A theoretical background on a possible modified rangefinding equation for step-frequency radar in cardiac applications based on a spherical-wave model

Abstract

Step-frequency radar represents a potential alternative sensor modality for non-invasive heart monitoring, with the aim of developing low-cost and easily portable technology for continuous monitoring of heart activity by sensing the motion of the heart surface as a radar-reflective target. This paper reports on an attempt to account for the deviation of the waveform of the traveling signal from the simple plane-wave approximation typically used for far-field radar, due to the limited distance between the radar source of a chest-mounted sensor and the internal target of the heart surface. Accordingly, this study applied a modification to the discrete Fourier transform converting received frequency-domain data into travel-time-domain data to be used in assessing the distance of reflective targets from the radar via modification of the approximate representation of the radar signal from a plane wave to a spherical wave.