The Realization Of One-way Acoustic Wave Propagation With Artificial Acoustic Structure

Recently, the investigation of acoustic rectification effect and artificial acoustic materials has been given more attention. Inspired by electric diode, research on various types of waves has never stopped. After optical wave, the use of specially-designed artificial structures on acoustic and heat wave has made a magnificent break though. At the first time, unidirectional nonreciprocal transmission of acoustic and heat wave was realized respectively by Chinese and Singaporean researchers. Acoustic rectification study shows that operation frequency range is decided by photonic crystal (PC) and frequency conversion depends on nonlinear acoustic material respectively. Unlike acoustic metamaterials, PC is periodic artificial composite structure or material and the effective wavelength of its band-gaps and the lattice dimension of periodic material are at the same magnitude. Distortion, harmonics, excess attenuation, acoustic saturation and cavitation will occur when acoustic propagations in nonlinear acoustic material. However, due to low conversion efficiency in nonlinear system with parameter uncertainty in experiments, researchers around the world dedicated effort to make asymmetrical acoustic propagations real in linear system. On the other hand, it is also a huge challenge to realize one-way transmissions of acoustic energy in linear system because of reciprocity principle. This dissertation gives out intensive and systematic study on acoustic rectification effect in PC and artificial acoustic structures.In Chapter Ⅰ, the history of acoustic rectification and asymmetrical acoustic propagations as well as latest update is presented. At meantime, theories and experiments of acoustic propagations in PC are elaborated and an introduction of the main content of this study is put at the end of this chapter.In Chapter Ⅱ, energy band theory of periodic crystals and common approximate analysis methods are introduced. Meanwhile, the related acoustic waveguides theories are mentioned, including propagation modes in acoustic waveguides.In Chapter Ⅲ, theories and computation methods of acoustic propagations in artificial material are listed. This section focuses on using plane wave expansion and finite element method (FEM) to calculate band gap structure of periodic PC.In Chapter Ⅳ, FEM was brought into the study of band gap structure of sound wave in PC and its filtering properties on incident sound waves combines with acoustic waveguides methods to make the First linear unidirectional acoustic transmission waveguide and realize acoustic asymmetric propagation in bounded space. Research has conducted systematically on how filling ratio, size of PC, operating emission area and quasi-periodicity of crystal structure effect on transmission spectra and acoustic energy distribution in one-way acoustic transmission waveguide.In Chapter Ⅴ, it is the conclusion of this study and prospects for the future work.The innovations of this study are listed below:1. In the first time, PC was put into two-dimensional acoustic waveguide in bounded space and the first linear unidirectional acoustic transmission waveguide was designed by utilizing filtering properties of band gap on incident sound waves combines with acoustic waveguides. It realized acoustic asymmetric propagation in bounded space and further more there will be a corresponding, easily-designed, one-way transmission structure according to different bending angles of pipes. This ground-breaking work is valuable to related (foundational) research and application areas.2. The first three-dimensional linear unidirectional acoustic transmission waveguide structure was made and the prototype was measured the forward and reverse transmission spectra in the waveguide. This experiment has confirmed the effectiveness of this original structure. Various factors which might affect transmission efficiency and cut-off frequency are also discussed.3. This new design has high forward transmission efficiency as well as strong reverse cut off ability. Meanwhile, influences on transmission spectra and acoustic energy distribution in one-way acoustic transmission waveguide, such as filling ratio, size of PC, operating emission area and quasi-periodicity of crystal structure are carefully investigated. The advantages of this model are easy to set up, high transmission efficiency and high-contrast energy fluxes at forward and reverse directions and it improved forward transmission efficiency of nonlinear unidirectional acoustic structure greatly.