From Stargate Wiki
- "...they obviously absorb different forms of energy..."
- — Samantha Carter
A shield is an energy barrier designed to repel both physical and energy-based objects for the primary purpose of protection of another object.
- "Atlantis has ten of these emitters with which it creates the city's shields."
- — Rodney McKay
Shields are barriers of energy which absorb and deflect various other forms of energy and physical attacks as well as radiation and heat. Shields can have one side that allows passage for objects such as weapons fire and even people, either to keep objects out or keep them in. Shields rely on emitters to be active, usually multiple emitters all of which need to be active in order for the shields to operate. The shield energy will eventually be depleted and the shield will fail and the emitters need to be recharged before the shields can be reactivated. (SG1: "Serpent's Song", "Evolution, Part 1", ATL: "Echoes", "The Daedalus Variations", "The Return, Part 2", SGU: "Incursion, Part 2")
Shields can be powered by multiple forms of energy fed to its emitters. The emitters eventually run out of energy and the shields fail, as such the energy needs to be recharged in order for continual function of the shields. Supplying more energy to the shields will increase their strength however their emitters can still burn out after continual use. Some shields can use energy weapons fire as a source of power somehow channeling it to increase strength. (SG1: "Lost City, Part 2", "Beachhead")
The Ancients had the most powerful shield technology ever created. City-ships have large dome shields capable of resisting intense weapons fire, radiation and natural phenomenon such as coronal mass ejections as well as maintaining atmosphere within the city during hyperspace travel. The shield can be active for a long time provided their is no stress on the shields. Atlantis also has a shield over the Stargate to prevent unwanted visitors. The Ancients also had small personal shield emitters which create a form-fitting shield to protect the wearer from physical attacks but allowed air to get through. (ATL: "Rising", "The Eye", "The Siege, Part 3", "Echoes", "Hide and Seek", "Irresponsible")
Destiny and the seed ships have powerful shields that can resist the intense gravitational forces, stresses and heats in the coronsphere of a star. These shields are also capable of resisting intense weapons fire and are required for use of the Faster-Than-Light engines on the ships to maintain structural integrity of the ship during transit from the intense forces. Destiny also creates shields over hull breaches to maintain atmosphere. (SGU: "Light", "Space", "Incursion, Part 2")
The Asgard have powerful shield technology capable of resisting weapons fire from Ori Motherships. Their shields cannot be activated while in hyperspace. Asgard shield technology was given to the Tau'ri who modified it. (SG1: "Camelot", "Small Victories")
The Goa'uld have powerful shield technology which is capable of withstanding nuclear weapons and resisting the intense heat and radiation of a corona of a star for several hours. Other shields are used as part of trap devices which allow for things to enter but not to exit. The hand devices also have shields which allow for slower moving objects to pass through but not for projectiles of energy weapons fire. Some Goa'uld shields were upgraded with knowledge from Anubis which made them capable of withstanding Tollan Ion cannons fire, O'Neill-class battleship weapons but not Drone weapons. (SG1: "The Nox", "Within the Serpent's Grasp", "The Serpent's Lair", "Secrets", "Enemies", "Between Two Fires", "Revelations", "Lost City, Part 2")
The Ori possess powerful shield technology which protects their ships which are powerful enough to withstand a large ship colliding with it as well as multiple weapons fire from a variety of different sources. The shields can withstand attacks from Drone weapons but at significant damage. The Ori also possess other shield technology which is capable of utilizing energy used against it as a form of power. (SG1: "Beachhead", "Camelot", "Flesh and Blood", "The Road Not Taken")
The Tau'ri had reverse-engineered shields from Goa'uld and Ancient technology and eventually gained Asgard shields. The shield strength can be increased when more power is supplied to them however the emitters can only handle so much before they require a rest and to be recharged. Rodney McKay came up with a new way of increasing shield strength on the 304's. (SG1: "Prometheus", "Unending", ATL: "Echoes", "Tao of Rodney")
The Tok'ra make use of one-way sheilds which encapsulate the target and allow for others to enter, these shields create a box around the target, most likely from Goa'uld shield technology. The Tok'ra also use some shield on their bases to hold prisoners. (SG1: "Evolution, Part 1", "Prototype", "Exodus")
The Travelers have powerful shields on their ships for protection capable of withstanding Wraith, Vanir and Asuran weapons fire. They also use shields to create a stable atmosphere to keep their hangar bays pressurized. (ATL: "Travelers", "Be All My Sins Remember'd", "The Lost Tribe")
The Vanir have shields on their ships as well as smaller protective shields on their armored suits. Their ship-based shield weapons are much weaker than their Ida galaxy counterparts and their suit shields are also able to resist sustained weapons fire for some time before it will fail. They also have shield technology on their drilling platforms, possibly as the means in which is tunnels through barriers. (ATL: "First Contact", "The Lost Tribe")
Wraith ships do not posses shields for defensive purposes like other ships instead relying on their dense hulls. Wraith do however had soem form of shield technology which can be used to hold dangerous prisoners. (ATL: "The Siege, Part 3", "The Lost Boys", "The Hive", "Reunion")
The Bedrosian and Optricans possess some form of shield technology which are deployed by shuttles, the shields will stun anyone who touches it. The Hebridians and Serrakin also have shields which they use on their ships which protect them from energy weapons fire as well as heat and radiation. The Oannes also have shield technology which allows for entry and egress underwater without allowing the water in. Nakai also have powerful shield technology on their ships capable of resisting fire from the weapons on Destiny. (SG1: "New Ground", "Space Race", "Fire and Water", SGU: "Space")