Reliable and Tunable Elastic Interface States in Soft Metamaterials

Abstract

Interface states, which possess great advantages in the localization and confinement of waves or energy, have been extensively realized in the electronic, [1-4] photonic, [5-17] acoustic systems, [18-23] and also, the elastic systems, [24-31] recently. Reflection phase match principle is verified to be a useful methodology in the formation of interface states, which has been successfully demonstrated in both symmetric [8,17,22,28] and nonsymmetric [6,11,12,24] acoustic or photonic systems. On the one hand, interface states in 1D mirror symmetric systems [8,17,22,28] have been theoretically and experimentally well developed, which were accustomed to exploiting deformed geometries to reverse the bulk bands. Topologically protected interface states can be generated within the overlapped bandgap between two combined distinct components. However, the emergent interface state is fixed and unchangeable in the fabricated composite. However, on the other hand, broken mirror-symmetric structures own an advantage in the dynamical manipulation of the interface states, which can be realized simply through modifying or adjusting its asymmetric geometry construction. For instance, interface states in 1D graphene-embedded photonic crystal heterostructures, [6] 1D composite photonic structures, [11] compound metasurface/photonic crystal configurations, [12] and the elastic metamaterials with spiral inclusions, [24] all of them have successfully adjusted the emergent position and frequency range of the interface states and provide diverse implementation strategies. Meanwhile, soft materials, which benefit from their intrinsic configurable and deformation characteristics, have been artificially architected to manipulate the propagation of elastic wave [32,33] or sound. [34] Deformation can also be exploited as a new degree of freedom to modulate the gap range and properties. Lately, the deformation-conducted tunable elastic topological states in perturbed aluminum beams [27,29] and deformed soft honeycomb lattices [28] further promoted the utilization of soft deformable materials and also the application scenarios of vibration control and energy harvesting. [35] However, the generation of easily and stably-tuned elastic interface states in soft materials remains challenging, which was extremely restricted by the symmetric geometry parameter and the topological generation approach. In proposed configurations, [28] complicated mechanical deformation and complex mechanical loadings were absolutely needed, which apparently hindered the real applications. Here, we implement the dynamically tuned elastic interface states in soft elastic metamaterials in a more reliable and convenient way, which can be manipulated simply through compressing or stretching a mirror-symmetric metamaterial composite simultaneously. The feasible configuration is composed of two hexagonal boron nitride (h-BN) structure-inspired soft periodic metamaterials and conducted by mirroring one elastomeric

Tailoring Structure‐Borne Sound through Bandgap Engineering in Phononic Crystals and Metamaterials: A Comprehensive Review

“…These valley states are proven to yield opposite 1/2 pseudospins, leading to robust edge states that are immune to certain defects. Local resonance structures have been used to break the SIS in lattices formed by mechanical beams [164,165,[273][274][275][276][277][278][279][280][281] (see example in Figure 6e), and soft materials, [282,283] where the SIS is broken by the variation of resonators in the different valleys. The valley eigenstates have been observed with opposites 1/2 spins, which are characterized by valley-Chern numbers.…”

Recent advances in topological elastic metamaterials

“…Considering the simplicity and universality of the SSH model, this 1D topological system has been implemented in various elastic wave platforms [62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81]. For instance, Huang et al [77] realized the elastic analogue of the SSH chain in a 1D shear horizontal (SH) guided wave system, which consists of two semi-infinite solid phononic crystal (PC) plates with different Zak phases, connected to each other to form the topological interface modes at the zone-center band gap, or at the zone-boundary band gap, or both.…”

Topological Transition in Spiral Elastic Valley Metamaterials

“…This is one of unique aspects of our spiral valley system in contrast to conventional symmetric valley system. Spiral is the natural chiral element, where the right-handed and left-handed spirals can be transformed by parity inversion [19,20]. In order to explore the effect of chirality on the topology of the bands, we fix d = 2 mm and choose several configurations made from combinations among chirality, rotation angle, and number of turns.…”