The Impact of Parasitic Components of Capacitors and Heating Capacitors on the Adaptive Tuning of a Power Amplifier in the Inductive Supply System for Medical Implants

An adaptive class E power amplifier (PA) maintains a constant output power level of inductive supply systems for medical implants irrespective of the displacements of the transmitting and receiving inductive coils. One of the key issues in designing this amplifier is to study the impact of the parasitic components of capacitors and heating capacitors in the load network on adaptive tuning. In this study, two cases of realizing variable shunt and variable series capacitance in the load network of a class E PA are considered. In the first case, in the place of each capacitance, an array of NP0 capacitors is used. In the second case, both variable capacitances are realized as arrays of X7R capacitors. The results of numerical simulation and an experiment show that heating X7R capacitors in the PA’s load network leads to a decrease in the output power in the inductive supply system. At the same time, when NP0 capacitors are used in the PA under consideration, the decrease in the output power and overall efficiency of inductive supply systems is due to the parasitic components of these capacitors, whereas heating these capacitors has no impact on the output characteristics of inductive supply systems.