Sonic boom in soft materials: The elastic Cerenkov effect

We report an experimental evidence of an elastic sonic boom in soft materials. Our approach is based on the ultrasonic remote generation, inside soft media, of a supersonic moving source radiating shear waves in a Mach cone. In analogy with the Cerenkov electromagnetic radiation emitted by a beam of charged particles moving at a speed greater than the speed of light, an intense shear wave is radiated in soft materials. Such Mach waves are sensitive to medium elasticity inhomogeneities and are of great interest for ultrasound-based medical imaging applications. (C) 2004 American Institute of Physics.