Parasitic Capacitance Associated With Inductive Sensors Used in MIT Imaging

Abstract

Magnetic induction tomography (MIT) has recently been accomplished using a single inductive sensor, but under the assumption that it behaves as an ideal inductor. When performing a scan with a sensing coil that typically consists of a collection of concentric circular printed circuit board (PCB) copper traces connected in series, small amounts of parasitic capacitance arise that contribute to measured tank circuit loss. Results of this work quantify the magnitude of parasitic capacitance and associated losses. For current inductive sensors, capacitance-related loss is shown to diminish considerably when the coil is positioned more than ~2 cm from a target boundary. Recognizing that single-coil MIT scans generally position the coil within 2 cm of a target boundary, a correction is proposed, which enables a more accurate measurement of true inductive loss. Previously published scan data over agarose phantoms are then reexamined to show the negative impact on imaging fidelity that results when capacitance-related losses are ignored. Image comparisons are made using full 3-D image reconstruction, demonstrating that failure to compensate for parasitic capacitance loss can degrade image fidelity.