Due to their unique geometry and the chirality, carbon coils were supposed to have unique electrical and optical properties that could be used in nanoelectronics [1]-[3]. In particular, carbon coils are understood to play the good electromagnetic wave absorbers because the coil geometry had an effective form for inducing current through an inductive electromotive force [1] [2]. Furthermore, the demand of lightweight and moldable materials for the portable electronic devices, the polymer-matrix composites, instead of the metal-based materials, for the electromagnetic interference (EMI) shielding materials are more and more required [4] [5]. In this respect, carbon coils are regarded as the promising candidates for EMI shielding materials.

In general, the geometry of carbon coils (d-CCs) was known to be very diverse at as-grown state [6]. Furthermore, their diameter could be varied from the nano-size to the micro-size scale. So, the electrical properties of the carbon coils could be varied depending on their geometry including the diameter, as in case of carbon nanotubes [7]. For the practical application of carbon coils, therefore, it is essential to achieve the geometrically controlled carbon coils. In our previous reports, the continuous injection of SF₆ gas flow during the overall reaction could give rise to d-CCs [8]. The dominant formation of the geometrically controlled carbon microcoils (g-CMCs) could be also obtained by manipulating the incorporation of SF₆ flow during the reaction [9] [10]. With regard to the manipulating the incorporation of SF₆ flow, our previous reports strongly confirmed that the formation of the geometrically controlled carbon coils is possible by the in situ cycling on/off modulation process employing C₂H₂/SF₆ flow [10]. The in situ cycling on/off modulation process can be simply achieved by turning a gas flow rate on or off during the reaction. Furthermore, it was understood that the increased number of cyclic on/off modulation processes of C₂H₂/SF₆ flow suppresses the formation of carbon microcoils (CMCs), while developing carbon nanocoils (CNCs) [9].

In this work, we investigated the shielding properties of the d-CCs and g-CMCs in the polymer composites. The d-CCs with polyurethane (PU) composite (d-CC@ PU) and g-CMCs with PU composite (g-CMC@PU) were obtained by dispersing d-CCs and g-CMCs in PU, respectively. The electromagnetic wave shielding properties of d-CC@PU or g-CMC@PU composites were measured according to the weight percent of d-CCs or g-CMCs in PU and the thickness of the composites layers in the frequency range of 0.25 - 4.0 GHz. Based on these results, we also discussed and compared the main shielding mechanism of d-CC@PU and g-CMC@PU composites.

For the deposition of d-CCs and g-CMCs, a home-made thermal chemical vapor deposition system was employed. C₂H₂, H₂ were used as source gases. The incorporated additive gas, SF₆, was continuously or on/off cyclic injected into the reactor during the reaction. Figure 1 shows the detailed manipulation schemes for these gases flows according to the different processes with the samples.

The detailed reaction conditions were shown in Table 1.

For d-CC@PU and g-CMC@PU composites, d-CCs and g-CMCs were dispersed in PU solvent with the addition of dimethyl formamide (DMF) using ultrasonic system.