Researchers from North Carolina State University and Duke University have developed a metamaterial made of paper and aluminum that can manipulate acoustic waves to more than double the resolution of acoustic imaging, focus acoustic waves, and control the angles at which sound passes through the metamaterial. Acoustic imaging tools are used in both medical diagnostics and in testing the structural integrity of everything from airplanes to bridges.
"This metamaterial is something that we've known is theoretically possible, but no one had actually made it before," says Yun Jing, an assistant professor of mechanical and aerospace engineering at NC State and corresponding author of a paper describing the work.
The metamaterial, shown here, is made of paper and aluminum -- but its structure allows it to manipulate acoustic waves to more than double the resolution of acoustic imaging, focus acoustic waves, and control the angles at which sound passes through the metamaterial. Acoustic imaging tools are used in both medical diagnostics and in testing the structural integrity of everything from airplanes to bridges.
Credit: Chen Shen, North Carolina State University
Metamaterials are simply materials that have been engineered to exhibit properties that are not found in nature. In this case, the structural design of the metamaterial gives it qualities that make it a "hyperbolic" metamaterial. This means that it interacts with acoustic waves in two different ways.
From one direction, the metamaterial exhibits a positive density and interacts with acoustic waves normally - just like air. But from a perpendicular direction, the metamaterial exhibits a negative density in terms of how it interacts with sound. This effectively makes acoustic waves bend at angles that are the exact opposite of what basic physics would tell you to expect.
The practical effect of this is that the metamaterial has some very useful applications.
For one thing, the metamaterial can be used to improve acoustic imaging. Traditionally, acoustic imaging could not achieve image resolution that was smaller than half of a sound's wavelength. For example, an acoustic wave of 100 kilohertz (kHz), traveling through air, has a wavelength of 3.4 millimeters (mm) - so it couldn't achieve image resolution smaller than 1.7 mm.
"But our metamaterial improves on that," says Chen Shen, a Ph.D. student at NC State and lead author of the paper. "By placing the metamaterial between the imaging device and the object being imaged, we were able to more than double the resolution of the acoustic imaging - from one-half the sound's wavelength to greater than one-fifth."
The metamaterial can also focus acoustic waves, which makes it a flexible tool.
"Medical personnel and structural engineers sometimes need to focus sound for imaging or therapeutic purposes," Jing says. "Our metamaterial can do that, or it can be used to improve resolution. There are few tools out there that can do both."
Lastly, the metamaterial gives researchers more control over the angle at which acoustic waves can pass through it.
"For example, the metamaterial could be designed to block sound from most angles, leaving only a small opening for sound to pass through, which might be useful for microphones," Shen says. "Or you could leave it wide open - it's extremely flexible."
Right now, the prototype metamaterial is approximately 30 centimeters square, and is effective for sounds between 1 and 2.5 kHz.
"Our next steps are to make the structure much smaller, and to make it operate at higher frequencies," Jing says.
The paper, "Broadband Acoustic Hyperbolic Metamaterial," was published online Dec. 16 in the journal Physical Review Letters. The paper was co-authored by Ni Sui of NC State and Yangbo Xie, Wenqi Wang and Steven Cummer of Duke.
Matt Shipman | EurekAlert!
Research shows black plastics could create renewable energy
17.07.2019 | Swansea University
A new material for the battery of the future, made in UCLouvain
17.07.2019 | Université catholique de Louvain
Augsburg chemists and physicists report how they have succeeded in the extremely difficult separation of hydrogen and deuterium in a gas mixture.
Thanks to the Surface Acoustic Wave (SAW) technology developed here and already widely used, the University of Augsburg is internationally recognized as the...
Adjusting the thermal conductivity of materials is one of the challenges nanoscience is currently facing. Together with colleagues from the Netherlands and Spain, researchers from the University of Basel have shown that the atomic vibrations that determine heat generation in nanowires can be controlled through the arrangement of atoms alone. The scientists will publish the results shortly in the journal Nano Letters.
In the electronics and computer industry, components are becoming ever smaller and more powerful. However, there are problems with the heat generation. It is...
Scientists have visualised the electronic structure in a microelectronic device for the first time, opening up opportunities for finely-tuned high performance electronic devices.
Physicists from the University of Warwick and the University of Washington have developed a technique to measure the energy and momentum of electrons in...
Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.
Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...
For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.
Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...
24.06.2019 | Event News
29.04.2019 | Event News
17.04.2019 | Event News
23.07.2019 | Life Sciences
23.07.2019 | Life Sciences
23.07.2019 | Physics and Astronomy