2D Dynamic Directional Amplification (DDA) in Phononic Metamaterials

Abstract

Phononic structures with unit cells exhibiting Bragg scattering and local resonance present unique wave propagation properties at wavelengths well below the regime corresponding to bandgap generation based on spatial periodicity. However, both mechanisms show certain constraints in designing systems with wide bandgaps in the low-frequency range. To face the main practical challenges encountered in such cases, including heavy oscillating masses, a simple dynamic directional amplification (DDA) mechanism is proposed as the base of the phononic lattice. This amplifier is designed to present the same mass and use the same damping element as a reference two-dimensional (2D) phononic metamaterial. Thus, no increase in the structure mass or the viscous damping is needed. The proposed DDA can be realized by imposing kinematic constraints to the structure’s degrees of freedom (DoF), improving inertia and damping on the desired direction of motion. Analysis of the 2D lattice via Bloch’s theory is performed, and the corresponding dispersion relations are derived. The numerical results of an indicative case study show significant improvements and advantages over a conventional phononic structure, such as broader bandgaps and increased damping ratio. Finally, a conceptual design indicates the usage of the concept in potential applications, such as mechanical filters, sound and vibration isolators, and acoustic waveguides.

Extraordinary optical transmittance generation on Si3N4 membranes

“…[4][5][6][7][8] Although less developed compared to plasmonic (electron-based) metamaterials, phononic metamaterials have been recently attracting increasing attention allowing, for instance, the control of the phonon propagation and heat transport at a microscopic level. [9][10][11][12] Moreover, they are employed in several applications, working as mechanical filters, 13 beam steerers, and lenses, 14 reaching a similar level of feasible applications as plasmonic metamaterials do. One of the striking advantages concerning artificial materials relies on the possibility to manipulate electromagnetic radiation at a sub-wavelength scale, looking for field concentration and enhanced optical transmission.…”

Experimental Study of Phononic Structures With Dda Enhanced Unit-Cells

“…In this paper, inspired by the benefits induced by the insertion of DDA mechanisms within the structure [18][19][20][21], one-dimensional inertial amplified lattices are designed for the mitigation of low-frequency mechanical vibrations. To this end, a DDA-enhanced phononic metamaterial chain is constructed and tested, consisting of LEGO® Technic bricks.…”

A negative stiffness dynamic base absorber for seismic retrofitting of residential buildings

“…Aiming to overcome the large mass requirement of the above system, various methodologies have been proposed to artificially increase the inertial forces, as in Kalderon et al 21 In Giaralis and Taflanidis, 22 a modification of the TMD has been proposed that includes the addition of an inerter. The so‐called tuned mass damper inerter (TMDI) incorporates an inertance element, which aims to generate an apparent increase of the TMD's inertia, without increasing its actual mass.…”