Researchers in the UK have created a tractor beam — the formerly fictional ray that can pick up and carry things without touching them — while no one was looking.
At first glance, seeing the beam work can look a lot like the old science experiment of making a ping pong ball float on a current of air. In a video released by the University of Bristol, particles are seen floating above a grid of speakers, which are microscopically positioned to create sound waves that surround the particle. The person controlling the apparatus can then move the particle any way she or he sees fit.
The really impressive part, however, comes when a beam from above hovers over the particle, moving it with the same precision. However, here's the rub: No air pressure is used. Instead, the scientists used the power of sound.
By sound, we don't mean stuff you can hear. The human ear can hear sounds of certain frequencies (famously, our dogs can hear sounds in other frequencies), but sounds that we can't hear are still sounds, and they still have sound waves. Sound waves are doing work all around you, from ultrasounds (which operate above the upper limit of what we can hear) to elephant calls (which can be many decibels lower than any human can hear).
Every sound has a wave, and every wave moves through space. If focused properly, those waves can actually move particles or groups of particles. In the past, researchers have been able to move particles using sound, as long as they were enclosed from all sides by speakers. However, this is the first time physicists and engineers have been able to exploit this ability with such precision and from only one direction, so that it can be used to move a particle virtually anywhere.
The researchers hope that the technology can be used in the future to move tiny medical devices or medicine within human bodies without the need for surgical cuts or other invasive measures.
"It was an incredible experience the first time we saw the object held in place by the tractor beam," said an excited Asier Marzo, the lead author of the study, in a press release. "All my hard work has paid off. It's brilliant."
The device, which they call an "acoustic hologram," is detailed in the journal Nature Communications.
