Abstract
In this paper, resin-based photocurable polymer materials for stereolithography, digital-light-processing (DLP), and polymer-jetting additive manufacturing techniques were characterized from 0.2 to 1.4 terahertz (THz) for their comprehensive dielectric properties, e.g., refractive index, absorption coefficient, dielectric constant, and loss tangent, by using laser-based THz time-domain spectroscopy. A total of 14 photocurable 3D-printing polymers were chosen, owing to their suitability, in terms of printing resolution, material characteristics, and so on, for millimeter-wave (mm-wave) and THz applications. The measurement results from 0.2 to 1.4THz, the dielectric constants of all photopolymer samples under test are between 2.00-3.10, while the loss tangents are from 0.008 to 0.102, which are quite useful for many applications, e.g., 3D printed antennas and THz transmission lines, which were demonstrated by an asymptotically quasi-single-mode Bragg fiber microfabricated by DLP micromanufacturing technique using HTM140-V2 photopolymer, which is previously reported at the nominal frequencies from 0.246 to 0.276 THz.
Highlights
Additive manufacturing technology has attracted much attention to modern three-dimensional (3D) fabrication processes due to its rapid prototyping capability, especially with a broad diversity of dielectric and metallic materials that can be used to fabricate design prototypes of almost any 3D structures
The fused deposition modeling (FDM) technique achieves the lowest printing resolution along with high surface roughness, as compared to the other additive manufacturing processes. This limits their usability to bands below 400 GHz [14] owing to the large printable structure size compared to the guided wavelength and excessive propagation losses at higher frequencies caused by surface roughness
The THz radiation is focused onto the sample, after which a second set of off-axis parabolic mirrors are used to re-collimate and focus the THz transmitted through the sample onto the second photoconductive antennas (PCA) for detection
Summary
Additive manufacturing technology has attracted much attention to modern three-dimensional (3D) fabrication processes due to its rapid prototyping capability, especially with a broad diversity of dielectric and metallic materials that can be used to fabricate design prototypes of almost any 3D structures. It has become even more interesting recently since it has a capability to accurately manufacture functional devices with microscale features with a good repeatability [1]–[4], which is very suitable to microfabricate functional mm-wave and THz components such as dielectric lens antennas [6]–[8], waveguides [9]–[11], sensors [9], and filters/splitters [12]–[16] for realizing low-cost complex THz systems. General layer heights of a single FDM printed path range practically from 50 to 500 μm with the smallest achievable single layer width of approximately 100 μm, which is typically limited by the nozzle size and viscosity of the melted filament materials flowing through the nozzle aperture, and the best achievable surface roughness of approximately 35 μm [17]
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