Sensitivity of Single Coil Electromagnetic Sensors for Breathing Measurements

We propose a novel approach to optimizing the sensitivity of a single coil sensor based on a theoretical model derived from electromagnetic theory. The thorax is subject to variations in conductivity due to respiratory and cardiac activities and our electromagnetic sensor is designed to measure these changes. We derive a theoretical model for changes in impedance of a current carrying coil caused by a volume conductor located axially above the coil. We model the effect that changes to coil impedance have on the frequency of oscillating circuits and we design two circuits that will optimize this effect. We test our theoretical model by using conductive phantoms to measure frequency changes in our sensor. Finally, we test our sensor’s ability to detect changes in lung volume through in vivo trials with six participants performing breathing manoeuvers.