Applied Physics Seminar | Harnessing Structural Periodicity for Wave Control: From Fundamental Physics to Sensing, Harvesting, and Space Systems

Abstract: Structural periodicity offers a powerful physical framework for controlling elastic and
acoustic wave propagation across multiple length scales. Periodic architectures such as
metamaterials, phononic crystals, and metasurfaces give rise to rich physics including bandgaps,
mode coupling, anisotropy, and negative refraction that enable wave manipulation beyond what
is possible in homogeneous media. In this talk, I will present how these wave–structure
interactions can be systematically designed and exploited for applications in sensing, energy
harvesting, and space systems. The first part of my talk focuses on gradient-index phononic
crystals (GRIN-PCs) realized through spatially varying unit-cell geometry. By tailoring effective
refractive index profiles, we demonstrate controlled focusing of multimodal guided elastic waves
in conformal, curved geometries. These structures enable wave energy concentration at
prescribed locations, offering a physics-based strategy to mitigate attenuation and enhance signal
localization in extended structures. I will then introduce negative-refraction-based phononic
crystal lenses, which leverage dispersion engineering to achieve subwavelength focusing beyond
the diffraction limit which is an effect of fundamental interest for high-resolution imaging and
wave localization. The second part of my talk explores reconfigurable elastic metasurfaces
designed for full wavefront control. By engineering phase gradients at the unit-cell level, we
realize anomalous refraction, wave steering, and energy redirection, with particular emphasis on
harvesting low-frequency elastic waves. Theoretical predictions are validated experimentally,
highlighting the close interplay between dispersion engineering and physical realizability. The
final part of my talk extends metamaterial concepts to space designs, where mass efficiency and
precision are critical. I will discuss how architected metamaterials enable novel in-space
manufacturable structures, including extended solar arrays and antenna systems, illustrating how
wave-informed structural design can address challenges in next-generation space technologies.

Speaker bio: Dr. Serife Tol is an Associate Professor in the Mechanical Engineering
Department at the University of Michigan, Ann Arbor. She received her Ph.D. (2017) from
Georgia Institute of Technology and her M.S. (2012) and B.S. (2009) degrees from Middle East
Technical University (METU, Ankara, Turkiye), all in mechanical engineering. She worked as a
Test and Analysis Engineer in the Defense Systems Technologies Business Sector at ASELSAN
(Turkiye, Ankara) between 2009 and 2012. Dr. Tol’s research interests include metamaterials,
metasurfaces, phononic crystals, smart materials, electromechanical systems, vibrations, and
wave propagation. Her research program has been funded by NSF, DARPA, ONR, DoE, and
NASA. She is also the recipient of the John F. Ullrich Education Excellence Award (2023) and
ASME C.D. Mote Jr. Early Career Award (2024).