Engineering zero modes in transformable mechanical metamaterials

Abstract

In the field of flexible metamaterial design, harnessing zero modes plays a key part in enabling reconfigurable elastic properties of the metamaterial with unconventional characteristics. However, only quantitative enhancement of certain properties succeeds in most cases rather than qualitative transformation of the metamaterials’ states or/and functionalities, due to the lack of systematic designs on the corresponding zero modes. Here, we propose a 3D metamaterial with engineered zero modes, and experimentally demonstrate its transformable static and dynamic properties. All seven types of extremal metamaterials ranging from null-mode (solid state) to hexa-mode (near-gaseous state) are reported to be reversibly transformed from one state to another, which is verified by the 3D-printed Thermoplastic Polyurethanes prototypes. Tunable wave manipulations are further investigated in 1D-, 2D- and 3D-systems. Our work sheds lights on the design of flexible mechanical metamaterials, which can be potentially extended from the mechanical to the electro-magnetite, the thermal or other types.

Unraveling the Broadband Emission in Mixed Tin‐Lead Layered Perovskites

“…Recently, Zhang and co‐workers reported that charge transfer states could be effectively formed in heterostructures of RPP prepared by mixing PEA 2 PbI 4 :PEA 2 SnI 4 crystal. [ 32 ] It is envisaged that the domains of PEA 2 SnI 4 and PEA 2 PbI 4 may occur because the tin and lead compounds have different Gibbs free energies of formation leading to the heterostructures. [ 48–50 ] In this picture, low‐energy luminescence would stem from a charge‐transfer state formed by electron–hole coupling between two chemically different domains.…”

“…[ 14,15,31 ] Recently, broadband emissions from mixed divalent metal 2D perovskites have been reported. [ 25,29,32,33 ] Tin (II) has been considered the most suitable candidate for Pb 2+ replacement because of their similar electronic states with lone‐pair orbitals. [ 34–39 ] Therefore, the substitution of Pb 2+ by Sn 2+ is expected to give rise to a minimal perturbation in the lattice structure.…”

“…reported that the red‐shifted broad emission could be due to PEA 2 PbI 4 :PEA 2 SnI 4 interfaces in thin films, as demonstrated in mechanically fabricated double‐layered PEA 2 PbI 4 /PEA 2 SnI 4 heterostructures. [ 32 ] Kuang et al. recently pointed that there are two independent STEs emitters in Pb−Sn alloyed single crystals, (C 10 NH 22 ) 2 Pb 1−x Sn x Br 4 .…”

Magneto‐Mechanical Bilayer Metamaterial with Global Area‐Preserving Density Tunability for Acoustic Wave Regulation

“…[28] Conventional metamaterials have fixed unit cell geometries and, accordingly, fixed properties, which limits their applicability. In response, active metamaterials have emerged, which can transform between preprogrammed shapes when subjected to external stimuli, such as mechanical loads, [29][30][31][32] heat, [33][34][35][36] electrical currents, [37][38][39][40] or magnetic fields. [41][42][43][44] These shape transformations often involve internal deformations of the unit cells, which also change the area density and the overall dimensions of the metamaterial.…”

Non-reciprocal and Non-Newtonian Mechanical Metamaterials

“…Metamaterials with tunable mechanical properties [11][12][13][14] , in particular having a rich dynamical behavior [15][16][17][18][19][20][21][22] or exhibiting non-reciprocity 23,24 , are extremely attractive for numerous applications, such as control of the propagation of acoustic and elastic waves [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] . Beyond the homogenization limit, the idea of dynamic shear, bulk, or mass density is commonly used and accepted for waves 41 .…”