A new method for creating complex sound fields in three dimensions to manipulate objects in liquids and air without touching them - acoustic holograms - is reported in a paper published in this week’s Nature.
The study describes a fast and cheap approach that utilizes a 3D-printed plastic plate placed in front of an ultrasound speaker to create sound fields that are 100 times more complex than those produced by current techniques, and may help improve medical imaging and drive new applications of ultrasound.
Sound, and ultrasound in particular, can be used to manipulate objects in liquid and air without physically contacting the objects. However, current approaches typically require arrays of speaker-like devices called transducers (which convert electrical signal into sound) that need to be carefully connected and controlled to shape the desired sound field in 3D, and are limited in the size and complexity of the field they can produce.
Peer Fischer and colleagues use a 3D printer to create a plastic plate - an acoustic hologram - that, when placed in front of a single transducer, alters the sound waves to create the desired sound field. They use the system to force microparticles suspended in water to converge into a ‘dove of peace’-like image. They also show the system can be used to move objects along a specific path in liquid, and to suspend drops of liquid in air. The authors suggest that their acoustic holograms enable the rapid fabrication of complex sound fields that are appropriate for super-resolution imaging, selective heating, and personalized medicine.