"Ethereal shield" skill gem

"Ethereal shield" gem, which works like shield, but it's a magic skill.
It works for a certain period of time, partially absorbing damage, and accumulating part of the damage from each hit. When the duration expires, a character takes accumulated damage.
Example :
Shield duration is 5 sec.
During this time, character takes 3 hits with 100 HP damage.
30% of this damage was absorbed by shield, so character has taken 70 HP damage from each hit.
But when duration is over - character takes 90 HP damage, which was absorbed by shield.
Something like this.
Damage can be reduced by shield for a small percentage, in addition.
This skill can be used with int shields, or without...
It can be a talisman which automatically start blocking and absorbing damage for period of time, when character takes a first hit.