The theory of Anti-magic is a simple one, yet the execution of such an ability is incredibly complex. Only the most powerful of magic users or most knowledgeable of scientists who understand the usage of magic at a fundamental level can possibly comprehend the precise nature of the use of anti magic. The basis of the theory follows below:
When a magic user ‘senses’ magic, it is because when a spellcaster casts magic they give off an aura from the dimension they are pulling energy from. Therefore, an anti-magic device or spell would have to cut off the connection between the caster and the planes of energy. To do this one must use Nullification Crystals; green emerald-like objects that for reasons unknown cut off all extra-planar activity around them.
On it's own one crystal will only nullify magic within a meter or two, but by employing technology to "extend" or "broadcast" the aura the effectiveness can be increased to cover large areas or even be contained within one room or structure. This method is costly due to the uncommon nature of Nullification Crystals and the technology required to amplify their effects. Because of this proper anti-magic containment facilities or devices are restricted to large factions and specialized correctional institutions.