Seen any Star Wars films?Then you know all about牵引光束— a sort of gadgetry that enables a spacecraft to grab a smaller ship and drag it along as if it were lashed with a cable,所有这些都是通过使用某种不可见的力量，而编剧实际上并不费心去解释。
Well,多亏了英国布里斯托尔大学的研究人员，现在你可以建立你自己的装置，创造出一种新颖的牵引光束——一种利用声波从一个方向捕获的光束，levitate and pull objects.All you need is access to a3-D printer,这样你就可以根据他们在网上发布的文件打印零件了，and a little time for assembly.他们甚至提供了一个关于如何构建设备的视频：
There's a catch,of course.不要计划用这种牵引光束牵引任何航天器，since it's only capable of moving really small objects — ones the size of beads or small insects.
University of Bristol research assistant Asier Marzo,the lead author of anarticleon the project recently published in the journal Applied Physics Letters,says that the acoustic tractor beam relies on the fact that sound is a mechanical wave that carries momentum.
"For instance,if you put rice on a table with the radio playing very loud,the rice will move;or if you are in a concert,you can feel your chest vibrating," he says via email."If we use ultrasound,we can employ more powerful waves without them being painful for the human ears."
He explains that when a pair of sound-emitting devices create a standing wave — that is,sequences of low-amplitude nodes and high-amplitude antinodes — it's possible for solid particles to get trapped in the nodes.这是科学家几十年来一直能做到的一个诀窍。But Marzo and colleagues have taken that idea to another level.
"Our systems have lots of tiny speakers all emitting with the same amplitude and frequency," he says."We carefully yaboengineer their phases to make them create interference patterns with the shapes that we want." Basically,what they're creating is anacoustic hologram—a three-dimensional shape made from sound,它可以把一个固体物体从响亮的区域推到较安静的区域。
Marzo和其他研究人员,与一家名为“超触觉”的公司合作，用这个概念创造了第一个声学牵引光束，他们在书中描述的this 2015 articlein the journal Nature.
"This was extremely cool,but was complex and expensive and so only we could run the experiments," ultrasonics professorBruce Drinkwater写电子邮件。"So,this got us thinking about,could we strip this device down to its essentials and design a tractor beam that could be made for under £100?而且，from the paper,你可以看到我们实现了这个目标。”这个数字大约是122美元。
Marzo also is excited about the idea of giving away the concept,so that other people can experiment with it."I guess I will regret this when I am starving without work," he says.“但是我认为让科学变得容易是很有价值的，这样每个人都可以参与其中。”
While you might imagine a giant version of the device someday towing ships or trapping enemy aircraft,Marzo says the acoustic tractor beam's real potential is moving far tinier stuff.这样的装置，例如，might someday be used to manipulate particles inside the human body — to relieve pain from a kidney stone,for instance,or to move a capsule containing a drug to the right spot in the body.
“这是可能的，since sound travels even better through water or our bodies than through air," Marzo says.
声学牵引梁可能具有制造应用。“我对非接触式生产线的想法非常兴奋，”德林沃特说。"Here I imagine object (probably small) being assembled without contact.This could have applications in pharmaceuticals or electronics,where it's really important to avoid contamination."
And Marzo also imagines an even more dazzling possibility.Since future versions of the technology might someday enable the individual levitation of thousands of particles at a time,it could lead to the development of 3-D digital display screens "in which each pixel is made of a levitating particle," he says.