Abstract
We have measured the sub-THz electrical response of screen printed carbon nanotube-poly(methyl methacrylate) (CNT-PMMA) polymer composites and silver nanoparticles up to 220 GHz. The measured electrical losses of the CNT-PMMA composites using mm long coplanar waveguide geometries showed a reduction in signal loss with increasing frequency; a behaviour opposite to that found in conventional metallic conductors. We show that the low electrical losses are associated with the capacitive coupling between the nanotubes and discuss potential high frequency applications. An enhancement in the electrical performance of low temperature screen-printed silver nanoparticles [nAg] has been measured at frequencies up to 220 GHz. We show that for frequencies above 80 GHz the electrical losses in coplanar waveguide structures fabricated using nAg at 350°C are lower than those found in conventional thick film Ag conductors consisting of micrometer-sized grains and fabricated at 850°C. The improved electrical performance is attributed to the better packing of the silver nanoparticles resulting in lower surface roughness by a factor of three. We discuss how the use of silver nanoparticles offers new routes to high frequency applications on temperature sensitive conformal substrates. S-band (2-4 GHz) microstrip patch antennas were designed, simulated and tested. Multiwall carbon nanotubes (MWCNTs) and silver made from nanoparticles (nAg) comparison to a reference sample of bulk copper (Cu) was made. All antennas were printed on flexible polymide Kapton organic substrates. From the antenna return toss measurements, we found a shift from resonance frequency towards higher values in Cu and nAg, which is attributed to the fringing fields around the antenna which makes the patch seems shorter in dimensions. However, the capacitance coupling between the carbon nanotubes within the printed patch is shown to be the prime reason for the opposite shift to tower frequencies.