Acoustic/Elastic Wave Propagation In Coupled Resonator Waveguides

When the defects are introduced into the phononic crystal,the defect states generated in the band gaps localize at the defects,and decay rapidly far away from the defect.Therefore,it is possible to localize and guide the wave propagation by designing defects in the perfect phononic crystal.Coupled-resonantor waveguide based on the coupling effect between a sequence of defect cavities have simultaneously strong wave confinement and low group velocity,and can be used to design rather arbitrary circuits.Furthermore,the propagation of elastic waves in a solid matrix can be controlled through changing fluid fillings based on the fluid-solid systems.So,they have essential applications in vibration reduction and noise isolation.In this thesis,the acoustic and elastic waves propagating in both periodic and aperiodic coupled-resonator waveguide are investigated.The fluid-solid interaction in fluid/solid phononic crystals is studied.The work is conducted by combining numerical simulations,theoretical model analysis and experimental investigations.The main contents and conclusions include:1.For acoustic wave propagation in a periodic coupled-resonator waveguide,the channeled spectrum model is developed to predict accurately the transmission properties.Different kinds of periodic coupled-resonator acoustic/elastic waveguides are designed and their transmission properties are investigated experimentally.The influence of the material viscosity and of geometric parameters on guided waves is discussed.The results show that the channeled spectrum model can accurately predict the number of oscillations.Channeled spectra depend on the length of the waveguide but are almost independent of the circuit details,including the number of turns.With the increase of the viscous damping,spectral oscillations in the channeled spectrum tend to be washed out.Strong confinement of Lamb waves along different coupled-resonator waveguides is observed.Numerical simulations and experimental results are in good agreement.The slab thickness is found to have little influence on the dispersion of in-plane guided Bloch waves,contrast with the hole length.2.For elastic wave propagation in an aperiodic coupled-resonator waveguide,an approximate model of the phononic polymer is proposed to explain the collective resonances of a chain of phononic microresonators.The vibration properties of the aperiodic coupled-resonator waveguide on different resonators and frequencies are measured.The results show that the approximate model can predict the number of resonance frequencies in the phononic polymer which is the same as the number of resonators in the chain.The collective resonance at the same frequencies of the defect resonators is explained by nearest-neighbor evanescent coupling.The limitation of the periodicity is broken by the aperiodic coupled-resonator waveguide and thus the transmission along the rather arbitrary circuits is realized.Simulations and experiments agree well.3.The real band structures,complex-wavevector band structures,complex-eigenfrequency band structures and the resolvent band structures are calculated in one-dimensional locally resonant sonic crystal.The influence of the material viscosity and of the lattice constant are discussed.The influence of the level of water filled in the waveguide on the transmission properties is investigated numerically and experimentally.The results show that the wave attenuation and the resonant band gaps are affected obviously by the lattice constant as well as the material viscosity in the complex-wavevector band structures and complex-eigenfrequency band structures.The continuous tunability of the band gaps is realized by changing the level of water inside the waveguide,effectively changing the cross-section and thereby the dispersion of the evanescent guided waves.The experimental and numerical results are consistent.4.The transmission properties of different kinds of coupled-resonator acoustoelastic waveguides are investigated,based on the fluid/solid phononic crystal.The influence of the distance between the nearest resonators and the polarization of the wave source to the wave properties is discussed.The effect of the fluid fillings and the fluid-solid interaction on the band structures is studied.The gradual modification of spectral transmissions as the number of the fluid-filled cavities increases is examined.The transmission properties of the reconfigurable waveguides are researched numerically and experimentally by positive or negative filling method which are realized by filling or removing a fluid into or from the structures.The results show that the coupled acoustoelastic propagation of well-confined waves is achieved.The evanescent coupling strength depends on the separation between the defect cavities.The different defect modes can be independently generated and controlled by selecting excitation frequencies and polarization.The fluid fillings and the fluid-solid interaction contribute to the propagating bands shifting to lower frequencies and the switching between the band gaps and passing bands,as well as the additional propagation modes.Strongly confined energy in the straight waveguide of both aluminum by positive filling and epoxy by negative filling phononic metaplates is realized.Furthermore,the transmission of strongly confined Lamb waves along the bent waveguide with strict 90? bend is achieved only in epoxy metaplate by negative filling due to the higher concentration degree and lower attenuation of energy.Experimental results are found to agree satisfactorily with numerical results.The channeled spectrum theory and the approximate model of the phononic polymer proposed in the present research provide a theoretical foundation for the research of the wave transmission properties in both periodic and aperiodic coupled-resonator waveguides.The tunable manipulation of the wave characteristics is realized owing to the fluid-solid interaction,which offers more possibilities for designing new acoustic devices.