On the UWB medical radars working principles

In the last 20 years, a lot of research activity has been carried out on UWB radar in medicine. Over the years, many implementations of medical UWB radars have been presented in literature. An interesting medical application for these devices is the wireless monitoring of vital signs. Heart and breath rate were successfully detected with such devices but in spite of the many working examples presented, the authors are still convinced that a solid explanation of the operation of such radars is lacking. UWB radar output signals are indubitably correlated with the respiration and heart activities but where do they come from? The classic explanation as per the McEwan’s patent of 1996 proposes that the signal is due to deep echoes reflections from the heart wall and blood. This fact does not seem a realistic explanation of the phenomenon.