Sound waves have proven to be an effective alternative to manipulating microscopic particles, which has traditionally involved the use of optical tweezers – a technology championed by Nobel Prize winner Arthur Ashkin.
However, these tools require static and controlled conditions to function effectively. Given the limitations of optical tweezers in dynamic environments, researchers have now turned to this innovative approach.
Led by Romain Fleury of EPFL’s Wave Engineering Laboratory, this method aims to redefine precision in uncontrolled environments by applying the principles of wave pulse shaping.
What are sound waves?
Sound waves are vibrations that travel through a medium such as air, water, or solid materials. These waves are created when an object vibrates and causes the surrounding molecules to vibrate.
This vibration creates regions of compression and rarefaction in which the particles are pushed closer together or spread apart. These alternating regions propagate as a wave through the medium.
Sound waves are characterized by their frequency, wavelength and amplitude. Frequency, measured in Hertz (Hz), determines pitch, with higher frequencies producing higher pitches.
The wavelength is the distance between two consecutive compression or rarefaction points, while the amplitude refers to the height of the wave, which in turn affects the loudness of the sound.
Humans perceive sound when these waves reach the ear and cause the eardrum to vibrate. These vibrations are then converted into electrical signals in the inner ear and interpreted by the brain, allowing us to hear and recognize different sounds.
The core of this new method, called “Wave Momentum Shaping,” is the use of sound waves.
The research team led by Romain Fleury of EPFL’s Wave Technology Laboratory has developed a technique that moves objects regardless of their environment or physical properties.
All you have to do is know the position of the object, and the sound waves do the rest, gently pushing the objects along, just like you would push a hockey puck with a stick. This analogy is taken literally in their experiments.
Imagine a ping pong ball floating on water, controlled by audible sound waves emitted from speakers. Positioned in a large tank, a camera from above captures the ball’s position as sound waves guide it along a predetermined path. The ball’s interactions with these sound waves are analyzed in real time, allowing precise control of its movement.
Expanding the potential
The researchers did not limit themselves to moving spherical objects. Their experiments also included controlling the rotation of objects and maneuvering more complex shapes, such as an origami lotus flower.
The technique is based on the conservation of momentum, a principle that gives the method its simplicity and versatility.
It is this straightforward yet flexible approach that positions wave pulse shaping as a promising technology for a wide range of applications.
Promising applications in medicine and beyond
The potential of this technology extends far into the biomedical field, where it could revolutionize the delivery of treatments.
For example, it could improve drug delivery systems by transporting them directly to target areas such as tumor cells.
This method offers a noninvasive alternative that could reduce the risks of conventional drug delivery methods.
Furthermore, the application of this technique in tissue engineering could prevent the contamination or damage that often occurs during physical manipulation of cells.
The researchers can also imagine using the technology in 3D printing, where it could precisely arrange microscopic particles before they are solidified into structures.
Looking to the future: sound waves and beyond
While their current focus is on sound waves, the researchers believe that the principles of wave pulse shaping could also be applied to light, potentially expanding its range of effects.
With support from the Spark program of the Swiss National Science Foundation, their next goal is to scale down the experiments from macro to micro scale by using ultrasound waves to move cells under a microscope.
This innovative technique, developed in collaboration with international researchers from institutions such as the University of Bordeaux, Nazarbayev University and the Vienna University of Technology, represents a significant advance in the manipulation of objects in uncontrolled environments.
As the team continues to refine and expand the capabilities of wave pulse shaping, its impact on science and medicine is bound to grow, opening new avenues for research and application in areas where precision is of paramount importance.
The study was published in the journal Natural physics.
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