A team of scientists have used sound waves to levitate tiny objects without a wizard or wand in sight.

The breakthrough, published today in Nature Communications, could lead to developments in areas as diverse as high-powered "tractor beams"; or manipulating drug delivery in the human body.

Co-author Bruce Drinkwater, Professor of Ultrasonics at the University of Bristol, said while other groups had successfully levitated objects, this had been achieved only by surrounding the object with speakers.

However, Professor Drinkwater and colleagues managed to move the tiny objects - less than one millimetre in size - using a single-sided array of loudspeakers.

The use of a single-sided device to manipulate objects in mid-air extends the potential of the technology as items would no longer need to be surrounded by loudspeakers, Professor Drinkwater said.

He said their new study built on the work of researchers at the University of Dundee.

The Dundee team had shown there was a force attracting some acoustic waves back to their sound source.

"But they did not move anything and their system could not trap and hold any objects stable," he said.

"So, we have gone from knowing that the force exists to turning it into a stable working device."

In the paper, the researchers reveal they have not only levitated very small objects but could move them in a controlled manner using acoustic "tweezers", "twisters" and "cages" to manipulate the objects.

Success lies in 'brute-force inversion'

Ironically, Professor Drinkwater said the team's success lay in the absence of a mathematician amongst them.

"Not being mathematicians, we did not seek elegant solutions but used what I call 'brute-force inversion' to solve the problem," he said.

This involved simulating as many possible configurations of sound sources and drive signal as possible and analysing the results to see which would "trap" the object.

They then used the computer's predictions to run practical experiments to test the results.

Professor Drinkwater said the successful sound wave configurations had interesting characteristics.

"The successful ones were all either tweezer, twister or cage-like [in shape]."

Tractor beams, delivering cancer drugs and other new potentials

Professor Drinkwater said the importance of developing a single-sided device was that it expanded the potential of the technology and paved the way for the development of 'tractor beams' that could pull objects toward the sound source.

"Single-sided devices potentially enable in vivo manipulation since the device could be applied directly on to the skin with the manipulation taking place inside the body; similar to an ultrasound scanner but for manipulating particles (that is, drug capsules, kidney stones or micro-surgical instruments)," the researchers note in the paper.

Potential uses Tractor beams - Beam me up Scotty!

Tractor beams - Beam me up Scotty! Manipulation of objects within the body - delivering drugs to tumours or removing kidney stones, for example.

Manipulation of objects within the body - delivering drugs to tumours or removing kidney stones, for example. Non contact production lines - for handling delicate objects

"This is a significant advantage over two-sided opposed arrangements, which require the target area to be sandwiched by the arrays; also, single-beam traps do not have repeated patterns that could accidentally trap other particles."

Professor Drinkwater said the development could also lead to "non-contact production lines" for handling delicate or dangerous materials without contact.

However he was most excited about the technology's potential in treating diseases such as cancer by delivering drugs more efficiently.

"If we could hold drugs (or more likely microcapsules with drugs inside) in the place where they are needed and then slowly release them we could use much smaller doses, which would result in less side effects," he said.



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