Radio-wave electrical conductivity and absorption-dominant interaction with radio wave of exfoliated-graphite-based flexible graphite, with relevance to electromagnetic shielding and antennas

This work reports the radio-wave (200-2000 MHz) electrical conductivity sigma of exfoliated-graphite-based flexible graphite (FG). The sigma (in-plane) is <= 1.1 x 10(5) S/cm (carbon thickness t = 0.063 mm) - lower than sigma of aluminum by one order. The sigma decreases with increasing frequency f and increasing t. However, the DC conductivity increases with increasing t, due to the defects. The skin depth delta decreases with increasing f and decreasing t. The f-dependence of sigma is attributed to that of delta. The essentially linear relationship between root sigma sp and 1 / root f occurs for all t ranging from 0.063 to 0.405 mm, with the slope increasing with decreasing t, in accordance with electromagnetic theory. The interaction is dominated by absorption, with the absorption contribution increasing with increasing frequency and decreasing t, and exceeding 87.8% for the smallest t. Both shielding effectiveness SET and absorption loss SEA increase slightly with increasing f, while the reflection loss decreases slightly. The SEA/t increases with increasing f and with decreasing t. For the smallest t, it exceeds 691 dB/mm and the power loss exceeds 97% when the penetration depth exceeds 0.05 mm. Both aluminum and FG provide absorption bandwidth exceeding 1800 MHz. Applications include electromagnetic interference (EMI) shielding and flexible antennas. (C) 2019 Elsevier Ltd. All rights reserved.