An application of the Harmonic Resonance technology, sonic repulsor fields are specialized barriers developed by GDI. Continuous sonic waves are emitted from posts, creating a stationary repulsion field. Placed in urban Blue Zones, these sonic walls were used to stop Tiberium from spreading into cities such as London or Munich. Fields that were destroyed in the Third Tiberium War by the Scrin caused London and Munich to be overrun by Tiberium.
GDI has adopted the technology for military purposes, allowing the creation of defensive fencings around key structures (such as the Barracks or Construction yards), preventing assimilator/saboteur infiltration or sabotage, as well as keeping Commandos from destroying the structures with their explosives. The fields also increase the armor of the structures (i.e. Nuclear missiles and Rift Generators can no longer destroy a Tech Center in one hit). The shields, however, can be taken down once the hub is destroyed, or units can enter or destroy areas or buildings within the field by using aircraft.