Sound waves move objects: Breakthrough in physics

Sound waves are vibrations that propagate through a medium such as air, water, or solid matter.

These waves are generated when an object vibrates and sets the surrounding molecules into oscillation.

This oscillation creates regions of compression and rarefaction, in which particles are pressed closer together or pushed apart. These alternating regions propagate through the medium as a wave.

Sound waves are characterised by their frequency, wavelength, and amplitude. The frequency, measured in Hertz (Hz), determines the pitch of the sound, with higher frequencies producing higher pitches.

The wavelength is the distance between two successive points of compression or rarefaction, while the amplitude indicates the height of the wave, which influences the volume of the sound.

Humans perceive sound when these waves reach the ear and cause the eardrum to vibrate. These vibrations are then converted by the inner ear into electrical signals and interpreted by the brain, enabling us to hear and recognise different tones.

Sound waves as a tool: Simple yet effective

At the heart of this new method, referred to as “wave impulse shaping,” is the use of sound waves.

The research team led by Romain Fleury from the EPFL Laboratory for Wave Engineering has developed a technique that moves objects regardless of their surroundings or physical properties.

All that is required is the position of the object, and the sound waves do the rest, gently pushing the objects, much as one might move a hockey puck with a stick. This analogy is taken literally in their experiments.

Imagine a table tennis ball floating on water, moved by sound waves from speakers. In a large tank, a camera captures the ball's position from above, while sound waves guide it along a predetermined path. The ball's interactions with the sound waves are analyzed in real time, enabling precise control of its movement.

Expanding the potential

The researchers were not content with moving spherical objects. Their experiments also included controlling the rotation of objects and maneuvering more complex shapes, such as an origami lotus.

The technique is based on the conservation of momentum, a principle that lends the method its simplicity and versatility.

This simple yet flexible approach makes wave impulse shaping a promising technology for a wide range of applications.

The potential of this technology extends far into the biomedical field, where it could revolutionize the way treatments are administered.

Among other things, it could improve drug delivery systems by pushing medications directly into target areas such as tumor cells.

This method offers a non-invasive alternative that could reduce the risks associated with conventional drug delivery methods.

Furthermore, applying the technique in tissue engineering could avoid contamination or damage frequently caused by the physical manipulation of cells.

The researchers also envision its use in 3D printing, where they could precisely arrange microscopic particles before solidifying them into structures.

A look into the future: sound waves and beyond

Although the researchers are currently focusing on sound waves, they believe that the principles of impulse shaping could also be applied to light, which would expand the scope of its application.

With support from the Swiss National Science Foundation's Spark program, they next plan to extend the experiments from the macro to the microscale, using ultrasound waves to move cells under a microscope.

The study is published in the journal Nature Physics .