10% respectively. The C-C and C-S WPT systems attained 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.