Monitoring Upper-Limb Activity Based on Radio Frequency Time-of-Flight Distance Measurement

Unobtrusive human motion tracking has been facilitated by realizing various sensing technologies in the form of a network of wearable sensors. These sensors are well-suited for applications that call for continuous or tele-motion tracking, nevertheless, the research for characterizing their performance in different applications is ongoing. The study presented in this paper explores the potential of constructing a wearable sensor system based on radio frequency time-of-flight distance measurement for monitoring activities of upper limbs. In this regard, a prototype sensor is developed and experimentally characterized. The performance of the system is then evaluated in an elbow flexion-extension scenario and it is shown that the system can be easily calibrated for use in different environments and is able to estimate the hand distance from body with an accuracy of 4.66 cm. This preliminary study is presented as a proof-of-concept that designing a wearable sensor system based on radio frequency time-of-flight distance measurement is feasible and can be a potential solution for telemonitoring of upper limb activity in a free-living environment.