 This has enabled single sided levitation as well as manipulation of large numbers of particles simultaneously.Another approach which is growing in popularity is the use of 3D-printed components to apply the phase delays necessary for levitation, creating a similar effect to the PATs but with the advantage that they can have a higher spatial resolution than the phased array, allowing more complex fields to be formed.These are sometimes referred to as Acoustic Holograms, Metasurfaces, Delay lines or Metamaterials.