Complex Permittivity Measurement Technique for a 3D Printed Rectangular Dielectric Rod using an NRD Guides at 60-GHz Band

Complex permittivity measurement method of thermoplastic resin rod is studied using millimeter wave transmission characteristics of a 3D printed NRD guide. The NRD guide consists of two parallel aluminum plates and a thermoplastic resin rod printed with an FDM type 3D printer. Three kinds of the dedicated thermoplastic resin rods for the 3D printer and a PTFE rod are measured at 60 GHz band by the proposed technique. Measured result of relative permittivity for the PTFE rod validate the usefulness of the proposed method, although accurate loss tangent measurement needs improvement. Relative permittivity of the 3D printed thermoplastic resins are about 0.85 times lower than the original resin filaments due to air void in the printed structure. The proposed method has enough measurement resolution of relative permittivity to distinguish an original material and a 3D printed material.