Published November 18, 2022
Metamaterials have the potential to keep aircraft safe by absorbing vibrations at specific frequency ranges. But what happens when those ranges need to be changed mid-flight?
A collaboration between the University at Buffalo School of Engineering and Applied Sciences and the U.S. Air Force Research Lab (AFRL) has shown it’s possible to electronically tune the frequency ranges in which a metamaterial can dampen vibrations.
“The frequencies which govern the vibrations are dictated by several factors, such as flight dynamics or weather conditions. As these conditions vary, they force you to dampen the vibrations at different frequencies. We can give you a very rapid response here,” says Mostafa Nouh, associate professor in the Department of Mechanical and Aerospace Engineering and director of the Sound and Vibrations Laboratory.
A paper on the findings, “Uncovering Low Frequency Band Gaps in Electrically Resonant Metamaterials through Tuned Dissipation and Negative Impedance Conversion,” which was published in the Smart Materials and Structures journal, was recently recognized by the American Society of Mechanical Engineers (ASME). It received the Best Paper Award in Mechanics and Materials Systems from ASME’s Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS) division. The award was presented at ASME’s 2022 SMASIS Conference, which was held on Sept. 12-14 in Dearborn, Mich.
It was the second year in a row that Nouh and co-author Jesse Callanan, who graduated earlier this year with a PhD in aerospace engineering, won the award. Their paper on nonreciprocal waves in a resonant metamaterial earned the honor at the 2021 SMASIS.
“If you trace the award back to 1993, you find a couple of names that have won the award twice, but usually a few years in between. This is the first time that anyone has won it back to back,” Nouh says. “This is a testament to the hard work of my co-authors and collaborators.”
This year’s paper focused on band gaps, the range of frequencies at which a material can block vibration. Metamaterials — any material engineered to have properties not found in naturally occurring materials — can be designed to have band gaps at specific frequencies. Engineers normally have to either alter the metamaterial or create a new design altogether when these band gaps need to be adjusted.
However, the paper’s experimentally proven hypothesis shows band gaps can be quickly adjusted with an electrical input. It introduces a new, smart metamaterial whose band gaps can be electronically tuned to quickly adapt to changing environments.
“The material is given some voltage and responds by shifting over to a different frequency range, or a wider one, in which it can block the incident vibrational excitations,” Nouh says. “Even though the vibrations themselves are mechanical, we are changing the field of play from mechanical to electrical in order to control these vibrations, where parameters are much easier and faster to tune on the fly.”
The findings could help the Air Force avoid vibration damage, and therefore cut costs. Extending the service life of aircraft can be expensive, but it’s usually less expensive than buying new aircraft, according to a Congressional Budget Office report from 2018. It would cost the Department of Defense an average of $15 billion a year to replace its current fleet, the report found.
“It’s a very huge investment to build just one of those airplanes,” Nouh says. “You don't want them damaged just because of some vibrations, which we know we can mitigate.”
The collaboration between UB and the Air Force was made possible via a grant from the National Science Foundation’s Non-Academic Research Internships for Graduate Students (INTERN) program. It allowed Callanan to work on the project at the AFRL facilities in Dayton, Ohio, during the 2020 fall semester. Callanan continued the work back at the Sound and Vibrations Laboratory the following semester.
“It's pretty well known that government research institutions are consistently on the cutting edge of scientific and technological development, and my time at AFRL helped me to understand what kind of role I could play in that development process,” says Callanan, who is now a postdoctoral research associate at the Los Alamos National Laboratory (LANL) in New Mexico. “I was able to work effectively at that level at AFRL, and I think that was a huge boost as far as proving my skills and getting me an opportunity at LANL.”
Co-authoring the paper with Nouh and Callanan was Abigail Juhl, a materials research engineer at AFRL; Carson Willey and Vincent Chen, researchers from Dayton-based defense contractor UES, Inc.; as well as Jonathan Liu, a Miami University student now pursuing a PhD at North Carolina State University.
“If it wasn't for the AFRL and their support of the entire project, the award wouldn't have happened,” Nouh says. “So I really want to thank them for that.”
It could be years until the paper’s findings are adopted in a commercial application, as is typical for proofs of concept at the fundamental research stage.
“The National Science Foundation’s mission is high-risk, high-reward ideas which lead to transformative research. High risk-high reward doesn't mean that you incrementally change something that is already there — it means you think about the next big thing.” Nouh says. “Everything, including your cell phone, has been, at some point in time, a crazy idea in someone's garage or lab or, in this case, university."