Imagine a world where you can move objects reliably using speakers — literally. Using the latest advances in acoustic technology, scientists have developed a revolutionary technique to accurately manipulate objects with sound waves, even in chaotic environments.

This breakthrough could transform fields from medicine to manufacturing, opening up important possibilities for precise, non-contact control over the microscopic and macroscopic alike.

Optical tweezers

In 2018, they awarded the Nobel Prize in Physics for something that sounds like science fiction. Arthur Ashkin was awarded the prize for inventing “optical tweezers“: precise laser beams that can be used to manipulate microscopic particles.

By exerting small forces on microscopic particles or molecules, optical tweezers can hold, move, and position them without physical contact. This is useful in various fields in health, physics, and chemistry. It also enables researchers to study the mechanical properties of biomolecules, investigate cellular processes, and explore interactions at the nanoscale.

But there’s a catch: optical tweezers need controlled or static conditions to work properly.

“Optical tweezers work by creating a light ‘hotspot’ to trap particles, like a ball falling into a hole. But if there are other objects in the vicinity, this hole is difficult to create and move around,” says Romain Fleury, head of the Laboratory of Wave Engineering at the Swiss Federal Institute of Technology Lausanne.

So, what if you want to use the same technology in a more realistic environment? This is where the new study comes in.

From concept to a real environment

Fleury and postdoctoral researchers Bakhtiyar Orazbayev and Matthieu Malléjac have been working on this for four years. They’ve developed a method that doesn’t really care about what environment the method is used in. All that’s needed is the objects’ exact position, and then soundwaves can work the magic.

“In our experiments, instead of trapping objects, we gently pushed them around, as you might guide a puck with a hockey stick,” Fleury explains.

In their experiments, the researchers used a setup consisting of an acoustic waveguide filled with water. A movable ping-pong ball served as the target object, and cylindrical scatterers created a complex scattering environment. Arrays of speakers and microphones were positioned on either side of the waveguide to control and measure the incident and outgoing waves.

To understand the science behind wave-momentum shaping, it’s essential to delve into the concept of the scattering matrix (S matrix). The S matrix describes how an incident wave is scattered by an object. By measuring this matrix in real-time, researchers can determine how the object affects the wave and use this information to shape subsequent waves optimally.

By continuously measuring the S matrix as the ball moved, the researchers could adjust the wavefronts to apply the necessary momentum to guide the ball along a desired path. This iterative process allowed for precise control over the ball’s movement, even in the presence of dynamic changes in the environment.

Controlling objects inside your body

The applications for this technology are virtually endless, but Fleury emphasizes one particular goal: biomedical applications. Because the technique is non-invasive and virtually harmless, it can be used to deliver targeted drugs or other treatments.

“Some drug delivery methods already use soundwaves to release encapsulated drugs, so this technique is especially attractive for pushing a drug directly toward tumor cells, for example.”

Because the inside of the human body is rarely a smooth and predictable environment, this type of technology holds great promise. However, there are still some big challenges to overcome.

For instance, one significant challenge is scaling the technique to handle smaller or more complex objects, particularly in three-dimensional environments. The researchers’ current setup is primarily two-dimensional, but adapting it for three-dimensional manipulation will require advancements in measuring and controlling wavefronts in all directions. Another challenge is maintaining precision over the entire process, which is essential in biomedical applications.

Despite these challenges, the robustness and versatility of wave-momentum shaping make it a promising tool for future innovations. By refining the technique and addressing these challenges, researchers can unlock its full potential and revolutionize various fields that rely on precise object manipulation.

The study was published in Nature.