Shield generator
A shield generator, deflector generator, deflector shield generator, or shield emitter, was the physical component of starships, space stations, and other installations, utilized for the generation of protective energy screens with which to defend against outside attacks. In combat situations, it was common for a vessel to target weapons fire at an adversary's shield generators, in an attempt to disable or weaken their shield strength. (; ; )

Technical data
The Federation utilized mercassium, a synthetic composite, in the constructions of their shield generators, a technology they did not share. ()

If shield strength were to be lowered to a dangerous level, shield emitters could be brought up to full power by taking the shields offline and recharging the emitters. However, as this tactic would leave the ship vulnerable for the duration of the recharge cycle, it was considered extremely dangerous, and was rarely used. ()

Overview
In 2154, Degra was able to knock out the shield generators of a Xindi-Reptilian warship, allowing the crew of  to target the warship's weapons. Degra subsequently destroyed the warship, to prevent its crew from reporting the fact that Degra had entered into an alliance with the Enterprise crew. ()

That same year, Commander Shran supplied the Enterprise crew with the coordinates of the shield generator of what appeared to be an Andorian battle cruiser which was attacking Enterprise. However, upon firing weapons at the coordinates, it was discovered that the attacking vessel's shields were still at maximum power. It was later determined that the vessel was not, in fact, Andorian, but was rather a Romulan vessel disguised as an Andorian ship. ()

Later that year, in an attempt to retrieve Ambassador Soval, who had been abducted by Shran, Lieutenant Malcolm Reed, Enterprises tactical officer, fired upon the shield generator of Shran's vessel, in an attempt to use the transporter to retrieve Soval. ()

In 2367, after an encounter with a Borg cube, the crew of the  experienced difficulties in keeping the auxiliary aft shield generators online, although Commander Shelby estimated that they could be back to full operating capacity within three hours. ()

Later that year, while engaged in combat with a Cardassian vessel, Captain Picard ordered Lieutenant Worf, the Enterprises tactical officer, to concentrate weapons fire on the Cardassians' engines and shields. The tactic was successful, with the Enterprise scoring a direct hit causing "moderate damage to their aft shield generators", with continued phaser fire scoring multiple hits, causing "power failure in forward shields", forcing the Cardassian ship to stand down. ()

In 2368, Enterprise engineering teams installed five new shield generators at the Human colony on Moab IV, in order to fortify the structure's structural integrity so that it could withstand the gravitational forces of a stellar core fragment passing near the planet. ()

During the Cardassian occupation of Bajor, Bajoran Resistance fighters would often take small ships close to Cardassian freighters, and overload their shield generators with directed phaser fire. In 2369, Major Kira Nerys, first officer of Deep Space 9, suggested using the same tactic with a runabout, in order to rescue Doctor Bashir, whose body had been taken over by the Kobliad criminal Rao Vantika, aboard the Norkova. The plan was overruled by Commander Sisko, however, as the Norkova was hauling a shipment of deuridium, and the risk of a hull breach spreading the substance throughout the Bajoran system was too high. ()

The same year, Miles O'Brien, Deep Space 9's chief of operations, ordered the computer to restart all shield generator subsystems and received a 98.3% efficiency report. With this task, O'Brien tried to show Commander Sisko the "strange behavior" of the computer voice. ()

In 2370, Captain Picard, while posing as a member of Arctus Baran's mercenary group, disabled the shields of a Federation outpost on Calder II by targeting the outpost's shield generator with a phase-resonant pulse configured to a precise frequency. This allowed the group to beam up a series of archaeological artifacts without destroying the outpost. ()

The same year, in an alternate quantum reality, a Cardassian attack on the Enterprise caused an overload in the ship's shield generators. This resulted in an inability of the crew to raise the shields, and major damage to the Enterprise. ()

In 2371 in an alternate timeline, a Romulan Warbird attacked Deep Space 9, starting by destroying the station's shield generators, in order to hinder the crew's ability to defend the station. Although the attack ultimately resulted in the destruction of the station, this timeline was negated by Chief O'Brien, who traveled back in time and managed to warn the crew of the Romulans' presence, thereby averting the attack. ()

Later that year, newly promoted Captain Sisko ordered a complete overhaul of the 's deflector shield generators, in preparation of an anticipated Tzenkethi attack. ()

In 2372, during the Klingon attack on Deep Space 9, Chancellor Gowron ordered the station's shield generators targeted, resulting in the disabling of two of them. This allowed Klingon boarding parties to beam aboard the station. ()

In 2373, when the Defiant became trapped within an energy barrier surrounding a planet in the Gamma Quadrant, the crew encountered their own descendants, who claimed that, upon attempting to leave, the Defiant would be thrown back in time and crash on the planet. Jadzia Dax, collaborating with one of the colonists, Yedrin Dax, formulated a plan whereby the Defiant could safely leave the energy barrier, which included synchronizing the ship's shield generators. ()

In 2374, a sneak attack by the Jem'Hadar on the Defiant resulted in the disabling of the ship's shield generators and impulse engines. This allowed Jem'Hadar soldiers to board and take over the ship. ()

In 2375, One, a Borg drone enhanced with 29th century technology, was able to access the 's shield generators, reconfiguring the shields to disrupt a tractor beam with which a Borg sphere had locked onto Voyager. ()

Later that year, Lieutenant Commander Worf conceived of a means by which Captain Picard could beam aboard the Son'a collector while its shields were raised, by maneuvering their ship within one hundred meters and transporting him between the collector's shield generators. ()

The same year, the crew of Deep Space 9 was supplied with a new  ship, whose shield generators had been completely reconfigured in order to negate the advantage of the Breen's energy-dampening weapons. ()

Later that year, the crew of Voyager utilized spatial charges to destroy the primary shield generator aboard a Borg sphere, as part of "Operation Fort Knox," their attempt to steal a Borg transwarp coil. ()

In 2376, Captain Janeway suggested to Commander Chakotay that he perform a diagnostic of Voyagers shield generators, which was considered way overdue. Later, Lieutenant B'Elanna Torres scored a direct hit to the aft shield generators of Penk's starship. ()

That same year, Captain Janeway ordered the shield generators of a damaged Borg cube targeted, in an attempt to rescue members of her crew who were being held captive. The effort proved futile, however, as the cube's generators were too deep inside the vessel. Janeway subsequently ordered Harry Kim, who was also on the cube, to attempt to deactivate the generator, but he was discovered by an adolescent drone before he could complete his mission. ()

In 2377, Irina, a Terrellian pilot, interfaced a phase inverter designed to cause a system overload with her ship's shield generator. This severely injured her copilot, giving Irina an excuse to withdraw from the Antarian Trans-stellar Rally, which she planned to bomb in an attempt to sabotage a recently signed peace treaty. ()

In the late-24th century, Captain Janeway and the Voyager crew developed ablative generators, extremely advanced shield emitters capable of forming a protective layer of near-impenetrable armor around the hull. Along with transphasic torpedoes, this technology was specifically designed to defend against the Borg. In 2404, Janeway, at this point an admiral, traveled back in time to 2378 on an illegal mission to change history, and delivered this technology to the Voyager crew. Using the generators, the crew was able to successfully penetrate the Borg defenses protecting a transwarp hub, and enter a conduit bound for the Alpha Quadrant. ()

Background information 
The phrase "shields up," which saw widespread use in Star Trek, probably had its origin in classical warfare, when infantry would raise their s 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.''

de:Schildgenerator
Energy technology
Shield technology