The power of energy in wave form is a fundamental part of our understanding of life, it is still a science in its infancy.

It is also the key to many of science fictions greatest inventions; tractor beams, sonic screw drivers and even levitation. These futuristic devices will only become a reality when we can convince light and sound to act counter intuitively, to pull instead of just push.

Recently a team of Scottish and American scientists have pushed (or more precisely pulled) the boundaries of how much pull force they can achieve using sound. With a million times more power than previous tractor beams the team were able to move a 1 cm large triangular shaped object

The forces of light and sound are gentle, they may seem to lack substance but both do exert a very gentle force. Shine a light on an object, or play a sound, and the waves will strike and skater or reflect off the object. Each photon or sound wave that strikes the object leaves just a little bit of energy (and information) behind.

With the light pointed straight at the object most of the energy reflects off the face, exerting a push force in the direction the light beam is traveling, a force generated as the waves bounce off the object.

To avoid this push force the team set the flat base of the triangle to face between emitters. The beams are focused to bounce off the sides of the triangle which drastically lowers the force hitting the flat front of the triangle and creates a low pressure at the front. High pressure is generated on the sides of the triangle as beams skater off. This difference creates the pull force.

The latest tractor beam was constructed using dual ultrasound beams made up of a thousand ultrasound emitters and a triangular shaped object. In their experiments the ultrasonic array is placed at the bottom of a tank of water. Powering up the array the scientists were able to draw the hollow plastic triangle objects down towards the emitters.

Optical tractor beams have also been tested in the past and they work in much the same way but are much less powerful, able to only move microscopic objects.

The interaction between matter and waves is a field of science that is still full of surprises. This is the place where strange effects live and new discoveries can be made.

Reference: Physics APS