BBC Earth (Asia) - - Update -

Here’s an idea that is re­ally gain­ing trac­tion: for the first time, Uni­ver­sity of Bris­tol en­gi­neers have cre­ated an acous­tic trac­tor beam capable of trap­ping ob­jects larger than the wave­length of the sound be­ing used.

This dis­cov­ery could lead to tech­nol­ogy capable of ma­noeu­vring drug cap­sules around the body, con­tainer-less trans­porta­tion sys­tems, and even the lev­i­ta­tion of hu­mans for med­i­cal or other pur­poses, the en­gi­neers say.

Re­searchers pre­vi­ously thought that acous­tic trac­tor beams were lim­ited to levitating small ob­jects. This is be­cause pre­vi­ous at­tempts to trap par­ti­cles larger than the wave­length of the sound be­ing used were un­sta­ble, with lev­i­tated ob­jects spin­ning out of con­trol.

The team found a work­around for this prob­lem by us­ing rapidly fluc­tu­at­ing tor­na­does of sound – es­sen­tially a twister­like struc­ture made up of a loud sound sur­round­ing a silent core. They were then able to in­crease the size of the silent core, al­low­ing it to hold larger ob­jects.

Us­ing ul­tra­sonic waves at a pitch of 40kHz, a fre­quency above hu­man hear­ing but de­tectable by dogs, the re­searchers held a two-cen­time­tre poly­styrene sphere sta­tion­ary in the trac­tor beam. The sphere was more than two acous­tic wave­lengths in size, mak­ing it the largest ob­ject to be trapped in a trac­tor beam.

The find­ing gives hope that larger ob­jects, such as hu­mans, could be lev­i­tated us­ing the same tech­nique, the re­searchers say.

“Acous­tic trac­tor beams have huge po­ten­tial in many ap­pli­ca­tions,” said Prof Bruce Drinkwa­ter, who su­per­vised the re­search. “I’m par­tic­u­larly ex­cited by the idea of con­tact­less pro­duc­tion lines where del­i­cate ob­jects are as­sem­bled without touch­ing them.”

A poly­styrene ball lev­i­tates in ul­tra­sonic sound­waves

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