The Hall effect of elastic waves has attracted much attention due to its unique properties.A hexagonal lattice phononic crystal plate model is designed in this paper.By changing the spatial symmetry of the unit cell,a...The Hall effect of elastic waves has attracted much attention due to its unique properties.A hexagonal lattice phononic crystal plate model is designed in this paper.By changing the spatial symmetry of the unit cell,a band gap for the A0 Lamb wave is opened.The existence of the edge state of the phononic crystal plate is obtained by finite element simulation.It is found that both zigzag-type edge and bridge edge are topological edge states by analysis of the band structure of the supercell.A rectangular model with a straight channel is designed and the simulation results show that the two types of channels are topologically protected only for the A0 mode Lamb wave but not for the S0 mode.In addition,the results of numerical simulation are verified by experimental data measured by a laser vibrometer.Finally,it is found that neither upside V-shaped channels nor channels with defects will affect the stable propagation of A0 Lamb waves along the proposed route.This proposed model and method are helpful in broadening the means of regulating elastic waves in phononic crystal structures,and extending practical application of topological edge states in such structures.展开更多
Extensive studies have revealed the phenomenon of directional wave propagation in phononic crystals(PnCs)and metamaterials,due to the functionality of energy and information transportation along specified paths.Distin...Extensive studies have revealed the phenomenon of directional wave propagation in phononic crystals(PnCs)and metamaterials,due to the functionality of energy and information transportation along specified paths.Distinguished from previous elastic media,this work combines finite element simulations and experiments to investigate directional flexural wave propagation in viscoelastic PnC plates.The sample of cross-shaped viscoelastic PnC plate is fabricated from epoxy resin with characterization of viscoelasticity by Kelvin-Voigt model.Firstly,non-negligible discrepancies of wave attenuation are observed between complex band structures of unit cell and transmission spectrum of finite PnC plate.In comparison,complex dispersion and modal analysis on the basis of supercell more accurately capture the wave attenuation ranges.Secondly,both simulations and experiments confirm the phenomena of flexural wave propagation along either single or two orthogonal directions.The complex band structures of supercell are employed to help predict the spatial attenuation of evanescent wave within directional bandgaps.The characterization results,with combination of low-order evanescent modes,agree well with numerical simulations and experimental measurements.In addition,the orthotropy index and concentration index of wave transmitting are proposed to evaluate the directional wave propagation.For wave transmitting in a single direction,there is significant and positive correlation between concentration index along the propagating direction and the imaginary part of wavenumber along its orthogonal direction.This work could shed light on the directional propagation of flexural waves,which is beneficial to the design of viscoelastic devices and waveguides.展开更多
In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of p...In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of positive-negative(PN)junctions.Unlike piezoelectric phononic crystals,the coupled Bloch waves in PSC phononic crystals are attenuated due to their semiconductor properties,and thus the solution of Bloch waves becomes more complicated.The transfer matrix of the phononic crystal unit cell is obtained using the state transfer equation.By applying the Bloch theorem for periodic structures,the dispersion relation of the coupled Bloch waves is derived,and the dispersion,attenuation,and bandgap are obtained in the complex wave number domain.It is found that the influence of the PN junction cannot be neglected.Moreover,the effects of the PN junction under different apparent wave numbers and steady-state carrier concentrations are provided.This indicates the feasibility of adjusting the propagation characteristics of Bloch waves through the regulation of the PN heterojunction.展开更多
摘要The Hall effect of elastic waves has attracted much attention due to its unique properties.A hexagonal lattice phononic crystal plate model is designed in this paper.By changing the spatial symmetry of the unit cell,a band gap for the A0 Lamb wave is opened.The existence of the edge state of the phononic crystal plate is obtained by finite element simulation.It is found that both zigzag-type edge and bridge edge are topological edge states by analysis of the band structure of the supercell.A rectangular model with a straight channel is designed and the simulation results show that the two types of channels are topologically protected only for the A0 mode Lamb wave but not for the S0 mode.In addition,the results of numerical simulation are verified by experimental data measured by a laser vibrometer.Finally,it is found that neither upside V-shaped channels nor channels with defects will affect the stable propagation of A0 Lamb waves along the proposed route.This proposed model and method are helpful in broadening the means of regulating elastic waves in phononic crystal structures,and extending practical application of topological edge states in such structures.
基金supported by the National Natural Science Foundation of China(Grant Nos.12021002 and 12302023).
摘要Extensive studies have revealed the phenomenon of directional wave propagation in phononic crystals(PnCs)and metamaterials,due to the functionality of energy and information transportation along specified paths.Distinguished from previous elastic media,this work combines finite element simulations and experiments to investigate directional flexural wave propagation in viscoelastic PnC plates.The sample of cross-shaped viscoelastic PnC plate is fabricated from epoxy resin with characterization of viscoelasticity by Kelvin-Voigt model.Firstly,non-negligible discrepancies of wave attenuation are observed between complex band structures of unit cell and transmission spectrum of finite PnC plate.In comparison,complex dispersion and modal analysis on the basis of supercell more accurately capture the wave attenuation ranges.Secondly,both simulations and experiments confirm the phenomena of flexural wave propagation along either single or two orthogonal directions.The complex band structures of supercell are employed to help predict the spatial attenuation of evanescent wave within directional bandgaps.The characterization results,with combination of low-order evanescent modes,agree well with numerical simulations and experimental measurements.In addition,the orthotropy index and concentration index of wave transmitting are proposed to evaluate the directional wave propagation.For wave transmitting in a single direction,there is significant and positive correlation between concentration index along the propagating direction and the imaginary part of wavenumber along its orthogonal direction.This work could shed light on the directional propagation of flexural waves,which is beneficial to the design of viscoelastic devices and waveguides.
基金Project supported by the National Natural Science Foundation of China(Nos.11872105,12072022,11911530176,and 12202039)。
摘要In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of positive-negative(PN)junctions.Unlike piezoelectric phononic crystals,the coupled Bloch waves in PSC phononic crystals are attenuated due to their semiconductor properties,and thus the solution of Bloch waves becomes more complicated.The transfer matrix of the phononic crystal unit cell is obtained using the state transfer equation.By applying the Bloch theorem for periodic structures,the dispersion relation of the coupled Bloch waves is derived,and the dispersion,attenuation,and bandgap are obtained in the complex wave number domain.It is found that the influence of the PN junction cannot be neglected.Moreover,the effects of the PN junction under different apparent wave numbers and steady-state carrier concentrations are provided.This indicates the feasibility of adjusting the propagation characteristics of Bloch waves through the regulation of the PN heterojunction.