Shielding effectiveness of nickel-coated polycarbonate film

Abstract

Nickel coated on polycarbonate film has been investigated to determine its shielding effectiveness (SE). An effective method to measure the SE is by placing the coated film in an open side of a metal square box (3" x 3" x 3") and exposed to RF Source. Using the U.S. Military Standard 285 and revised version of ASTM-D4935 as reference and at 100 MHz to 3 GHz frequency range, the SE of nickel coated on polycarbonate film can be experimentally determined by taking the difference between the RF Signal with and without the shield as measured using Advantest R3131A Spectrum Analyzer. Theoretically, SE can be solved by mathematically adding all factors such as absorption loss, reflection loss and multiple reflection losses that causes the signal to attenuate from source to receiver. Nickel was coated using high vacuum deposition system with substrate placed inside the vacuum chamber and nickel pellets inside of alumina coated tungsten boat. Conductivity and permittivity of a material greatly affect its shielding effectiveness.
Polycarbonate film has very low conductivity hence it has almost a zero dB attenuation when used as shield. Nickel coated on polycarbonate film greatly increases the shielding effectiveness without any significant changes on its physical properties such as weight and formability. The produced coated film can be used as shielding material for portable electronic devices such as cellular and mobile phones and laptop computers.
Result of the experiment shows that measured SE (average) is 42.5 dB while its theoretical value is 44.5 dB. Reflection loss comprise most of the attenuation with 84% of the measured SE, 13% was contributed due to multiple reflection loss. Because of a very thin nickel layer, only 3% was attenuated due to absorption.