Broadband sound sink/absorber via a structure with deep sub-wavelength thickness is of great and continuing interest in physics and engineering communities. An intuitive technique extensively used is to combine components (resonators) with quasi-perfect absorption to piece together a broad absorbing band, but the requirement of quasi-perfect absorption substantially places a very strict restriction on the impedance and thickness of the components. Here, we theoretically and experimentally demonstrate that a compact broadband acoustic sink that quasi-perfectly absorbs broadband arriving sound waves can be achieved with coherently coupled “weak resonances” (resonant sound absorbing systems with low absorption peaks). Although each component exhibits rather low absorption peak alone, via manipulating the coherent coupling effect among the components, they collectively provide a remarkably improved performance over a wide frequency range with a significantly compressed thickness. To illustrate the design principle, a hybrid metasurface utilizing the coaction of parallel and cascade couplings is presented, which possesses an average absorption coefficient of 0.957 in the quasi-perfect band ($\alpha >0.9$) from 870 to 3224 Hz with a thickness of only 3.9 cm. Our results open new avenues for the development of novel and highly efficient acoustic absorbers against low frequency noise, and more essentially, suggest an efficient approach towards on-demand acoustic impedance engineering in broadband.

通过具有深亚波长厚度的结构的宽带声音接收器/吸收器在物理学和工程界中具有巨大且持续的兴趣。一种广泛使用的直观技术是将具有准完美吸收的元件（谐振器）组合在一起，拼凑出一个宽吸收带，但准完美吸收的要求实质上对元件的阻抗和厚度有非常严格的限制。在这里，我们从理论上和实验上证明，可以通过相干耦合的“弱共振”（具有低吸收峰的共振吸声系统）来实现准完美吸收宽带到达声波的紧凑型宽带声学接收器。虽然每个组分单独表现出相当低的吸收峰，但通过操纵组分之间的相干耦合效应，它们在广泛的频率范围内共同提供了显着改进的性能，并且厚度显着压缩。为了说明设计原理，提出了一种利用并联和级联耦合作用的混合超表面，它在准完美带中的平均吸收系数为 0.957（$\alpha >0.9$) 从 870 到 3224 赫兹，厚度仅为 3.9 厘米。我们的研究结果为开发针对低频噪声的新型高效吸声器开辟了新途径，更重要的是，提出了一种实现宽带按需声阻抗工程的有效方法。