Analysis of Q-Factor for AM-SLM Cavity Based Resonators Using Surface Roughness Models

Abstract

This research delves into losses of X-band cavity resonators manufactured using additive manufacturing-selective laser melting (AM-SLM) compared to the standard subtractive manufacturing milling technology. Measured losses are benchmarked in terms of resonator (quality) $Q$ -factor. The measured data is further modelled using the Groiss and one-ball Huray models taking into account the implications of surface roughness and electrical conductivity. The unloaded $Q$ -factor is derived from frequency-dependent scattering ( $S$ ) parameters obtained from measurements and full-wave simulations. Surface roughness was found to impact the $Q$ -factor significantly and the resonant frequency marginally. Cavities based on AM-SLM technology exhibit higher roughness compared to milling and lowers the $Q$ -factor. A fusion of both manufacturing methods by milling AM-SLM cavity walls demonstrates an augmented $Q$ -factor compared to a directly printed cavity. In the study it was also found that the Groiss model tends to overestimate the $Q$ -factor owing to AM-SLM's rougher surface, while the one-ball Huray model furnishes precise projections by establishing a link between surface roughness and powder particles. Electrical conductivity's influence on $Q$ -factor was also investigated, showing negligible impact with increased surface roughness. Further, side walls of the AM-SLM cavity were more susceptible to surface roughness, compared to the cavity front walls due to higher surface current density. This study underscores the significance of analyzing surface roughness and electrical conductivity in AM-SLM cavity resonators and highlights the suitability of the one-ball Huray model for accurate $Q$ -factor prediction of microwave structures with rough surfaces.