Unlike electrical flux, there is no substance that can act as an insulator to magnetic flux. If a magnet is placed on a table and a glass holding a few iron nails positioned over it, the iron nails will loosely align themselves according to the magnetic field present, going from one end of the magnet to the other. The iron nails further away from the magnet form lesser number of these lines while those close to the magnet are more concentrated.
Similarly, if a glass is placed between the poles of a horse shoe magnet, there will be no significant change in the orientation of the magnetic field. This is because magnetic fields are neither created nor removed, and only redirected. If instead of a glass, a magnetic material is placed within the magnetic flux, it will be redirected as the magnetic lines of force are strongly attracted toward this material. This forms the fundamental idea behind substation emf shielding, which finds widespread applications in the industry such as in RFID chips, electronic devices, telecommunications, microwave oven, shield cables and much more.
Those electrical measurement systems that leverage magnetic fields and require high level of precision in emf shielding often show erroneous readings due to the presence of stray magnetic fields around. By placing a magnetic substance with high permeability, such as soft iron around the instrument, which acts as a means of redirecting the magnetic flux towards the shielded volume, the measuring instrument is suitably shielded. Electromagnetic radiations comprise of magnetic as well as electric fields. The electric field displaces the electrons within the conductor, causing current to flow. This displacement of charges within the conductor nullifies the field, causing the current to stop. For varying magnetic fields, the eddy currents are generated to cancel the magnetic fields, causing electromagnetic radiation. This is how electromagnetic shielding takes place, which is required to block high frequency interference fields of 100 kHz or above.
The magnetic shielding materials that are usually available are usually ferromagnetic in nature, which means they are attracted towards magnet. Ferromagnetic materials can work as good shields because of their property of pulling the magnetic fields towards themselves and away from the material to be shielded. Putting a ferromagnetic material between two magnets that attract each other will change their behavior such that they are both attracted toward the shield. If it is put between two magnets that repel each other, they will still be attracted toward the shield and will stick to it. Get to know more about field testing such as vibration testing over here http://www.compeng.com.au/vibration-and-shock-testing/.
Magnetic shielding is necessary, to provide a controlled magnetic environment for magnetic sensor devices and determine their behavioral characteristics and orientation of magnetic flux, both economically and accurately. The amount of shield varies with the permeability of the shield being used.