Yongyuan Jiang

By combining theoretical, numerical, and experimental approaches, this study presents a comprehensive investigation into the transmission spectrum of a one-dimensional phononic crystal (PC) composed of periodically stacked glass coverslips separated by water layers. The results reveal bandgaps, defect states, and band edge resonances in the range of 0.6–7.5 MHz. Wideband acoustic waves are excited within the defect layer of the PC and in free space via the photoacoustic effect. Ultrasound radiation is strongly enhanced at the resonant frequency of 0.836 MHz, with an acoustic energy density enhancement of (30.8 ± 0.6)×, while radiation at other frequencies is significantly suppressed. These findings strongly suggest that the enhancement originates from an increased acoustic density of states, although material absorption suppresses the enhancement at higher frequencies. This work provides direct insights for developing MHz ultrasonic emitters for biomedical applications and advances fundamental research in megahertz ultrasound.

In this work, we designed an underwater acoustic metasurface absorber composed of steel shell and rubber layer. The synergistic interaction between local resonance effect of the absorber cavity and viscoelastic property of the rubber layer significantly reduces the effective sound speed and enhances energy dissipation. The acoustic absorptivity will exceed 0.44 when the dual ports are set to equal length. Further by optimizing the structural parameters, the absorber works at exceptional point, offering asymmetric near-perfect absorption and high reflection. In addition, an acoustic absorption unit equipped with an extra rubber ring has been developed. Through the connection of two units, an average unilateral acoustic absorptivity of 0.88 on the unilateral side and the bilateral asymmetry of 22 are attained within the frequency range from 86 Hz to 140 Hz. The hydrostatic pressure resistance of underwater structures has also been confirmed through simulation analysis.

Efficient and robust transmission of sound energy across the water-air interface remains challenging due to severe impedance mismatch and environmental perturbations. Here, we propose and experimentally demonstrate a composite structure by coupling impedance matching acoustic metamaterials with Floquet topological waveguide array for sound transmission through different media. The metamaterials, whose operating frequency is located at frequency band of topological edge state, are employed to compensate the impedance mismatch. By engineering the driving pulse protocol of waveguide array, π-mode edge state is selectively excited while bulk states degenerate, enabling robust energy transmission under topological protection. A thin membrane is introduced to improve the robustness against the interface fluctuations when the water-immersion depth is less than 60 mm. According to experimental results, the correction coefficient in metamaterials during analysis process of impedance matching is modified to a complex form, reducing the discrepancy between analysis and simulated results. This work provides a paradigm for combining topological physics with acoustic metamaterials, and offers new opportunities for robust cross-medium communication, sensing and energy transmission.

The encirclement of exceptional points (EPs) in parametric space has been realized in optical waveguides, microwave cavities, nitrogen-vacancy centers, and so on. However, it often suffers from complex gain–loss manipulation. An acoustic platform to realize the evolution encircling the EP is highly desirable. In this work, an unclosed evolution protocol is proposed, which consists of parallel coupling and buffering branches and evolves through five distinct stages. Buffering the variation of Hamiltonian, inducing the transition to a low energy state, the evolution with favorable adiabaticity guarantees the EP encircling no longer depends on the precise loss manipulation. A non-Hermitian acoustic waveguide coupler (AWC), which is composed of combined cavities and air slit arrays, is presented to realize the encirclement. Experimental results of chiral phase conversion in a 0.5 m long AWC, spanning a broad bandwidth from 9.5 to 17.5 kHz, confirm the simplicity and effectiveness of state evolution encircling the EP. This work paves the way for AWC as a platform for non-Hermitian topological physics and facilitates the practical deployment of acoustic devices.

We propose a method to achieve a coherent switch of optomagnonic entanglement in a cavity optomagnonic system with non-Hermitian coupling. The strength of photon-photon and photon-magnon entanglement can be controlled by tuning the relative phase angle of two nanoparticles and optimizing the detuning of two optical modes. We show that the bipartite entanglement is significantly enhanced by selecting a suitable optomagnonics coupling strength in the presence of the exceptional points (EPs). The relative phase not only enhances the entanglement strength but also increases the entanglement domain over a wide range of detuning compared to the Hermitian system. By manipulating the system toward or away from EPs, versatile tunability of the tripartite entanglement, mean photon, and magnon numbers can be achieved. Additionally, the direction of asymmetric transmission can also be well tuned in a highly asymmetric way via non-Hermitian coupling. The study of controlled entanglement may provide the theoretical basis and reference for the research and development of new tunable quantum devices.

In this work, five-waveguide (five-WG) acoustic couplers with planar configurations are designed based on quantumlike adiabatic transfer, through which the incident waves can efficiently transfer from the middle WG to the other two WGs with a customized intensity ratio. The five WGs are connected by space-varying cylindrical scatterers, and the coupling between two adjacent WGs is determined by two Gaussian pulses with a certain delay. Since the evolution process of acoustic waves can adiabatically follow the dark state, the coupler could have a broadband and stable performance. Moreover, it is easy to change the ratio of the beam splitting by utilizing different peak values of the coupling between the middle three WGs. The agreements between analytical, numerical, and experimental results confirm the feasibility of the design, providing an effective solution for high-performance acoustic beam splitters with customizable output intensities.

We present a first-principles study of the structural, electronic, and magnetic properties of TM(PAH)0/+ (TM = Fe, Co, Ni; PAH = C10H8, C16H10, C24H12, C32H14) complexes and explore the laser-induced spin dynamics as well as their stability with respect to various laser parameters. For each complex, the most stable configuration shows that the TM atom prefers to adsorb at the hollow site of the carbon ring with a slight deviation from the center. The electronic structure and spin localization of the complexes are found to be largely affected by the TM type. Driven by various laser pulses, spin-crossover scenarios are achieved in all structures, while spin-transfer between TM and PAH is achieved in Ni(C10H8), Ni(C16H10), and Ni(C24H12). The influence of the laser energy and chirp on the dynamics is also investigated, providing important information regarding the stability and sensitivity of the dynamical process. All results are believed to reveal the physics nature of the TM–PAH systems, to guide the experimental realization of their ultrafast spin dynamics and thus to promote their applications in future spintronics.