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.