Development of Wireless Implantable Micro Flow Sensor for Conditional Monitoring of VP Shunts

Abstract

This dissertation describes the development of a self-contained high-frequency high sensitivity implantable microfluidics flow sensor using MTJ magnetic sensors to detect motion of slow-moving fluids. A motivating application for the proposed device is the development of an implantable flow sensor, capable of monitoring the amount of cerebral spinal fluid drained from the ventricles of the brain. Micro-fabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultra-sensitive MTJ magnetic field sensor placed outside of the lumen of the catheter. Numerical and experimental results are provided demonstrating a resolution of 0.4 ml/h, a working range of 0-40 ml/h, and a maximum uncertainty of 4% RMS. The present study identifies thermal noise as the main source of low-frequency drift. Using thermal compensation, it was found that the drift can be reduced below 2 ml per 24-hr. Combining an array of four transducers operating in series, it has been demonstrated that a sensitivity can be increased 10.9-fold. Furthermore, the report examines the long-term structural stability of the sensors and produces a corrosion report suggesting a lifespan of 15 to 55 years. MRI compatibility analysis showed a sensitivity reduction of 64% in the device. Several in vivo recalibration methods were introduced to eliminate the calibration error. A protein deposition study showed stable sensor performance under 1.5 mg/ml protein concentration.