Bi-Directional Stretchable Capacitors for Self-Tuning MRI Receive Coils

Over the past several years, stretchable electronics have received significant research attention due to their wide range of applications in wearable sensors for electrophysiological monitoring. Among the various sensor types, capacitive devices are most widely used due to their high durability, reusability, and low hysteresis. This work introduces a new capacitive sensor design from annular interdigital geometry with a bi-directional stretch anisotropy that depends on the opening angle of its annular rings. Numerical analysis, electrostatic, and non-linear material stretching simulations are presented. It is demonstrated that the capacitance of the sensor remains stable at an annular ring angle of 180° with stretching in any direction. This type of design can be useful in applications where capacitance and/or resonance frequency stability is of importance. To this goal, we demonstrate a stretchable radio-frequency coil for magnetic resonance imaging using the proposed capacitor to maintain a stable resonance frequency with stretching.