Dielectric property determination of hybrid Al₂O₃-filled MWCNT buckypaper by the rectangular cavity perturbation technique

This study investigated the complex dielectric permittivity of freestanding multiwalled carbon nanotube buckypaper (MWCNT-BP) and a synthesized hybrid alumina-filled buckypaper (Al₂O₃-BP) composite with different alumina loadings (5–30 wt%). The non-destructive microwave transmission technique for complex permittivity determination involving cavity perturbation was employed to characterize a set of Al₂O₃-BP sheets. This was done by filling a rectangular cavity resonator with a standard dielectric Teflon sample and then performing permittivity measurements for the buckypaper (BP) samples in the X-band frequency range (7–12 GHz). Field-emission scanning electron microscopy (FESEM) was used to analyze the morphology of the MWCNT-BP and the alumina-loaded BP composites. DC electrical resistivity measurements clearly demonstrated conductor–insulator transition. The effect of alumina loadings on the dielectric properties of the synthesized hybrid Al₂O₃-BP sheet is discussed.