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Piezoelectric energy harvesting of mechanical waves exhibits great potential applications in electricity generation for low-powered electronic devices. In this work, the metasurface-assisted phononic cavity is proposed for the enhancement of piezoelectric energy harvesting of elastic flexural waves. By employing the two-dimensional plate-type metamaterial, we construct a phononic cavity that possesses the ability to localize and amplify the flexural waves. On the other hand, for the purpose of flexural wave focusing, a sparse metasurface is inversely designed based on the interference theory through the particle swarm optimization algorithm. For collaborative wave manipulation, the sparse metasurface is set in front of the phononic cavity. Additionally, piezoelectric patches are attached within the phononic cavities. The wave characteristics of the metasurface-assisted phononic cavity are studied by using the finite element method. For comparison, a conventional phononic cavity (i.e., cavity without metasurface) and a reference bare plate are also considered. Due to the wavefront control ability of the metasurface, more flexural waves are guided into the phononic cavity region. Thus, compared with the reference plate, the power amplification ratios of the metasurface-assisted cavity and the conventional cavity are 102 and 7, respectively. The electrical outputs of the phononic cavity are remarkably boosted by the assistance of the sparse metasurface. [Display omitted] • A new strategy is proposed for enhancing energy harvesting of flexural waves. • The metasurface-assisted phononic cavity is designed for wave manipulation. • The sparse binary metasurface is constructed for the focusing of flexural waves. • The metasurface is inversely designed using the particle swarm optimization. • The power amplification ratio of the proposed metamaterial harvester reaches 102. [ABSTRACT FROM AUTHOR]

In this study, we propose the three-dimensional (3D) phononic crystal-based coupled resonator waveguides (PnCCRWs) for the guidance of acoustic waves along complex routes. The proposed 3D PnC exhibits a complete acoustic band-gap. The point defect mode with a frequency in the band-gap is achieved via the introduction of a point defect into the perfect PnC. The 3D PnCCRWs are constructed by appropriately setting the PnC point defects in the designed paths. These PnC point defects interact with the neighboring ones, which leads to the propagation of the acoustic wave energy along the designated PnCCRWs. Notably, the interaction between the neighboring PnC point defects can be well described by the tight-binding model. The waveguiding ability is demonstrated numerically and experimentally for three different PnCCRWs integrated in the same PnC structure. In addition, the viscothermal effect on the transmission properties of the PnCCRWs is also investigated. The proposed 3D PnCCRWs exhibit their flexibility, which may stimulate additional design rules for complex 3D phononic circuits. • The design of phononic crystal-based coupled resonator waveguides is proposed. • The waveguiding along 3D complex routes is verified numerically and experimentally. • The tight-binding model describes the interaction between phononic crystal defects. • The viscothermal effect on the transmission property is investigated. [ABSTRACT FROM AUTHOR]

The propagation of elastic waves in a piezoelectric slab covered with periodically structured coatings or the so-called stubbed phononic crystal slab is investigated. Four different models are selected and the effects of distribution forms and geometrical parameters of the structured coatings on complete bandgaps are discussed. The phononic crystal slab with symmetric coatings can generate wider complete bandgaps while that with asymmetric coatings is favorable for the generation of multi-bandgaps. The complete bandgaps, which are induced by locally resonant effects, change significantly as the geometry of the coatings changes. Moreover, the piezoelectric effects benefit the opening of the complete bandgaps. [ABSTRACT FROM AUTHOR]

In this paper, a phononic crystal (PnC) Luneburg lens is designed for harvesting the mechanical energy of Rayleigh surface waves. The square-latticed PnC is formed by drilling holes periodically in an aluminum matrix. The PnC Luneburg lens for Rayleigh surface waves is constructed by spatially modulating the hole radius of each PnC unit-cell according to the refractive index profile of a conventional Luneburg lens. To convert mechanical energy into electricity, a piezoelectric disk is attached at the focal point of the PnC Luneburg lens, where the Rayleigh surface waves are focused. Compared with the reference harvester on a homogeneous aluminum matrix, the electric power outputs are significantly enhanced by the PnC Luneburg lens harvester for two typical directions, namely the Γ X and Γ M directions. For either the Γ X or Γ M direction, the amplification ratio of the PnC Luneburg lens harvester is over 14. [Display omitted] • The phononic crystal Luneburg lens is proposed for focusing Rayleigh surface waves. • The piezoelectric energy harvester based on the phononic crystal Luneburg lens possesses high amplification ratios. • The phononic crystal Luneburg lens exhibits high rotational isotropy in the piezoelectric energy harvesting. • The phononic crystal Luneburg lens can also be used as a collimator for Rayleigh surface waves. [ABSTRACT FROM AUTHOR]

Abstract: Phoxonic crystal is a promising artificial periodic material for optomechanical systems and acousto-optical devices. In this paper, two-dimensional phoxonic crystals with veins in square, triangle and honeycomb lattices are investigated. Detailed discussion is presented on the variation of the photonic and phononic bandgaps with the geometry and lattice form of the structure. The results show that simultaneous large complete photonic and phononic bandgaps can exist over a wide range of geometry parameters for the square and honeycomb lattices. These large regions offer good tolerance for the technological realization and flexibility in designing this phoxonic crystal structure. [Copyright &y& Elsevier]

Abstract: In this paper, the elastic band structures of two-dimensional solid phononic crystals (PCs) with both negative and positive Poisson''s ratios are investigated based on the finite difference domain method. Systems with different combinations of mass density ratio and shear modulus ratio, filling fractions and lattices are considered. The numerical results show that for the PCs with both large mass density ratio and shear modulus ratio, the first bandgap becomes narrower with its upper edge becoming lower as Poisson''s ratio of the scatterers decreases from −0.1 to −0.9. Generally, introducing the material with a negative Poisson''s ratio for scatterers will make this bandgap lower and narrower. For the PCs with large mass density ratio and small shear modulus ratio, the first bandgap becomes wider with Poisson''s ratio of the scatterers decreasing and that of the host increasing. It is easy to obtain a wide low-frequency bandgap by embedding scatterers with a negative Poisson''s ratio into the host with a positive Poisson''s ratio. The PCs with large filling fractions are more sensitive to the variations of Poisson''s ratios. Use of negative Poisson''s ratio provides us a way of tuning bandgaps. [Copyright &y& Elsevier]