In this work, we present a type of binary metasurface (BM) to generate an acoustic Airy beam in air. Two coding bits, a rectangular cavity (bit “0”) and a waveguide with seven Helmholtz resonators (bit “1”), are adopted to construct the acoustic structure, which offers degrees of freedom to manipulate the transmitted field. The operating band is capable of customizing in an ultrabroadband of 3000–15 000 Hz owing to the linear-like phase shift and high transmittance of the coding bits. To verify the feasibility of the design, a BM with a certain parameter (w = 5) is fabricated with photosensitive resin via stereolithography, and the working band is customized as 4000–5500 Hz. The experiment results show that the apparent self-bending beam is able to be generated in a broadband, which agree well with the numerical simulation. In addition, we further demonstrate that self-focusing can be realized by taking advantage of two symmetrical BMs conveniently, which improve the functionality of the coding bits. These results may provide potential application in biomedical ultrasound and nondestructive testing.

Polarization modulation and multichannel beam generation are crucial in multichannel communication and high-resolution imaging at THz frequency. In this work, we present a polarization-reprogrammable coding metasurface composed of VO₂/Au composite concentric rings (CCRs). Owing to the phase-change property of VO₂, the CCR is designed as a digital coding element for the polarization conversion. When VO₂ remains insulator state at room temperature, the y-polarized incident wave is transformed into x-polarized wave, which can be regarded as digital state 0. When VO₂ converts into metal state at critical temperature (68 °C), the polarization of reflected wave stays unchanged, corresponding to digital state 1. Any desired linear polarization state of reflected beam is achieved by taking advantage of different coding sequences in a programmable manner. Furthermore, by combining phase gradient with polarization coding states, we propose an anisotropic programmable metasurface to control the multi-channel reflected beams dynamically. By arranging distinct coding sequences, we show that the EM reflected beams can be manipulated flexibly. The proposed programmable metasurface paves new ways towards THz polarization manipulation, signal detection and information communication.

Shortcut to adiabatic passage (STAP), initially proposed to accelerate adiabatic quantum-state transfer, has been widely explored and applied in quantum optics and integrated optics. Here we bring STAP into the field of acoustics to design compact couplers and functional metamaterial. The space-varying coupling strengths of acoustic waveguides (WGs) are tailored by means of dressed states in a three-level system, accounting for the desirable acoustic energy transfer among three WGs with short length. We show that the acoustic coupler has a one-way feature when loss is introduced into the intermediate WG. More uniquely, when the propagation of acoustic wave is designed to mimic a Hadamard transformation, an acoustic metamaterial can be constructed by arraying several couplers, possessing the beam-splitting function and unidirectional, broadband performances. Our work bridges STAP and the acoustic coupler as well as metamaterial, which may have profound impacts on exploring quantum technologies for promoting advanced acoustic devices.

To generate directional transmission characteristics of acoustic waves, we constructed two abnormal transmission models based on the protocell. The simulation results showed that the band gap characteristic of the phononic crystal structure can be used to realize the directional transmission effect. We also found that the acoustic frequency has a great influence on the acoustic transmission characteristics of artificial acoustic structures. Because the artificial acoustic structure based on phononic crystals has the advantages of design flexibility, it can be customized according to the actual engineering application. Our results provided a new direction for engineering applications such as directional transmission of acoustic waves and acoustic diodes.