Single-Step 3D Printing of Flexible Ferroelectret Sensors with Large Air Cavities

Flexible sensors based on ferroelectrets can utilize the full potential of the widely adopted 3D printing process, capitalizing on its accessibility, freedom of design, and range of materials. However, 3D printing faces limitations in accuracy and poor surface quality for small dimensions, particularly constraining the ability to manufacture precise ferroelectrets as mechanical sensors that require complex structures with well-defined air cavities. In this work, we explore the printing process to overcome these limitations and present a complex structure printed in a single step with a large air cavity and adaptable surface quality. We present a complex structure printed in a single step with a large air cavity, while ensuring mechanical stability of the structure and its piezoelectric sensitivity as a ferroelectret sensor. We print two sample groups out of polypropylene with reduced material extrusion and demonstrate surfaces without defects and low surface roughness, measuring down to 4.9 µm. Mechanical tests reveal regions with linear bending stiffness of 0.48 N/mm for loads below 0.11 N and 2.47 N/mm for loads ranging from 0.17 N to 0.28 N, respectively. Treated as a ferroelectret sensor, the samples achieve a sensitivity of up to 5.71 nC/N, well within the range of comparable ferroelectrets. The ferroelectret sensor elements presented are well-suited for 3D printing sensor arrays, particularly in applications such as tactile interfaces, i.e. requiring measurements of small forces across large areas.