Matlack develops design method to impact ultrasound, optical imaging, more
Assistant Professor Katie Matlack, with colleagues from ETH Zurich, the University of Bologna, and Caltech, has developed a precise and versatile way to design weakly coupled metamaterials that control waves in complex and advanced ways. They used the method to design an acoustic lens, a zero-velocity metamaterial, and a mechanical topological insulator.
Their results were published yesterday in a paper, “Designing Perturbative Metamaterials from Discrete Models,” in Nature Materials.
The weak interaction allowed the researchers to associate each element of the discrete model with individual geometric features of the metamaterial, thereby enabling a systematic design process. The mechanical topological insulator is particularly impactful because it provides a highly sought-after solution to the problem of systematically designing a topologically protected, defect-immune mechanical waveguide.
Their new method enables scientists to take a discrete model (such as a mass-spring model), and use elements of data-driven design with a metamaterial effective theory to encode that behavior into the metamaterial—by finding the geometry of a material that has the same dynamic behavior of that discrete model. To do this, the team introduced the concept of “perturbative metamaterials,” metamaterials with weakly coupled unit cells.
This is significant because identifying material geometries that lead to metamaterials with desired functionalities presents a challenge for this field. Their method can quickly explore large design spaces, and uses advanced mathematical/computational tricks to “find a needle in a haystack” and find the right geometry for the application desired.
The method is also versatile, in that it allowed Matlack and her colleagues to report many different behaviors—representing an advantage over other methods that focus on designing for a specific behavior. As additional proof of this, Matlack’s collaborators went on to use the method to create a new phase of topological matter in the phononic domain, results of which have been published in a separate Nature paper.
Applications of this new design method could be relevant to any system that would benefit from finer control on wave propagation (in terms of sensitivity and precision), such as ultrasound imaging, sonar/ultrasound communication, antennas, optical fiber, and optical imaging.
While Matlack’s paper focuses on mechanical metamaterials, the method could be used to develop new metamaterials in other domains, such as thermal or photonic systems. Its limitations are that it works only over a certain range of frequencies, and it requires high-precision manufacturing.
“Our design method is basically a systematic way to discover new metamaterials, which could lead to exciting applications such as programmable materials, damage-tolerant structures, and acoustic or heat lenses,” said Matlack.
Matlack runs the Wave Propagation and Metamaterials Laboratory at Illinois. She joined MechSE in January 2017.