Abstract
The refractive indices, attenuation coefficients, and level of birefringence of various 3D printing plastics may change depending on the printing parameters. Transmission terahertz time-domain spectroscopy was used to look for such effects in Copolyester (CPE), Nylon, Polycarbonate (PC), Polylactic acid, and Polypropylene. The thickness of each sample was measured using an external reference structure and time-of-flight measurements. The parameters varied were printer nozzle size, print layer height, and print orientation. Comparison of these parameters showed that a printer’s nozzle size and print layer height caused no change in real refractive index or attenuation coefficient. A change in printing orientation from vertical to horizontal caused an increase both in real refractive index and in attenuation coefficient. In vertically printed samples, the increase in birefringence was proportional to the increase in layer height and inversely proportional to nozzle size. There was no measurable intrinsic birefringence in the horizontally printed samples. These effects should be taken into account in the design of FDM 3D printed structures that demand tailored refractive indices and attenuation coefficients, while also providing a foundation for nondestructive evaluation of FDM 3D printed objects and structures.
Highlights
Terahertz time-domain spectroscopy (THz-TDS) is increasing in popularity as a method for noncontact and nondestructive material characterization
The nozzle size, layer height, and orientation are not typically recommended by filament or printer manufacturers. ese printing parameters are typically chosen by the user depending on the desired results of the printed part
3D printed samples were designed and fabricated with the intent to observe any changes in the printed materials of real refractive index, attenuation coefficient, and birefringence
Summary
Terahertz time-domain spectroscopy (THz-TDS) is increasing in popularity as a method for noncontact and nondestructive material characterization. Ese measurements were printing parameter independent and analyzed using the quasispace minimization algorithm which uses the imaginary part of the complex refractive index to calculate its absorption coefficient [12, 13]. Another previous reference reported an absorption coefficient of 10 cm−1 at 500 GHz for a PLA 3D printed sample [14]. Is paper differentiates itself from previous studies by investigating the changes in the refractive index and absorption coefficient in the THz gap using electric field transmission measurements of a 3D printed structure due to varying printing parameters used in the 3D printing process. No optical property variations due to changes in printing parameters have been previously reported
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