Deflector shield
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A deflector shield is a fictional technology commonly found in science fiction. Typically, deflector shields (often referred to as simply "shields") are some form of force field designed to protect against weapons by deflecting or absorbing their impact. The field is projected along the surface of, or into the space around, a starship, space station, planet, moon, or building. Some are small enough for a person to wear in combat, such as in the Dune or Stargate universe. They are often depicted as translucent or invisible film-like surfaces that glow when impacted.
The concept goes back at least as far as the 1920s, in the works of E.E. 'Doc' Smith and others; and William Hope Hodgson's The Night Land (1912) has the Last Redoubt, in which the remnants of humanity shelter, protected by something very like one. Although fictional, deflector shields have some resemblance to real devices such as magnetic field generators or plasma windows.
The phrase "Shields Up!" which saw widespread use in Star Trek, probably had its origin in classical warfare, when infantry would raise their shields to defend against incoming arrows or other projectiles. The order would be given when it was time for the soldier to raise his shield from the carry position. The intuitive connotation of raising or lowering one's guard (as in boxing) is no doubt responsible for the ubiquity of the expression in science fiction.
The abilities and exact functionality of deflector shields vary; in some works (such as in the Star Trek universe), deflector shields can stop both energy beams (e.g. phasers) and physical projectiles, both natural and artificial; in others, such as the Star Wars universe, there are multiple types of deflector shields—so-called ray shields which are designed to stop energy beams (such as laser and blaster weapons), and particle shields which are designed to stop kinetic projectiles, missiles, bombs, etc.
Deflector shields usually work by absorbing or dissipating the energy of the incoming attack; prolonged exposure to such attacks weakens the shield and eventually results in the shield's collapse, making the ship's hull (or building's walls, or planet's surface) vulnerable to attack. Larger deflector shield systems, or those powered by bigger energy sources, can absorb/dissipate more damage before failing -- so that larger starships, for example, can mount much stronger shields than a small, single-person starfighter, much in the way that a sea-going battleship has much thicker armor than a tiny patrol boat. However, in some universes, shields are completely invulnerable to all technology of the time, yet can only be operated for a limited period of time, or at a great expense of energy. This is often used in games to give the player temorary invulnerabilty, such as the Iron Curtain used by the Soviet Union in Command & Conquer: Red Alert 2, along with many online games.
In some science fiction works, a shield does not deflect attacks but rather absorbs them, dissipating the energy of the attack. These shields are most commonly called "screens", "defensive shielding", or even more common, simply "shields."
Other names for a deflector shield include "deflector screen", "defensive screen", "screen", or "defensive shielding".
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[edit] Personal shields
Personal shield generators, whilst providing great protection to conventional weaponry, often prove vulnerable to slow moving projectiles as in the spear thrown by Rogue Trooper in 2000 AD or the dagger thrown by Colonel Jack O'Neill to penetrate Goa'uld shields in the Stargate universe, the rationale being that a personal shield must allow relatively slow-moving air to pass through it to allow the wearer to breathe. But it is not necessarily so, since in Stargate Atlantis, McKay uses a personal shield and can't even drink a coffee.
The personal shield used by John Crichton in Farscape is only activated by pulse weapon fire, and automatically shuts down after a certain period of time to conserve energy. The shield is designed to protect against pulse fire, but will even allow its user to stand in molten lava and remain unharmed, though the user must continually shoot themselves with a pulse weapon to prevent the shield from deactivating. This deactivation leaves the wearer vulnerable to attacks that use other energy like the kinetic energy of a rock.
In the Dune Universe the use of Holtzman effect personal shield generators is risky, for hits by laser weapons (lasguns) can trigger a large atomic explosion.
[edit] Deflector shields in Star Trek
[edit] Deflector shields in Halo: Combat Evolved and Halo 2
In the video games Halo: Combat Evolved and Halo 2, rechargable energy shields are worn by Covenant Elites, placed as stationary defenses, and equipped by the Human Spartan-IIs as a core component of their MJOLNIR powered armor. While not "deflector" shields in the most literal sense (all but the "riot shield" absorb energy, much like a Langston Field) Shields in the game are temporarily disabled after absorbing a set amount of energy; however, after a significant time, the shield self-restores (by some uncited mechanism). "Jackal" enemies have what resemble riot shields based on similar technology, deployed from a buckler-type device worn on the forearm, while the Elites originally had a shield similar to a Jackal's arm shield in the E3 preview for Halo: Combat Evolved.
[edit] Deflector shields in Stargate
Shields are seen many times throughout the Stargate universe, the most powerful usually being Ancient shielding followed by Asgard shields. The Goa'uld system lords carry personal shields that can resist the energy of a staff weapon blast or machine-gun fire from an SGC standard issue P90 with ease. However, Goa'uld personal shields allow the user to breathe and interact with objects outside the shield, and the field is designed to allow slow-moving objects to penetrate it. This can make the user vulnerable to thrown knives, spears, arrows and other slow-moving projectile weapons.
