A robust PEEK/silver-coated hollow waveguide for terahertz bendable transmission in hot and cold environments

The rapid development of terahertz (THz) technology makes the study of THz waveguide indispensable. In the current research on terahertz waveguides, there is still a lack of flexible waveguides for stable transmission in hot/cold environments. In this work, a mechanically strong and high-and low-temperature resistant PEEK (polyether ether ketone) tube was selected as the structural tube. On the basis of plasma treatment on the surface of PEEK tube, a high-performance silver (Ag) coated hollow THz waveguide was prepared. The results indicate that the plasma treatment can greatly improve the surface bonding strength between the PEEK tube and the silver film, which enhances the bending performance of the PEEK/Ag-coated hollow waveguide. For the 3-mm-bore waveguide, the minimum bending radius can reach 3 cm without damaging waveguide structure. Meanwhile, the superior thermal properties of the PEEK tube and its good bonding with the silver layer allow the waveguide to transmit terahertz waves stably at high (150 °C) and low (−78.5 °C) temperatures with the no more than 5% fluctuation in output power. In addition, the PEEK/Ag-coated hollow waveguide has extremely low transmission loss compared to other previously reported terahertz waveguides. In the 4.25-mm-bore waveguide sample, the straight transmission losses for 0.3 and 0.1 THz wave is 0.67 and 1.26 dB/m at room temperature (25 °C). When the bending angle of the 4.25-mm-bore waveguide increases from 0 to 180°, the transmission loss increases to 1.02 dB/m at 0.3 THz.