Professor Bruce Drinkwater (University of Bristol) 

Abstract: Acoustic (or ultrasonic) beams are used widely in engineering, science and medicine. Beams are integral to medical and non-destructive testing imaging systems where the focal spot size determines resolution. However, these beams can become distorted, e.g., when propagating through polycrystalline metals or across the skull into the brain. Beams are also key to techniques that use the acoustic radiation force to transfer momentum to manipulate objects, i.e., acoustical tweezers or tractor beams. Here the beams must be carefully shaped to create the correct local force field. This talk first describes the properties of acoustic beams, how they are distorted and how this can be corrected. The various experimental techniques for the creation of beams are then explored. Acoustic holograms and metasurfaces lead to particularly exquisite control of beam shape yet are currently static. Arrays of individual emitters can provide dynamic beam control but are currently lower in resolution. In this talk these approaches are explained and example devices introduced. Throughout the talk the various applications of acoustic beams are highlighted including both imaging and biomedical manipulation. The latter has enabled the creation of artificial tissues such as muscle.