Sound Insulation Properties Of Metamaterial-based Honeycomb Sandwich Plate Structure

The honeycomb sandwich plate structure is the most common light structure in aircraft,car,high-speed railway,aircraft carrier and other equipment cabin,and its sound insulation property?sound transmission loss,STL?is an important index to measure the performance of the cabin for noise control.Honeycomb sandwich plate structure characterizes light weight and high rigidity,and its sound insulation property is excellent in the high frequency band.But its sound insulation property is limited by the mass law in the low frequency band,which fails to meet the requirements of the modern equipment.So it is necessary to develop a new theory and new technology of sound insulation and noise reduction for honeycomb sandwich plate structure.In recent years,the development of acoustic metamaterial technology for low-frequency sound insulation provides a new way of thinking.Acoustic metamaterials are a new type of acoustic material or structure composed of specially designed artificial microstructure units?such as local resonance units?arranged in the matrix material periodically,featuring extraordinary mass density,elastic modulus and other characteristics.A new type of metamaterial structure can be designed by analogy with the idea of acoustic metamaterials.Such structures can achieve extraordinary equivalent mass density properties,thus breaking the limits of the mass law and achieving an efficient sound insulation under the light-weight condition in the low frequency range,which offers a promising prospect for noise reduction.In this paper,a new type of metamaterial-based honeycomb sandwich plate structure is constructed by adding“spring-mass”periodically local resonators to the structure of honeycomb sandwich plate.The paper introduced the basic theory,and then performed calculations for sound insulation characteristic.Further work presented analyses.Finally,the work conducted a design for a new metamaterial-based honeycomb sandwich plate structure.The main contents and results are as follow:1.Based on the dynamic equivalent method of honeycomb sandwich plate and the second equivalent model of“plate-resonator”,the study develops the calculation method for an efficient acoustic insulation of the metamaterial-based honeycomb sandwich plate.According to the intrinsic relationship between structural bending stiffness and wave vector,a new dynamic equivalent method is proposed for calculating the equivalent bending stiffness of honeycomb sandwich plate,namely"wave vector inversion method".This method is potential to be widely and commonly applied in many fields with its high accuracy in calculation.An effective medium method is conducted for the calculation of sound insulation properties of an infinite metamaterial-based honeycomb sandwich plate based on the equivalent dynamic model of plate-resonator.This method enjoys its main advantages due to the high efficiency and accuracy in calculation.The above methods provide a powerful tool for the study of sound insulation properties of metamaterial-based honeycomb sandwich plate.2.The extraordinary sound insulation properties of the honeycomb sandwich plate are explored and the sound insulation mechanism is revealed.The STL curve of the metamaterial-based honeycomb sandwich plate clearly shows that the metamaterial-based honeycomb sandwich plate produces a significant STL peak near the resonant frequency,and its STL peak is much larger than that of the equal mass sandwich plate of the STL.In addition,the generation mechanism of the STL peak is also revealed from the view of dynamic quality.The results show that the mutual coupling between sandwich plate and resonator leads the dynamic mass of acoustic metamaterial-based honeycomb sandwich plate to infinite at resonance frequency.3.The influence of various parameters on sound insulation properties of metamaterial-based honeycomb sandwich plate is systematically analyzed.The results show that the smaller the elevation angle?is,the better the STL is.Increasing the resonator mass m_r or reducing the resonator rigidity k_r can adjust the position of the STL peak of the mezzanine plate of the metamaterial to low frequency.Enhancing the resonator damping?_r can help smooth the STL peak and dip.When the additional mass ratio?_m of the resonator is increased,and the STL near the acoustic peak is up.The honeycomb length l₁,wall thickness t₁,the thickness h_s of the face plate and the thickness h_c of the core layer have a significant effect on the STL of the metamaterial-based honeycomb sandwich plate.In addition,by employing the multi-frequency modular resonance unit,the STL peaks of the band has been effectively widened.4.The investigation designed and then fabricated the metamaterial-based honeycomb sandwich plate.Further work built a test platform for sound insulation properties.The experiment tested sound insulation properties and then proved that the metamaterial-based honeycomb sandwich plate has good sound insulation and noise reduction in low frequency.In short,this paper aims at the requirements of sound insulation and noise reduction of modern equipment cabin-structure.The work constructed a metamaterial-based honeycomb sandwich plate structure,which is commonly used in the cabin.The investigation systematically studied the sound insulation properties of the metamaterial-based honeycomb sandwich plate,the sound insulation mechanism and the influence parameters of the sound insulation properties.The work in this paper is expected to provide a new technical approach and for realizing sound insulation and noise reduction of the equipment cabin-structure,which paves a road for the development of acoustic metamaterials and related theories.