Inductive Power Transfer Class-E Amplifier Design for Active Implantable Medical Devices

Active Implantable Medical Devices (AIMDs) are continuously evolving; nowadays, though the devices are always much more complex and sophisticated, the power supply is a common challenge. It must guarantee safety, durability, and efficiency. A common technique is Wireless Power Transfer (WPT), and Class-E amplifiers are a possible solution in high-efficiency power amplifier (PA) applications. In the literature, higher frequencies begin to be more studied, principally to reduce coil dimensions and orientation sensitivity. The aim of this work is the development of a Wireless Power Transmitter through a Class-E amplifier at a carrier frequency of 13.56MHz (ISM radio band); the performance of the device developed has been evaluated to assess the capability of this solution in WPT. The device has been initially simulated to size the components of the circuit correctly: LTspice and Python environments have been interfaced to optimize design choices, the solution with the highest efficiency is searched through an automatic algorithm. It consequently runs different LTspice simulations, varying through specific patterns the component values of the model, searching for an optimum efficiency that guarantees the minimum level of power delivered desired. Afterward, the prototype was tested on a breadboard; a simple receiver was developed for preliminary verification of the transmitter. A Printed Circuit Board (PCB) was then designed and fabricated; due to the radio frequency (RF) application, particular constraints were considered during the system's development. Power dissipation, efficiency, thermal performance, and the comparison with the expected transistor drain voltage and current behavior have been analyzed. A specific current sensing circuit has been designed and developed to support precise and accurate measurements. Lastly, a testbench has been developed to better evaluate the performance test in different conditions. It guarantees an accurate variation of distance, misalignment, and angle between the transmitter and the receiver. Both distance and misalignment have been tested up to 20mm, while the angle has been tested up to 3 degrees. In the future, integration into a complete WPT system is recommended to better study the device's performance and capability. The design of a power management system, that changes the transmitter output power based on the power delivered to the receiver, could give more robustness to the actual solution.