Electromagnetic measurements of composites containing barium strontium titanate or nickel zinc ferrite inclusions from 1 to 4 GHz

Composites with barium strontium titanate (BST) or nickel zinc ferrite (NZF) spherical inclusions mixed in a silicone matrix were manufactured at volume fractions ranging from 5% to 25%. The dielectric and magnetic parameters were measured from 1 to 4 GHz using a coaxial airline. The relative permittivity increased from 2.74 +/- 0.01 for the polydimethylsiloxane (PDMS) host material to 7.45 +/- 0.33 after combining PDMS with a 25% volume fraction of BST inclusions. The relative permittivities of BST and NZF composites were relatively constant across all measured frequencies. The relative permeability of the composites increased from 1.001 +/- 0.001 for PDMS to 1.43 +/- 0.04 for a 25% NZF composite at 1 GHz. The relative permeability of the 25% NZF composite decreased from 1.43 +/- 0.05 at 1 GHz to 1.17 +/- 0.01 at 4 GHz. The NZF samples also exhibited low dielectric and magnetic loss tangents from 0.005 +/- 0.01 to 0.091 +/- 0.015 and 0.037 +/- 0.001 to 0.20 +/- 0.038, respectively, for all volume fractions, although the dielectric loss tangent did increase with volume fraction. For BST composites, all volume fraction changes of at least 5% yielded statistically significant changes in permittivity; no changes in BST volume fraction yielded statistically significant changes in permeability. For NZF composites, the change in permittivity was statistically significant when the volume fraction varied by more than 5% and the change in permeability was statistically significant for variations in volume fraction greater than 10%. The DC electrical breakdown strength of NZF composites decreased exponentially with increasing volume fraction of NZF, while BST composites exhibited no statistically significant variation with volume fraction.