Designing a multiplexing metasurface to exhibit diverse functionalities has been a trend in electromagnetics, acoustics, and mechanics. Here, we report a simple method to design the 2-bit coding acoustic metasurface by combining the Helmholtz resonator-like structures. Each meta-atom has four coding modes to independently modulate the wave fronts at two different frequencies. The equivalent circuit principle and decoupling effect are theoretically and numerically analyzed to clarify the underlying physical mechanism of our design. We filter and suppress the redundant diffraction beams to realize perfect negative reflection by controlling the number of outgoing diffraction modes. Considering the impact of loss, we simulate the scattered pressure and directivity of far field radiation for oblique illumination at two predesigned frequencies, the results of which show good agreement with the predicted ones. Our work may have potential in the design of multiplexing, frequency-selective, and programmable acoustic devices.

设计多重超颖表面以显示各种功能已成为电磁，声学和机械学的趋势。在这里，我们报告了一种简单的方法，通过结合类似亥姆霍兹谐振器的结构来设计2位编码声学超表面。每个超原子具有四种编码模式，可以在两个不同的频率上独立地调制波前。对等效电路原理和去耦效果进行了理论和数值分析，以阐明我们设计的潜在物理机制。我们通过控制出射衍射模式的数量来过滤和抑制多余的衍射光束，以实现完美的负反射。考虑到损耗的影响，我们模拟了在两个预先设计的频率下倾斜照明的远场辐射的散射压力和方向性，结果与预测结果吻合良好。我们的工作可能在多路复用，频率选择和可编程声学设备的设计中具有潜力。