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Positional misalignments of coils cause a sharp drop in the power transfer efficiency (PTE) of wireless power transfer (WPT) systems. To minimize this deterioration of the PTE, this study introduces a sphere-shaped (Rxs) to a three-coil magnetic resonance-coupled WPT system for implantable devices. To assess the significance of Rxs, its performance was compared to the well-known circular planar (Rxf), half-sphere-shaped (Rxhs), and solenoid (Rsl) coils. Moreover, a small and efficient voltage doubler as a rectifier was designed. This voltage doubler has a high conversion efficiency of 89% with an output voltage of >3 V at 15 dBm. To validate the concept, prototypes of the coils and voltage doubler were fabricated and measured in saline and minced pork. The PTEs of the Rxf, Rxhs, Rsl, and Rxs coils-based WPT systems were studied under different lateral and angular misalignments in both simulations and measurements. In perfect alignment conditions, the measured PTEs of Rxf, Rxhs, Rsl, and Rxs WPT systems were 7.68%, 10.18%, 25.01%, and 22.38%, respectively; however, when the (Rx) receiver coils rotated by 90°, the PTEs were 0%, < 0.2%, 0.15%, and 5.4%, respectively. Under lateral misalignments of $dx =25$ mm, the PTEs were 0.82%, 1.91%, 2.4%, and 4.87%, respectively. Furthermore, the PTE for the Rxs-based WPT system was measured in saline- and minced-pork-filled boxes and a saline-filled American Society for Testing and Materials (ASTM) model under different misalignment conditions to expand its applicability range to deep-body non-static implants. Both the simulated and remeasured results show that the proposed Rxs-based WPT system presented an improved and stabilized PTE under positional misalignments. [ABSTRACT FROM AUTHOR]

The interactions of medical implants in the human body with electromagnetic fields from newly introduced high-field technologies such as near-field wireless power transfer (WPT) are of great concern. In this study, the effects of implants on the specific absorption rate (SAR) in a head model were computationally evaluated in the immediate vicinity of a WPT system operating at 6.78 MHz with a transferred power of 50 W. The SAR in the head model located 30 mm above the WPT system was evaluated with a skull plate, bone plates (different shapes), miniplate, fixtures, and a deep brain stimulator. The results indicated that even small implants had notable effects on the SAR distribution and corresponding local peak and mass-averaged SAR values. Apart from the size and shape of the implant, the crucial factor influencing the SAR was the implant’s position with respect to the WPT system. Therefore, various position configurations were simulated for the WPT system to determine the worst case scenario for each specific implant. Although the local peak SAR value was increased by a factor of 600 in the worst-case scenario (for the skull plate), the SAR $_{\text{1}g}$ and SAR $_{\text{10}g}$ were only increased by factors of seven and four, respectively. Compliance with international safety limits was studied, followed by computing the maximum allowable transmit power (MATP). It was found that, without the implant, the MATP satisfying SAR $_{\text{1}g}$ was 43 W for the designed WPT system, and was reduced to 6.9 W in the presence of the skull plate. [ABSTRACT FROM AUTHOR]

Numerical dosimetry with regards to a resonance-based wireless power transfer (RBWPT) system for charging electric vehicles (EVs) has been conducted. The RBWPT system operating at 13.56 MHz frequency with a transferred power of 5.3 kW is placed below the center of the vehicle body. Specific absorption rate (SAR) in anatomically-based human models Duke and Ella with and without a medical implant is evaluated using four exposure scenarios (i.e., Duke and Ella models sitting in the EV without an implant, the Ella model: With an InterStim neurostimulator implant, having a prosthetic hip implant, or having a cardiac pacemaker implant). The results indicate that change in radio frequency (RF) energy absorption occurs when conductive implants are placed in the near field of an RF source. Enhancement of the SAR close to the implants is predicted. The peak averaged SAR over 10 g of tissues exceeds the standard limiting value posed by international guidelines except for the leadless pacemaker, which is in compliance with the prescribed limits. However, the temperature increase never exceeds the localized temperature rise limit of 2 °C. Compliance with the recommended limits of SAR in the worst-case exposure scenario is likely to limit the transferred power. [ABSTRACT FROM AUTHOR]