Remote monitoring of vital signs (VS) is an emerging technology with a vast number of possible uses from hospital care to the automotive industry and assisting living environments. Radio-frequency (RF) sensing enables the remote and unobtrusive measurement of VS without the need to wear any special device or clothing and under any lighting conditions. A demonstrator of RF vital signs sensing was designed and prototyped based on a continuous wave reflectometer involving a Software Defined Radio platform. The sensor operates at 110 GHz. The feasibility of remote respiration and heart rate (HR) monitoring was investigated. The breathing pattern was found to affect significantly the reliability of the HR estimation. The potential of remote VS sensing at distances up to 10 m was theoretically explored.

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The skin response to high radio frequency has been associated with the human physical condition and most prominently with the stress. The objective of this study is to investigate the possibility to detect mental and light physical stress through the measurement of skin reflectance in the mm-wave/sub-THz band. Two frequency bands have been considered, 75-110 GHz (Band-I) and 325-500 GHz (Band-II), while the measurements have been performed in the three different locations, the arm, the dorsal side of the hand and the fingertip. The measurement setup is discussed in detail and the reflectance spectrum is demonstrated. The results illustrate a difference in skin reflectance under rest and stress in Band-II which ranges from 3.5 dB at the finger to 7 dB at the hand. The outcomes of this study indicate the feasibility of stress detection through skin reflectance measurement and serve as a suggestion for deeper exploration of higher frequency bands.

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