Shift of resonance frequency of long conducting fibers embedded in a composite

An experimental study on the dipole resonance of long high-conducting fibers embedded in an inhomogeneous composite sheet was conducted. The location of the resonance characterizes the effect of the inhomogeneous environment on the electromagnetic response of the fibers. It is shown that the resonance frequency is determined completely by the thickness and permittivity of the composite sheet, in particular, with the anisotropy of the permittivity. No effect due to inhomogeneity of the environment is observed. This is in disagreement with the scale-dependent effective medium theory (SDEMT) that is conventionally exploited to model the permittivity of fiber-filled composites, because this theory shows that the response of the fibers depends on the inhomogeneity scale of the environment. Therefore, although the SDEMT provides qualitative agreement with the observed behavior of fiber-filled composites, it must be further improved to obtain better quantitative agreement with experimental data. The experimental data obtained can also be useful to the development of microwave dielectrics with complex frequency dispersion behavior, which are necessary for many microwave applications.