startrekfreedom.com/wiki/index.php/De…The basic principle of regenerative shielding was to quickly analyze an attacking weapon's frequency and then modulate shield freqency to increase damage mitigation without depleting shield energy.
Regenerative shields were used on Borg vessels and Borg drones. When in combat, Borg drones could be killed by phasers but only for the first several shots. The phaser became ineffective if used at the same setting after multiple shots. The phaser's effectiveness could be extended though by adding a frequency modulation chip. (TNG: "Q Who", "The Best of Both Worlds", "The Best of Both Worlds, Part II") However, Borg drone shields appeared to be less resilient to projectile weapons; when the Borg attempted to assimilate the USS Enterprise-E in 2063, Jean-Luc Picard lured two drones into the holodeck and used a holographic Thompson submachine gun to kill the two drones. (Star Trek: First Contact)
Starships from other races equipped with this type of shielding included sensors integrated within the shield systems' own energy that alters the frequency to better protect the ship.
The battle systems of Starfleet's Prometheus-class starships included regenerative shielding, ablative armor, and multi-vector assault mode. (VOY: "Message in a Bottle")