Make your own sonic tractor beam

Ever wanted to move an object with sound? Now you can.

After building the first single-sided acoustic tractor beam that can trap and pull an object using sound waves, Asier Marzo has now created a version that can be made using a 3-D printer. In addition to publishing the paper in Applied Physics Letters, Marzo has released a step-by-step YouTube video to help you get started.

We spoke to Marzo about his work.

ResearchGate: Can you tell us a little about the single-sided acoustic tractor beam you developed last year? How does it work?

Asier Marzo: Tractor Beams are waves that can attract objects towards the source. Scientists managed to create them using lasers, but we used sound to generate a functional tractor beam. Sound can move heavier objects than lasers and can operate in air or water without damaging the trapped objects.

We generated acoustic holograms that surround the trapped particles from all directions. Three types of holograms were proven to be the most effective; those that were shaped as tweezers, tornadoes, or bottles. To generate the holograms we used dozens of tiny speakers all emitting with the same amplitude and frequency but with different phases, creating three-dimensional interference patterns.



RG: What kind of uses does it have?

Marzo: There was the purely experimental objective of proving that acoustic beams can generate pulling forces. More practically, using sound opened up lots of applications in contactless processing. For instance, samples of blood can be levitated for optical inspection without any occlusion, chemical compounds can be merged without containers that contaminate them, or kidney stones could be moved from the outside of the body without any incisions.



RG: What challenges did you encounter in making it 3-D printable?

Marzo: Getting a design that could be printed with a common 3-D printer was a challenge because some of the holes are less than two millimeters in diameter. The printer can certainly create narrower conduits, but they tend to get clogged.

Apart from the 3-D printing itself, getting cheap and readily available electronics was also challenging. We tested several possibilities before arriving at the current ones.

RG: Does the 3-D printable version differ much from the original?

Marzo: The original version is more versatile in the type of traps it can create and the fact that it can refocus the trap electronically at any point. That is, the original version can rotate and move the particles in any direction whereas the 3D-printable version can only move them up and down. We think this trade-off could be beneficial for some applications: the 3D-printable version only moves the particle up and down, however it is also cheaper and less complex.

A portable Tractor Beam levitating a 3mm diameter expanded polysterine sphere. Credit: Asier Marzo.
A portable Tractor Beam levitating a 3mm diameter expanded polysterine sphere. Credit: Asier Marzo.

RG: What does someone need to build it? Can anyone do it?

Marzo: We have released instructions that show you how to build your own acoustic tractor beam step by step with components that you can buy on the internet for less than £70. The builder would need some basic skills, like soldering, but it is a nice way to get started with electronics.

In fact, a future project is to create a kit with all the necessary parts and then show school students how to build a tractor beams and what sort of experiments can be done with them.

RG: Do you have any tips for building it?

Marzo: In the YouTube video there are some optional steps that show you how to test the signals: when they are generated, when they are amplified and when they are outputted by the transducers. It may be tempting to skip these steps, but they are useful in checking that everything is working correctly. Tinning the tips of the wires will facilitate putting several of them in the same connector.

More important, do not get frustrated, we will do our best to answer your questions.

RG: What’s next for you?

Marzo: We would like to continue this trend of making our research Open Access and releasing step-by-step videos of how to reproduce it. We think there is great value in making science accessible so that everyone can take part in it.