Ring of Kinetic Blasts

This steel ring appears to be made of several tiny servos and gears, slowly moving as the ring is worn. Each time the wearer takes a step, the gearwork within the ring slowly cranks up power.
Up to twice a day the ring can be used when working correctly. When the wearer holds their fist out, aiming it at a target, a blast of invisible force lances out toward the target. This is made as a standard attack. The attack is made against the target's flat foot AC (due to speed and invisibility of the attack.) The target sustains 20d10 points of physical (not magical) force damage, reflex save of 20 for half. If the save is failed, the target is knocked back 1d6x10 feet and knocked prone. A second save vs. a fort of 20 must be made or the victim is stunned for 1d4 rounds.
Unfortunately, the ring was cursed. Instead of fully absorbing energy as it should, it can be used repeatedly round after round by eating parts of the wearer. It must be worn on a finger or two and each time it is used, the gears and servos sever the digit and chew up about 1" of the digit in the process. If some way was found to bypass the curse, then the ring can only be used twice a day.