Dispersion field

A dispersion field, or dispersal field, was a type of energy emission which could block sensors and transporters.

In 2152, the Torothans, who suspected the crew of the of collaborating with dissenter Zobral, activated an orbital dispersion field utilizing a series of artificial satellites, in order to prevent the crew from detecting anything on the surface below one hundred kilometers. Although the field covered approximately one half of one of the planet's continents, Lieutenant Reed managed to devise a plan whereby he could get clear readings by disabling three of the satellites. Subcommander T'Pol, however, overruled this plan, believing that such an action would provoke the Torothans into taking aggressive actions against Enterprise. 

In 2369, Lieutenant Commander Geordi La Forge, chief engineer of the USS Enterprise (NCC-1701-D), managed to deduce that a Cardassian vessel had recently been inside the McAllister C-5 Nebula, upon detecting minor hull degradation along the Cardassians' warp nacelles, the distribution pattern of which was indicative of recent exposure to a molecular dispersion field. As the nebula was the nearest location where the Cardassians could have encountered a dispersion field, the crew of the Enterprise realized that the Cardassians were hiding in the nebula, preparing to invade the Federation system of Minos Korva. 

Tau, an interstellar pirate native to the Delta Quadrant, utilized dispersion fields around his installations in order to prevent theft of his acquisitions. Such a field was encountered by the crew of the USS Voyager in 2374, when attempting to retrieve their stolen main computer processor. 

In 2375, the Borg Queen activated a dispersal field in order to prevent a rescue team from Voyager from retrieving Seven of Nine, whom the Queen was holding captive. Seven managed to deactivate the field, but the Queen quickly adapted, raising the field again. On Seven's suggestion, Captain Janeway fired on the Queen's power node with a phaser rifle, disrupting her command interface, negating the field and allowing them to escape. 

A year later, a group of five adolescent drones, the last survivors of the crew of a Borg cube, utilized a dispersal field to mask their approach to the Delta Flyer. This left the crew of the Flyer unaware of the cube's approach until it was in visual range.