Microwave Reflection Model for Human Respiration Based on a Circular Membrane

Despite their inability to provide distance or angular information, single-channel continuous-wave radar systems are widely used to measure vital parameters. Their popularity arises from the simplicity of the required components, the low demands on the sampling rate and processing effort, and their low costs. To obtain health data such as respiration rates, heart rates, or heart rate variability, the change of the signal phase due to the displacement of the body surface is measured. Typical signal models in the literature only consider the phase as relevant information and assume that the body surface behaves as a point-like target. This work introduces a more accurate signal model for human respiration based on a circular membrane and demonstrates that the amplitude can also be employed for reliable vital parameter detection.