Study On Low Frequency Sound Absorption Performance Of Fish Like Porous Coupling Structure

In today's society,noise has been called the third largest pollution source besides air pollution and water pollution,especially low-frequency noise.It has complex sources,long wavelength and can easily pass through obstacles.It is one of the most difficult problems in noise pollution.Low frequency sound waves have more obvious propagation advantages in aqueous media.Many fish are very sensitive to low-frequency sound waves and can "hear" low-frequency sound waves.Because the fish has no outer ear,the sound wave must enter the listening organ after passing through the fish scale,fish meat and other tissues.In this process,the role of fish scale and fish meat on low-frequency sound wave is "sound transmission".At the same time,due to the difference between the impedance of fish organ and tissue and the impedance of water,as well as the internal cavity structure of fish body,the phenomenon of "sound absorption" will occur at the same time of sound transmission.Aiming at the problem of low-frequency sound absorption,this paper takes typical fish as the object,studies the micro and macro structure of fish scale,fish meat and cavity,and analyzes its sound absorption and sound transmission mechanism,so as to provide a new idea for the research of low-frequency sound absorption.Based on the basic method of bionic modification based on engineering bionics,this paper studies the bionic sound-absorbing structure from the perspective of bionic coupling and nonsmooth theory,taking the body surface morphology and muscle tissue of fish as the starting point.Firstly,the digital characteristics of the surface scale morphology of three typical fish are studied,the unit and geometric distribution characteristics of shield scale and hard scale are quantitatively analyzed,the arrangement structure and physical properties of muscle tissue are analyzed,and the mechanical properties of three kinds of fish are compared.The results show that the scale structure of fish has different degrees of periodic lines and arrangement,The shield scale and the hard scale have micro seams or microporous cavities of a certain size,and the cavities are connected in series with the subcutaneous muscles of the fish,forming a coupled sound-absorbing system.Then,the impedance tube acoustic test system is used to study the low-frequency sound absorption coefficient of shark,sea bass and flounder muscle and the sound absorption characteristics of the composite structure of scale and cavity.The results show that muscle and fish scale have higher sound absorption coefficient at medium and low frequency,among which shark muscle and shield scale structure have the best sound absorption coefficient,and the sound absorption peak shifts to low frequency with the change of thickness.According to the arrangement of scales on the body surface of three typical fish,the bionic sound-absorbing structure is designed based on the micro perforated plate structure,and the sound-absorbing coefficients of the bionic sound-absorbing structure under different perforation rate and back cavity depth are discussed.The results show that the lower perforation rate and higher back cavity depth can effectively realize the shift of sound-absorbing peak to low frequency.In order to improve the low frequency sound absorption performance of the bionic sound absorption structure,the total transfer matrix of the composite structure is deduced through the transfer matrix method for the mechanical impedance plate of the aluminum foam material and its composite sound absorbing structure,and the formula for calculating its sound absorption coefficient is obtained.The results show that the composite structure with mechanical impedance plate has better sound absorption effect at low frequency,and there are two sound absorption peaks in higher frequency,which are caused by cavity resonance and mechanical impedance plate resonance respectively.