Copper coated PEEK hollow waveguide and durability investigations for low-loss and bendable transmission of low-frequency terahertz wave

This work aims to develop a low-loss, bendable and durable terahertz (THz) hollow waveguide (HWG) based on cost-effective copper (Cu) and polyether-ether-ketone (PEEK) tubing. The as-prepared PEEK/Cu-coated HWG exhibited low transmission losses of 1.37–2.31 dB/m at 0.3 THz and 1.77–4.42 dB/m at 0.1 THz under bending conditions (0°-180°, radius 15 cm). The waveguide was found to be vulnerable to damage from the copper oxidation, especially in hot and humid environment, which could cause the transmission loss increasing up to 17.11 dB/m after 80 h of accelerated aging treatment (85 °C,85 RH%). In addition, the transmission loss reached 7.01 dB/m after six times temperature cycling tests (-40 °C-85 °C). A thin (∼300 nm) uniform polystyrene (PS) film was deposited on the copper reflective layer to improve its oxidation-resistant performances. The Cu/PS HWG achieved low transmission losses of 1.41–2.47 dB/m at 0.3 THz and 1.80–4.63 dB/m at 0.1 THz (0°–180°) and little deterioration in transmission loss (<0.11 dB/m) after even 200 h of aging treatment and ten times temperature cycling tests. The dispersion |β2| of this waveguide sample is less than 1.59 ps/THz/m within 0.3–1.5 THz range. The results show that the Cu/PS PEEK HWG could enable low-loss, bendable and durable transmission of low-frequency THz wave and can be potentially used in some practical applications such as THz sensing and 6G communication.