  Metacomposites are a type of engineering composite materials with
metamaterial properties. We propose a design of hybrid filler consisting of
ferromagnetic microwire and carbon nanotube to enable a tunable microwire
metacomposite. There shows a sophisticated dependency of plasma frequency and
bandwidth of double negative region on the carbon nanotube coating. Factors
such as coating thickness, uniformity, morphology and number of microwires
conspire to the formulation of the double negative characteristics. The
intricate role of CNT on modulating negative {\epsilon} and {\mu} is elucidated
by the plasma frequency formula and split-close paths model based on the
layer-like structure of CNT coating.
