Though there are few that can claim to truly understand the lore that dictate the workings of power fields, even among the Archmagi of the Mechanicus, such fields are a known factor in the 41^st Millennium. Since so few know how to make them each such field is very hard to come by and very expensive (if they are available for purchase at all). What fields do get made are churned out by rote, are very old, or are of xenos manufacture. Needless to say repairing such systems are as difficult and expensive as getting them in the first place.

Refractor fields: Advanced body armour offers very good protection against a variety of weapon types, but does fail to protect against hi-power energy weapons. Things like heavy lasguns, plasma guns and melta weapons can cut through even the thickest armour in a way not duplicated by projectile weapons. The refractor field does something to remedy this problem by creating a force-field effect that diffuses (electromagnetic) energy, causing las-beams (and other derived direct energy beams) to loose coherency and penetrating power before reach the target.

The refractor field doesn't completely prevent damage from energy weapons, it only blunts it. Since the field extends well away from the wearer it offers limited protection against shape-charge or plasma-bolter ammunition. And a refractor field also has a very limited effect on projectile weapons. The refraction effect might cause a slight change in the path of a bullet or bolt, but not enough to prevent it from striking the target with full force. Refraction fields are even less useful against melee weapons; the slow and steady application of kinetic energy used to swing a weapon completely negates the field's effect. Given the field's limitations it is only by wearing a refractor field in conjunction with body armour that a warrior can enter the battlefield knowing he's well protected from most threat scenarios.

A refractor field, like most power fields, consist of a control unit, a generator unit, projection nodes, and a power supply. The control unit can be tied into the control systems of a suit of body armour if desired. The projection unit is commonly worn as a large and heavy belt (sometimes including an auxiliary control unit – on/off button etc.). The projection nodes are either built into the belt unit or scattered across the armour (for better coverage and reduced power consumption). The power supply is either a large and powerful battery (a 5-pound atomic-stack battery can last for hours, while a smaller and/or less advanced battery might last only minutes) or a power generator (a 20-pound micro-fusion backpack could provide near-indefinite endurance).

Refractor fields can be made very small, possibly small enough to be worn as heavy jewellery (a large pendant for example) or more commonly a thick belt. The problem is that such small units will have very short endurance, and may also have limited coverage/reduced refraction effect because there are too few projection nodes. As such they are not suitable for military use, but have their place in self-defence scenarios.

Adeptus Astartes Chapters usually have a reserve of refractor fields that are issued to units that are expected to come under intense anti-armour fire; such as assault marines charging dug-in-infantry for example, or Terminators teleporting into choice hot-zones. The combination of PA/Terminator armour and a refractor field can keep a Marine alive for the crucial moments needed to eliminate the enemy, saving the God-Emperor valuable resource in terms of Marines and equipment.

Conversion field: A conversion field converts incoming energy into light and heat and directs it away from the field's owner. Conversion fields are a much rarer and more advanced type of power field than conversion fields. They are made exclusively by the Adeptus Mechanicus – in very small numbers and for select clients only. Unlike refraction fields, which only work primarily against direct energy weapons, conversion fields offer protection against most forms of attack, except attacks with melee weapons (once again the relative slowness of a melee attack prevents this field type from blocking it). Although conversion fields can protect the wearer from most types of damage it is advisable to wear body armour as well; a conversion field cannot completely protect the wearer against more powerful weapons. Conversion fields see little use on the battlefield, not just because they are rare and expensive, but because they have one major drawback – the light/heat flare generate by a hit can blind nearby friendly soldiers and also marks out the user as a target for further fire. It is ideal for VIPs and other non-military targets.

Barrier field: Barrier fields, sometimes called flux fields, do not try to refract, divert or convert energy. Instead they stop it by generating a counter-force. A barrier field in idle mode generates a infinite feedback-loop of static energy. The field typically takes the form of a hemisphere. If a weapon or other force effect strikes the barrier field it immediately generates a counter-force effect, thereby eliminating the incoming attack. Barrier fields are effective against most attacks, even melee strikes (it will forcefully push away any striking weapon). Slow-moving strikes, thrusts in particular, have a good chance of bypassing the field. Although the barrier field is more effective than both the refractor and conversion types it does have some drawbacks; even in idle mode it draws a fair amount of power and when it is struck it required a very large amount of energy. This makes barrier fields rather less suitable for soldiers who cannot carry a sufficient energy supply. The static energy effect also gives away a faint radiance and becomes quite visible in dusty or polluted atmospheres.

Displacement field: Displacement fields are the most potent personal shield technology known to the Adeptus Mechanicus. A holdover from the Dark Age of Technology it uses phase-disruption technology to protect the wearer – related to the techno-arcana that power teleporters. Whenever the sensor-field detects an incoming attack it shift the wearer into another phase-state, effectively preventing the rest of the universe from interacting with him. The field doesn't stop the attack, it just lets it pass through the target. Incidentally this makes displacement fields nearly useless against melee attacks; the phase-out lasts only for a split second, enough to let a bullet or beam through, but a sword will still be inside the user when he phases back in. Some Magi have experimented with longer phase-out times, but this is dangerous; the danger of being phase-disrupted (i.e. you constituent atoms are scattered into the Immaterium, which is quite fatal) increases astronomically once phase-out time crosses a certain threshold.

Void field: Void fields take field technology one step forward by combining the best features of both barrier and displacement fields. In essence it is a field effect that instead of phasing out the target, phases out the actual attack. Whatever damage isn't dealt with this way is stopped by the void field's secondary phase; a multi-function barrier/conversion/refraction effect. Void fields are bulky, require huge amounts of energy, and a lot of maintenance. As such they are not usually fund as personal protection. They main use is as the primary defence of Imperial capital warships and Titan war-machines.

Holo fields: The Eldar are fond of power fields, in particular holo fields. They are more properly categorized as ECM since they do not protect the target as such, only prevent the enemy from gaining a clear shot at the target (typical xenos cowardice).