Embedded Ultrasound Doppler Radar for Real-Time Sub-Millimeter Motion Sensing

Abstract

Acoustic signals and ultrasound are common and effective methods to analyze system behavior and measure physical motion. This work presents a modular sensing system that utilizes continuous-wave ultrasound Doppler radar to detect sub-millimeter motion. The system architecture combines a directional ultrasound transducer with a multi-channel MEMS microphone array, supported by a multicore microcontroller with a real-time operating system and external signal processing. The core technologies of the prototype are applicable to various sensing tasks, such as machine condition monitoring or medical applications. Its accuracy and precision are demonstrated through a contactless heart rate monitoring application that measures and visualizes heartbeats in real time. The system was validated through tests with artificial motion sources and measurements from human volunteers. The evaluation shows a maximum heart rate deviation of 0.04 beats per minute (BPM) compared to simultaneous electrocardiogram (ECG) measurements, confirming the high accuracy of the system. A beat-to-beat timing analysis confirms accuracy sufficient for heart rate measurement, while a conclusive assessment of heart rate variability remains bounded by the resolution of the electrocardiogram reference used and is left to future work. Built on commercial off-the-shelf hardware, the system provides an accessible and adaptable foundation for embedded acoustic and ultrasonic sensing.