Irina I. Nefedova

Dielectric Constant Estimation of a Carbon Nanotube Layer on the Dielectric Rod Waveguide at Millimeter Wavelengths

A method has been developed to estimate dielectric properties of a layer containing carbon nanotubes (CNTs) randomly arranged in plane, deposited on a dielectric rod waveguide (DRW). In the framework of this method, a theoretical model of a layered DRW with extended narrow walls and perfect electric conductor walls was used to fit the experimental results. The experimental results were obtained by measuring the wave propagation characteristics ( S11 and S21) of a DRW unloaded and loaded with different CNT layers at 75-110 GHz. The developed model allows derivation of the dispersion equation of the wave excited in the loaded DRW in an analytical form. The propagation constant is then found numerically through the fitting process with measurement results. Additionally, the complex permittivity of the CNT layer can be estimated using the surface conductivity model of the CNT and mixing formulas. Both methods give reasonable and comparable results. The obtained results (ε = 1- j5×103) allow full-wave simulation (e.g., HFSS) of DRW structures loaded with CNT layers with a thickness of 60 nm or more. Simulation and measurement results agree rather well.

Conductivity of Carbon Nanotube Layers at Low-Terahertz Frequencies

Wave propagation in a dielectric rod waveguide loaded with carbon nanotube (CNT) layers was studied experimentally at the wide frequency range of 75-320 GHz. Analytical calculations and computer modeling indicate that the measured losses at low-terahertz frequencies are due to conductivity of the CNT layer. The observed rapid decrease of the conductivity with increasing frequency is related to finite lengths of CNTs.

Dielectric constant measurements of carbon based nanomaterials and silver nanowires at millimeter wave frequencies

The aim of this work is to study dielectric properties of thin carbon nanotube and silver nanowire layers at 75-110 GHz frequency range. The method is based on S-parameter measurements of loaded and unloaded sapphire rod waveguides.

Optically controlled millimetre wave phase shifter

Phase shifting in a dielectric rod waveguide, loaded with a carbon nanotube layer illuminated with light from a tungsten lamp, was studied experimentally at the frequency range of 75-110 GHz. Close to a linear dependence of phase shift on the optical power intensity with almost independent behavior of the losses is observed The phase shift of 30 degrees with less than 1 dB extra loss for 1.26 mW/mm2 light intensity was achieved.

W-band phase shifter based on optimized optically controlled carbon nanotube layer

Phase shifting in a dielectric rod waveguide (DRW), loaded with carbon nanotube (CNT) layers of different thickness, was studied experimentally under light illumination in the frequency range of 75–110 GHz. The dependence of efficiency of the phase shifting, in terms of phase shift per light intensity and millimeter wave attenuation, on the optical transparency of the CNT-layer is investigated in this paper. The best result, a phase shifter of 0–15° with less than 0.1 dB additional signal loss in the W-band was achieved for a 95% transparent CNT layer at 23 mW/mm2 light intensity of a tungsten halogen lamp (main radiation spectrum is 550–680 nm). The overall insertion loss of the phase shifter including two DRW tapering sections serving as transitions to rectangular waveguides are 3 to 5 dB in the W-band, about 2 dB is attributed to the CNT DRW section. This comprises, for the first time, an optically-controlled CNT-based DRW phase shifter with phase shift and insertion loss levels suitable for practical applications.

Millimeter wave conductivity of silver nanowire network

Wave propagation in a dielectric rod waveguide loaded with a layer of silver nanowires was studied experimentally at millimeter wave frequencies. Then based on the measurement results, analytical calculations were used to estimate conductivity of the silver nanowire layer at millimeter wave frequencies. Numerical simulations based on the calculated conductivities were performed and good agreement of simulated and measured results was achieved.