Interconnection morphology effects on the radio frequency response of carbon nanotube sponges

In this work, the high-frequency response of a multiwalled carbon nanotube (MWCNT) film grown on a silicon substrate is compared with that of MWCNT sponges (CNSs). Different from the CNT film, CNSs are a self-standing material that can operate in the absence of a supporting substrate, showing high flexibility, light weight, and mechanical robustness. We tested our synthesized CNSs as active material for the production of antennas working in the radio frequency (RF) range to determine whether CNT sponges present, in addition to practical advantages over CNT films, also an actual performance gain. The antenna built from CNSs shows an enhanced response gain compared with that of the MWCNT film, with both antennas having a maximum positioned around 4.8 GHz. After identifying the best CNT-based sample, the experiment focused on improving the CNS antenna's response. In particular, we observed that the response of <i>S</i> ₁₁ = -22.6 dB around 4.8 GHz from the CNS antenna improved after a mild treatment with ethanol, reaching S₁₁ = -32.6 dB measured after 10 min of waiting. This observed effect is studied in detail with scanning electron microscopy and Raman spectroscopy, which point to significant modifications of the CNS's inner morphology after the treatment. Signal reception tests simulating real-world operation conditions were also carried out at two different distances to evaluate the practical application of the CNS as RF antennas. The ethanol treatment was also applied for these tests, and an increase in the response up to 45% was found for the two studied positions.