Just a guess, I would guess the original shield in the old Rikti Crash Site zone was probably built into the zone.
There are a couple of FXs for the shield, but I don't know how they work and they're not used in any of the demos I have.
ENEMYFX/Rikti/MotherShipShield/MotherShipShield.fx
ENEMYFX/Rikti/MotherShipShield/MotherShipShieldDeact.fx
ENEMYFX/Rikti/MotherShipShield/Repulse_Hit.fx
FX in demos