transmission coefficient s 22 the reverse reflection coefficient and s 12 the reverse transmission coefficient the units of s parameters are decibels db while the reflected wave r was measured by the transceiver 816 the transmitted wave t was measured by a transceiver 818 which supplied a signal to a port 820 in the test set 814 the emi shielding effectiveness of cnt polymer composites with various loadings of carbon nanotubes as a function of frequency is presented in fig9 the results exhibit that the shielding effectiveness of all composites is almost independent of frequency from 8 2 ghz to 12 4 ghz also it can be seen from fig9 that the shielding effectiveness of such composite enhances gradually with increasing cnt loading in the composite shown as percentage by weight or wt the shielding effectiveness of the cnt polystyrene composite containing 7 wt cnts is measured to be u02dc 26 db in the measured frequency region the polystyrene matrix in the composite is electrically insulating and does not contribute significantly to shielding as a result the formation of conductive cnt networks in the insulating polymer matrix renders composite the ability to effectively shield electromagnetic radiation these results imply that such cnt polystyrene composites can be commercially applied for the emi shielding materials the specific emi shielding effectiveness of the foam composite containing 7 wt carbon nanotubes is calculated to be 33 1 db u00b7 cm 3 g which is much higher than that of typical metals compared to 10 db u00b7 cm 3 g for solid copper thus the present invention can provide an effective and lightweight emi.