Sonic repulsion field was a type of defensive technology used by the Global Defense Initiative. It appeared as a campaign-only defense in Command & Conquer 3: Tiberium Wars and a support power in its expansion, Kane's Wrath.
An application of harmonic resonance technology, sonic repulsion fields were sonic barriers projected from multiple stationary hubs. Originally used to contain Tiberium fields in Blue Zone cities such as London and Munich. They were later repurposed to protect vital military structures from enemy sabotage.
In Tiberium Wars, sonic repulsion fields appear in the Scrin missions London and Munich. They are used by GDI to contain Tiberium fields, and need to be destroyed or shut down to allow Tiberium to spread in the city. They are simply named "Wall Hub" in the game.
In Kane's Wrath, sonic repulsion field is a GDI support power and the counterpart to Nod's laser fencing. When used, the power deploys a sonic repulsion field around the selected GDI structure. Structures protected by sonic repulsion fields cannot be captured by engineers or demolished by GDI and Nod commandos, though they also cannot be repaired by friendly engineers. Protected structures take halved damage from all types of weapons.
The sonic repulsion field will be destroyed if its parent structure's health drops below 33%. It cannot be used on GDI power plants and support structures other than the ion cannon control. It also cannot be used on the structures of other factions.
A sonic repulsion field and several sonic emitters in Munich