Tunable three-dimensional nonreciprocal transmission in a layered nonlinear elastic wave metamaterial by initial stresses

In this work,the three-dimensional(3 D)propagation behaviors in the nonlinear phononic crystal and elastic wave metamaterial with initial stresses are investigated.The analytical solutions of the fundamental wave and second harmonic with the quasilongitudinal(qP)and quasi-shear(qS_(1) and qS_(2))modes are derived.Based on the transfer and stiffness matrices,band gaps with initial stresses are obtained by the Bloch theorem.The transmission coefficients are calculated to support the band gap property,and the tunability of the nonreciprocal transmission by the initial stress is discussed.This work is expected to provide a way to tune the nonreciprocal transmission with vector characteristics.

Active feedback control of sound radiation in elastic wave metamaterials immersed in water with fluid-solid coupling

Due to their potential properties unlike traditional materials and structures,elastic wave metamaterials have received significant interests in recent years.With the coupling between the acoustic and vibration,their mechanical characteristics can be tuned by the active feedback control system at low frequency ranges in which the traditional passive control is limited.This work illustrates that the superior performances of the effective mass density and sound pressure level(SPL)of an elastic wave metamaterial can be significantly changed by the active control,in which the periodic array of local resonators and orthogonal stiffeners are included.Significantly,based on the locally resonant mechanism,the negative density occurs over a frequency range.Due to the effects of lattice constant,structural damping and other parameters,the SPL with the function of fluid-solid coupling are illustrated and discussed.

Sound Transmission Comparisons of Active Elastic Wave Metamaterial Immersed in External Mean Flow

Using the active feedback control system on the elastic wave metamaterial,this research concentrates on the sound transmission with the dynamic effective model.The metamaterial is subjected to an incident pressure and immersed in the external mean flow.The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside.The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms.Based on the dynamic equivalent method,the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter.With the coupling between the fluid and structure,the expression of the sound transmission loss(STL)is derived.This research shows the influence of effective mass density on sound transmission properties,and the STL in both modes can be tuned by the acceleration and displacement feedback constants.In addition,the dynamic response and the STL are also changed obviously by different values of structural damping,incident angle(i.e.,the elevation and azimuth angles)and Mach number of the external fluid with the mean flow property.The results for sound transmission by two methods are compared,i.e.,the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one.This paper is expected to be helpful for understanding the sound transmission properties of both pure single-and double-plate models.