研究目的
To present a MPP absorber with inhomogeneous perforations and multi-cavity depths to improve its absorption frequency bandwidth.
研究成果
The inhomogeneous MPP with multi-cavity depths improves absorption bandwidth compared to homogeneous MPPs. Optimal performance is achieved by designing sub-MPPs with specific perforation ratios and hole diameters, and by adjusting cavity depths to control bandwidth without reducing amplitude. Experimental results validate the theoretical model, showing good agreement. Future work could extend to multiple sub-MPPs or double-MPP systems for wider bandwidth.
研究不足
The model neglects the effect of impedance discontinuity between sub-MPPs, which may cause differences in experimental results. The study is limited to two sub-MPP areas and normal-incidence sound; it does not address oblique incidence or more complex configurations. Manufacturing variations and material properties could affect performance.
1：Experimental Design and Method Selection:
The study uses an electrical equivalent circuit model to predict the acoustic impedance and absorption coefficient under normal-incidence sound. The model is based on Maa's formulations and revised to include multi-cavity depths and inhomogeneous perforation parameters.
2：Sample Selection and Data Sources:
MPP samples are fabricated from PVC-U material with specific structural parameters (e.g., hole diameters, perforation ratios, cavity depths) as listed in Table 1. The samples are designed to fit an impedance tube for measurement.
3：The samples are designed to fit an impedance tube for measurement.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Impedance tube with inner diameter of 33 mm, loudspeaker, two 1/2-in pre-polarised free-field acoustic microphones (GRAS 40AE) with 1/2-in CCP pre-amplifier (GRAS 26CA), Brüel & Kj?r sound calibrator type 4231, National Instruments data acquisition card, SigLab 20-42 signal analyzer, MATLAB for data processing, PVC-U material for MPP fabrication.
4：Experimental Procedures and Operational Workflow:
Samples are placed in the impedance tube; white noise is generated via a loudspeaker; microphones measure sound pressure; calibration is done with a sound calibrator; data is acquired and processed to calculate absorption coefficient using the transfer function method per ISO 10534-2; tests are repeated three times for reliability.
5：Data Analysis Methods:
Absorption coefficient is calculated using MATLAB based on the measured pressure signals; theoretical predictions are compared with experimental results.
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