The Highly Effective EMI Shielding Materials for Electric and Magnetic Fields over the Wide Range of Frequency in Near-Field Region

The effects of the electrical resistivity and permeability of conductive paste and magnetic paste materials on the near-field shielding effectiveness (SE) were investigated using strip-line and loop-probe methods. The silver paste of 3.4 x 10(-5) Omega . cm of volume resistivity showed more than 30dB of electric field SE and the SE increased as the thickness of conductive layer increased. For the magnetic field SE showed max 60dB as the thickness increased. However, in low frequency below 10MHz, the magnetic field SE was max 3dB in the case of 10 mu m thickness. Magnetic sheets made of soft magnetic materials having permeability of 200 mu showed 11dB of magnetic field SE at 1MHz. The hybrid paste having conductivity of 1.8 x 10(-4) Omega . cm and permeability of 23.7 mu showed SE of 13.5dB for the magnetic field and 63.9dB for electric field at 10MHz, respectively. The paste having conductivity of 3.7 x 10(-2) Omega . cm and permeability of 53.4 mu, showed 7.6dB for magnetic field at 10MHz. In low frequency below 10MHz, the permeability had dominant influence on the magnetic field shielding in the near-field region. As the frequency increases, the SE is mainly affected by the conductivity of hybrid pastes.