Physics-Based Modeling of Ferroelectric Hysteresis for Ceramic Capacitors in Inductively Coupled Microstimulators

In this article, we present a physics-based model for nonlinear and hysteretic ferroelectric capacitors in inductively coupled microstimulator circuits. The purpose of this model is to predict the system's dynamic response as a function of the dielectric material properties, with the aim of optimizing the performance in passive power control applications. We describe the workflow starting from the extraction of the dielectric material properties of commercial ceramic capacitors to the implementation into the physics-based model of the overall circuit. Selected capacitors were experimentally characterized at frequencies above 100 kHz by means of both small signals (5 mV rms , ±25 V dc , and ±40 V dc ) and large signals (±25 V ac and ±40 V ac ). Our results show that the developed model is well suited for accurately predicting the circuit's stimulation current for highly nonlinear capacitors and exhibits higher precision compared to commonly used models based on differential capacitance. Preliminary in vitro measurement results are finally described to provide proof of concept of the envisioned model-based passive power control in implantable microstimulators.