Polarization cloak

From Memory Alpha, the free Star Trek reference.

A polarization cloak is a sophisticated cloaking device used by Ramuran tracers to hide themselves and their ships. Tracer ships can fire weapons through the cloak, while remaining untargetable themselves. The personal version of a polarization cloak can be disrupted by a magneton sweep.

In 2374, the former tracer Kellin modified the USS Voyager sensors to penetrate the Ramuran polarization cloaks, albeit only for a brief time. (VOY: "Unforgettable")