Hong-bo Zhang

Lamb wave band gaps in a homogenous plate with periodic tapered surface

In this paper, we present the numerical investigation of Lamb wave propagation in a homogenous plate with periodic tapered surface, which gradually increases the width from the lower base to the upper base. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are studied by using the finite-element method. We investigate the effects of the geometrical parameters (including the ratio of the lower base width to the upper base width, and the ratio of the upper base width, the thickness of the tapered surface, and the thickness of the homogenous plate, respectively, to the lower base width) on the band gaps. Numerical results show that the band gaps can be effectively shifted by changing the geometrical parameters. Especially, the width of the first band gap changes approximately linearly by changing the ratio of the upper base width to the lower base width and in return. The transmission bands of the structure with the tapered surface are more flat than thos...

Lamb waves in phononic crystal slabs: Truncated plane parallels to the axis of periodicity

A theoretical study is presented on the propagation properties of Lamb wave modes in phononic crystal slabs consisting of a row or more of parallel square cylinders placed periodically in the host material. The surfaces of the slabs are parallel to the axis of periodicity. The dispersion curves of Lamb wave modes are calculated based on the supercell method. The finite element method is employed to calculate the band structures and the transmission power spectra, which are in good agreement with the results by the supercell method. We also have found that the dispersion curves of Lamb waves are strongly dependent on the crystal termination, which is the position of the cut plane through the square cylinders. There exist complete or incomplete (truncated) layers of square cylinders with the change of the crystal termination. The influence of the crystal termination on the band gaps of Lamb wave modes is analyzed by numerical simulations. The variation of the crystal termination leads to obvious changes in the dispersion curves of the Lamb waves and the widths of the band gaps.

ONE-DIMENSIONAL PHONONIC CRYSTAL SLABS BORDERED WITH ASYMMETRIC UNIFORM LAYERS

We investigate theoretically the propagation of Lamb waves in a one-dimensional phononic crystal (PC) slabs bordered with asymmetric uniform layers based on the supercell plane wave expansion (SC-PWE) method. The validity is proved by using the finite-element (FE) method with Comsol Multiphysics 3.5a. The effect of changing the thickness of substrate and superstrate on the variation of the band gap width and frequency are studied when the total thickness of the loading layers is fixed. We also investigate the property of band gap maps by changing the total thickness or the material of the loading layers. The results show that the band structure can be tuned by changing the material or the thickness of the substrate or the superstrate. These structures may be used as filters and acoustic sensors.

Local Resonance Broadband Gap in a Homogeneous Plate with Periodic Truncated Cones

We investigate the band structures in a homogeneous plate with periodic truncated cones for the square lattice based on finite element method (FEM). The radius of the truncated cone is gradually reduced from the lower base to the upper base. Compared to the classical stubbed phononic plates, a considerable enlargement of the bandwidth by a factor of 2.04 is obtained by varying the semiangle of the truncated cone, while the truncated cones weight is only 65.19% of that of the cylinder of the stubbed case. Moreover the relative bandwidth is also enlarged by a factor of 1.68. We show that this band gap enlargement is due to the acoustic waves of different wavelengths is localized at the different parts of the truncated cone. These characteristics of elastic or acoustic waves suggest potential applications in aerospace.

Lamb wave band gaps in one-dimensional magnetoelastic phononic crystal plates

In this paper, we present the theoretical calculations of the dispersion curves of Lamb mode waves in one-dimensional magnetoelastic phononic crystal (PC) plates by using the finite element method (FEM) and the plane wave expansion (PWE) method. The effects of filling fraction and plate thickness to lattice pitch ratio on the first band gap (FBG) are analyzed under different magnetic boundary conditions. The numerical results show that the FBG characteristics are significantly influenced by different magnetic boundary conditions. Further calculations demonstrate that the filling fraction and the plate thickness to lattice pitch ratio are the most important parameters that affect the width and location of the FBG.

Acoustic wave transmission in asymmetric dual-metal gratings

In this work, we investigate asymmetric acoustic transmission (AAT) in dual-metal grating structures composed of two gratings with different structures. The calculated results show that AAT can be obtained in both directions. By modulating the structural parameters, the transmittance approaches to 0 and 0.63 in the two opposite directions, respectively, because transmission suppression occurs in one direction. We find that the AAT phenomenon originates from the coupling between the two single-metal gratings. Such kind of A AT could open possibilities in achieving novel acoustic devices.

Asymmetric lamb wave propagation in graded grating phononic crystal slabs

The unidirectional transmission of Lamb wave in low-frequency domains is realized by graded grating phononic crystal slabs This exotic phenomenon stems from the threshold frequency of the fundamental antisymmetric Lamb mode conversion to the fundamental symmetric Lamb mode is different at the different locations of the acoustic diode. This should be potentially significant in helping design chip-scale directional phononic devices.

One-dimensional phononic crystal slabs bordered with asymmetric uniform layers

We study the propagation of Lamb waves in a one-dimensional phononic crystal slabs bordered with asymmetric uniform layers based on the supercell plane wave expansion method (SC-PWE). The phononic crystal slabs are made of silicon and tungsten. The uniform substrate and superstrate layers can be tungsten layer, rubber layer or one is a tungsten layer and another is a rubber layer. The thickness or material of the substrate is different from that of the superstrate. The validity is proved by using the finite-element (FE) method with the Comsol Multiphysics 3.5a. The results show that the band structure can be tuned by changing the thickness of the substrate or the superstrate. These structures may be used as filters, sensors or wave guides.