Wearable Loop Sensor for Unambiguous and High-Resolution Joint Kinematics Monitoring

We have recently introduced wearable loop sensors that are based on Faraday's law to seamlessly monitor real-world kinematics while overcoming shortcomings in the state-of-the-art. The latest sensor of this wearable ecosystem employs loops in longitudinal configuration (LC) to monitor joint flexion and rotation, but its resolution degrades due to ambiguities (more than one states of motion for the same sensor reading). Here, we demonstrate that resolution degradation exacerbates in the presence of noise, and report a new wearable sensor that eliminates ambiguities to improve resolution. The sensor entails a longitudinal-transmitter placed above the joint and a transverse-receiver, followed by a longitudinal-receiver, placed below the joint (namely, longitudinal-transverse-longitudinal configuration, LTLC). These two receivers help segregate flexion and rotation, thereby eliminating ambiguities in deciphering angles and boosting resolution manifolds as compared to LC. Proof-of-concept simulation and in vitro experimental results show excellent agreement. Compared to LC, flexion angle resolution improves by up to 153.8 times (0.013° to 2°) under low noise and 38.4 times (0.13° to 5°) under high noise. Improvement for rotation angles is similar/higher. Specific absorption rate results also confirm excellent electromagnetic safety. LTLC is the first in the wearable loop ecosystem that can monitor both joint flexion/rotation without ambiguities, improving resolution even in the presence of noise. LTLC shows high promise for monitoring clinically relevant kinematics in real-world settings that are, unavoidably, subject to noise. Its high resolution also empowers the monitoring of fine movements that could not be previously captured outside the lab.