Multi-adaptive shield

From Memory Alpha, the free Star Trek reference.

Multi-adaptive shielding was developed by Erin and Magnus Hansen for use on the USS Raven (NAR-32450) during their three year mission studying the Borg. It is a form of shielding designed to hide a vessel from Borg sensors.

In 2375, the technology was incorporated into the systems of the Delta Flyer when the shuttle was used in a mission to rescue Seven of Nine after her capture by the Borg. However, as the Borg had assimilated Magnus Hansen, they were able to adapt and still detect the Delta Flyer. However, upon engagement with the Borg, the Delta Flyer was able to keep changing the shielding before the Borg could adapt, until the Borg managed to grab them with a blind tractor beam shot. (VOY: "Dark Frontier")