3D printing of a fiber optic pressure sensor

Soil pressure is an important parameter for soil tillage. This study provides an alternative method for the fabrication of novel fiber optic pressure sensors which can be used for the measurement of soil pressure in the field. Optical Frequency Domain Reflectometry (OFDR) based distributed fiber optic sensor was adopted as a sensing element and embedded inside 3D printed prototypes to fabricate pressure sensors. During the fabrication process, both internal temperature and strain distributions of the printed Polylactic Acid filament (PLA) were systematically monitored and analyzed. Monitoring data show that the inner temperature rise of all prototypes is limited (less than 45 ℃) in comparison with the printing temperature of the printer nozzle (220 ℃). Both the peak temperature and the obtained temperature at the end of printing are linearly proportional to the change in infill densities. Both the measured peak strain and final strain at the end of printing are less than 580 με, which resulted from the thermal expansion of melted PLA extruded out of the printer's nozzle. All measured strains were found to increase linearly as the increase of infill densities. Calibration tests of pressure sensors, including static and cyclic loading tests, and soil compaction tests, indicate that the measured strain of the fiber optic sensor embedded inside the pressure sensor can be used to calculate vertical pressure applied on the top surface.