Authors: Jordan Penfold, Cera Gowans, David T Fullwood, Anton E Bowden
Mentors: David T Fullwood
Insitution: Brigham Young University
Wearable nano-composite strain sensors created at Brigham Young University are used for biomechanical studies of human motion, due to their ability to follow and sense skin deformation. The manufacturing process for these sensors involves combining the raw materials that make up the sensors – silicone, nickel nanoparticles and nickel-coated chopped carbon fibers – in a planetary mixer, followed by extrusion of the uncured slurry through a syringe with a specialized tip. After extrusion, the sensor material strips are cut to length and subsequently casted and cured. However, undesirable variability in the final piezoresistive properties of the sensors was discovered. This variability was hypothesized to be attributable to sensor positioning during extrusion process. For example, fiber alignment may change as the extrusion process develops, or internal voids may be more evident in sensors cut from different parts of the extruded slurry. To test this hypothesis, several batches of sensors were created with precise records of each sensor position after extrusion. Some sensors were also set aside for CT scans to analyze their void content and nickel concentrations.
The results suggested that the sensors located on the initial and terminal ends of the extruded slurry strips had statistically significant differences in piezoresistive properties when compared to the sensors from the central portion of the material strips. Sensors cut from the ends of extruded strips were more likely to have a lower standard deviation of average resistances while strained and relaxed, and were more likely to pass quality control inspection. As a result of this research, we learned that sensors with more consistent physical properties could be obtained by intentionally shortening the strips of slurry produced during the extrusion process (e.g., creating sensor batches with exclusively “end” sensors). After applying this change in methodology, sensor batches usually had more consistent physical properties when compared to sensors made with previous methods.