Interferometric Microwave Sensing for Medical Diagnostics
This presentation focuses on the medical application of continuous wave 24GHz radar systems based on the interferometric principle. The six-port network, introduced by Engen and Hoer in the 1970s for power measurements, is used as a microwave interferometer to measure relative distances. This passive structure enables high phase resolution with low power consumption and low cost. For the application in the medical field, the high relative distance resolution can be utilized for measurements of different physiological phenomena. Starting with breathing, the largest movement of the vital signs, down to the smallest vibrations of the heartbeat are analyzed with the distance measure of the radar. In addition, working at 24GHz clothing and bed sheets are nearly invisible for the radar, which enables monitoring of patients without touching nor undressing. Not having to wire a patient also simplifies the work of the personnel. Next to the system, the signal processing from high frequency to diagnostically evaluable data of the vital signs, like breathing and the heartbeat will be discussed. In a clinical study, test persons were measured in different scenarios to prove the ability to measure heart sound with radar. In this scenario, gold standard reference sensors were used to evaluate the radar measurement. In the following, the heart sounds are segmented using a state-of-the-art algorithm based on a hidden semi-Markov model to determine the heart rate precisely and eventually to use pathological heart sounds for further diagnostics. In addition, possible breathing patterns can be identified by analyzing the respiratory movement and frequency.