| Nowadays,the level of social science and technology is increasing and developing fast.While improving people’s quality of life,scientific and technological progress has also brought some negative effects,one of which is the aggravation of noise pollution.In the process of industrial,engineering and social noise control,medium and high frequency noise is easily blocked by obstacles such as walls and green plants on the propagation path due to its short wavelength,strong energy carried by sound waves and weak penetration ability.However,the low-frequency noise possesses a long wavelength,weak acoustic energy,strong penetration ability,and weak natural attenuation,which is difficult to control.The traditional method can only rely on measures such as thickening the sound insulation wall and increasing the density of the blocking surface to suppress the propagation of low-frequency noise,but the cost is increased and the noise reduction effect is not particularly ideal.Membrane acoustic metamaterial(MAM)is becoming the mainstream structure in the field of low-frequency noise control due to its light weight and good low-frequency sound insulation performance.This paper first studies the theoretical system mainly involved in the design process of membrane metamaterial structure,namely the basic theory of membrane metamaterial noise reduction,the mechanism analysis of membrane structure noise reduction,and the equivalent medium theory.According to the derivation of the equivalent mass law,when the incident sound frequency is greater than the first natural frequency of the system,the membrane metamaterial structure exhibits a negative equivalent mass density,the mass block and the membrane produce reverse vibration,the average normal displacement of the membrane plane is close to zero,and the membrane surface is approximately a rigid plane.It can achieve almost total reflection of incident sound waves and achieve excellent sound insulation performance.The basic method of sound insulation analysis is determined,which provides a theoretical basis for studying the sound insulation mechanism of reflective film acoustic metamaterials and subsequent membrane structure simulation.Secondly,the sound insulation performance of the membrane acoustic metamaterial structure is simulated by using the acoustic-structure coupling module of the finite element analysis software COMSOL..Through the modal analysis of the sound insulation valley of the sound transmission loss curve of the membrane structure and the vibration mode at the corresponding sound insulation peak,the basic sound insulation mechanism of the membranetype acoustic metamaterial structure is summarized.By changing the different preset data of membrane metamaterials,the regulation law of the influence of structural parameters on the sound insulation curve of the system is summarized.Inspired by the above research on the sound insulation mechanism of the membrane-like metamaterial structure,a membrane-like metamaterial structure with a "X"-shaped swing arm attached to a cylindrical iron sheet as a mass block is proposed.The working mechanism of the designed new membrance-like metamaterial structure to achieve better broadband sound insulation performance is illustrated by numerical simulation.Based on the parametric analysis of the structural parameters of the cylindrical mass block and the material parameters of the "X" swing arm in the new structure,the adjustment law of the structural parameters of the additional mass block on the sound insulation ability of the new membraneacoustic metamaterial structure is summarized.The research and analysis demonstrat that the newly designed membrane structure can achieve good continuous broadband sound insulation performance in the low frequency band.Moreover,the overall sound insulation performance is superior.The "X" shaped central mass film acoustic metamaterial test sample was eventually made,and the sound insulation performance of the innovative structure was tested with a 100 mm impedance tube.The actual noise reduction effect is analyzed and the accuracy of the simulation results is also verified. |
