Acoustic tractor beam could levitate humans 漂浮在声音之上——行走云端不是梦！

你曾经梦想过在云朵上行走吗？目前，科学家已经成功利用牵引波束实现让物体浮在空中的愿景，那么人类实现“漂浮”离我们还有多远呢？

Researchers at the University of Bristol have crafted a tractor beam that uses acoustic vortices — basically sound tornadoes — to keep small objects aloft, a good step toward potentially levitating humans.

布里斯托大学的研究人员利用声涡旋（基本可以理解为声音旋风）制造出了牵引波束，使小物体可以浮在空中，这可就向实现人体悬浮迈出了很大一步。

"Acoustic researchers had been frustrated by the size limit for years, so it's satisfying to find a way to overcome it," Asier Marzo, a research associate in Bristol's Department of Mechanical Engineering, said in a statement released by the university.

阿瑟尔·马尔佐是布里斯托大学机械工程系的助理研究员，他在布里斯托大学发布的一份声明中说到：“声学研究人员多年来一直无法克服物体尺寸的限制，令人满意的是，我们在这项实验中终于找到了解决这一难题的方法。”

Talk about a flotation device
悬浮设备

Acoustic tractor beams have proven capable of trapping and holding particles in midair, but anything larger than the sound wave used to create the beam and it would spin about in an unstable fashion until it was ultimately ejected from the vortex. Improving acoustic tractor beams, however, was a worthwhile pursuit since they could levitate non-metal objects that magnetic tractor beams couldn't.

经证明，声学牵引波束能够捕获并使粒子保持在半空中，但是如果这些粒子比声波波长大，它们就会以不稳定的方式旋转，直到最终从涡旋中弹出。 然而，为完善声学牵引波束而做的努力是值得的，因为它们可以使非金属物体悬浮在空中，而这是磁性牵引波束做不到的。

What the Bristol researchers did was create multiple vortices that would rapidly fluctuate their spinning directions. These changes in directions create stability for whatever object is floating in the vortices.

布里斯托大学的研究人员创造出了多个涡旋，这些涡旋可以通过快速波动来改变自己的旋转方向，而方向上的改变可以使物体在涡旋中漂浮得更稳。

The reason why an object larger than the sound wave would originally spin out of control was because some of the force from the sound wave would cause a little bit of the spin levitating the object. That extra spin would make it unstable and zip right out of the vortex.

比声波大的物体会被甩出涡旋，原因在于声波的部分力量会使悬浮的物体产生轻微的旋转。 这种额外的旋转会导致物体不稳定，并从涡旋中飞出。

This new tractor beam, with its multiple vortices, changes up the directions of the sound waves, and that in turn creates stability for the object. The result is that the tractor beam is able to keep a polystyrene sphere measuring about 2 centimeters, or more than twice the size of the 40hkHz-pitched wavelengths (audible to bats, not humans), stable and aloft.

这种带有多个旋涡的新型牵引波束可以改变声波的方向，从而使物体更稳定。 牵引波束能够使直径大约2厘米的聚苯乙烯球，或者是两倍于40hkHz波长（蝙蝠可以听到，而人类不可以）的物体稳定在空中。

It's the largest object ever to be kept in the air by a tractor beam, according to the university statement.

布里斯托大学称，这是牵引波束所能悬浮的最大物体了。

For now, let's focus on the practical
实际应用

From a practical standpoint, the researchers see their tractor beam as a way to improve the construction processes for assembling delicate machinery and to assisting in precision medical procedures.

从实际应用的角度来看，研究人员认为，牵引波束可以用于组装精密机械及协助精确医疗操作。

"In the future, with more acoustic power it will be possible to hold even larger objects. This was only thought to be possible using lower pitches," Mihai Caleap, a senior research associate at Bristol, said in the statement.

“在将来，声波能量越大，它所能托举的物体也就越大，但这只能在声音频率较低时实现，”布里斯托大学的助理研究员米哈伊·卡利普说。

So while human levitation may be a ways off, the only way for the science to go from here is up, up, up.

实现人类在空中的“漂浮”已经不是梦想，科学家们正努力让人类离蓝天更近一步。