MechanismEditA.T. Fields are normally invisible barriers but become visible to the naked eye when colliding with other things. They are mainly used as an almost impenetrable shield; only the most powerful weapons are capable of breaching them. And even then, damage to the Angel is generally minimal. Through most of the series, the only thing that can reliably penetrate an A.T. Field is another A.T. Field, as seen in Episode 02 when the Evangelion Unit-01 "corrodes" Sachiel's A.T. Field.
Some Angels are sophisticated enough to use A.T. Fields as a method of attack or movement. Sachiel, Israfel and Bardiel can be seen making jumps assisted by their A.T. Fields, while Sahaquiel and Zeruel use theirs to attack, with Sahaquiel using it to destroy satellites and Zeruel in the Rebuild to shove attackers away.
It is revealed later in the series that every living thing with a soul possesses an A.T. Field: Angels and Evangelions just have A.T. Fields so strong that they are easily detectable and can even stop physical attacks. The boundary within an A.T. Field is subject to different physical laws as decided by it's creator, and in the case of Angels this effect is so powerful that they are able to create seemingly supernatural phenomena within the enclosure of their Field. While substantially weaker in human souls, the A.T. Field nevertheless provides a vital function: Bounding the ego and sense of self of a person from everyone else, allowing them to exist as an individual. Without an A.T. Field, it becomes almost impossible for souls to define their own existences without substantial conscious effort, causing the physical body of the soul to degenerate into pure LCL.
- "This is the light of my soul. A sacred territory in which no one may intrude. Aren't you Lilin even aware that your AT field is merely that wall that encloses every mind that exists?" - Kaworu in Episode 24
The weakness of the A.T. Field was, in case, the Lance of Longinus, an ancient and unbreakable weapon as well as its duplicates, is able to penetrate any A.T. Field, no matter how strong it is.
The A.T. Fields appear usually as octagonal or hexagonal fields. They are often orange, though pastel purple and red ones have also been used. Rather than traditional force-fields, A.T. Fields appear to behave more like membranes that twist and tear as they are penetrated.
Rebuild of EvangelionEdit
In the Rebuilds, the A.T. Fields present all of the same properties so far, and are once again used as weapons by the Evas.
In the same battle with Zeruel, Unit-01 creates an artificial arm with its A.T. Field, and uses it as a weapon, taking the form of a ring of geometric shapes which blast the Angel back.