A metaphasic shield is a modified defensive shield that allows a starship to operate in close proximity to a star for an extended period of time. In series, the system was developed by a Ferengi scientist, Dr. Reyga, and tested by flying a shuttlecraft into a star using a live pilot. When the system appeared to fail (appearing to kill the pilot), he seemed to commit suicide. It was later revealed that the system worked just fine, the failure was staged, and Reyga was murdered in order to steal the design.
What actually occurs is unclear, but the name suggests that a metaphasic shield differs from the standard frequency pattern of Star Trek shields. Normally, the shield oscillates at a specific rate, creating peaks and troughs in the protection afforded by the shield.
The hypothesis for metaphasic shields is that there are multiple waves in the shield, with their peaks and troughs offset, leaving no low points in the defense. Such a system would function similar to how 3-Phase AC power functions. In the case of 3-Phase power, three AC signals are run down the same power grid, each one 120° out of phase with the others. How many signals would make up a metaphasic shield system is not known.
The downside of a metaphasic shield is that weapons like phasers could not be synchronized to "fire through the gaps", so a ship using metaphasic shields could not fire weapons. However, given the multiple signals and sufficient computer control software, one of the multiple signals could be left on at the moment of firing while the others are made to "blink off", allowing a ship to fire weapons and maintain the advantages of the system. Since an enemy could not predict when these moments of vulnerability would exist, it would be almost impossible for an enemy to exploit those moments of opportunity. Combat functionality was not a consideration in the original design, however.
Metaphasic shielding remains experimental. The original inventor was assassinated, and there is no indication that significant effort is being put into further development. It has the distinction of being a technology of the week that was remembered and used in a subsequent episode.
- TNG "Suspicions": The Enterprise participates in testing of the newly invented system.
- TNG "Descent" (Part 2): While temporarily commanding the Enterprise, Dr. Crusher recalled that information about Dr. Reyga's process was stored in the ship's computer. Technicians were able to use the process to adapt the ship's shields, allowing the Enterprise to hide in the local star's corona to evade a rogue Borg ship.
- VOY "Resistance": A prison facility on an alien planet was protected by metaphasic shields. The crew of the Voyager were able to circumvent the shield with "radion beams".