Complex Permittivity Measurements of Single-walled Carbon Nanotubes at Microwave Frequencies

We report on the high frequency complex permittivity characterization of single-walled carbon nanotubes (SWNT) using broadband and narrowband frequency range techniques. SWNT suspensions, powder and fiber were investigated and the samples were a mixture of semiconducting and metallic nanotubes. Shielded opencircuited coaxial probe (50 MHz to 10 GHz) and dielectric microwave resonators were developed for this project. Two dielectric resonators supporting TE011 (3.4 GHz) and TM011 (6.5 GHz) modes and one TE01δ split-post resonator (12 GHz) were employed. An excellent correlation was observed between the values obtained from the coaxial probe and tubular resonator techniques. From our calculations, average conductivities of SWNT and surfactant suspensions were found to be 1.16x10 S/m and 1.66x10 S/m, respectively. In addition, a split-post dielectric resonator technique was developed to investigate origin of rf/microwave losses in SWNT samples. Resonant frequency and quality-factor Q changes introduced by SWNT interaction with the TE01δ mode electric and microwave fields were measured. The resulting frequency and quality factor maps allowed to distinguish between electric and/or magnetic fields induced losses.