Microwave dielectric characterisation of 3D-printed BaTiO3/ABS polymer composites

Abstract

3D printing is used extensively in product prototyping and continues to emerge as a viable option for the direct manufacture of final parts. It is known that dielectric materials with relatively high real permittivity-which are required in important technology sectors such as electronics and communications-may be 3D printed using a variety of techniques. Among these, the fused deposition of polymer composites is particularly straightforward but the range of dielectric permittivities available through commercial feedstock materials is limited. Here we report on the fabrication of a series of composites composed of various loadings of BaTiO3 microparticles in the polymer acrylonitrile butadiene styrene (ABS), which may be used with a commercial desktop 3D printer to produce printed parts containing user-defined regions with high permittivity. The microwave dielectric properties of printed parts with BaTiO3 loadings up to 70 wt% were characterised using a 15 GHz split post dielectric resonator and had real relative permittivities in the range 2.6-8.7 and loss tangents in the range 0.005-0.027. Permittivities were reproducible over the entire process, and matched those of bulk unprinted materials, to within ~1%, suggesting that the technique may be employed as a viable manufacturing process for dielectric composites.

Figure 1. Coils of extruded filament, produced as feedstock for a fused deposition 3D printer.

Left: unloaded ABS polymer. Right: BaTiO₃/ABS polymer composite containing 50 wt% BaTiO₃. Scale bar, 10 cm.

Figure 2. 3D-printed polymer composite parts.

(a) Example rod-connected diamond photonic crystal structures printed in ABS polymer (left, ε′ = 2.57) and 50 wt% BaTiO₃/ABS polymer composite (right, ε′ = 4.95). Scale: each cubic structure has overall side length of 32 mm (8 mm unit cell). (b) Example 1D, 2D, and 3D periodic structures and a 1D graded structure printed using a combination of ABS polymer and 50 wt% BaTiO₃ in ABS polymer composite. Scale: each cubic structure has side length of 16 mm.

Figure 3. Scanning electron microscopy (conventional secondary electron imaging) of 3D printed parts.

(a) Cross section of a part printed with unloaded ABS polymer (scale bar, 10 μm). (b) Cross section of a part printed with 50 wt% BaTiO₃ in ABS polymer composite (scale bar, 10 μm). (c) A further, lower magnification, image of the 50 wt% printed part demonstrates that the particles are visibly well dispersed over length scales up to ~1 mm (scale bar, 50 μm).

Figure 4. The real part of the permittivity and the loss tangent of 3D printed parts for various loading fractions of BaTiO₃ in ABS.

1σ random uncertainties are within the thickness of the data symbols.

Figure 5. Real part of the permittivity ε′ as a function of frequency for ABS polymer only and 70 wt% BaTiO₃/ABS polymer composite.

Figure 6. Comparison of ‘good’ and ‘bad’ quality prints using 50 wt% BaTiO₃/ABS polymer composite.

(a) A photograph of a typical good print (left) and a bad print (right) indicates that, externally, the prints appear largely similar. (b) A typical X-ray tomography image shows relatively little voiding in the good quality sample, whereas a corresponding typical image for the bad quality sample shows a relatively high level of voiding. The tomography slices show planes that are vertical with respect to the orientation shown in the photograph. The bad quality print is shown for illustration only, and all other data reported in this Article concern good prints of the quality shown in (b). Scale: cubes are 1 cm³.