Electromagnetic shielding effectiveness of galvanostatically synthesized conducting polypyrrole films in the 300–2000 MHz frequency range

Abstract

Both far-field (plane wave) and near field shielding effectiveness (SE) measurements have been conducted on electrochemically synthesized conducting polypyrrole (PPy) films with wide ranging conductivity levels (10 −2 S/cm to 45 S/cm). Co-axial transmission line, TEM test cell and TE 10 waveguide techniques were employed to measure shielding effectiveness as a function of polymer conductivity, frequency and temperature. Highly doped polypyrrole films exhibited shielding levels, above 40 dB from 300 MHz to 2 GHz, which can make them attractive for consideration in shielding applications. However, a loss of 10 to 15 dB in the shielding effectiveness, for the samples aged for a period of two years at room temperature, was observed. SE of PPy films increased with the increase in the dopant concentration and decreased with frequency reaching a plateau at higher frequencies. However, corrected SE values as a function of frequency appeared relatively flat. The measurements made directly on the TEM-t cell would simulate high impedance condition (E-field) due to the capacitive coupling, and use of the correction factors therefore eliminated this condition, giving rise to corrected far-field SE values. Using the theory for plane wave shielding effectiveness of thin material shields, the agreement between the theory and experimental results were tested. Effect of temperature on the plane-wave SE of a lightly doped (0.006 M p-TS) PPy film was also investigated. Results showed significant increase in the SE with temperature. At room temperature the lightly doped PPy film with a dc conductivity of 0.01 S/cm was almost transparent to microwaves with very little reflection or absorption. However as the temperature increased SE increased significantly because of the increase in conductivity of the sample.