While conventional topological states can be used for robust acoustic energy transportation,the energy capacity is limited and the propagation route is also heavily constrained.In this work,we show that Landau levels ...While conventional topological states can be used for robust acoustic energy transportation,the energy capacity is limited and the propagation route is also heavily constrained.In this work,we show that Landau levels in acoustic systems can offer exciting new avenues for transporting acoustic energies.In particular,we realize valley-dependent Landau levels in a two-dimensional inhomogeneous acoustic system induced by synthetic in-plane magnetic fields.The band diagrams of the 0th-and 1st-order Landau levels are experimentally measured and their robustness of propagation against defects is also experimentally validated.Promising ways for acoustic energy transportation enabled by the Landau levels,such as large-area transportation and snake-like transportation are experimentally demonstrated.Importantly,we achieve topological propagation along an arbitrary prescribed path using unique features of the valley-dependent Landau levels for the first time in experiment,which is a significant advancement beyond what can be achieved using conventional acoustic topological states based on valley/spin Hall physics.These remarkable features open up promising opportunities for developing novel acoustic devices to realize robust,broadband,and flexible large-area acoustic energy conveying.展开更多
Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum(OAM) essential for applications ranging from object manipulation to acoustic communication. However, th...Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum(OAM) essential for applications ranging from object manipulation to acoustic communication. However, their flexibility in terms of chirality control has thus far been limited by the lack of reconfigurability and degrees of freedom like spin–orbit coupling. Here we show that this restriction can be lifted by controlling the individual on–off states of two coherent monopolar sources inside a passive parity-time-symmetric ring cavity at an exceptional point where the counter-propagating waves coalesce into one chiral eigenmode. One of the sources satisfies the chirality-reversal condition, generating a travelling wave field fully decoupled from and opposite to the chiral eigenmode, while the other source is phase-shifted such that the wave generated by the first source can be canceled out, and the remaining sound field circulates in the same direction as the chiral eigenmode. Such non-Hermitian selective excitation enables our experimental realization of acoustic vortex emission with switchable OAM but free of system reconfiguration. Our work offers opportunities for chiral sound manipulation as well as integrated and tunable acoustic OAM devices.展开更多
We demonstrate a conformally mapped multifunctional acoustic metamaterial Mikaelian lens.Mikaelian lens is a gradient medium with a hyperbolic secant refractive index profile that can realize functions like beam self-...We demonstrate a conformally mapped multifunctional acoustic metamaterial Mikaelian lens.Mikaelian lens is a gradient medium with a hyperbolic secant refractive index profile that can realize functions like beam self-focusing.Unlike the conventional design approaches,with a conformal transformation method,only isotropic material parameters with gradient refractive index profiles are required for the construction of such lens.To realize desired gradient index distribution,we carefully design a new type of crosschannel-shaped acoustic metamaterial,whose refractive index can be effectively modulated by simply changing the slit opening size.The distinct capabilities of the metamaterial Mikaelian lens in manipulating acoustic waves are experimentally verified with the fabricated sample.Simultaneous sound guiding and Talbot effects,which normally require respective geometrical and wave acoustic approximations,are observed in simulations and experiments.Furthermore,those effects of shaping acoustic wave propagations were validated within a relatively wide frequency range.Our study reveals how the conformal transformation method can help to bridge the ray acoustics with wave acoustics.It offers opportunities to the development of novel multifunctional acoustic devices for various applications,such as sound and particle manipulations.展开更多
基金supported by the University-Industry Collaborative Education Program of the Ministry of Education of China(Grant No.220804972162224)the National Natural Science Foundation of China(Grant Nos.92263208 and 12102134)+3 种基金the National Key R&D Program of China(Grant Nos.2022YFA1404400 and 2022YFA1404403)the Fundamental Research Funds for the Central Universities,the Research Grants Council of Hong Kong SAR(Grant Nos.15214323,15200922,15202820,and AoE/P-502/20)the Hong Kong Innovation and Technology Commission via project“Smart Railway Technology and Applications”(Grant No.K-BBY1)the Faculty Development Scheme(FDS)RGC Project(Grant No.UGC/FDS24/E04/21).
