Measurement Technique for Microwave Surface Resistance of Additive Manufactured Metals

• Published in: IEEE transactions on microwave theory and techniques Vol. 69; no. 1; pp. 189 - 197
• Main Authors: Gumbleton, Richard, Cuenca, Jerome A., Hefford, Samuel, Nai, Kenneth, Porch, Adrian
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Additive manufacture; Aluminum base alloys; Anisotropy; Current measurement; materials measurement; Measurement techniques; Metal plates; Metals; Microwave theory and techniques; parallel plate; Parallel plates; Powder beds; Random errors; resonant cavity; Rough surfaces; Roughness; Surface layers; Surface resistance; Surface roughness; Surface treatment; Titanium base alloys
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.3035082

Additive manufactured (AM) metals are a subject of much interest for their performance in passive microwave applications. However, limitations could arise due to artifacts, such as surface texture and/or roughness resulting from the manufacturing process. We have, therefore, adopted a parallel plate microwave resonator for the accurate measurement of the surface resistance of flat metal plates, allowing for microwave current flow in two orthogonal directions by simply exciting a different resonant mode (at 5.3 and 6.4 GHz), without the need to remove and refix the sample. The systematic and random errors associated with the measurement of surface resistance are very small, less than 1% and 0.1%, respectively. The technique is demonstrated with measurements on a range of samples of the alloys, AlSi10Mg and Ti6Al4V, manufactured by laser powder bed fusion, in addition to traditionally machined samples of bulk metal alloys of aluminum and brass. For AM samples of AlSi10Mg, we have studied the effect on the surface resistance of directional roughness features, generated by the laser raster paths, in directions transverse or parallel to microwave current flow. Importantly for passive microwave device applications, we demonstrate that these samples exhibit no systematic anisotropy of surface resistance associated with such surface features.