Conventional series-coupled or parallel-coupled sound absorbers can only work effectively in a fixed frequency range, of which the absorption spectra can not be allowed to divide. Here, a parallel-coupled hierarchical structure with two relatively independent frequency bands of sound absorption is proposed. The hierarchical structure is composed of two type subunits of embedding neck Helmholtz resonator (ENHR) and segmented neck Helmholtz resonator (SNHR). Sound energy in the high-frequency region is dissipated in the first layer by the multiple local resonances coupling of ENHRs. The second layer effectively captures and absorbs low-frequency energy through the coupling of multiple SNHRs with varying parameters. The comprehensive discussion on the effects of acoustic impedance and structural parameters highlights the superior capability of this structure in impedance modulation. To demonstrate its broadband absorption performance, a hierarchical structure consisting of 20 subunits is employed. Finally, a above 90% broadband quasi-perfect absorption over a frequency range from 450 Hz to 1750 Hz is achieved under a thickness of 48 mm. Furthermore, a dual-band modular design concept for frequency-selective absorption is presented based on the tunability and independence of the two absorption bands. Therefore, the proposed hierarchical structure achieves reconfigurability by replacing either the first or second layer, thereby breaking away from traditional parallel design methods and providing a practical approach to controlling noise sources whose spectral characteristics change with operating conditions.

中文翻译：

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用于宽带吸声的并行耦合分层可重构结构

传统的串联或并联吸声器只能在固定的频率范围内有效工作，该频率范围内的吸收谱不能被分割。这里，提出了一种具有两个相对独立的吸声频带的并联耦合分层结构。该分层结构由嵌入式颈亥姆霍兹谐振器（ENHR）和分段颈亥姆霍兹谐振器（SNHR）两种类型的子单元组成。高频区域的声能通过 ENHR 的多重局部共振耦合在第一层消散。第二层通过多个具有不同参数的 SNHR 的耦合有效地捕获和吸收低频能量。对声阻抗和结构参数影响的综合讨论凸显了该结构在阻抗调制方面的优越能力。为了展示其宽带吸收性能，采用了由 20 个子单元组成的分层结构。最终，在 48 mm 的厚度下，在 450 Hz 至 1750 Hz 的频率范围内实现了 90% 以上的宽带准完美吸收。此外，基于两个吸收带的可调性和独立性，提出了频率选择性吸收的双频带模块化设计概念。因此，所提出的分层结构通过替换第一层或第二层来实现可重构性，从而摆脱传统的并行设计方法，并提供控制频谱特性随工作条件变化的噪声源的实用方法。