Research On Multifunctional Elastic Wave Control Of Active And Passive Acoustic Laminate Metamaterials

The 20th century,which can be regarded as the electronic century,has clearly shown that the extreme physical properties of living nature and man-made devices are particularly apparent under resonance conditions.The achievements of modern civilizations such as televisions,computers,electronic communications and the Internet are all due to the various resonant elements.However,most of the standard resonant components and mechanisms based on them can no longer meet the growing demands of high-tech innovation fields such as optics,acoustics and electronics.It was expected that further progress would be related to the creation of new structures which would have unique resonance properties.Thus,a new type of man-made structures with distinct resonance properties were proposed at the turn of the 20^th and 21^st centuries.The local resonance acoustic metamaterials are artificially periodic composites that can exhibit some unique properties not available in nature,such as negative mass density and negative bulk modulus.Based on these concepts,many acoustic/elastic metamaterials with resonant units are designed to achieve a wider bandgap at subwavelength scale,for emerging application such as low frequency vibration suppression/sound wave isolation,cloaking,waveguide et al.Based on the negative effective mass and negative effective bending stiffness characteristics of the local resonance metamaterials,the multifunctional elastic wave control performance of the active and passive laminate acoustic metamaterials is investigated in detail.This paper focuses on the design of mechanical local resonance structures,damping application,tunable band gap structures,hybrid local resonance structures,key parameters of microstructure,multi physical coupling field modeling and the application of laminate acoustic metamaterials in automobile vibration and noise reduction.The main contents and innovative work are summarized as follows:1.A new design concept is proposed for engineering plates with wide bandgap at low frequency.The calculation methods of band gap of anisotropic local resonant metamaterials are improved.Due to the superior strength to weight ratio of CFRP,the laminate acoustic metamaterials are able to have a much wider stopband than the conventional metamaterial plates proposed in recent years.At same time,the bandgap only exist in a narrow frequency range for most of mechanical acoustic metamaterials.To solve this problem,the laminate acoustic metamaterials with multi-stopband(MSLAM)are proposed.Based on the Laminate theory,Kirchhoff Plate theory,Hamilton principle and structural-acoustic coupled system theory,a finite element analysis model of the structure is established.According to the dispersion analysis,two stopbands are observed around the absorbers'resonant frequency.Based on the finite element modeling,the multi-stopband behavior has been confirmed.In addition,the effects of damping of vibration absorbers are discussed in this work.By adding the appropriate damping to the vibration absorbers,the two stop bands can be combined into a wider stopband.Subsequently,the analyses of multi-stopband laminate acoustic metamaterials in the structural-acoustic coupled system are performed.The excellent performance of multi-stopband laminate acoustic metamaterials has been applied to the front panel of vehicle,and the noise of passenger compartment cavity is reduced significantly.2.The electrical and mechanical properties of piezoelectric materials are explained through four types of piezoelectric constitutive equations.And based on them,a piezoelectric shunt damping model is established.The control principle of the piezoelectric shunt damping system is explained.The frequency range and key factors of the negative equivalent elastic modulus in the resonant shunt circuit and the negative capacitance shunt circuit are investigated.Moreover,by introducing the damping factors,the characteristics of the negative capacitance piezoelectric shunt system are analyzed.3.A lightweight adaptive laminate acoustic metamaterial(ALAM)with higher design freedom for wave attenuation aimed at the defect of non-adjustable band gap of traditional mechanical local resonance metamaterials is proposed.The arbitrary directional attenuation constants as well as the effective properties of the ALAM are derived analytically based on the developed bandgap analysis model of hybrid laminate metamaterials which consider the wave field transformation,electro-mechanical coupling and shunting circuits'effects.A comprehensive analytical model is first developed to reveal the tunable wave attenuation capability in regard to the equivalent bending stiffness of ALAM.The tunable wave attenuation behavior has been confirmed through finite element modeling(FEM)in COMSOL.According to the results,the ALAM can generate a relatively broadband low-frequency bandgap without significantly increasing the weight of the metamaterial.Numerical results reveal that the location of the bandgap depends not only on the parameters of the piezoelectric shunting circuit but also on the laminate.In addition,the bandwidth and wave attenuation amplitude can be tuned actively by varying the thickness of the laminate and the piezoelectric patches as well as the resistance and inductance.Moreover,by introducing the negative capacitance shunting circuit into the piezoelectric patches,the bandwidth can be enlarged significantly.4.The mechanisms of the mechanical and electromechanical locally resonant bandgaps are fundamentally different.By combining the two types of mechanisms,we design a hybrid piezoelectric laminate acoustic metamaterial(HPLAM).The HPLAM possesses both a negative mass density as well as a negative bending stiffness by properly utilizing both the mechanical and electric elements.A multi-physical analytical model is first developed to investigate and reveal the tunable wave manipulation abilities in terms of both the effective negative mass density and negative bending stiffness of the HPLAM.The flexural wave attenuation property can essentially be switched between‘Enhance/Eliminate'states by adjusting the shunting circuit.Numerical results demonstrate that the two bandgaps can be combined into a larger single bandgap to increase bandwidth,or that two bandgaps can be set individually to increase flexibility to customize the frequency response.The validity of the programmed waveguide is confirmed by wave transmission analysis in COMSOL.