Effect of Flexibility of Composites on Performances of Sensors with Micro-structured Inverted Pyramid Arrays

Two kinds of thermoplastic polyurethane/short carbon fiber/carbon nanotube(TPU/SCF-CNT) composites with different flexibilities were prepared by an extruder. By using compression molding, the replicas with micro-structured inverted pyramid arrays on the surfaces were molded from the two composites with the conductive paths comprised by SCF and CNT. Then two kinds of flexible sensors were prepared by assembling the composite replica with the corresponding composite flat plate face-to-face. It was demonstrated that the contact resistance between the replica and flat plates of the sensor under pressure was significantly reduced due to the deformation of the bottom edges of the inverted pyramid. Although the sensor assembled by using the more flexible composite had a slightly larger hysteresis coefficient, it exhibited a higher sensitivity (0.32 kPa(-1)) in the linear region of 0-2.5 kPa, which is attributed to the larger deformation of the bottom edges of the inverted pyramid and the increased conductive paths inside the composite under pressure. Both sensors exhibited short response times stemming from rapidly changing contact resistance caused by the deformation of the bottom edges of the inverted pyramid. In addition, the sensors prepared in this work maintained a relatively stable resistance response during 500 s (approximately 1580 cycles) of cyclic compression/release tests (under a peak pressure of ca. 3 kPa). The results demonstrated that it is feasible to fabricate higher performance flexible sensors with inverted pyramid arrays on the sensing element prepared by compression molding.