Multi-material additive manufacturing of low sintering temperature Bi2Mo2O9 ceramics with Ag floating electrodes by selective laser burnout

Additive manufacturing (AM) of co-fired low temperature ceramics offers a unique route for fabrication of novel 3D radio frequency (RF) and microwave communication components, embedded electronics and sensors. This paper describes the first-ever direct 3D printing of low temperature co-fired ceramics/floating electrode 3D structures. Slurry-based AM and selective laser burnout (SLB) were used to fabricate bulk dielectric, Bi2Mo2O9 (BMO, sintering temperature = 620–650°C, εr = 38) with silver (Ag) internal floating electrodes. A printable BMO slurry was developed and the SLB optimised to improve edge definition and burn out the binder without damaging the ceramic. The SLB increased the green strength needed for shape retention, produced crack-free parts and prevented Ag leaching into the ceramic during co-firing. The green parts were sintered after SLB in a conventional furnace at 645°C for 4 h and achieved 94.5% density, compressive strength of 4097 MPa, a relative permittivity (εr) of 33.8 and a loss tangent (tan δ) of 0.0004 (8 GHz) for BMO. The feasibility of using SLB followed by a post-printing sintering step to create BMO/Ag 3D structures was thus demonstrated

Aligning Material Extrusion Direction with Mechanical Stress via 5-Axis Tool Paths

Mechanical properties of parts fabricated via the Material Extrusion (ME) process can be improved by optimising process settings, however, their properties are strongly influenced by build orientation due to the stair-stepping effect initiating cracks whilst under load. 5-axis ME enables the fabrication of parts without the layer-by-layer restrictions that conventional 3-axis strategies impose. By aligning extrusion direction with high stress tensors, 5-axis tool paths can be used to reduce the effects of weak inter-layer bonds. To establish performance differences between parts manufactured by either strategy, wave spring-inspired geometry was selected for production, due to the multi-directional tensile loads acting throughout the material. 5-axis and 3-axis tool paths were generated via the Grasshopper 3D virtual environment within Rhinoceros 3D and MakerBot Desktop, and manufactured using a 5AXISMAKER and a MakerBot Replicator 2, respectively. To evaluate performance differences between the two strategies, compression tests were conducted on the parts.Mechanical Engineerin

Synthesis and dielectric characterisation of a low loss BaSrTiO3/ABS ceramic/polymer composite for fused filament fabrication additive manufacturing

Composite polymer/ceramic filaments for material extrusion-based fused filament fabrication additive manufacturing, using barium strontium titanium oxide (BST) ceramics and acrylonitrile butadiene styrene (ABS) thermoplastics were produced; their dielectric and physical properties have been characterised for the first time. The dielectric properties, relative permittivity (εr), quality factor (Q×f) and dielectric loss (tanδ) were measured as a function of ceramic solid loading (%) at 5 GHz for 3D printed samples. A relative permittivity εr = 6.05, Q×f = 10,433 GHz and dielectric loss tanδ = 0.007 were obtained for a BST/ABS ceramic polymer composite, with 50 wt% (15 vol%) solid loading. The composite materials exhibit reduced dielectric losses compared to standard laminates currently used in the radiofrequency (RF) and telecommunications industry. Based on polymer/ceramic composite filament, a prototype microstrip patch 5 G antenna and a hemispherical dielectric lens were designed and manufactured. Through testing, it shows good antenna performance with a centre frequency of f0 = 3.78 GHz and a (−10 dB) bandwidth of 90.6 MHz. The dielectric lens increased the antenna gain by 3.86 dBi

Direct ink writing of bismuth molybdate microwave dielectric ceramics

Additive manufacturing via direct ink writing and microwave dielectric characterisation of commercially produced low sintering temperature bismuth molybdenum oxide ceramics, have been both performed for the first time, following a powder-to-product holistic approach. We demonstrated that direct ink writing is an excellent candidate for producing dielectric substrates to be used for wireless telecommunication applications operating at microwave (MW) frequencies, with great repeatability and properties comparable to ceramics fabricated via conventional processing routes. The optimum density (relative density of ρr ≈ 93%) of the 3D printed test samples was obtained by sintering at 660 °C for 2 h, resulting in a relative permittivity εr = 35.7, dielectric loss tanδ = 0.0004 and microwave quality factor Q × f = 14,928 GHz. Sintering at higher temperatures promoted a porosity increase due to mismatching grain growth mechanisms and phase decomposition, that collectively hindered the test samples’ microwave dielectric performance in terms of achievable relative permittivity (εr) and dielectric loss (tanδ)

Additively manufactured ultra-low sintering temperature, low loss Ag2Mo2O7 ceramic substrates

Ultra-low sintering temperature silver molybdenum oxide (Ag2Mo2O7) ceramics have been printed using direct ink writing (a material extrusion additive manufacturing process) for the first time. An optimum densification conditions of 460 °C / 2 h was determined, resulting in relative permittivity, εr = 13.45, dielectric loss, tanδ = 0.0005, microwave quality factor, Q × f = 17,056 GHz and the temperature coefficient of resonant frequency τf = −121 ppm/°C. The results were comparable to the dielectric properties of conventionally fabricated ceramics. A series of metal/ceramic antenna designs were produced via dual-printing and co-firing, to demonstrate the potential of Ag2Mo2O7, to be used as a co-firable dielectric material for functional integrated circuits and/or microwave RF devices through multi-material direct ink writing