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One Way Effect in Acoustic Band-gap Material

Author: LiXueFeng
Tutor: ChenYanFeng；LuMingHui
School: Nanjing University
Course: Materials Physics and Chemistry
Keywords: Phononic crystals Lamb wave Unidirectional transmission Nonreciprocal Time reversal Abnormal transmission
CLC: TB33
Type: Master's thesis
Year: 2011
Downloads: 146
Quote: 1
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Abstract

Phononic crystals (phononic crystal), acoustic metamaterials (acoustic metamaterial), acoustic superlattice including artificial phonon band gap materials has aroused great attention due to their novel physical effects. Phononic crystal is a periodic composite structural materials, acoustic metamaterials are artificial materials does not exist in nature, with the effective density or the effective elastic modulus using the locally resonant. Artificial phonon band gap material for people to provide effective means of regulation of the propagation of sound waves, have important applications in the field of acoustic imaging, detection, sensing, information processing, etc.. Acoustic wave propagation artificial phonon bandgap material on theoretical and experimental study of the system. Mainly includes the one-way transmission of sound waves in the crystal structure of the asymmetric phonon effect Lamb wave phonon bandgap crystals, waveguides, and single-pass effect, one-dimensional periodic groove structure of single slit sonic asymmetric abnormal transmission effect . 1. System in the theoretical and experimental study asymmetric phononic crystals acoustic one-way transfer effect, combined with the pattern of diffraction effects lead to transition the direction of the band gap of the phonon crystals from equal frequency line (EFS) and band the point of view of the mechanism of the effect of such a single-pass, and calculated the impact of a higher order diffracted wave transmission spectrum. Nonlinear media and one-dimensional phononic crystals before the this acoustic single pass model differs from the combination of the composite structure, is completely linear systems, and has a large bandwidth, high conversion efficiency, low energy loss advantages. The adjustable acoustic waves in the phononic crystals. Systematic study of the four corners of the pillars asymmetric single-pass effect. Quadrangular pillar by rotating, changing the scattering cross section of the acoustic wave, thereby modulating the energy band structure of the crystal of the phonon, and in the case does not affect the single-pass effect of the band gap of the first direction, such that the unidirectional transmission of the second band gap gradually converted to a double-pass. 3. Analyzed and discussed the symmetry of the problem fluctuate unidirectional transmission system proposed single-pass effect must also satisfy the time reversal and space inversion symmetry breaking, the time of the evanescent wave inversion characteristics and the time reversal symmetry Several mechanisms are discussed from the point of view of the Hamiltonian. Using finite element analysis (FEM) is studied theoretically generated Lamb wave phonon crystal band, found that the generation of the band gap exists Bragg scattering and locally resonant two mechanisms. Duty cycle very the round hole Lamb wave phononic crystal band gap direction, to combined diffraction structure design and simulate the effect of a one-way transmission of Lamb waves. Lamb wave phonon crystal structures of the experimental system, including excitation and interference detection. Calculate the three-dimensional close-packed structure hypersonic phonon band. The experiment using laser ultrasonic interferometer detecting abnormality two acoustic transmission evanescent wave of the surface of the surface of the diffracted wave and acoustic model (EAT), to visually detect the presence of such SAW, confirmed the SAW of EAT important role. Design surface asymmetric cyclical structure of the one-dimensional single slit, found that the spread of asymmetric and unidirectional bunching effect. Establish an analytical model to explain the single-pass effect. Discussed transmittance and the bunching effect of such models the impact of several mechanisms: slit resonance mode, the recess resonance mode, the surface acoustic wave. In summary, this paper artificial phonon bandgap materials to achieve sonic unidirectional or nonreciprocal propagation phenomenon system using different analytical calculation method designed several artificial structure on a theoretical simulation to achieve sonic unidirectional propagation model, and experimentally confirmed. Involves not only the very forefront of physics, such as symmetry, time reversal, non-reciprocal, abnormal transmission, also relates to the application of technical phononic crystal preparation, measurement, surface wave detection. Artificial phonon band gap materials with the quantum system analogy it can make more clearly to the electronic systems in the physical image; combined with the design and development of the high-frequency acoustic device also has important practical significance.

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