Non-explosive reactive armor

Non-explosive reactive armor (NxRA), also known as non-energetic reactive armor (NERA), is a type of vehicle armor used by modern main battle tanks and heavy infantry fighting vehicles. NERA advantages over the explosive reactive armor (ERA) are that they are inexpensive, completely passive and thus easy to integrate on armored vehicles.
Operating mechanism.
NERA operating principle relies on the speed deviation of a shock wave propagating in different materials.
When a projectile such as a shaped-charge jet hits the front metal plate, this generates a shock wave that will travel at high speed inside the metallic layer and then encounters a confined non-metallic material with elastic properties. Due to the lower propagation velocity of the non-metallic material, the shock wave diffracts and causes a brutal acceleration of the metallic back plate whose deformation is hard enough to destabilize and shear the shaped-charge jet and consume it.
Layout.
NERA typically consists of three-layer composite sandwich structure sloped between 50° and 60°. In order to guarantee an excellent multi-hit capability against threats, the sandwiches are overlapped in a spaced configuration forming an array.
Materials.
The two metallic plates in the NERA sandwich are made of steels of different hardness and thickness. Rubber was firstly used as inner non-metallic material but nylon, polycarbonate, glass, elastomer and Glycidyl azide polymer (GAP) are also used.