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3D-Printing a Sonic Tractor Beam

04 January 2017

Tractor beams are devices that can attract one object to another from a distance. For nearly 20 years now, researchers have been working to develop realistic and working versions of the technology, and some have even succeeded at the microscopic level.

Now, researchers have managed to adapt the technology into a handheld version that anyone can use—and even 3-D print at home.

Asier Marzo, a doctoral student at the Public University of Navarre, assisted in the development of the first-ever single-sided acoustic tractor beam, which can trap or pull an object with the use of sound waves from only one direction.

Marzo, who is now a research assistant at the University of Bristol, leads a team that has turned the technology into a version that is printable by just about anybody.

Not only has his team released a fully detailed how-to video to the public, but it has also disclosed the results of the work and it will appear this week as an open-access paper in Applied Physics Letters.

Sonic levitation is not a new concept, and you can find a variety of Youtube videos conveying the use of sound waves to move macroscopic objects or to create patterns in flowing water and resting sand. This technology is different. It is not simple sonic levitation used to push objects around, but rather it involves the pulling and trapping of objects and small beads- even insects- at their foci.

The technology is based on similar physics used to construct optical traps, which has been used for decades. These tractor beams are true to their meaning as they are consistent with pulling and trapping at the foci.

"The most important thing is that it can attract the particle towards the source," said Marzo. "It's very easy to push particles from the source, but what's hard is to pull them toward the source; to attract the particles. When you move the tractor beam, the particle moves, but otherwise the trap is static. It can levitate small plastics; it can also levitate a fly and small biological samples. It's quite handy."

The initial versions of this device that proved the concept to be possible weren’t much larger than the 3-D printable versions the team presents in its work. Though the first technology was much more complex and required expensive electronics.

"Previously we developed a tractor beam, but it was very complicated and pricey because it required a phase array, which is a complex electronic system," added Marzo. "In this paper, we made a simple, static tractor beam that only requires a static piece of matter."

Most of the expense was attributed to the range of active components that electronically shaped sound waves, manipulating where, as well as how, they interfere to create the resulting object trapping environment just above the array.

This new passive, static matter approach comes from the special architecture of the matter, designed to replace the current phase array components and to shape sound waves not electronically, but structurally. The sound can now be generated from a single source, so as it passes through carefully designed elements the waves are shaped by the internal structure of the 3-D printed material – one reason why it is simple and affordable.

"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. The sound passes through these tubes and when it exits the metamaterial, it has the correct phases to create a tractor beam," said Marzo.

The team focused on enhancing the design, with an effect mainly determined by the shape of the tubes, to allow for fabrication with a common 3-D printer, ensuring it could be handled even by at-home users.

"We needed to engineer the tubes very well to allow them to be 3-D printed with a normal 3-D printer. A normal 3-D printer has a lot of limitations," said Marzo. There was primarily a challenge with resolution, requiring a design that would not be compromised by the lack of precision of lower-end 3-D printer nozzles.

With the main obstacle of resolution design overcome, the team developed the remaining tractor beam system using easily accessible components, some of which can be found through suppliers like Arduino. Aside from the use of incredibly accessible components, they also produced an in-depth how-to video for its construction.

"There will be a set of instructions with a list of the needed components and a step-by-step video. The components are very simple, like an Arduino and a motor driver, and everything can be bought on Amazon for less than £50 (about $70)," said Marzo.

Aside from landing you a title as a very impressive 3-D hobbyist, these tractor beams have plenty of practical uses and may potentially become a new tool for studying low-gravity effects on biological samples. As Marzo pointed out, this type of micro-gravity research is already of interest to biologists, encouraging them to find individual application for this new device.

"Recently there have been several papers about what happens if we levitate an embryo, how does it develop? Or what happens if we levitate bacteria?" he said. "For instance, they discovered salmonella is three times more [virulent] when it's levitated. Certain microorganisms react differently to microgravity." This is one example of how biologists are already thinking of uses for this tractor beam technology.

The device has three design options, each capable of trapping profiles suitable for varying object sizes relative to the wavelength of sound used. However, trapping objects larger than half of the wavelength of sound still poses a challenge to Marzo’s team, even for the full lab implementation where the group traps heavier objects and liquids. For practical frequencies, just above what humans can hear, this limits the size of trappable objects to a few millimeters.

As Marzo and his team work to overcome lingering challenges and improve on the device’s capabilities, their developments pave the way for endless uses and adjustments from the maker community. So with that said, the real question is: what could the tractor beam do for you?

Source: AIP Publishing



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