Devices operating at GHz frequencies can be based on ferroelectric kink-domains moving at supersonic speed. The kinks are located inside ferroelastic twin boundaries and are extremely mobile. Computer simulation shows that strong forcing generates velocities well above the speed of sound. Kinks are accelerated from v = 0 continuously with Döring masses in the order of skyrmion masses under constant strain rates. Moving kinks emit phonons at all velocities, and the emission cones coincide with the Mach cones at supersonic speed. Kinks form avalanches with the emission of secondary kinks via a mother-daughter nucleation mechanism and may be observable in acoustic emission experiments. Supersonic kinks define a new type of material; while mobile domains are the key for ferroelastic and ferroelectric device applications at low frequencies, it is expected that fast kink movements replace such domain movements for materials applications at high frequencies.The authors appreciate the support of the Natural Science Foundation of China (51320105014, 51621063, and 51231008) and 111 project (B06025). E.K.H.S. is also grateful to the Engineering and Physical Sciences Research Council (EP/K009702/1) and the Leverhulme Foundation (RPG-2012-564) for support
