Absorption-dominant radio-wave attenuation loss of metals and graphite

Abstract

Absorption-dominant radio-wave (0.2–2.0 GHz) attenuation loss is comparatively reported for materials of high electrical conductivity, namely metals (aluminum and steel) and graphite. These materials exhibit similarly high absorption loss (≤ 91.5%) and similarly low reflection loss (≥ 8.5%), both as fractions of the total loss in dB. The absorption loss is high (< 55 dB) and the reflection loss is low (< 10 dB) for both graphite and the metals. The absorption-dominant attenuation loss of these high-conductivity materials is in contrast to the notion that high conductivity (due to the high impedance mismatch with air) generally causes reflection-dominant attenuation loss. The metals and graphite are in foil form, with the graphite being thicker than the metals. The linear absorption coefficient (directly related to the absorption loss per unit thickness) is lower for graphite (≤ 93 mm−1) than the metals (≤ 394 mm−1), due to the greater thickness of the graphite. The absorption loss and fractional absorption loss contribution increase with increasing frequency, whereas the reflection loss decreases, as consistent with electromagnetic theory. On the other hand, from the viewpoint of the fractional loss in power, reflection dominates over absorption for all three materials in the entire frequency range. For shielding, the metals are more effective than graphite if the absorption loss per unit thickness (< 3400 dB/mm) is considered. For stealth, graphite is advantageous to the metals in the low reflection loss, though it is disadvantageous in the low absorption loss per unit thickness.