Force field

A force field, sometimes known as an energy shield, force shield, or deflector shield is a barrier, typically made of energy or charged particles, that protects a person, area or object from attacks or intrusions. Force fields tend to appear often in works of speculative fiction.

In real life
A University of Washington in Seattle group has been experimenting with using a bubble of charged plasma to surround a spacecraft, contained by a fine mesh of superconducting wire. This would protect the spacecraft from interstellar radiation and some particles without needing physical shielding.

Likewise, Rutherford Appleton Laboratory is attempting to design an actual test satellite, which should orbit Earth with a charged plasma field around it.

Workers at a 3M factory in South Carolina have encountered electrostatically-charged air that impeded movement, with the problem fixed by properly grounding the equipment causing the stray charges.

Plasma windows have some similarities to force fields, being difficult for matter to pass through.

In fiction
Science fiction and fantasy venues postulate a number of potential uses for force fields:


 * A barrier to allow workers to work in areas that can be exposed to the vacuum of space, keeping the atmosphere inside while allowing certain other objects to pass through.
 * Emergency quarantine of an area afflicted by a harmful biological or chemical agent or occupied by enemy forces.
 * The extinguishing of a fire by forcing the reaction to use up all the available oxygen in the confined space.
 * As a shield (in some cases large enough to cover an entire planet) to protect something from damage by natural forces or enemy attack.
 * To create a temporary habitable space in a place not usually suited to sustaining life.
 * As a security method to direct someone in a particular direction for capture, or to confine a captive in a particular area.

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 a force field.

The abilities and exact functionality of energy shields vary; in some works (such as in the Star Trek universe), energy shields can stop both energy and particle weapons (e.g. phasers) and normal projectiles, both natural and artificial; in others, such as the Star Wars universe, there are multiple types of force fields that defend against different sorts of attacks.

Energy 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. An example of this is the aerial Scrin Battleships in Command and Conquer 3: Tiberium Wars. Larger energy 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 seagoing battleship has much thicker armor than a tiny patrol boat. In some instances, shields are actually able to incorporate at least some of the projectile's kinetic energy into themselves, making the shield stronger with each hit.

In some works, 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 temporary invulnerability (for example, the "Iron Curtain" used by the Soviet Union in Command & Conquer: Red Alert). In other examples, shields are invulnerable, yet they are unreliable, meaning they can't block everything. One such example is Haegemonia, where the basic deflector shields deployed in the late stages of the Earth-Mars civil war were capable of blocking projectiles with an average chance of 30% (meaning shots went right through the shield 70% of the time). This ratio was later improved, yet these shields weren't completely invulnerable; in addition, although the most advanced shields used at the beginning of the Human-Kariak-Darzok war boasted an impressive 80% blocking ratio, they were largely ineffective (only about 40%) against missile weapons, a lethal liability on planetary shields.

Very rarely, weapons designed specifically against shields also appeared (such as the "phasing cannon" in X-COM: Interceptor: it was designed to rapidly deplete the target craft's shields so that it can be finished off or disabled quickly). These pieces of equipment were designed to shut down or otherwise weaken the targeted ship/building/planet's shields so that other weapons can be brought to bear on the vulnerable hull/walls/planetary surface. An example of this type of anti-shield weaponry is a projectile that is capable of destroying the shield itself (notably the "Shield Breaker" round designed for use in the Exitus sniper rifle, which is in turn used by Vindicare Assassins in Warhammer 40,000, often against individuals using personal shields). In Supreme Commander: Forged Alliance, an Aeon Illuminate unit, called the Absolver, is armed with a Shield Disruptor cannon, doing massive damage to shields, but are useless against other units.

Examples

 * The ability to create a force field is a popular superpower in comic books and associated media. While only a few characters have the explicit ability to create force fields (for example, the Invisible Woman and Violet Parr), many can emulate it with other powers, such as Green Lantern's energy constructs, Jean Grey's telekinesis, and Magneto's manipulation of electromagnetic fields.
 * In the various Star Trek series, shields that function in an unexplained manner serve as a primary protection against weapons fire from enemy ships; these shields also generally block the use of transporters while active. Also, inside ships, force field generators can seal off ship atmosphere from the vacuum of space, as in the case of a hull breach caused by an attack or explosion.
 * In the Star Wars universe, deflector shields are standard issue on most ships and perform a function similar to that of their Star Trek counterparts. Unlike Star Trek, multiple kinds of shielding are required to guard against different weapons and interstellar debris.
 * In the popular RTS Starcraft, all Protoss units and buildings are surrounding by slowly-regenerating psionic force fields, which will dissipate after taking a set amount of damage, allowing the health of the unit to be attacked directly.
 * In Neon Genesis Evangelion, AT fields are explained to be simultaneously the defensive barrier generated by the Angels and Evangelions and the psychological barrier that separates the identities of different people, with the only difference between the two types being that the Angels and Evangelions can project it outwards.
 * In the Dune universe, personal shields have been deployed that can stop objects with high kinetic energy. As well, when struck by an energy weapon, the subsequent reaction makes both the shield and emitter explode on a nuclear scale. In response to this, many have returned to using melee weapons, slowed before strike to penetrate the shield. Shields cannot be used on Arrakis as they attract nearby sandworms and drive them into killing frenzy. The Fremen, who are used to acting without the slow-down necessitated by the shields, take advantage of this to hurt their enemies with devastating efficiency.
 * In Isaac Asimov's Foundation universe, personal shields have been developed by scientists specializing in miniaturization. Used by Traders, they are unknown to other inhabitants of the Galactic Empire.
 * In the Halo Series, shielding is used by the main character's MJOLNIR powered assault armour, made by the UNSC from reverse-engineered alien technology. It can protect against projectile weapons to a large degree, yet not so well against plasma weaponry. Hits will strain the shield and eventually deplete it, but if the wearer can stay out of the line of fire for a while, the shield will recharge back to full strength. Additionally, shields can be overcharged to absorb up to 300% damage compared to normal operating mode, at the expense that an overloaded shield can't recharge until fully depleted.
 * In Sins of a Solar Empire, shields protect against all damage, but take an equivalent amount of damage. They constantly regenerate. Shields can be bypassed with Phase Missiles, tech which is exclusive to the Vasari faction. Shields, like Phase Drives, are standard equipment on all combat ships bigger than a fighter. Shields can be upgraded up to four times.
 * In Outlaw Star, several characters are equipped with personal Light Shields, which absorb all but the most powerful weapons fire, but have limited power and can only be operated for seconds or minutes. The shield generator can also be overloaded and destroyed if the shield sustains too much damage.
 * In Earth 2150 and its sequel, the energy weapons introduced late into the war increased casualties significantly on all sides of the conflict. To this end, the Lunar Corporation designed and fielded an energy shield system that was capable of defusing electrical discharges, laser beams, plasma bolts and harmonic resonance waves. Their adversaries, the Eurasian Dynasty and the United Civilized States, soon learned of this new system and stole its research data from the LC's research site in Madagascar. The result was an imperfect replica which only operated at 50% output compared to the original model (which had a maximum output of 3600MW). The shield could only block high-energy emissions, rendering it useless against weapons that resort to kinetic or explosive force to achieve damage. It loses charge from each energy impact, though the shield can recharge itself from the vehicle/structure's main power source, given enough time. An external power source greatly speeds up the process. Later on, the shield was made partially obsolete with reflective armor being installed onto vehicles.
 * In Supreme Commander, shields also protect against all damage, except nuclear missiles. Some units have personal shields, and there are mobile and fixed shield generators. Shields collapse when no power is available or when it has taken too much damage. It will regenerate over time.