Study on microperforated panels backed by panel-type resonators for improved low frequency and broadband sound absorption

Abstract

The microperforated panel (MPP) is perceived as the next generation of sound absorber as it possesses certain advantages over the conventional porous sound absorber. Despite the benefits of MPP over traditional porous absorber, the MPP faces challenges in terms of having limited bandwidth and poor absorption performance in the low frequency region. In recent decades, researchers have mainly focused in extending the bandwidth and improving the low frequency sound absorption commonly at the expense of overall thickness. However, there are still limited research works that focuses on i) the simultaneous improvement of low frequency absorption and bandwidth, ii) the analytical and numerical study to predict sound absorption of MPP backed by panel type resonator, iii) the mechanism behind the absorption characteristics, iv) a highly compact design relative to the wavelength of acoustic wave absorbed with enhanced low frequency absorption and wide bandwidth. Hence, the study aimed to improve the low frequency sound absorption and bandwidth of MPP compound structure while remaining relatively thin when compared to the wavelength of acoustic wave it effectively absorbed.
The main findings of this research work can be described as follows:
1. By exploiting the resonance phenomenon of panel resonator, this study proposes backing the MPP with a panel resonator tuned to low frequency to enhance low frequency sound absorption. A low frequency absorption is observed but a deep absorption valley follows immediately at frequency above the peak impeding the improvement in absorption bandwidth.
2. The mechanism behind the absorption characteristics of MPP backed by a panel-type resonator is revealed by analysing the data extracted from finite element analysis. The low frequency absorption peak and dip are found to be influenced by the vibro-acoustic characteristics of different components. The understanding on mechanism behind absorption characteristics provide insight into further optimizing the absorption performance.
3. Based on the knowledge established on the mechanism behind absorption characteristics, this study proposes using multiple miniature resonators attached on panel resonator to improve the absorption performance. The resonators are tuned to possess resonant frequencies which coincide with the region with poor absorption to enhance the performance. The results demonstrated that local resonance of resonators induces additional absorption peak at valley region forming a continuous half-absorption band.
4. Since the presence of resonators shows enhancement in sound absorption performance, this study also investigates the effect of different critical parameters in resonators design on the absorption characteristics. This provides an insight into optimizing the design of resonators; thus, this study also demonstrates the feasibility of searching the optimal design using the particle swarm optimization method.
5. The sound absorption in the low frequency region is often approached by introducing additional resonating structures at the expense of greater complexity and bulkiness. This study proposes a novel hybrid resonator in which a single structure exhibits both Helmholtz resonance and structural resonance phenomena in the low frequency region enhancing low frequency absorption. The proposed structure exhibits two low frequency sound absorption peaks attributed to different resonance phenomena in a single panel structure. The absorption peak associated with the Helmholtz resonance differs from structural resonance as it is contributed by the viscous losses in both the MPP perforations and Helmholtz neck region.
6. A circular Helmholtz neck has minor effect on the structural vibration characteristics of the hybrid resonators. Hence, it is proposed in this study to replace the circular neck into a rectangular slit-type neck to tune the structural resonant frequency of hybrid resonator. The geometry and location of Helmholtz neck show significant influence on the structural resonant frequency of panel and modify the overall absorption characteristics accordingly.
In conclusion, this research work has systematically studied the potential of MPP in absorbing acoustic wave. A fully coupled vibroacoustic model is developed to predict the absorption characteristics of MPP compound sound absorber with its accuracy verified through finite element analysis and experiments. The results obtained have verified the effectiveness of the proposed MPP compound sound absorber in absorbing low frequency noise and possesses a wide band. The understanding on mechanism behind absorption characteristics and proposed improvements contributes to the body of knowledge in the field of acoustic absorber and will be purposeful for the design and application of such MPP compound sound absorber.

Date of Award	15 Nov 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Dunant Halim (Supervisor), Xiaosu Yi (Supervisor) & Hao Chen (Supervisor)