Magnetic shielding is a process that limits the coupling of a magnetic field between two locations. Unlike electricity, magnetic fields cannot be blocked or insulated, which makes magnetic shielding necessary.

This is explained in one of Maxwell’s Equations, del dot B = 0, which means that there are no magnetic monopoles. Therefore, magnetic field lines must terminate on the opposite pole. There is no way to block these field lines; nature will find a path to return the magnetic field lines back to an opposite pole. This means that even if a nonmagnetic object — for example, glass — is placed between the poles of a horseshoe magnet, the magnetic field will not change.

Instead of attempting to stop these magnetic field lines, magnetic shielding re-routes them around an object. This is done by surrounding the device to be shielded with a magnetic material. Magnetic permeability describes the ability of a material to be magnetized. If the material used has a greater permeability than the object inside, the magnetic field will tend to flow along this material, avoiding the objects inside. Thus, the magnetic field lines are allowed to terminate on opposite poles, but are merely redirected.

Requirement for EMF Shielding

EMF shielding is required where there are occupied areas (apartments, offices or retail spaces) located next to or above substations, switch rooms or high current power cabling, to reduce occupants exposure to 50 Hz EMF fields associated with the high current carrying cables and transformers.

Areas outside external building walls, parking garages and walkways or thoroughfares are not normally considered to be occupied areas as they are only used for transitory purposes (i.e. no long term occupation)

As a general rule 4 layers of “M36 shield” EMF shielding material is applied to these installations. The sheets should be applied to all surfaces between the substations and/or switch rooms and occupied areas and should extend a further 1 m around the adjacent wall.

EMF Shielding material

“M36 Shield” is ideal for EMF shielding of 50 Hz power frequency magnetic fields from substations, switchboards and associated electrical cabling.

When magnetic fields encounter “M36 Shield”, the magnetic forces are both absorbed by and redirected away from the area of concern.

“M36 Shield” is supplied in individual sheets measuring 1 m x 2.4 m x 0.5 mm. Typically 4 or more layers are required with the butt joints of each layer staggered away from the butt joint of the layer below.

M36 Magnetic Shielding graph

Performance characteristics

The EMF shielding performance of “M36 Shield” will vary according to the intensity of the magnetic field it is subjected to (the higher the magnetic field the better the attenuation performance).

2 layers of “M36 Shield” are expected to provide a reduction to magnetic fields by a factor of 3 to 6 times (10 to 15 dB of attenuation), while each subsequent layer of “M36 Shield” will have diminishing attenuation performance (as the magnetic field intensity is reduced).

High permeability magnetic shielding M36 results

Installation method

Fixing of EMF shielding material is performed with the use of masonry anchors to concrete slabs, or screws into timber studs. EMF shielding material can also be layered and fixed in place with contact adhesive, although mechanical anchoring should be used in addition as a precaution for wall and ceiling surfaces. No special training is required to install EMF shielding material and tradespeople (plasterers, carpenters & electricians) will find installation relatively straight forward.

EMF Shielding display examples

The EMF shielding material is fixed in place and to make the fixing appear neat, use approximately 8 fixings per sheet. Multiple layers can be fixed at the same time if you allow 100mm overlap. Layers can also be glued together using contact adhesive prior to application to make handling easier.

overlapping EMF Shielding

Overlapping EMF shielding material showing staggered butt joints
(3 layers depicted as an example)

corner installation EMF Shielding

Typical corner installation of EMF shielding material
(100 mm minimum overlap)

(3 layers depicted as an example)

overlapping glued EMF Shielding

EMF shielding material can also be installed with the sheets glued together and joints with a minimum overlap of 100mm
(3 layers depicted as an example)

cable tray installation EMF Shielding

Typical installation of EMF shielding material over a cable tray (100 mm minimum overlap)
(100 mm minimum overlap)

(3 layers depicted as an example)

concrete slab installation EMF Shielding

EMF shielding material above power cabling fixed to concrete slab sheets should extend 0.6 m past he outside of power cabling
(3 layers depicted as an example)

Material quality

When determining the number of EMF shielding sheets you require it is important to allow for 10 cm overlap on edges and 15% waste. Here is an example of a calculation to determine the required material quantity:

Example for an area of 90 m2 with 4 layers (“M36 Shield” sheet size is 1 m x 2.4 m)

{Area (m2) x number of layers x 1.15} / 2 m2

{90 m2 x 4 layers x 1.15} / 2 m2 = 207 sheets of “M36 Shield”

This calculation makes allowance for 100 mm overlap and 15 % extra for off cut / waste

EMF Shielding material sheets