Session: 03-07-01: Material Processing of Flexible/Emerging Electronics, Sensors, and Devices I

Paper Number: 91749

91749 - Effects of Infill on the Additive Manufacturing of Piezoresistive Pressure Sensors 

As additive manufacturing has evolved and grown in recent decades, the production process has expanded its use from research to industry to at-home hobbyists. Fused Filament Fabrication (FFF) has presented itself as a common additive manufacturing method to users because of its low cost, simplicity, and wide range of materials. The introduction of conductive polymer composites into FFF has brought about widespread capabilities, particularly in the areas of flexible sensors, printed electronics, and other multi-functional materials. Piezoresistive sensors have especially been of interest due to their use in wearable electronics and structural health monitoring coupled with the increasing commercial availability of conductive thermoplastic filaments. However, while much research has been devoted to the geometrical parameters in piezoresistive sensors in conventional manufacturing, little has been investigated with respect to additive manufacturing. Even so, the sensor geometry is often designed by the user in FFF with the aim that the material will be 100% solid, which is unrealistic and neglects to account for the constraints of infill – the printed material between the outer walls of the generated design. This also ignores the advantage that the infill, in terms of both percentage and geometry, can offer to increase the sensitivity of the sensor. This paper investigates such sensitivity changes with respect to varying infill percentage and geometry using a commercially available thermoplastic polyurethane-carbon black conductive filament. Thermoplastic polyurethane provides a soft and flexible polymer matrix, especially in contrast to other thermoplastics in FFF, while carbon black is often considered one of the cheapest conductive fillers available. Square pressure sensors were printed using commercial FFF equipment and mechanically tested under compression while simultaneously recording the electrical properties using a voltage divider circuit to observe the electromechanical response. This provides valuable insight to the change in resistance with respect to strain, better known as the gauge factor. Infill percentage was varied at relatively low volume percentages (5-15%) to increase the sensitivity to weight ratio, allowing for the calculation of what this paper refers to as the specific gauge factor. Infill geometry was also varied using common patterns (Concentric, Grid, Gyroid, Honeycomb, Lines, and Cubic) available through most free slicing software interfaces to expand the ease-of-implementation of the results. This work demonstrates the potential for low-cost additive manufactured piezoresistive sensors applicable to many 3D-printing enthusiasts and researchers alike without the requirement of expensive compounding equipment further opening doorways for future innovation and lowering the cost barrier for those without the luxury of an abundance of manufacturing resources.

Presenting Author: James Banks Texas State University

Presenting Author Biography: James D. Banks is currently pursuing his Ph.D. in Materials Science, Engineering, and Commercialization at Texas State University. He received his B.S. in Chemistry from the University of Montana in 2018 and his M.S. in Mechanical Engineering from Queen Mary University of London in 2019. His research interests focus on advanced manufacturing of multi-functional polymer composites.

Authors:

James Banks Texas State University
Meysam Khaleghian Texas State University
Anahita Emami Texas State University