Dielectric properties of epoxy–barium titanate composite for 5 GHz microstrip antenna design

Design of Dielectric Resonator Antenna Using Dielectric Paste

In this publication, the use of a dielectric paste for dielectric resonator antenna (DRA) design is investigated. The dielectric paste can serve as an alternative approach of manufacturing a dielectric resonator antenna by subsequently filling a mold with the dielectric paste. The dielectric paste is obtained by mixing nanoparticle sized barium strontium titanate (BST) powder with a silicone rubber. The dielectric constant of the paste can be adjusted by varying the BST powder content with respect to the silicone rubber content. The tuning range of the dielectric constant of the paste was found to be from 3.67 to 18.45 with the loss tangent of the mixture being smaller than 0.044. To demonstrate the idea of the dielectric paste approach, a circularly polarized DRA with wide bandwidth, which is based on a fractal geometry, is designed. The antenna is realized by filling a 3D-printed mold with the dielectric paste material, and the prototype was found to have an axial ratio bandwidth of 16.7% with an impedance bandwidth of 21.6% with stable broadside radiation.

Dielectric Properties of BaTiO3-Epoxy Nanocomposites in the Microwave Regime

We synthesized BaTiO₃–epoxy nanocomposites (particle size < 100 nm) with volume fractions up to 25 vol. %, whose high-frequency complex permittivity was characterized from 8.2 to 12.5 GHz. The maximum dielectric constant approaches 9.499 with an acceptable loss tangent of 0.113. The dielectric loss gradually saturates when the particle concentration is higher than 15 vol. %. This special feature is an important key to realizing high-k and low-loss nanocomposites. By comparing the theoretical predictions and the experimental data, four applicable effective-medium models are suggested. The retrieved dielectric constant (loss tangent) of 100-nm BaTiO₃ nanopowder is in the range of 50–90 (0.1–0.15) at 8.2–12.5 GHz, exhibiting weak frequency dispersion. Two multilayer microwave devices—total reflection and antireflection coatings—are designed based on the fabricated nanocomposites. Both devices show good performance and allow broadband operation.

Addition of microcrystalline cellulose to an alkyd resin/titanium dioxide film: effect on dielectric properties

In this study, various composite films were prepared by varying the amounts of long-oil Alkyd Resin (AR), Titanium Dioxide (TiO₂) and Microcrystalline Cellulose (MCC). The effects of each component, TiO₂ and MCC, on the properties and microstructure of the dry film were determined by examining images obtained by scanning electron microscopy (SEM) and studying the evolution of dielectric properties, the dielectric constant and the loss factor, against frequency at room temperature. Results showed that the introduction of the TiO₂/MCC powder with a weight ratio larger than 1 and a volumetric pigment concentration (VPC) less than 50% allowed a better dispersion of the particles and fitted well the Linchtencker logarithmic mixing law and the Maxwell-Garnett theory. Finally, a marked improvement of the dielectric constant with respect to those of pure alkyd resin and AR/TiO₂ composites was observed.