DUPLET or "Nozh" reactive armor image - Tank Lovers Group

T-84 is equipped with a special and unique multi-layered explosive reactive armor called DUPLET or NOZH "knife" which defeats all known tandem-HEAT warheads and APFSDS penetrators. It has two to three layers of ERA modules (3 layers on the turret front/hull sides and 2 layers on the glacis/turret roof).

It works different from normal ERA by using innovative techniques of defeating warheads:

Each module is filled with special shaped metal elements. When an APFSDS penetrator (or HEAT round) hits the ERA module, it initiates the elements inside the Duplet module; each element is forming a directed stream of fragments which cut the penetrator and thereby break the core into separate fragments (like a knife cutting the penetrator core into pieces), therefore damaging its integrity and destroying it.

Even triple-charge HEAT rounds (which have 3 separate stages of shaped charge warheads) would have difficulty penetrating this special design of ERA.

Just watch the video it explains everythign much simpler