High-Permittivity and Low-Loss Electromagnetic Composites Based on Co-fired Ba0.55Sr0.45TiO3 or MgCaTiO2 Microfillers for Additive Manufacturing and Their Application to 3-D Printed K-Band Antennas

Abstract

Six types of high-permittivity and low-loss electromagnetic (EM) composites based on a polydimethylsiloxane (PDMS) or cyclo-olefin polymer (COP) host matrix, reinforced by Ba0.55Sr0.45TiO3 or MgCaTiO2 microparticle fillers with volume loading concentration up to 49 vol. %, have been prepared and characterized up to 20 GHz using cavity resonators. These high dielectric permittivity (high-k) ceramic powders were sintered at temperatures up to 1,500°C to further enhance their dielectric properties. The 49 vol. % loaded PDMS-Ba0.55Sr0.45TiO3 composites with 1,340°C sintered fillers have a relative permittivity (ɛr) of 23.51 and a loss tangent (tanδd) <0.047 at frequencies up to 20 GHz. Meanwhile, the 39 vol. % loaded PDMS-Ba0.55Sr0.45TiO3 composites with 1,340°C sintered fillers have a ɛr of 15.02 and a tanδd <0.042 at frequencies up to 16 GHz. On the other hand, the 37 vol. % loaded PDMS-MgCaTiO2 composites with 1,100°C sintered fillers have an ɛr of 12.19 and a tanδd <0.021 at frequencies up to 20 GHz. The 49 vol. % loaded PDMS-MgCaTiO2 composite specimen has a measured ɛr of 16.33 and tanδd <0.021 between 0.4 and 20 GHz. In addition, thin-sheet specimens made of 25 vol. % COP-MgCaTiO2 prepared by fused deposition modeling have a ɛr of 4.74 and a tanδd <0.0018 up to 17 GHz. Similarly, 25 vol. % COP-Ba0.55Sr0.45TiO3 samples have a ɛr of 4.92 and a tanδd <0.0115 at frequencies up to 17 GHz. For demonstration of a device prototype, a 19.6-GHz microstrip patch antenna was printed by employing a molded PDMS-MgCaTiO2 composite substrate and microdispensed silver ink (CB028) to form the conductive layer, achieving a 20-dB return loss and ~10% bandwidth. Evidently, these newly developed polymer-ceramic composites are well suited for applications up to the K-band and are amenable to be adopted by 3-D printing technologies.