UNIVERSITY PARK, Pa. — Seismic waves make the Earth quake, shaking the developments on the planet’s surface. But what if there were a way to stop those seismic waves from reaching buildings, bridges or entire towns? What if the energy from the waves could potentially be redirected or even harnessed, just by building a structure on the ground? 

Parisa Shokouhi, associate professor of engineering science and mechanics and acoustics at Penn State, is interested in the possibility of controlling this type of stress wave. Known as surface waves, they move along the border between two differing media; a common example is an ocean wave moving along the boundary between water and air. Shokouhi’s interest motivated her to pursue a Penn State Multidisciplinary Seed Grant in 2017, which served as the first step toward an external grant.

“From controlling ground motion to filtering certain frequencies in very tiny electronics, the concept is the same,” Shokouhi said. “No matter the size, if you change particular characteristics of the surface, you can make the waves reflect in a certain way.” 

Now, with a $641,162 National Science Foundation grant, Shokouhi is exploring the possibilities of surface wave control using an array of resonating elements collectively called a metasurface that could redirect waves in the material it is attached to. As principal investigator, Shokouhi is working with co-principal investigator Cliff Lissenden, collaborator on the seed grant and professor of engineering science and mechanics and acoustics; co-principal investigator Mary Frecker, professor of mechanical engineering and biomedical engineering; and Daniel Giraldo Guzman, a mechanical engineering doctoral student. This fundamental research could have applications in seismic wave control or next-generation electrical systems with further research, according to Shokouhi.

Metasurfaces are not new. The novelty of this project, Shokouhi said, is the approach the researchers are taking to solve the problem: Rather than test different designs by trial and error, they are defining certain criteria for the metasurface’s performance first and tailoring its design accordingly. 

“Our approach is unique,” Lissenden said. “We’re designing features into a surface to control wave propagation in the solid media that’s bounded by that surface.” 

Shokouhi and Lissenden are using numerical modeling to provide parameters for the metasurface, and Frecker is responsible for coordinating and directing their design optimization. After a resonator is prototyped, Shokouhi and Lissenden will analyze its wave control performance and provide input if design changes need to be made.

The work is highly collaborative, similar to the seed grant that prompted it, according to the researchers. 

“This project is a great opportunity for me to do what I enjoy: collaborate across disciplines,” Frecker said. “Parisa and Cliff have expertise in wave propagation and mechanics that complements my experience in design optimization.” 

The methods and findings of the research will be incorporated into graduate and undergraduate courses as well as educational workshops for K-12 teachers through a collaboration with the Penn State Center for Science and the Schools.

“None of this would have been possible without the seed grant,” Shokouhi said. “That program helps us researchers to turn ideas into much more extensive studies.”