The term “shadow waveguide” sounds like it comes from a sci-fi, but it’s actually a technique developed by engineers to manipulate matter with sound.
VIDEO: There are no physical structures in this video. The “walls” that conduct particles through a liquid are actually complex combinations of sound waves created by a new technique called a shadow waveguide. Source: Junfei Li, Duke University
Researchers at Duke University in the US have come up with a new kind of acoustic tweezers that use sound waves to move tiny objects without touching them. They range from microrobotics to drug delivery to biomedical sciences (such as tumor targeting or surgery)
This new method uses complex acoustic patterns to guide small particles in a fluid. According to a study published in the journal Science Advances, the research team used two sound sources to create a tightly closed acoustic field in a chamber and move particles through it.
Previous techniques have already shown that acoustic tweezers they are able to capture, rotate and move various particles. However, there were limitations, and current arrangements often use multiple sound sources that act on the particles side by side. Self-manipulation of the particles has been achieved by forming solid channel structures in the chamber, but this can damage the particles and slow them down.
This new shadow waveguide technique can affect individual particles without internal structures. “We wanted to introduce acoustic wave energy into the chamber and use a structure outside the chamber to control the shape of the sound waves inside the chamber,” explained Steve Cummer, a researcher at Duke University and co-author of the study. He added: “The result is a kind of optical fiber for sound that shapes the propagation of sound and deliberately leaks some of its energy into the chamber – it’s a kind of sound shadow – to direct the particles in it through virtual channels.”
Shadow waveguides are created by 3D printed molds filled with polydimethylsiloxane (PDMS) silicone into which air ducts are built. These channels dictate where and how the sound waves enter the chamber and thus how the particles are directed. The conductive mold remains outside the chamber, but PDMS has very similar properties to water, so sound waves can easily travel from the conductor to the chamber.
Using this lineup, the team placed two sound sources in the chamber. at both ends of the chamber and used them to move the particles through the chamber, achieving a precisely controlled speed in complex orbits.
“Acoustic devices are very difficult to reconfigure, but we would very much like to figure out how this would be possible because this would be a dramatic improvement in the usability of the technique, “said Duke co-author Junfei Li, a researcher at the same time, pointing out the direction in which they are pursuing their research.
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