Mutual injection-locked SIL sensor array for vital sign detection with random body movement cancellation

This paper presents a self-injection-locked (SIL) sensor array for cancelling the effects of random body movement on the detection of vital signs. To achieve this goal, a subject is seated between two SIL sensors to measure rates of respiration and heartbeat using the Doppler shift, and the effects of random movements by the subject are cancelled by wireless mutual injection locking (MIL) of the two sensors. In the experiments, a prototype for such a two-sensor array with a spacing of 2 m was implemented at 2.4 GHz, providing accurate and reliable cardiopulmonary monitoring of a subject who exhibited random body motions of several centimeters.