Investigation of an embedded closed-loop stimulation current control principle based on the use of nonlinear ceramic capacitors

• Published in: Current directions in biomedical engineering 2021-10, Vol.7 (2), p.53-56
• Main Authors: Olsommer, Yves, Ihmig, Frank R.
• Format: Article
• Language: English
• Subjects: electroceuticals; ferroelectric material; implantable medical device; inductive coupling; Mathcad; neurostimulation; nonlinear capacitor
• ISSN: 2364-5504; 2364-5504
• DOI: 10.1515/cdbme-2021-2014

Over the years, a constant progress in the development of implantable medical devices (IMD’s) can be observed. On one hand, the advanced implantable electronics enable the implementation of numerous smart functionalities, on the other hand, the variety of electronic components including sensors and a bulky battery severely restrict their degree of miniaturization and reliability. To overcome this limitation, our approach is to realize smart functionalities in leadless and battery-free IMD’s emerging from frugal innovation by exploiting the intrinsic nonlinear properties of the components to be used anyway. The aim of this work is to deepen the understanding of the dynamic behavior of circuit topologies of nonlinear ferroelectric ceramic capacitors and to investigate their potential use for an embedded closed-loop control of the stimulation current. We characterized a selection of 40 commercial ceramic capacitors by measurement and simulation. The degree of nonlinearity resulting from a circuit topology consisting of one, two series and two parallel connected nonlinear capacitors was modeled and evaluated in Mathcad. We present a model with parameterized nonlinear capacitors to simulate the dynamic behavior of an inductively coupled implantable system. The stabilization and amplitude of the stimulation current is controlled by two features. These features are in turn controlled by the circuit topology and the degree of nonlinearity of the capacitors. We found that a high degree of nonlinearity allows the stimulation current to be stabilized within a reasonable range, but it makes the system more prone to instability. However, our model needs to include the dynamic behavior of ferroelectric materials used as dielectric in ceramic capacitors to extend the current investigations and to deepen the understanding of the physics behind the nonlinear properties of ferroelectric capacitors.