Search

Achieving vibration and/or wave attenuation with locally resonant metamaterials has attracted a great deal of attention due to their frequency dependent negative effective mass density. Moreover, adaptive phononic crystals with shunted piezoelectric patches have also demonstrated a tunable wave attenuation mechanism by controlling electric circuits to achieve a negative effective stiffness. In this paper, we propose an adaptive hybrid metamaterial that possesses both a negative mass density as well as an extremely tunable stiffness by properly utilizing both the mechanical and electric elements. A multi-physical analytical model is first developed to investigate and reveal the tunable wave manipulation abilities in terms of both the effective negative mass density and/or bending stiffness of the hybrid metamaterial. The programmed flexural wave manipulations, broadband negative refraction and waveguiding are then illustrated through three-dimensional (3D) multi-physical numerical simulations in hybrid metamaterial plates. Our numerical results demonstrate that the flexural wave propagation can essentially be switched between “ON/OFF” states by connecting different shunting circuits. [ABSTRACT FROM AUTHOR]

The transformation method is a powerful tool providing the constitutive parameters necessary for arbitrary geometric transformations of solution fields. These constitutive parameters, in elasticity, describe a constitutive law that, unlike conventional Hooke's law, is polar and chiral and that no known solids exhibit. This raises the question of whether polar and chiral elastic solids can be designed from the bottom up as architected lattice-based materials; this design task is a major challenge in the field of transformation elasticity. The present study aims to provide a theoretically justified design methodology based on a discrete transformation method. The key idea is to let the gradient of the geometric transformation operate not only on the elastic properties but on the underlying lattice-based architecture of the solids. As an outstanding application, we leverage the proposed design paradigm to construct a polar lattice metamaterial subsequently used for elastic carpet cloaking purposes. Numerical simulations are carried to show excellent cloaking performance under different static and dynamic mechanical loads and thus demonstrate the validity of the proposed designs. The approach presented herein could promote and accelerate new designs of lattice topologies for transformation elasticity in particular and can be extended to realize other emergent elastic properties and to unlock peculiar field-warping functions other than cloaking in static and dynamic contexts. [ABSTRACT FROM AUTHOR]

This paper studies the distributed filtering problem for sensor networks with communication delays. A leader-following-based Kalman filtering algorithm with delay compensation is applied, and a fully distributed weight design approach is proposed to guarantee the convergence of the algorithm. For the leaders, which are defined as the sensors that can directly obtain the measurements of the target, standard Kalman filters are applied; for the followers, a weighted average strategy with delay compensation is applied. To design the weights, a sufficient condition on the eigenvalues of the weight matrix is firstly provided by analyzing multiple linearly coupled algebraic Riccati equations. Then, a distributed weight design approach based on the sensors’ lengths of their shortest paths to the target node and their own parameters is proposed. And a parameter bound of each sensor, which can be distributively computed based on its neighbors’ information, is further explicitly given. Simulation examples are given to illustrate our results. [ABSTRACT FROM AUTHOR]