Silicon edges as one-dimensional waveguides for dispersion-free and supersonic leaky wedge waves Appl. Phys. Lett. 101, 031904 (2012) Surface acoustic wave band gaps in a diamond-based two-dimensional locally resonant phononic crystal for high frequency applications J. Appl. Phys. 111, 014504 (2012) In-plane confinement and waveguiding of surface acoustic waves through line defects in pillars-based phononic crystal AIP Advances 1, 041404 (2011) An acoustic bending waveguide designed by graded sonic crystalsOne of the outstanding challenges in phononic crystals and acoustic metamaterials development is the ability to tune their performance without requiring structural modifications. We report on the experimental demonstration of a tunable acoustic waveguide implemented within a two-dimensional phononic plate. The waveguide is equipped with a periodic array of piezoelectric transducers which are shunted through passive inductive circuits. The resonance characteristics of the shunts lead to strong attenuation and to negative group velocities at frequencies defined by the circuits' inductance. The proposed waveguide illustrates the concept of a controllable acoustic logic port or of an acoustic metamaterial with tunable dispersion characteristics. V C 2012 American Institute of Physics. [http://dx.

The band structure of a phononic crystal can be controlled by tuning the mechanical stiffness of the links connecting its constituting elements. The first implementation of a phononic crystal with adaptive connectivity is obtained by using piezoelectric resonators as variable stiffness elements, and its wave-propagation properties are experimentally characterized.

The creation of novel materials with advantageous properties and superior performance has been a crucial engineering challenge since the early days of mankind. In recent decades, this has resulted in the development of so-called metamaterials, [1] a term introduced to describe artificially made media with carefully designed and periodically arranged small-scale building blocks, whose macroscale physical properties can be controlled by the structural hierarchy and topology across micro-and meso-scales. [2] Mechanical metamaterials, a subclass thereof, offer an engineered response to static and dynamic mechanical loads. Interesting examples have demonstrated, e.g., negative Poisson effects, [3] negative dynamic bulk modulus, and negative effective density, [4] or tunable lowfrequency phononic band gaps. [5] Recent advances in micro-and nanofabrication techniques, especially of 3D technologies, [6] have significantly decreased the manufacturable size of characteristic features and have thereby started to dissolve the distinction between solids and structures. For instance, ultralight hollow-tube microlattice materials [7] were fabricated having unprecedentedly high density-to-stiffness ratios. Furthermore, structural solids with extremely high (almost fluid-like) bulk-to-shear-modulus ratios, often referred as pentamode materials, [8] were fabricated [9] and shown to suppress shear modes over wide frequency ranges. [10] As scalable nanomanufacturing is reaching technological maturity, we are in equal need of computational tools and a clear understanding of the underlying physics to guide the design process of such structural materials. Two predominant targets of mechanical metamaterial design have been the effective elastic moduli as well as phononic band gaps in the wave dispersion relations. While effective moduli and band gaps are commonly uniquely linked, we here propose a class of structural materials whose elastic moduli can be controlled independently of their dispersion relations by manipulating the distribution of mass across the small-scale unit cell, which will be specifically illustrated at the example of an auxetic lattice material.Auxeticity denotes a negative Poisson effect, i.e., auxetic materials, when stretched in one direction, will also expand in the lateral directions (and will show a decrease in crosssectional area when compressed uniaxially). While auxeticity is well-known to occur naturally in geological materials such as silicates [11] and zeolites, [12] it has recently attracted great interest in the engineering community. The first example of a synthetic auxetic material was reported by Lakes [13] who fabricated and tested reentrant honeycomb foams; other examples followed and realized auxeticity in polymers [14] and metals. [15] In all such examples, auxetic behavior arises from small-scale building blocks, which kinematically transform macroscopic translations into microscopic rotations and microstructural rearrangements. Potential applications of auxetic materials are myriad and mainly ...

Bi-stable composites are considered for vibration based energy harvesting, thanks to the broadband nature of their dynamic response. In this letter, a cantilevered piezoelectric bi-stable composite concept is introduced for broadband energy harvesting. The proposed configuration allows for exploiting the large strains developed close to the clamped root, significantly enhancing the harvesting effectiveness in comparison to previous settings. A simple model is used for designing the dynamic response aiming to maximise broadband oscillations. Experimental results reveal wide bands of high power conversion. Additionally, a shunting circuit suitable for broadband conversion is employed, further increasing the effectiveness of the proposed concept.

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