On 3D printing of thermoplastic polyurethane over woven fabric for wearable sensors

In the past two decades several studies have been reported on thermoplastic-based 3D printed sensors. However, little has been reported on wearable sensors prepared by thermoplastic printing on woven fabric, especially for four-dimensional (4D) properties. This study reports the 3D printing of thermoplastic polyurethane (TPU) on woven fabric by using a fused filament fabrication (FFF) setup for the fabrication of wearable sensors. Further, rheological, mechanical, voltage resistance (V-R), radio frequency (RF), and 4D capabilities of the 3D printed substrate have been established. The 3D printing of TPU on woven fabric was performed at 225(degrees)C nozzle temperature with a printing speed of 21 mm/s, and infill density was kept at 80% and 100%. The RF characteristics were calculated using a vector network analyser (VNA) which suggests that there is no shift in resonating frequency (2.60 GHz at -81 dB) for ring resonator printed with 100% infill density (with an increase in strain value), whereas for 80% infill density sensor there was a notable shift in resonating frequency (from 2.82 GHz at -75 dB to 2.71 GHz at -76 dB) when the sensor was strained under load which further lead to a change in dielectric constant (epsilon(r)) and loss tangent (tan delta).