A new metamaterial enables sound waves to manipulate underwater objects with no physical contact, enabling easier and more accessible operation in aquatic environments.
University of Wisconsin-Madison researcher Dajun Zhang presented the new metamaterial to peers on May 20 at the joint 188th Meeting of the Acoustical Society of America and the 25th International Congress on Acoustics. The work builds on other acoustic applications, like mapping the ocean floor or shattering kidney stones, to harness sound for human endeavors.
A Novel Acoustic Metamaterial
Metamaterials are novel composites containing structures that produce unique effects. In Zhang’s case, he structured his metamaterial with a sawtooth-patterned surface. The novel surface allows sound waves to exert different forces on the material due to how they divergently reflect off the unique shape of the material’s “teeth.” By targeting these waves, Zhang can precisely push and rotate a floating or submerged object attached to the material.
The resulting advancement in acoustic manipulation opens a path to greatly increasing the ease of underwater operations. Additionally, since the human body is primarily composed of water, surgery and drug delivery could be optimized with the metamaterial. That secondary application remains further in the future.
Testing the Waters with Sound
“Our metamaterial offers a method to apply different acoustic radiation forces on objects in liquid media, such as underwater robots and vehicles, parts for assembly, or medical devices and drugs,” said Zhang.
When testing the metamaterial, Zhang did not construct an object solely of the composite, but attached it to existing items. These included wood, wax, and plastic foam floating above the water, as well as other objects that he completely submerged. Acoustic waves successfully pushed, pulled, and rotated the objects in Zhang’s tests, with submerged objects demonstrating the material’s effectiveness for 3D manipulation.
(Credit: Dajun Zhang)
Scaling and Improving the Metamaterial
At this point, the greatest challenge to scaling Zhang’s work for commercial use is the limited capabilities of conventional manufacturing. Fortunately, Zhang has already advanced a solution that not only eases production concerns for his composite but also for underwater metamaterials in general.
“Current fabrication methods for underwater metamaterials do not provide the resolution or material properties required and are usually very expensive,” said Zhang. “To solve this issue, I developed a new fabrication method. This method is not only low cost and easy to implement but also achieves high fabrication resolution and large acoustic impedance contrast with water, which are keys to underwater metamaterials.”
Expanding Acoustic Technologies
Since sound travels through water at four times the speed it moves through air, acoustic technologies are highly useful under the waves. At the same meeting as Zhang, University of Texas at Austin scientist Connor Hodges revealed a new method to explore the depths for unexploded munitions using sound, potentially removing human bodies from the dangerous but necessary pursuit.
Also at the conference, Trinity Consultants presented new noise control techniques aimed at silencing large data centers. With expanding needs for large scale computing power, neighbors are becoming fed up with the noise of these installations, often built in residential areas.
As far as Zhang is concerned, the next step will be to push toward achieving smaller, more flexible paths toward the production of the material, with a specific focus on development of novel underwater robotics and medical applications.
“Our research opens new opportunities for both underwater acoustic metamaterials and remote manipulation,” said Zhang.
“Acoustic metamaterials and metasurfaces can now be used to generate forces remotely for underwater or in-body levitation, actuation, and manipulation applications.”
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.