Design and Optimization of Capacitive Links for Wireless Power Transfer to Biomedical Implants.

This paper provides a comprehensive overview of capacitive wireless power transfer (C-WPT) links for biomedical implants, and proposes an algorithmic approach to optimize their design for a theoretically feasible desired power transmission efficiency (PTE). Two C-WPT links, one involving external inductors for parasitic capacitance cancellation, and another without external inductors are presented. An accurate electrical model has been presented for both cases considering the finite conductivity of the body tissue and fringe fields emanated from the metallic plates. Ex-vivo experiments were conducted with beef tissue to demonstrate the viability of the model and the optimization algorithm. The analytical and simulation results show good agreement with the measurement (with real tissue) for both types of links across a wide range of operating frequency, including one with the highest reported frequency (∼14.6 MHz) among tuned links.

On the Non-idealities of a Capacitive Link for Wireless Power Transfer to Biomedical Implants.

This paper studies the performance of a resonant capacitive wireless power transfer (C-WPT) link for biomedical implants in the presence of non-idealities. The study emphasizes on finding an accurate electrical model of a practical C-WPT link, which can be used to investigate the performance of the link under different practical/non-ideal scenarios. A sound knowledge about these non-idealities is crucial for device optimization. For the first time, a circuit model has been presented and analyzed, which is applicable to a practical C-WPT link undergoing plate mismatch, flexion, tissue contraction, and stretching. Our model considers the finite conductivity of the body tissue and fringe fields formed by capacitor plates. Analytical and HFSSTM simulation results have been presented for different non-idealities, and are in good agreement. Additionally, we show a procedure to interpolate non-ideal case results. The study shows that plate misalignment (causing reduction in parallel plate overlap area) and skin tissue contraction (while muscle grows) are the most detrimental individual factors to the link performance. We recorded ∼32% and ∼14% power transfer efficiency decrease due to these two worst-case scenarios, respectively for a C-WPT link comprising of two pairs of 400 mm2 parallel plates (12 cm edge-to-edge separation) coated with 63.5 µm thick Kapton layer and aligned around a 3 mm tissue at 20 MHz.