Microwave Stethoscope: Development and Benchmarking of a Vital Signs Sensor Using Computer-Controlled Phantoms and Human Studies

This paper describes a new microwave-based method and associated measurement system for monitoring multiple vital signs (VS) as well as the changes in lung water content. The measurement procedure utilizes a single microwave sensor for reflection coefficient measurements, hence the name “microwave stethoscope (MiSt),” as opposed to the two-sensor transmission method previously proposed by the authors. To compensate for the reduced sensitivity due to reflection coefficient measurements, an improved microwave sensor design with enhanced matching to the skin and broadband operation, as well as an advanced digital signal processing algorithm are used in developing the MiSt. Results from phantom experiments and human clinical trials are described. The results clearly demonstrate that MiSt provides reliable monitoring of multiple VS such as the respiration rate, heart rate, and the changes in lung water content through a single microwave measurement. In addition, information such as heart waveforms that correlates well with electrocardiogram is observed from these microwave measurements. Details of the broadband sensor design, experimental procedure, DSP algorithms used for VS extraction, and obtained results are presented and discussed.