文摘While conventional topological states can be used for robust acoustic energy transportation,the energy capacity is limited and the propagation route is also heavily constrained.In this work,we show that Landau levels in acoustic systems can offer exciting new avenues for transporting acoustic energies.In particular,we realize valley-dependent Landau levels in a two-dimensional inhomogeneous acoustic system induced by synthetic in-plane magnetic fields.The band diagrams of the 0th-and 1st-order Landau levels are experimentally measured and their robustness of propagation against defects is also experimentally validated.Promising ways for acoustic energy transportation enabled by the Landau levels,such as large-area transportation and snake-like transportation are experimentally demonstrated.Importantly,we achieve topological propagation along an arbitrary prescribed path using unique features of the valley-dependent Landau levels for the first time in experiment,which is a significant advancement beyond what can be achieved using conventional acoustic topological states based on valley/spin Hall physics.These remarkable features open up promising opportunities for developing novel acoustic devices to realize robust,broadband,and flexible large-area acoustic energy conveying.
基金supported by Research Grants Council of Hong Kong(C6013-18G,15211918,and 15205219)the National Natural Science Foundation of China(11774297)+4 种基金support from the National Natural Science Foundation of China(12104383)Internal Research Fund of The Hong Kong Polytechnic University(ZZLC)supported by Hong Kong Research Grants Council(12302420,12300419,and 22302718)the National Natural Science Foundation of China(11922416 and 11802256)Hong Kong Baptist University(RC-SGT2/18-19/SCI/006)。
文摘Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum(OAM) essential for applications ranging from object manipulation to acoustic communication. However, their flexibility in terms of chirality control has thus far been limited by the lack of reconfigurability and degrees of freedom like spin–orbit coupling. Here we show that this restriction can be lifted by controlling the individual on–off states of two coherent monopolar sources inside a passive parity-time-symmetric ring cavity at an exceptional point where the counter-propagating waves coalesce into one chiral eigenmode. One of the sources satisfies the chirality-reversal condition, generating a travelling wave field fully decoupled from and opposite to the chiral eigenmode, while the other source is phase-shifted such that the wave generated by the first source can be canceled out, and the remaining sound field circulates in the same direction as the chiral eigenmode. Such non-Hermitian selective excitation enables our experimental realization of acoustic vortex emission with switchable OAM but free of system reconfiguration. Our work offers opportunities for chiral sound manipulation as well as integrated and tunable acoustic OAM devices.
基金The work was supported by the National Natural Science Foundation of China(Grant No.11774297)the university research grant G-YBXM from the Hong Kong Polytechnic UniversityY.L.acknowledges the support from the National Natural Science Foundation of China(Grant No.11704284).
文摘We demonstrate a conformally mapped multifunctional acoustic metamaterial Mikaelian lens.Mikaelian lens is a gradient medium with a hyperbolic secant refractive index profile that can realize functions like beam self-focusing.Unlike the conventional design approaches,with a conformal transformation method,only isotropic material parameters with gradient refractive index profiles are required for the construction of such lens.To realize desired gradient index distribution,we carefully design a new type of crosschannel-shaped acoustic metamaterial,whose refractive index can be effectively modulated by simply changing the slit opening size.The distinct capabilities of the metamaterial Mikaelian lens in manipulating acoustic waves are experimentally verified with the fabricated sample.Simultaneous sound guiding and Talbot effects,which normally require respective geometrical and wave acoustic approximations,are observed in simulations and experiments.Furthermore,those effects of shaping acoustic wave propagations were validated within a relatively wide frequency range.Our study reveals how the conformal transformation method can help to bridge the ray acoustics with wave acoustics.It offers opportunities to the development of novel multifunctional acoustic devices for various applications,such as sound and particle manipulations.
