Dual-Frequency Technique for Assessment of Cardiopulmonary Effective RCS and Displacement

In this paper, a technique for the precise assessment of key parameters relating to cardiopulmonary activity is presented. Dual-frequency radar measurements are described with quantitative analyses of the return signal, in terms of intensity and phase modulation magnitude. The first parameter is a measure of the radar cross section of the portion of the torso surface that is moving due to respiration and heartbeat activity. It is defined as the cardiopulmonary effective radar cross section (ERCS). The second parameter corresponds to the maximum displacement of the torso surface in the direction of incidence. This paper presents the first reported dual frequency radar system for determining cardiopulmonary ERCS and displacement. A system calibration procedure using spherical targets is described and displacement measurement is validated for the dual-frequency system. Preliminary testing results consistently showed an ERCS that is larger for the back of the torso and smaller for the side compared to the front, while the respiration depth is smaller in the prone position than in supine.