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2013-10-15, JoV Page 1 of 10
APPLICA TI ON NOTE
Going Wireless with Magnetic Shielding
BY JORGE VICTORIA AHUIR
1. Why we need Magnetic Shielding _______________________________
Magnetic Field Interferences are increasing in electronic devices due to a number of factors including
reduced separation distances of PCB’s, Integrated Circuits and many other sensitive components. In
addition to this the extended use of magnetically coupled communication technologies (Qi-WPC, NFC, RFID,
PMA, A4WP, WCT…) leads to more complex layout and proximity considerations.
With Ferrite materials it is possible to manage and predict magnetic flux flow and thereby improve efficiency
of power transfers, increase distances of near field communications and of course avoid additional unwanted
coupling effects which could lead to losses or noise.
2. Shielding with Ferrites________________________________________
Magnetic materials have a property which allows them to influence the magnetic field in its environment.
Materials such as ferrite have a greater permeability to magnetic fields (H) than the air around them and
therefore concentrate the magnetic field lines as can be seen in Fig 1. By strategic placement of ferrite
materials we are able to concentrate this magnetic field and therefore influencing the intensity and shape of
a field. We can utilise this effect to improve efficiency and reduce coupling effects. The parameter which we
use to quantify material characteristics with in a magnetic field is called the relative permeability which can
be defined as:
Figure 1 Ferrite material effect
We also have loses within the magnetic material which can be caused by hysteresis and eddy currents
internal to the material. These losses will transfer from magnetic field energy to heat, generating a self-
heating of the product. In order to quantify the losses of these magnetic flux redirections we must separate
the permeability into its complex form, the ideal part µ’ and the losses or reactive part µ”. As you can see
below we can express these 2 areas as a complete complex permeability.
