A review on single-beam acoustical tweezers: From tractor beam to selective trapping

Single-beam acoustical tweezers show promising prospects in various fields such as biomedical engineering, bubble-based controlled drug delivery, and acoustic material printing for microparticle manipulation and assembly. Acoustic vortices (including cylindrical and spherical types) not only carry pseudo-linear momentum enabling pulling/selective trapping and orbital rotation of particles (at off-axis incidence), but also possess pseudo-angular momentum that induces spinning rotation, thereby substantially enriching the degrees of freedom in acoustical manipulation. This review aims at providing a comprehensive literature on the rapidly developing tool of single-beam acoustical tweezers from the point of view of both theoretical development and representative experimental demonstrations. Furthermore, we discuss the perspectives and ongoing challenges for single-beam acoustical tweezers for applications in several potential fields.