Manipulation of orbital angular momentum for acoustic waves

Free and precise control over the wavefront of acoustic waves represents a fundamental problem in acoustics with wide applications in many important scenarios ranging from ultrasound imaging/treatment to stereo-sound reproduction. By utilizing the recently-emerged concept of acoustic metamaterials with unusual properties, it would become possible to break through the limitations in the functions provided by naturally achievable materials, allowing for new freedom of manipulating the acoustic wavefronts. In this talk, I will briefly review some recent advances obtained in our group on metamaterial-based manipulation on acoustic wavefront which has become a new frontier of science. The design and realization of a series of metamaterial devices with novel functionalities of steering acoustic wavefronts will be demonstrated, including acoustic rotators that can rotate the incident wavefront by a particular angle, acoustic metasurfaces capable of yielding arbitrary acoustic beams, and acoustic gradient-index systems bending, trapping and absorbing the acoustic waves by mimicking virtual potential wells, etc. Finally I will also discuss the possibility to bridge the gap between the fundamental metamaterial researches and the real world applications by revisiting and redesigning some classical structures that had been extensively applied widely in practice.