High-Frequency EMI Noise Suppression by Polymer-Based Composite Magnetic Materials
Rastislav Dosoudil, Jaroslav Franek, Marianna Usakova, Jozef Olah, Jozef Slama
DOI:
Abstract
The complex permeability and EM-wave absorption properties of hybrid polymer-based composite magneticmaterials (with MnZn and LiZn ferrite fillers and PVC matrix) prepared with constant total filler content (65 vol%) andparticle size (0-250 mm) have been investigated in the 1-1000 MHz frequency range. Within this filler concentrationthe permeability of composites changed continuously with the change of ferrite filler content ratio between two types offerrite fillers. The observed relaxation type of permeability dispersion was due to the domain wall and natural ferromagneticresonance phenomena and was also attributed to the high damping of spin motion. Measured values of permeability wereused to determine the EM-wave absorption properties (return loss RL, matching frequency fm, matching thickness dm andbandwidth Df for RL £ -20 dB). The calculation of these properties was based on a model of single-layered absorber backedby a perfect conductor using transmission-line and EM-field theory. The composite with the volume fraction ratio of hybridMnZn:LiZn ferrite filler set to 0.5:0.5 has shown a return loss of -57 dB (> 99 % power absorption) at fm = 714 MHz with the-20 dB bandwidth of Df = 232 MHz for an absorber thickness of 7.79 mm.