Unobtrusive monitoring of physiological signals in natural settings is important for precision diagnostics. Fully-passive wireless body-worn sensors are viable and promising for unobtrusive monitoring. In this study, the authors present a new class of fully-passive sensor, namely wireless resistive analog passive (WRAP) sensor. It uses resistive transducers at the sensors for converting physical stimulus to load modulation of carrier wireless signal at 13.56 MHz at low power (-20 to 0 dBm). The

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... sensor is simply composed of a loop antenna, a tuning capacitor, and a resistive transducer suitable for the type of physiological signals to be measured. The authors report the characterisation of WRAP sensors for various resistive loads of 1.2 ω to 82 kω at various co-axial distances (5-40 mm) between the TX and RX antennas. They have prototyped and characterised multiple WRAP sensors with several practical measurements of physiological signals such as heart rate, temperature, and pulse oximetry. They also demonstrate bio-potential measurement (down to 400 μV pp ) using metal-oxide-semiconductor field-effect transistor as the transducer. These results show the feasibility of developing a new type of body-worn fully-passive WRAP sensors for unobtrusive physiological signal monitoring at real-life settings for precision diagnostics of many disorders and tracking person-centric therapy efficacy.