Free-Standing, Transparent Carbon Nanotube Thin Films with High Specific Shielding Effectiveness

Carbon nanotubes (CNTs) are emerging as a candidate shielding material for RF technologies due to their multi-functional properties such as low density, flexibility, and excellent electrical properties. The present work provides a direct comparison of shielding measurements for single-wall (SWCNT) and multi-wall (MWCNT) free-standing thin films fabricated from chlorosulfonic acid dispersions. CNT thin film properties are varied to create a series of thicknesses ranging from ≈18 to ≈4000 nm, resulting in optical transparencies from 80 to 0%. Shielding effectiveness is measured using a rectangular waveguide setup from 10 to 15 GHz and shows frequency-independence with values up to 50 dB. Lower shielding effectiveness in MWCNT films relative to SWCNT films of equivalent mass is consistent with theoretical studies that propose a restriction of the electromagnetic interaction to the outer MWCNT walls. The present SWCNT and MWCNT films exhibit density- and thickness-specific shielding effectiveness of 3.3 × 10⁶ dB cm² g⁻¹, a 10× increase over emerging thin film and transparent conductive materials. Demonstration of shielding effectiveness has been made by measuring signal strength reduction from a Bluetooth device when attenuated by the CNT film. Thus, the present work advances the potential to incorporate transparent, conductive CNT films into RF technologies with arbitrary surface geometry.