Associate professor finds breakthrough in negative elastic wave refraction
Elastic waves are waves that travel on top of or through a material or liquid without causing any permanent changes to the substance’s makeup. Think of sound waves passing through the air, various wave types passing through a body of water, shockwaves from an earthquake, etc.
Now, imagine having the ability to exert some control over these waves and the myriad possible applications that could have.
Thanks to Guoliang Huang and his research team, those hypothetical applications are much closer to becoming a reality.
Huang, who joined the MU Mechanical and Aerospace Engineering department as an associate professor in August, recently had a paper published in the journal Nature Communications titled “Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial.” The paper details the creation of an elastic metamaterial with engravings that allow for the negative refraction of elastic waves.
“This concept, usually you need different materials — metal, rubber and metal again as a combination,” Huang said. “But we designed this material in single-phase material — steel.”
The fabrications were made in a steel sheet with lasers and are chiral microstructures, which means the top and bottom layers are identical in composition but arranged asymmetrically. It’s the first such material to be made out of a single medium.
The artificially engineered material also possesses what Huang called “double-negative properties in elastic media.” This refers to the creation of a negative mass density and bulk modulus in the material, meaning the response of the material to the waves is the opposite of how a material with positive density and bulk modulus would — for example, a material possessing a negative effective bulk modulus supports a volume expansion upon an isotropic compression harmonic loading.
The research began five years ago during Huang’s tenure at the University of Arkansas-Little Rock and was funded by a grant from the U.S. Air Force Office of Scientific Research with Program Manager Dr. Byung-Lip (Les) Lee. The goal then was to “apply principals of elastic metamaterials for the possibility of controlling and manipulating elastic waves.” Going forward, Huang said there are numerous possibilities with elastic waves and this material, including super-resolution sensors, acoustic devices and a superlens, thanks to the ability to more directly focus the waves.
“Eventually, this can be a tremendous application in structure health monitoring, detecting damage. … This structure now is a passive material,” Huang said. “Now we’re going to make this material active, integrating smart material in these structures. Then we can tune to any frequency. Then we can generate a significant response for any frequency, to make this broadband.”
Huang recently acquired additional funding from the Air Force Office of Scientific Research through 2017, giving him the time and resources necessary to explore the possibilities.