Abstract: 2～18GHz complex permittivity and complex permeability spectra of directionally grown
carbon nanotubes (CNTs) were studied. The permittivity of directionally grown CNTs is lower than that of CNTs prepared by common chemical vapor deposition (CVD)
method, but permittivity is evidently higher. TEM micrographs show that Fe nano-particles regularly
distribute in the center cavity of directionally grown CNTs. There are also Fe particles covered by carbon layers deposited on the outer surface
of directionally grown CNTs. The existence of Fe particles may explain the higher permeability of directionally grown CNTs. During the preparation of
directionally grown CNTs, the amount and velocity of catalyst feed-in can adjust the distribution of Fe particles in the sample of CNTs, thus providing a new route to modulate the electrical and magnetic properties
of CNTs.

Key words: carbon nanotubes, directionally grown, permittivity, permeability