A -shaped metallic metamaterial ͑geometrically, a combination medium of C-shaped resonators and continuous wires͒ is proposed to numerically investigate its transmission band near the resonant frequency, where otherwise it should be a negative-permeability ͑or negative-permittivity͒ stop band if either the C-shaped or continuous-wire constituent is separately considered. However, in contrast to the left-handed materials ͑LHMs͒ composed of split-ring resonators and wires as well as other metallic LHMs, this resonant transmission is a non-left-handed one as a result of the intrinsic bianisotropic effect attributed to the electrically asymmetric configuration of this -shaped metamaterial.

Acoustic metamaterials have attracted much attention in recent years. Acoustic cloaks, which make objects invisible to acoustic waves, are the most common use for acoustic metamaterials. In this paper, acoustic cloaks with arbitrary shapes are presented based on transformation acoustics. This method interprets the compression and dilation of space as appropriate properties of materials. The derived properties of the cloak with irregular shapes are highly inhomogeneous and anisotropic, much more complex than the annulus cloaks. The materials for this kind of cloak are impossible to find in nature, and difficult to fabricate with artificial materials. In order to overcome this difficulty, layered structure with isotropic materials is adopted to approximate the required properties of the cloak. Numerical simulations about the cloaks of arbitrary shape are performed to validate the design.

Acoustic metamaterials are artificial materials whose properties can be controlled at will. Acoustic cloaking is an important application. It can make some space acoustically invisible. In this paper, a model of transformation acoustics is proposed for a general tetrahedron. It contains three parts, each with homogeneous properties. Since most cloaks can be approximated by polyhedrons, they can be divided into a series of tetrahedrons. Thus, most cloaks can be built with homogeneous parts. Helmholtz equations are solved for the space with two polyhedral cloaks with COMSOL Multiphysics finite element software. The results show that the cloaks work well in hiding the space acoustically. In the models, all properties of each part are non-singular. Since all the parameters affect the properties of each part and some also affect the performance of cloaking, a balance can be found between performance and properties. It provides an easier and more realizable way to fabricate acoustic cloaks.

Acoustic metamaterials are artificial materials which can manipulate and control acoustic waves in way that may not exist in nature. Pentamode metamaterials, as one kind of metamaterials, have solid structures but behaves like fluid. One application is in building acoustic cloaks. In this paper, composite pentamode metamaterials with hexagonal unit cells are proposed. The phononic band structures of the unit cell show that there are band gaps within which only compressional modes exist. With variation of structures, highly anisotropic properties can be obtained. The influences of geometric dimensions and materials on the effective properties are analyzed. The composite structures introduce more degrees-of-freedom to tailor the effective properties.

Based on the substructure synthesis and modal reduction technique, a computationally efficient elastodynamic model for a fully flexible 3-RPS parallel kinematic machine (PKM) tool is proposed, in which the frequency response function (FRF) at the end of the tool can be obtained at any given position throughout its workspace. In the proposed elastodynamic model, the whole system is divided into a moving platform subsystem and three identical RPS limb subsystems, in which all joint compliances are included. The spherical joint and the revolute joint are treated as lumped virtual springs with equal stiffness; the platform is treated as a rigid body and the RPS limbs are modelled with modal reduction techniques. With the compatibility conditions at interfaces between the limbs and the platform, an analytical system governing differential equation is derived. Based on the derived model, the position-dependent dynamic characteristics such as natural frequencies, mode shapes, and FRFs of the 3-RPS PKM are simulated. The simulation results indicate that the distributions of natural frequencies throughout the workspace are strongly dependant on mechanism's configurations and demonstrate an axial-symmetric tendency. The following finite element analysis and modal tests both validate the analytical results of natural frequencies, mode shapes, and the FRFs.