Low-cost and scalable fabrication of wearable soft sensor for neck mobility measurement

The growing demand for wearable sensors has led to advancements in sports rehabilitation, robotic exoskeletons, e-textiles, and human-machine interfaces, among other fields. In particular, stretchable tactile sensors for human motion tracking have become essential to the shift of healthcare activities towards more personalized, data-centric frameworks. In this paper, the fabrication, characterization, and deployment of an elastomeric capacitive strain sensor for tracking the Neck Motion Complex (NMC) is presented for physiotherapy applications. The sensor patch consists of a flexible and biocompatible dielectric PDMS film coated on either face with patterned graphene electrodes and encased in protective layers for stick-to-skin applications. The sensor transduces the strain from planar neck bending into a capacitive change between the electrode layers that is quantified and calibrated against the angle of bend. The sensor patch is worn on the side of the neck over the sternocleidomastoid muscle to capture lateral bending motions in our tests. We also present a simple and scalable fabrication method using easily available and lowcost materials and tools. Furthermore, a miniaturized built-for-purpose capacitance data acquisition system with an onboard memory card was designed and tested. The complete system is fully wearable, autonomous, and non-intrusive. Calibration of the sensor versus strain and neck bend was achieved using a high precision tensile tester and Aurora EMI system respectively. Characterization of the electrode performance under strain was also conducted. It is hoped that further iterations of the sensor design will quantify range of motion (ROM) and multi-plane neck motions.