Compounding a High Dielectric Constant Thermoplastic Material for Production of Microwave Photonic Crystals through Additive Manufacturing

Additive Manufacturing techniques allow the production of complex geometries unattainable through other traditional technologies. This advantage lends itself well to rapidly iterate and improve upon the design of microwave photonic devices, which are structures with intricate, repeating features. The issue tackled by this work involves compounding a high-dielectric constant material that can be used to produce 3D topological structures using polymer extrusion-based AM techniques. This material was ABS based, and used barium titanate ceramic as the high-dielectric compound of the composite, and involved the use of a surfactant and a plasticizer to facilitate processing. Initial small amounts of material were compounded using an internal batch mixer, and studied using polymer thermal analysis techniques, such as thermogravimetric analysis, rheometry, and differential scanning calorimetry to determine the proper processing conditions. The production of the material was then scaled-up through the use of a twin-screw extruder system, producing homogeneous pellets. Finally, the thermoplastic composite was used with a screw-based, material extrusion additive manufacturing technique to produce a slab for measuring the dielectric constant of the material, as well as a preliminary 3D photonic crystal. The real part of dielectric constant of the composite was measured to be 12.85 in the range of 10GHz to 12GHz, representing the highest dielectric constant ever demonstrated for a thermoplastic AM composite at microwave frequencies. The dielectric loss tangent was equal to 0.046, representing a low-loss dielectric.