One of the most common passive defensive technologies in the ShyeMUSH universe is energy shielding. Unlike armor, which protects by absorbing or deflecting incoming attacks from its own physical structure, energy sheilding projects a non-physical protective barrier around the subject it is intended to protect.
The main advantage of an energy shield is its durability. Unlike armor, which degrades with use and must eventually be repaired or replaced, energy shields are replenished when power is supplied to them, so in theory they can operate indefinitely. Energy shields are also useful because they can provide a great deal of protection without adding a great deal of mass, preserving mobility.
Energy shielding has disadvantages as well. For one, because they are energy-based, they must receive a constant supply of power or they are useless. Energy shields also tend to be limited in the types of attack they can absorb, so they cannot protect against all conceivable forms of attack the way armor can. Finally, energy shielding is not terribly heavy, but it is bulky: nothing smaller than a spaceship or a large ground vehicle can carry them.
All forms of energy shielding operate on the same basic principle: power is supplied to an emitter that projects a field around the object it is intended to protect. This can be anything from a simple magnetic field to a space-time distortion field. When attacks are directed against the shield, energy is drawn from the shield to absorb or deflect the attack, and subsequently replaced by whatever is supplying power to the shields.
Although it is possible to provide constant power to an energy shield from a generator, the results are generally less than optimal. A power drain on the shields puts strain on the generator, and can cause failure, plus the rate at which a generator can provide power to a shield is usually much lower than the drain rate of the shield. Therefore, it is far more common for energy shields to be powered by a capacitor, which in turn is charged by the generator. This protects the generator, and allows the field emitter to recharge the shield almost instantly. While this makes the energy shield much stronger against attacks, it also means that once the capacitor is drained, the shield will fail.