Sonic levitation uses sound waves to push around macroscopic objects or create patterns in resting sand and flowing water. Based on similar fundamental physics used to create optical traps for decades, these tractor beams are true to their name in that they can trap small beads and even insects.
“The most important thing is that it can attract a particle towards the source,” said Marzo. “It’s very easy to push particles, but what’s hard is to pull them towards you. It can levitate small plastics; it can also levitate a fly and small biological samples.”
The simplicity (and affordability) of the passive, static-matter approach comes from the special architecture only viable using 3D printing techniques. It is designed to shape sound waves structurally instead of electronically meaning, as the sound passes through carefully designed elements, the waves are shaped by the internal structure of the 3D printed material.
“We can modulate a simple wave using what’s called a metamaterial, which is basically a piece of matter with lots of tubes of different lengths,” Marzo explained. “The sound passes through these tubes and when it exits the metamaterial, it has the correct phases to create a tractor beam.”
There are three designs of the device, each with trapping profiles suitable for different object sizes relative to the wavelength of the sound used. Designs and plans of how to build the tractor beam are available online, allowing anyone with access to a 3D printer to make one for around £50.