Flexible 3D Printed Ferroelectret Sensors Integrated into Smart Textiles for Unobtrusive Monitoring

The development of smart wearables, involving the sensor integration into textiles, has emerged in several applications, such as heart rate monitoring in healthcare contexts, smart insoles for gait analysis, or gesture recognition for virtual reality interfaces. A common challenge in this field is the incorporation of off-the-shelf sensors, which are often nonelastic, therefore, constrain the design, reduce sensitivity, and lead to increased costs. In this work, we present an additively manufactured ferroelectret sensor integrated into a textile with detachable electronics on an elastic strap. The sensor comprises a 3D printed layer of soft polylactic acid, creating a seamlessly fused, mechanically resilient compound. Its long-term charge stability results in the surface potential settling at 300V after 15 days and a piezoelectric coefficient of up to 201 pC/N for mechanical loads of 1 N, similar to state-of-the-art ferroelectrets. We demonstrate the sensor integration in the application of hand gesture recognition by deploying it into a sport bandage and reliably distinguish between three gestures, while the soft sensor proves suitable as an unobtrusive measurement device. As a result, this low-cost, biocompatible, and highly flexible sensor qualifies for the integration in various further applications, such as in medical and sports devices.