Development and characterization of 3d printed frequency selective surface structures in aerospace applications

In aerospace applications, 3D printed materials are not used extensively due to the small of amount of recorded data/information in the material library. But it does have a great potential to be used more often in the future aerospace projects. With the current progress of technology, the additively manufacturing methods gain a lot of attention due to its time efficient production and cost effectiveness. The fastest and cheapest methods of additive manufacturing are 3D-printed polymers most commonly generated by Fused Deposition Modeling. Other common methods of 3D Printers are Stereolithographic Apparatus and Selective Laser Sintering. The main goal in this study is to reduce Radar Cross Section caused by antenna structure using two separate approaches. The first approach is to use the combination of metamaterial and frequency selective surface structures together on the antenna radome. In this way, frequency selective surface will provide band-pass filtering property allowing certain frequencies to pass while reflecting all the others. In addition, the metamaterial structure acts as an electromagnetic absorber so that some of the reflected signals are absorbed yielding lower Radar Cross Section. The second approach deals with the replacement of metallic ground plane of the antenna with a frequency selective surface acting as a band-stop filter backed with electromagnetic absorber foam which also causes a reduced radar cross section. Metamaterial and frequency selective surfaces are all made from periodic structures and a dielectric substrate. In this study, 3D printed materials were used as the substrate of these periodic structures and their performances in terms of reducing radar cross section were compared. Fused Deposition Modeling is chosen to fabricate most of the test specimens in this study. And also, with Stereolithographic Apparatus method, some electromagnetic and tensile test specimens are fabricated. Only one type of photo-curable resin which is ANYCUBIC Basic Resin is used with Stereolithographic Apparatus 3D printing, then electromagnetic and tensile test specimens are fabricated. With Fused Deposition Modeling method, several types of 3D printer thermoplastic filaments are used, which are PLA (Polylactic acid), ULTEM9085-FR (PEI Polyertherimide flame retardant), PC (Polycarbonate), and NYLON6-FR (Polyamide6 flame retardant). After 3D printing of specimens with certain raster and also infill orientations, the mechanical strengths of these specimens are characterized by tensile tests. In addition to tensile tests, electromagnetic tests are also conducted upon the specimens that are manufactured with respect to relevant 3D printing materials with certain raster and infill orientation as multilayered frequency selective surface (FSS) structures. Eventually, electromagnetic characterization of the manufactured substrates along with the metamaterial and frequency selective surface designs are studied to obtain radar cross section reduction.