Time-varying phononic metamaterials

The introduction of the concept of time crystals 1 opened the possibility of looking for classical systems whose properties change in time. These analog systems are known as time-varying materials 2. In this talk, I will present two examples of time-varying systems. In one case, we consider a homogeneous slab with an acoustic impedance that varies with time in a periodic way with period T; this is, Z(t) = Z(t + T). Although it is a homogeneous medium, a band structure appears due to the time dependence of the impedance. However, rather than having the bands rather than being in frequency are in the wave-number space. The second example is a phononic crystal made of a periodic array of unit cells of two different materials. In this case, one of the materials shows a time-dependent impedance that introduces a second modulation on the system. The possible realization of time-dependent structures and the potential applications will be discussed. F. Wilkzek, Quantum Time Crystals, Phys. Rev. Lett. 109, 160401 (2012). E. Galiffi, R. Tirole, S. Yin, H. Li, S. Vezzoli et al. “Photonics of time-varying media,” Adv. Photonics, 4, 014002 (2022). Work partially supported by DGAPA-UNAM.