Yoon Ki Hong

Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges

We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer (50 MHz⩽M⩽13.5 GHz), we measured the S (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range (50 MHz∼1.5 GHz). The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured S parameters.

Electromagnetic interference shielding characteristics of fabric complexes coated with conductive polypyrrole and thermally evaporated Ag

Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σdc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag.

Oxidation of ammonia to nitrogen over Pt/Fe/ZSM5 catalyst: Influence of catalyst support on the low temperature activity

In this study, Pt/Fe/ZSM5 catalysts were applied to oxidation of ammonia, where the catalysts showed good low-temperature activity (≤ 200°C) for converting ammonia into nitrogen. With 1.5% Pt/0.5% Fe/ZSM5 catalyst, we could obtain 81% NH(3) conversion and 93% N(2) selectivity at 175°C at the short contact-time of w/f=0.00012 g min/mL. Through the characterization studies using high-resolution transmission electron microscopy (HRTEM) and X-ray spectroscopies (XRD, XPS), we could find that the active species was collaborating Pt/Fe species, which structure and activity were largely influenced by support material - in a positive way by ZSM5, rather than by Al(2)O(3) and SiO(2). When using ZSM5 as the support material, Pt was highly dispersed exclusively on the Fe oxide, and the valence state and dispersion of Pt changed according to Fe loading amount.