Summary
International Symposium on Electromagnetic Compatibility
2009
Session Number:24P3
Session:
Number:24P3-4
Modelling of Absorbing Material Containing Magnetic Platelets
M. Y. Koledintseva, J. L. Drewniak, Y. He,
pp.809-812
Publication Date:2009/7/20
Online ISSN:2188-5079
Summary:
Design of non-conductive absorbing-type wideband electromagnetic shielding materials is important for EMC/EMI purposes. Absorbing materials are able to eliminate possible surface currents, which are culprits of undesirable emissions. Application of ferrites for developing absorbing materials is attractive, since they possess a unique combination of high permittivity, spontaneous magnetization, and extremely low d.c. conductivity. However, neither hexagonal ferrites with high internal field of crystallographic anisotropy, nor arbitrarily, randomly shaped spinels can effectively absorb energy in the frequency range from 100 MHz to 2.5 GHz, which is currently the most interesting range for high-speed electronics applications. But if crystallographically “isotropic" particles of soft ferrites are shaped as platelets, they may exhibit high field of form anisotropy due to demagnetization. This may substantially increase their frequency range of application in absorbing materials and overcome Snoek's limit. An analytical model for a composite material containing magnetic platelets presented herein is based on the modified asymmetric Bruggeman's effective medium theory ("1/3-power rule") for permeability. The model takes into account crushing of bulk magnetic material and form factors of inclusions.