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Microwave performance and applications of additive manufactured components

Gumbleton, Richard James 2021. Microwave performance and applications of additive manufactured components. PhD Thesis, Cardiff University.
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Additive manufactured (AM) metals are of increasing interest for their performance in passive microwave applications, however several barriers exist to their large scale uptake. This thesis hopes to help address some of these barriers through the contribution of novel microwave techniques for the characterisation of metal AM parts and reporting of results from supporting experimental studies. A novel parallel plate resonator fixture is developed for the accurate measurement of the surface resistance of at metal plates produced by AM. This allows for microwave current flow in two orthogonal directions by simply exciting a different resonant mode. This has significance for the detection of anisotropy in a given plane that might arise through the laser scan path or vertical layer boundaries, for example, and is used here to assess the performance of individual wall surfaces, as they might appear in a manufactured waveguide component. Experimental studies are performed on the use of AM processes parameters to optimise the manufactured surfaces for low microwave loss, as well as quantifying the effects of several commonly used post-processing treatments. Improving microwave performance of unsupported, downward facing, surfaces is of particular interest and is investigated in this thesis, culminating in a ~ 40% reduction in surface resistance. Finally, a focus on practical applications in satellite technology is given through the evaluation of thermal properties of AM parts. A technique is described that uses fractional frequency shifts to evaluate the thermal expansion (CTE) of a cylindrical AM microwave cavity over an extreme temperature range (6{450 K) without the need for strict calibration. To the authors knowledge, this is the first time that CTE has been assessed over such a wide temperature range for AM parts, as is appropriate for space based components, using a passive microwave structure that can be adopted in a satellite communications system.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Microwave surface resistance; Metal additive manufacturing; Parallel plate resonator; Laser power; Materials characterisation; Microwave measurements
Date of First Compliant Deposit: 6 August 2021
Last Modified: 27 Sep 2022 01:21

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