What acts as a barrier to the magnetic field ?
The only way in which the magnetic field can be significantly attenuated is to use sheets of MuMetal. The sheets of MuMetal must be placed between the magnetic field source and the area or the room that needs protecting.
The MCL61 from Yshield (160€ M2) is not MuMetal. This product only attenuates the magnetic field by 10% as would a simple sheet of stainless steel (tested by Ondes Expertise).
What is MuMetal ?
MuMetal is composed of a subtle mix of iron and metal (80%) heated to over 1000° in order to increase attenuation performance. That explains the high price of these materials. The conception and installation must be carried out by a specialized company. Protective material for magnetic fields is also apt for electric fields when linked to an earth wire.
Tests and measurements using NFA 1000
Switching on electric heating in order to obtain a significant electric field in the electric panel. Here 6155 nT (nano Tesla) for the fixed 50 Hz magnetic field.
The Bioiniative 2012 recommendation advises not to exceed 50 nT for permanent exposure to a 50 Hz magnetic field.
The gradual installing of the MuMetal sheeting without moving the measuring device: you can already see the attenuation of the magnetic field measured (here 936 nT).
MuMetal sheeting optimally positioned: here 77 nT measured (photo below).
For information, the installing of a second piece of sheeting in parallel is no doubt very useful to significantly attenuate much higher magnetic field values.
Here in this example, MuMetal sheeting attenuates the 50 Hz magnetic field by 80, an attenuation of 38 decibels (dB).
CONCLUSION :
the installing of MuMetal sheeting is no doubt a costly solution but is very efficient in attenuating the 50 Hz magnetic field when it is impossible to distance oneself from the permanent magnetic field (a bedhead where there is an electric panel behind the wall).