Broadband acoustic absorbers with thin thickness are highly desired in practical situations such as architectural acoustics, yet it is still challenging to achieve high absorption by using structure with limited thickness. Here we report the theoretical optimal design, numerical simulation and experimental demonstration of a planar acoustic absorber capable of producing broadband sound absorption with deep-subwavelength thickness. The mechanism is that, we use a hybrid design of individual unit cell comprising multiple resonators with a coiled configuration for expanding the working bandwidth and downscaling the resulting device, and, on the other hand, the geometries of the constituent resonance elements are optimally designed by using genetic algorithm. Based on an analytical formula we derive for an efficient prediction of the absorption efficiency, the optimization process is accelerated and gives rise to an optimally maximized amount of absorbed energy with limited device thickness. As a result, the proposed absorber features planar profile, broad bandwidth, wide absorbing angle (the absorber works well when the incident angle of sound wave reaches 60°) and thin thickness (< 1/25 wavelength). In addition, the proposed scheme does not rely on extra sound-absorptive materials or the type of constituent solid material, which significantly simplifies the sample fabrication and improves the application potential of resulting device. The measured data agree well with the theoretical predictions, showing high sound absorption in the prescribed frequency range. We envision our design to further improve the performance of acoustic absorbers and find applications in practical situations in need of elimination of broadband acoustic waves within limited spaces.

在诸如建筑声学之类的实际情况中，高度希望具有薄厚度的宽带吸声器，但是通过使用有限厚度的结构来实现高吸收仍然是挑战。在这里，我们报告了能够产生深亚波长厚度的宽带吸声的平面吸声器的理论优化设计，数值模拟和实验演示。其机理是，我们使用单个单元的混合设计，包括多个具有线圈结构的谐振器，以扩展工作带宽并缩小最终器件的尺寸，另一方面，通过以下方式优化设计组成谐振元件的几何形状：使用遗传算法。基于解析公式，我们可以得出吸收效率的有效预测结果，从而加快了优化过程，并在有限的设备厚度下产生了最佳最大化的吸收能量。结果，所提出的吸收器具有平面轮廓，较宽的带宽，较宽的吸收角（当声波的入射角达到60°时吸收器工作良好）和较薄的厚度（<1/25波长）。另外，所提出的方案不依赖于额外的吸声材料或组成固体材料的类型，这大大简化了样品的制造并提高了所得装置的应用潜力。实测数据与理论预测非常吻合，表明在规定的频率范围内吸声能力强。