Downsized flexible capacitive strain sensing filament and its application in knee angle tracking during walking

Assistive Rehabilitation technologies have been a prominent research topic in recent years for patients who suffer from impaired lower extremity motor abilities. Continuous tracking of knee movement can provide valuable insight into the effectiveness of therapeutic or surgical interventions such as improvements in range of motion or stability over the course of the treatments. Video-based motion tracking is an industry standard for motion tracking, but its usage is limited in a clinical setting due to its prohibitive cost and space requirement. This study proposes a downsized flexible capacitive strain sensing filament that can be weaved into textiles to achieve in situ motion tracking. Its effectiveness is shown in a knee joint angle tracking with video-based motion capture as reference. Sensor-predicted knee angle is 99% accurate when compared to the reference with root mean square error of 1.79 degrees. An improved sensor is also fabricated and characterized to show enhanced performance.