This shield type is a new type of Protoss shield which will be used in Starcraft 2.Immortals (new Protoss Dragoons) have this type of shield which is only activated at very heavy gunfire, for instance;  against Tank attack which allows Immortals attacking against the sieged Tanks  without any loss (number is also important).Only this new ability can change the whole game strategy, especially at P vs T games.But remember that this shield can only be activated at high rates of fire which means you can kill enemy Immortals with low attack capacity units like Terran  Marines and Reapers.So here the army balance must be correctly and carefully designed to win the game.