Bösch, Wolfgang

Candau Carceller, Carlos

Gentili, Fabrizio

Reichartzeder, Dominik

Schwentenwein, Martin

TUGraz OPEN Library

Industry Days - Additive Manufacturing for RF/Microwave hardwareAbstract ID : 33Practical Considerations In The Development OfCeramic-Based Filters With Additive ManufacturingContentDielectric materials can be found in RF/microwave filters for a wide range of industrial applications.Compared with other technologies, dielectric resonator (DR) filters offer a perfect balance betweenperformance and miniaturization. These structures are capable of handling high-power levels whileproviding a quality factor (Q) comparable to that of pure waveguide implementations. In addition,the overall volume of the component is significantly reduced thanks to the use of dielectric materials.For that reason, these filters are emerging as the baseline design for many RF filters used in wirelessand satellite applications. Due to the difficulty in machining ceramic blocks, the shapes of thedielectric objects included in RF/microwave filters are usually simple: rods, pucks, rectangularblocks, etc. However, the successful development of additive manufacturing (AM) processes forceramic materials has opened up new geometrical configurations for filter designers to explore.Consequently, we can expect significant advances in key fields for the space industry due to theadditional geometrical flexibility provided by AM.Additive manufacturing of ceramic materials differs significantly from processes for metals andplastics. Having a clear understanding of the chemical and mechanical processes that are involvedin the creation of a given structure is key to successfully develop ceramic filters for RF/microwaveapplications. The proposed presentation in these Industry Days will focus on the different stepsof the lithography process for monoblock filters like the one shown in Fig. 1 (see attached files).These filters are completely built out of ceramic materials. After manufacturing, a layer of metalliccoating is applied on the exterior faces of the filter to create the metallic enclosure. Coaxial flangesare finally glued to the structure in order to provide input and output couplings.The lithography-based ceramic manufacturing (LCM) process developed by Lithoz and applied tothese filters involves three steps. First, a green body is manufactured by layer-wise curing of aphotoreactive ceramic suspension, building up a 3D object directly from the CAD model. Then,this green body is cleaned in order to eliminate the excess of material that has not been hardened.Finally, the green body is thermally treated to remove the organic binder (up to 600 ◦C) and sinteredat a materials specific sintering temperature to give the dense ceramics filter (> 1000 ◦C). Thesuccessful application of these three steps requires the filtering structure to fulfill certain geometricalspecifications. Therefore, filter designers should take into account new geometrical constraints duringtheir design process, not typically present when employing more traditional ways of manufacturingfilters. The main constraints of each step that will be discussed in the presentation are:• In the manufacture of the green body: the LCM process requires all the layers parallel to thebuilding platform to be properly supported. This means that hollow monoblock ceramic filters likethe one shown in Fig. 1 cannot be built with its bottom wall attached to the base plate, since thatwould required the top wall (where the connector openings are placed) to be supported from theinside of the filter (which is not readily accessible after manufacturing). Instead, the structure istilted as shown in Fig. 1 and supports are only placed in the exterior or the filter, where they canbe removed once the 3D block is created. At the same time, the use of these supports degrades thesurface roughness of the walls where they are attached. This impacts the performance of the finalfilter, slightly increasing the insertion losses. Consequently, it is important to minimize their usage,and structures that completely avoid these supports are preferred (when available).• Slurry removal: this procedure applies a cleaning solvent to remove the excess of slurry materialattached to the ceramic parts. The proper removal of the slurry is key to ensure that the manufactureis done with high geometrical accuracy. In order to do this, all the surfaces of the geometry haveto be easily accessible for the solvent to reach them, but also for the suction probe to extract theremaining solvent. As a consequence, the input/output coupling apertures have to be strategicallyplaced to allow this probe to reach the inner part of the filter.• Debinding and sintering: in order for the photopolymeric binder to be completely removed fromthe ceramic material, the filter cannot have excessively thick walls. Otherwise, traces of the bindermay be locked in the ceramic material leading to potential cracks after sintering.This contribution will give a review on design rules for manufacturing ceramic filters using the LCMapproach and the corresponding constraints on filter designs. As a result, RF/microwave designerswill gain knowledge on how to adapt their designs to improve their performance and increase thechances of a successful manufacture using ceramic-based lithography.JUSTIFICATION FOR THE CONSIDERATIONThis proposed presentation will provide a review on design rules for manufacturing ceramic filtersusing the lithography-based ceramic manufacturing approach, and the corresponding constraintson filter designs. As a result, RF/microwave designers will gain knowledge on how to adapt theirdesigns to improve their performance and increase the chances of a successful manufacture usingceramic-based lithography.Primary author(s) : Dr. GENTILI, Fabrizio (Technische Universität Graz, Graz, Austria); Dr.CARCELLER CANDAU, Carlos (Technische Universität Graz, Graz, Austria); Mr. REICHARTZEDER,Dominik (Lithoz GmbH, Vienna, Austria); Prof. BÖSCH, Wolfgang (Technische Universität Graz, Graz,Austria); Dr. SCHWENTENWEIN, Martin (Lithoz GmbH, Vienna, Austria)Presenter(s) : Dr. GENTILI, Fabrizio (Technische Universität Graz, Graz, Austria)Submitted by Dr. CARCELLER CANDAU, Carlos on Thursday 22 September 2016Last modied: Thursday 22 September 2016

Practical Considerations in the Development of Ceramic-based Filters with Additive Manufacturing

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Practical Considerations in the Development of Ceramic-based Filters with Additive Manufacturing

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