Efficiency analysis of simple structures of ferrite EMI suppressors in different ferrite materials

Abstract

The properties of ferrite material as well as geometrical parameters determine the efficiency of ferrite component in electromagnetic interference (EMI) applications. Due to the presence of ferrite material, EMI suppressor behaves as low pass filter (i.e. as a frequency dependent resistor) and provides signal free from distortions. Near ferrimagnetic resonant frequency, component has maximal impedance and efficiently suppresses noise. Better suppression can be achieved by making the conductive layer longer. Three simple structures are analyzed: Line, Zig-zag and Double coil. Nevertheless, longer conductive lines introduce parasitic capacitance, which causes the maximal impedance frequency shift towards lower frequencies. The aim of this paper is to investigate the efficiency of simple structures of EMI suppressors in different ferrite materials. Two Ni-Zn materials are used for fabrication of EMI suppressors: low permeability F14 material (suitable for suppression above 200 MHz; initial permeability er= 220), and high permeability F19 material (which is used for suppression in the range from 20MHz to 200MHz; er=1000). Comparison of the same structure with identical geometrical parameters in F14 and F19 material in the frequency range 1MHz–3GHz shows that the device in low permeability F14 material achieves greater impedance and better suppression (up to 25%).