Flexible 3D-printed sensors for wearable motion analysis and assistive devices

Objective The primary objective of this thesis was to evaluate emerging transducer technologies, with a focus on wearable, body-compliant sensors designed to support natural human locomotion. In order to achieve this, the flexible sensors developed include self-sufficient ferroelectrets, which are specifically treated polymer structures that exhibit some of the highest sensitivities among all piezoelectric sensors. They are of particular interest as they are 3D-printable, enabling application-specific customizations. Additionally, sensors for broader applications in human-machine interaction are developed to investigate emerging sensor materials, using additive manufacturing technology for rapid prototyping. Evaluations The evaluations explored include motion analysis using sensor-integrated insoles and muscle activity assessment at the lower limbs through force myography (FMG), which senses mechanical muscle deformations. Walking was analyzed as a cyclic motion to detect gait events, utilizing sensor insoles for plantar pressure measurements and FMG sensor patches for assessing muscle activity. In addition to gait, these sensor patches are evaluated during the sit-to-stand transition for early motion intention detection during momentary and powerful muscle actuation. The high sensitivity of these sensor-integrated insoles also enables them to capture cardiovascular-induced body sway (ballistocardiography, BCG) to reveal cardiorespiratory characteristics through enhanced signal processing.