Single-Coil Magnetic Induction Tomography Using the LDC-1101 Chip

Abstract

Single-coil magnetic induction tomography (MIT) has thus far relied upon traditional bridge techniques to measure inductive losses, falling well under 1 ohm. These measurements have been plagued by both noise and especially drift. This work considers methods based upon the Texas Instruments LDC-1101 chip, which measures LC circuit admittance while in resonance, from which we compute loss. Inductive loss is measured in a 4.0 cm diameter circular loop coil and compared with a quantitative theoretical result while the coil is axially positioned above a 2% aqueous potassium chloride solution contained in a 14 cm diameter petri dish filled to a depth of 2.0 cm. Results accurately capture the tail behavior of inductive loss as a function of coil-target distance. Then, using IR camera technology to track coil position, several 'manual' scans are performed over phantoms prepared from sodium chloride-doped agarose components. In particular, this work considers the ability of single coil scans to capture corners of square plugs, gaps between plugs and side-by-side plugs that differ in conductivity. With drift and noise greatly reduced, the role of sample size is tested, showing that going beyond about 350 samples produces little further benefit to image quality. Though coil position is tracked to within ±0.25 mm, the random nature of manual positioning suggests that a more deliberate positioning scheme is needed, e.g. robotically.