Abstract
Functionally graded materials (FGMs) that have gradient in permittivity (i.e., ε-FGMs) were fabricated from alumina/epoxy mixtures by a centrifugal method. In order to investigate the effects of filler shape on the fabrication conditions and property of FGMs, both non-spherical and spherical alumina powders with various sizes were employed as filler materials in the mixtures. Experimental results indicate that the spatial gradient in the number density and size of fillers can be intentionally regulated by changing the centrifugal conditions such as rotation velocity and operational time, as well as the shape and size of the fillers. Fillers with different shapes required different fabrication conditions such as the property of epoxy resin to be mixed, the size of the fillers, the centrifugal conditions, and so on, in order to obtain desirable profiles of filler gradient. It is concluded that due to the difference in both the viscosity of the mixture and the maximum packing fraction of fillers obtainable, the usage of the spherical fillers produces longer FGM columns with a wider range of change in permittivity between both ends and makes it easier to control the profiles of permittivity than the usage of the non-spherical fillers.
