Active Acoustic Metasurface: Complete Elimination of Grating Lobes for High-Quality Ultrasound Focusing and Controllable Steering

Focused ultrasound is important in clinical medical applications, to destroy tumor cells or treat a variety of neurological diseases, for example. The focused ultrasound field projected by a transducer array includes traditionally unavoidable side lobes, however, which may cause harmful heating in nontargeted regions. This work implements an active acoustic metasurface, comprising 16\ifmmode\times\else\texttimes\fi{}16 elements of subwavelength thickness, which can completely eliminate such side lobes. Experiments convincingly demonstrate that this active metasurface with programmable phase and amplitude distributions offers high performance in side-lobe-proof, steerable ultrasound focusing.