They're already in the main rulebook, on the Armour and Forcefields page of the Armoury.
It has a 50% to activate when hit, increased by the damage caused (e.g. a hit doing 13 damage would have a 50+13 = 63% chance to activate).
If it fails, you take the hit as normal. If it passes, the hit is negated and scatters the character D10 yards (stopping 1 yard short if it would put them into a solid object or a hazardous environment).