Harmonic resonance, now commonly called sonic technology, is a science developed by the Global Defense Initiative. The technology allows for the ability to generate harmonic resonance waves that can literally "shake its target to pieces".
Second Tiberium War
The harmonic resonance technology was developed in the Second Tiberium War in Hammerfest, Norway. The technology was based on special sonic crystals, which, under sufficient power, were capable generating sonic waves which could be amplified and directed as an extraordinarily effective weapon. This technology fell into the hands of the Brotherhood of Nod when they attacked and captured Hammerfest, but was recaptured by GDI forces under the command of Michael McNeil. The end result was the Disruptor. When General Soloman ordered the immediate destruction of the Banshee raiding party bases, the Disruptor was able to prove its worth by destroying those bases during that operation.
After the Firestorm Crisis, the Disruptor was phased out of military service. However, GDI engineers found another use for the harmonic resonance technology. They discovered the resonance frequency of Tiberium, and developed sonic resonators capable of breaking down Tiberium crystals. With the threat of Nod gone, GDI focused most of its efforts into Tiberium abatement.
Third Tiberium War
At the advent of the Third Tiberium War, the original sonic system had been fully developed into a Tiberium containment technology, examples being the Sonic emitter and Sonic repulsor fields. The emitters were first tested and deployed in Germany, where they were able to decontaminate a Yellow Zone and change its classification into a Blue Zone. Almost by accident, they proved themselves to be an excellent defence system against the Scrin invasion of Earth when the emitters in Munich were used against them.
A mobile variant of the sonic abatement system was the Shatterer, which uses a modified version of the aforementioned turret to propel concentrated waves of sonic energy deep into Tiberium fields, operating safely from a HoverTech-derived mobile platform. After the siege of Washington, D.C., GDI High Command redesigned the Shatterer into a combat vehicle.
Zone Operations Command, a branch of the GDI military that specializes in operating in areas of severe Tiberium infestation, makes extensive use of sonic weapons. Their Zone Raiders and modified Orca Mk. III utilized Sonic grenade launchers. ZOCOM also has its own more powerful version of the Shatterer called the Zone Shatterer, which can overload its sonic cannon for an extra powerful sonic blast. GDI has also developed a militarized version of sonic repulsor fields to protect buildings from enemy sabotage.
The same initiative that created ZOCOM also developed the Mammoth Armored Reclamation Vehicle, a massive anti-Tiberium tank armed with three powerful sonic cannons, capable of causing massive splash damage to the target area.
Even though the construction of the Tiberium Control Network has made sonic abatement technology mostly obsolete, sonic emitters are still used to contain a few underground Tiberium deposits. The GDI also continued to explore its military use, developing the Shockwave, a vehicle specifically designed to demolish reinforced structures; as well as the Sonic artillery, which is capable of disabling large groups of enemy.