Frequency Segmented Hybrid Inversion Method for Nonacoustical Parameters Estimation of Porous Foam Materials

The acoustic performance of porous materials is influenced by nonacoustic parameters like static flow resistivity, porosity, tortuosity, and viscous and thermal characteristic lengths. Conducting individual experiments to obtain the parameters is complex and time-consuming. This article introduces a frequency segmented hybrid inversion method (SIM) solely utilizing a standard impedance tube to estimate these parameters. The core of this method lies in using optimization algorithms to solve for the minimal difference between the real absorption coefficient values and the estimated values from acoustic models within different frequency ranges. What sets this method apart from other inversion techniques is its segmentation of the frequency range based on the sensitivity of each parameter to specific frequency bands. The inversion method comprises three steps: measuring static flow resistivity using impedance tubes, using the Hamet-Berengier (HB) model for porosity and tortuosity, and the Johnson-Champoux–Allard (JCA) model for viscous and thermal characteristic lengths. Testing with polyurethane foam validates the method, showing similarity with JCA inversion and commercial software (CS) results. Comparative analysis of the relative error rates between each method and the actual absorption coefficient values revealed that the proposed method achieved the lowest relative error rate within the study frequency range, at 1.4%. This indicates that the proposed inversion method simplifies the experimental process while ensuring accuracy of the results.