Characterizing the properties of metamaterials using laser flash

Thomas Pezeril (DMV, IPR) and his American colleagues from MIT and NSC Kansas City publish their work in Nature

An alternative to traditional materials

(source: Université de Rennes)

The recent emergence of mechanical metamaterials has revolutionized materials science and engineering. Their extraordinary mechanical properties combining high mechanical strength and extremely low density (metamaterials are 80-90% air), open up an infinite number of possibilities for an endless range of applications in mechanical engineering, replacing traditional materials.
Until now, the study of mechanical metamaterials has relied mainly on contact methods, such as nano-indentation, which provides valuable information on static mechanical properties such as stiffness and strength. However, these techniques require painstaking sample preparation and advanced expertise for test analysis, slowing progress in this promising field.

A non-intrusive approach thanks to laser flash

To address this challenge, Thomas Pezeril, a CNRS researcher at the Institut de Physique de Rennes (Université de Rennes/CNRS), and his American colleagues at MIT (USA) have developed an optical characterization method for rapidly and reliably extracting the dynamic elastic constants of metamaterials on the micrometer scale.
The key innovation lies in the use of a laser flash to excite the vibrational frequencies of 3D microstructures, coupled with a method for optically detecting these vibrations. Ultimately, in record time, the researchers obtain an echography of the effective elastic properties of the metamaterials under study. The data obtained in this way gives access to the mechanical spectrum at megahertz frequencies, including the stiffness and ultrasonic attenuation of the micro-architectured materials.
This non-contact, non-intrusive approach is revolutionary in the field of metamaterials. To validate this breakthrough technique, various 3D micrometric architectures with different crystallographic orientations were printed and tested, giving access to a complete view of their dynamic elastic surfaces, for all orientations in space. In addition, the researchers demonstrated that the technique could also identify defects within these microstructures via the signature of their dynamic responses.

Enabling the use of artificial intelligence in the process

In a field where the design of new metamaterials is slowed by the lack of experimental data to predict and optimize structure-property relationships, this method offers the possibility of generating a large database that can be used in machine learning.
This could accelerate the design and discovery of optimized metamaterials for a variety of dynamic applications, such as seismic protection of buildings, debris protection of satellites, medical ultrasound, etc.


Dynamic Diagnosis of Metamaterials via Laser-Induced Vibrational Signatures
Yun Kai, Somayajulu Dhulipala, Rachel Sun, Jet Lem, Washington DeLima, Thomas Pezeril & Carlos M. Portela
Nature, 2023.11.15