Dielectric Characterisation Methods for Additively Manufactured Ceramic Materials

Abstract

Additive manufacturing has recently emerged as a promising technique for fabricat ing microwave components with complex geometries that are difficult or costly to achieve using conventional manufacturing methods. By enabling greater geometric freedom, additive manufacturing has the potential to improve component perfor mance, reduce device size, and lower fabrication costs. However, to evaluate the suitability of additive manufacturing for high-frequency applications, it is essential to characterise how the fabrication process influences dielectric properties such as the relative permittivity and loss tangent. This thesis, conducted in collaboration with Saab, focuses on the development and evaluation of dielectric characterisation methods for additively manufactured ceramics, as well as on investigating the influence of fabrication and post-processing on their performance. Three dielectric characterisation methods were developed and evaluated: a parallel plate capacitor method, a dielectric resonator method, and a broadband transmission line method. The parallel plate capacitor method was used to characterise samples in the green body, sintered, and hot isostatically pressed (HIPed) states. Dielectric performance was found to be strongly dependent on material density, with a 0.6% increase in density corresponding to a 31.4% increase in relative permittivity and a 15.4% reduction in loss tangent. The relative permittivity remained stable over the temperature range 25◦C to 100◦C, varying by less than 2%, whereas the loss tangent increased by approximately 250%. In addition, the dielectric properties of the sintered and HIPed samples deviated from the manufacturer’s specifications, highlighting a significant influence of the fabrication process on the final dielectric performance. The findings demonstrate the importance of process optimisation in additive manu facturing of microwave ceramics and provide practical dielectric characterisation methods for evaluating and comparing fabrication parameters. The work con tributes to the understanding of how additive manufacturing and post-processing influence the dielectric properties of ceramic materials intended for microwave ap plications.