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

Abstract 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.