Waves in Multistable Mechanical Metamaterials

Multistable metamaterials have recently been conceived in diverse ways, 3D printing, casting, assembling, particularly within the family of flexible mechanical metamaterial architectures. A prototypical structure example consists in bistable mechanical units elastically coupled to their nearest neighbors. With such multistable metamaterials, we are particularly studying progressive fronts, also called transition waves, switching sequentially their multistable units from one equilibrium to another, and resulting in the local or global reconfiguration of the medium. In addition, these nonlinear metamaterials are also known to support a rich variety of nonlinear waves, as vector solitons, breathers, cnoidal waves, among others.  In this presentation, I will highlight the fundamentals and a selection of recent results on transition waves triggering, propagation, and discuss some of their potential applications. In general, these reconfiguration fronts obey nonlinear reaction-diffusion equations and show specific properties not necessarily found in other waves supported by periodic and/or nonlinear media, e.g., strong nonreciprocity, robustness, one-way propagation, extreme amplitude dependent behavior… These effects can be interesting for applications involving local or global reconfiguration of a medium, manipulating mechanical memory, controlling waves in space and time, mechanical computing or be the vector for material embedded intelligence. 

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Vincent Tournat currently holds a Research Professor position at CNRS and conducts research in the field of nonlinear waves and metamaterials at the Laboratory of Acoustics at Le Mans University in France. VT graduated with a major in solid state physics, acoustics & wave physics and defended his PhD thesis on nonlinear acoustics in granular materials in 2003. He then spent the year 2004 as a postdoc at Hokkaido University, Japan, working on laser picosecond ultrasonics, prior to starting at CNRS. During his first years at CNRS, he established two research groups on acoustics of granular media and laser ultrasonics, then participated in developing two other areas of research in his department, ultrasonic non-destructive testing, and acoustic metamaterials. For the last decade, his research focuses on nonlinear waves in flexible mechanical metamaterials. From 2007 to 2022, VT led the "Acoustics and Mechanics of Materials" research team of more than 50 people. His research achievements have been awarded prizes on several occasions, including the CNRS Bronze Medal in 2010 and the Silver Whistle early career award by the International Commission on Ultrasonics (ICU) in 2013. Until 2024, he has been the director of the Institut d’Acoustique - Graduate School (http://iags.univ-lemans.fr) created in 2017 and awarded the national label “Graduate School” (a selection of few Institutes comprising high impact research laboratories, departments, as well as recognized master, engineering and doctoral curriculae). VT has been regularly invited for research visits in Japan, Chile, Spain, USA and he is a visiting research Professor at Harvard University since September 2022.