Thunderous Reverberation

You brandish your shield and imbue it with the makings of a powerful arcane echo chamber. Until the start of your next turn, you gain a +2 bonus to your AC, including against the triggering attack. If the triggering attack fails, the attacker must make a Constitution saving throw, taking 2d10 Thunder damage on a failed save, half as much on a successful one.

At Higher Levels. 

When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d10 for each slot level above 2nd.