EMI shielding measurements of conductive polymer blends

TLDR

Although the samples met the good‑conductor approximation, most exhibited a crossover from electrically thin to thick between 1 MHz and 3 GHz, and existing near‑ and far‑field shielding theories fail to capture this transition. The study measured shielding efficiencies of conductive polymer blends, including intrinsically conductive polymers, in the near field using a dual‑chamber box and in the far field with a transmission‑line fixture. The authors derived expressions that accurately model shielding across the full frequency range and reported far‑field shielding up to 70 dB at 1 GHz for polyaniline‑based organic composites in a thermoplastic matrix.

Abstract

Shielding efficiencies for a number of blends containing a variety of conductive fillers, including intrinsically conductive polymers, have been measured in the near field with a dual-chamber box and in the far field with a transmission line fixture. Although all samples satisfied the classical good-conductor approximation, most of them exhibited a crossover from being electrically thin (thickness<skin depth) to being electrically thick (thickness>skin depth) over the frequency range of interest, 1 MHz to 3 GHz. The theoretical relations for both near-field and far-field shielding which are prevalent in the literature do not accurately describe this region of crossover. The authors have derived expressions which describe the behavior accurately over the entire range of interest. Far-field shielding efficiencies as high as 70 dB at 1 GHz were measured for purely organic composites consisting of an intrinsically conductive polymer, polyaniline, dispersed in a thermoplastic matrix.<<ETX>>