Carbon Nanotube/Polysiloxane Foams with Tunable Absorption\nBands for Electromagnetic Wave Shielding

Abstract

Carbon-nanotube-enhanced\nelastomers are excellent conductivity-adjustable\ncomposites. A series of carbon nanotubes/polysiloxane foams were fabricated.\nTheir electromagnetic (EM) absorption effects were studied when the\nfoams were stacked to multilayers or compressed by different ratios.\nIt was found that stacking the foam sheets creates a shift toward\nthe low-frequency side in the absorption band; the foam with less\nconductivity tends to have an absorption band covering a higher-frequency\nrange. Furthermore, variations in resistivity and relative permittivity\nas well as a tunable electromagnetic wave absorption behavior were\nobserved from the compression procedure of carbon-nanotube-incorporated\npolysiloxane foams. The shift toward a higher frequency, as well as\nan enhancement in absorption efficiency, was realized by foam compression.\nIt is believed that the foam thickness acts as a dominant factor for\nthe EM wave absorption band tunable properties. The highest EM wave\nabsorbing efficiency was observed from a polysiloxane foam with a\n1.8 wt % single-walled carbon nanotube content when the compression\nratio was controlled to 30%, reaching a reflection loss of −41\ndB accompanied by a 9.5 GHz wide absorption peak frequency shift.\nThese foams are considered to be highly valuable in electromagnetic\nwave absorption applications involving multiple absorption bands.