Noncontact Radar Sensing of Wrist Pulse Wave With Enhanced Accuracy and Flexibility

Wrist pulse wave (WPW) is an important vital sign signal for digital health. By recovering WPW in a noncontact manner with wearable sensors could provide a new approach for the diagnostics and prediction of various human conditions and diseases. To this end, this work proposes a self-injection locking (SIL) principle-based wrist-worn radar sensor with enhanced accuracy and flexibility. By accuracy, this sensor is advantageous for the high correlation coefficients compared to a contact sensor in the time domain. By flexibility, it can accommodate a variety of microwave antennas, enabling a range of related applications. In addition, the instability problem of the traditional SIL radar is analyzed jointly considering the conditions of the oscillator and the pulse signal, concluding a possible solution to the instability problem. Experiments are conducted by comparing the WPW data simultaneously collected by the fabricated 5.8 GHz sensor and a contact piezoelectric sensor. High correlation coefficients are observed at two typical sensor-skin distances: an average of 0.841 at 1 mm and 0.773 at 5 mm, showing high accuracy. This work could facilitate research works for a range of related biomedical applications.