Study On Acoustic Transmission Characteristics Based On Composite Waveguide

This paper mainly studies the acoustic transmission characteristics of composite waveguide,including its acoustic impedance variation characteristics and the existence of multiple resonance coupling effect,and discusses the practical application cases.This paper is divided into five chapters.Apart from the introduction of the first chapter and the summary and outlook of the fifth chapter,this paper mainly studies the following three parts.1.The control effect of sound waves on the composite waveguide: how to implement the subwavelength structure acoustic ultra low frequency sound wave control has been hot topic in the field of materials research,in recent years,a variety of research emerge in endlessly,this paper proposes a composite can achieve broadband acoustic waveguide structure regulation,the structure consists of a main waveguide and two spiral lateral tubes,connected by pipes in the middle.In order to achieve the purpose of broadband and low frequency regulation,we designed two kinds of spiral side branches in the composite waveguide.By changing the symmetry of the side branches to achieve coupling vibration,the acoustic impedance jump can be triggered,so that the size limit of the structure can be broken,and the low frequency acoustic regulation can be realized in the subwavelength structure.Theoretical research and simulation show that changing the symmetry of the composite structure will greatly affect the acoustic impedance variation of the structure.More importantly,the multi-mode vibration of the composite waveguide can be adjusted by simply adding water to change the effective length of the side pipe.The composite waveguide structure has a very important application value in the low frequency acoustic regulation.2.Asymmetric impedance matching method based on composite waveguide and its application: Due to the particularity of acoustic transmission,it is difficult to achieve high efficiency transmission in many occasions,especially for interfaces with large acoustic impedance differences.In this paper,the coupling vibration of composite waveguide is used to adjust the structural acoustic impedance to achieve the acoustic impedance matching between different media.Coupling vibration model depends on its structure size and symmetry,so this article in view of the water-the most common air interface,first to explore the structural parameters are studied through theoretical and simulation for complex waveguide acoustic impedance change and the influence of the energy transmission coefficient,find the most suitable for the actual application of structural parameters,and then through the experiment to verify the correctness of the theory and simulation.The final results show that the acoustic impedance of the composite waveguide can be adjusted by changing the structural parameters and their symmetry,and the multi-frequency tunable acoustic transmission can be achieved at the water-air fluid interface.The proposed composite waveguide structure provides a new method for acoustic impedance matching over the unmatched fluid interface.Compared with the traditional quarter-wavelength matching method,the proposed composite waveguide structure has the advantages of simple structure and high transmittance,especially in the water-air interface acoustic communication.3.Low-frequency wideband noise cancellation structure based on composite waveguide:noise pollution has become a serious environmental problem.The thickness of the traditional noise cancellation structure is equivalent to the working wavelength,so it is difficult to effectively control the low-frequency sound wave in practical application.In this paper,based on the coupling effect of multi-mode sound absorption and insulation mechanism,a coupling noise attenuation structure based on micro-perforated plate and composite waveguide is proposed.By designing different structural parameters,the noise attenuation band of micro-perforated plate and composite waveguide is combined to make the structure break through the original narrow band problem.At the same time,because the structure is interconnected,the coupling effect between the two can greatly improve the noise cancellation capacity and bandwidth of the structure.The coupling effect is mainly reflected in the low frequency,which can effectively suppress the noise within the range of100-1600 Hz.Importantly,theoretical analysis and experiments have proved that the average sound transmission loss of the structure is 20 d B between 100 Hz and 1600 Hz,and the thickness is only 6.2cm.In addition,it can also suppress noise while maintaining air circulation,in the field of noise control has a wide range of applications.