Microwave Stethoscope for Heart Sound by Near-Field Coherent Sensing
Heart sound at the S1 and S2 points in the cardiogram provides important diagnostic information for cardiovascular disorders. The century-old acoustic stethoscopes remain the main tool, but the signal quality deteriorates significantly over clothes and under noisy ambient. We demonstrate for the first time an UHF microwave technique to directly retrieve the heart sound through layers of clothing with improved user convenience and privacy. Adapted from the previous near-field coherent sensing technique, two system improvements on the frequency selection and balancing bridge design have enabled higher receiver gain to clearly retrieve the heart sound over layers of clothing. We performed dynamic time warping to compare the waveforms acquired from the acoustic and microwave methods, and present the effects of clothing and waveform signatures from individual users.