Fundamental limits of light-wave sensing for non-contact respiration monitoring

An experimental testbed was constructed to rigorously assess the fundamental limits of light-wave sensing-an economic, non-contact vitals monitoring approach previously reported. We improve the testbed using lock-in amplification and demonstrate that a photodetector and a commonplace array of infrared LEDs are sufficient to detect respiratory motion and quantify respiration rate up to 2.5 meters away. We propose a novel scattering model, from which we derive the performance limits of the light-wave sensing system in terms of a theoretical range resolution limited by the dynamic range of the system. Using a robotic breathing phantom, we experimentally assess, for the first time, the range resolution of the testbed system and compare this to theoretical predictions. This work also introduces a process for generating stochastic respiration patterns, which may prove broadly useful to the designers of breathing phantoms. Holistically exploring practical challenges and analytical models, this paper serves as a unique and comprehensive tutorial for understanding and designing light-wave sensing systems.