On The New Effects In Acoustic Metamaterials And Extraordinary Transmission For Solid Plates

During the past twenty years, a great deal of physics concepts in condensed matters. Physics were depended and extended. An outstanding example is that the band theory and electronic properties of solids were extended into the classical wave system made by hand. For electromagnetic/optic waves, such artificial materials are called photonic crystal or electromagnetic metamaterials. For acoustic/elastic waves, they are called phononic crystals or acoustic metamaterials. Because of the plentiful peculiar wave properties, these wave functional materials are becoming a bright research field in condensed matter physics. The contribution in this thesis is as the following:(1) FDTD (Finite Different Time Domain, FDTD) is a strong and applicability method of simulation. FDTD method is not good at dealing with Eigen problems. As the computer capacity limitations, FDTD calculation of only can be carried out in limited areas. We optimize the FDTD program by using the symmetry of the system itself of a new boundary condition:the mirror boundary conditions. With Using this boundary conditions:the two-dimensional FDTD program reduced half demand for resources (also the time inquire). It greatly improved the efficiency of FDTD program. And for the case of limited memory, by using mirror boundary conditions, we can calculate a larger system.(2) Through analytical and numerical simulation to study the phonon crystals band gap in the Bragg scattering and acoustic tunneling effect in locally resonant band gap of the similarities and differences between them. Although a universal behavior is exhibited for the group velocity in these systems, there is a qualitative difference for the phase velocity:it grows linearly with the sample thickness for the quantum case, whereas it almost keeps invariant for the classical case. The difference comes from the distinct origins of the forbidden zones. For the quantum case, the forbidden zone corresponds to the evanescent potential barrier, while for the classical case it corresponds to the band gap resulting from Bragg scatterings.(3) Acoustic metamaterials in the field of resonant bubble exhibit effective negative bulk modulus has been widely known. And it has been shown that a class of three-component phononic crystal with local resonant structure exhibits negative effective mass density at resonant frequency. This three-component phononic crystal can be regard as the two-oscillator model. When the core mass is approaching infinity, we can get the effective negative mass density in static force, which has been reported in one-dimensional system. In this paper, we extend it to two-dimensional solid phononic crystals. We also study the effect of the ability of rigid approximation. Finally, we get the same conclusions in three-dimensional systems.(4) This mode of implementation in the use of Lamb Wave Transmission hard board on the basis of the enhanced. It has been manifested that a remarkable acoustic transmission enhancement (ATE) at subwavelength can occur in a plate structure without any opening, which is created by the resonant excitation of nonleaky Lamb modes (NLMs). In this work, we consider a water-immersed brass plate drilled with a one-dimensional (1D) periodical array of rectangular side openings. These ATE peaks correspond to different vibration morphologies. One is associated with a strong vibration of fluid in individual openings, resembling the regular cavity modes. The others involve strong flexural vibrations in the solid plate. Considering that the system can be viewed as a combination of two identical plates patterned with solid bumps, by intuition one may anticipate that the coupled NLMs can be resonantly excited to induce the ATE effect. Beyond our expectation, however, there is still one more type of transmission peaks, which has been verified to be originated in the resonant excitation of standing plate modes (SPMs) that are localized in the upper and the lower walls of the cavities. As shown below, the peaks are always robust in the subwavelength region, which may bring new applications in ultrasonic devices.