In science fiction, tractor beams are used by a spacecraft to tow or repel another object. They are typically depicted as a beam of light that has the power to apply a gravitational force specifically on the intended target, but the real-life tractor beams studied in the lab have somewhat different properties. A group of researchers led by Gabriel Spalding of Illinois Wesleyan University and Michael MacDonald from the University of Dundee, Scotland have announced the post powerful acoustic tractor beam so far. Details of the device have been published in the journal Physical Review Letters.
In the 1970s, physicist Arthur Ashkin discovered that light was not only able to push matter along, but had the ability to pull microscopic bits of neutral matter to the part of the wave with the highest intensity, in what Ashkin described as “negative radiation pressure,” according to APS. This is the same principle that optical tweezers are based on. Building off of that same idea, researchers have now crafted a tractor beam capable of manipulating objects that are up to 1 cm in size with a force of a few millinewtons of force. Though this might seem small, it is far and away the strongest tractor beam yet. One centimeter is about six orders of magnitude larger than objects previously controlled by these beams.
Aside from the size of the object trying to be pulled, there are other limitations. The shape of the object also comes into play, as the beam has a difficult time with objects with a wide, flat side. The experiment involved pulling in triangular objects that had the projection at the back side. Additionally, because the beam works on sound which can’t be carried in the vacuum of space, this technology won’t be added onto any spacecraft.
There are plenty of potential medical uses for the technology, however. It could be used to manipulate individual cells, separating diseased cells from healthy ones. It could also be used to perform non-invasive surgery by focusing ultrasound beams to break up things like gallstones, cysts, or tumors.
The progress made toward a functional tractor beam is just one of the ways that Spalding is making our sci-fi dreams come true. His previous research involves a prototype of a functional sonic screwdriver like the one belonging to The Doctor and he has also worked on holographic arrays capable of interacting with real objects, not unlike Star Trek’s holodeck.
[Hat tip: Charles Q. Choi, Popular Mechanics]
[Main image details: Figure 1: (a) Nonconservative pushing force exerted on an object by a plane wave as a result of strong backscattering. (b) Decreasing of the pushing force due to an enhanced forward scattering in a nonparaxial beam. (c) The authors used a target designed to maximize the forward scattering of acoustic radiation, leading to a pulling nonconservative force towards the source: an acoustic tractor beam. Credit: APS/Alan Stonebraker]