Integrated Silicon Photovoltaics on CMOS With MEMS Module for Catheter Tracking

This paper presents an electromagnetic actuation-based optoelectronic active catheter tracking system for magnetic resonance imaging (MRI). The system incorporates a radio frequency (RF) microelectromechanical system (MEMS) resonator array actuated by the Lorentz force induced due to the strong dc magnetic field available in MRI environment. Power transfer to the system and the actuation detection are done optically via fiber optic cables that replace conventional conductive transmission lines; thereby, enabling the tracking system to function safely under MRI. The complementary metal–oxide–semiconductor (CMOS) receiver, optically powered by a supply unit housing an on-chip silicon photovoltaic cell, detects the location of the catheter tip. The RF MEMS resonator array transmits the position data by transducing the electrical signal into a resonant mechanical vibration linearly. The optical reading of this actuation can be done by diffraction grating interferometry or laser doppler vibrometry. The fabricated resonator array is tested with the optically powered CMOS chip (0.18- $\mu$ m UMC technology) in laboratory conditions. The driving electrical current supplied by the chip for resonator actuation is 25- $\mu$ A rms, where the magnetic field provided by the experimental setup is 0.62 T. The resonator array is observed to be functional with real-world application by showing a frequency response of 10 dB, which will be enhanced further under the stronger magnetic field available in 3-T MRI.