Characterization of rigid open-cell foams using direct ultrasonic simulation

Area of Science:

• Acoustics and Materials Science
• Porous Materials Characterization

Background:

• Experimental determination of tortuosity and characteristic lengths in high pore-density foams is costly and prone to signal-to-noise issues.
• Accurate material parameters are crucial for predicting acoustic absorption and material behavior.

Purpose of the Study:

• To propose and validate an ultrasonic simulation technique as an alternative to experimental methods for characterizing porous foams.
• To determine tortuosity and characteristic lengths of high pore-density foams using a direct fluid model simulation.

Main Methods:

• Utilized ACTRAN® acoustic simulation software to model ultrasonic pulse propagation through foam structures.
• Employed a direct fluid model and analyzed high-frequency asymptotic behavior of the propagation index (Nr2) versus inverse square root of frequency (1/f).
• Validated simulation results by comparing with electric conduction boundary value problem solutions.

Main Results:

• Successfully estimated tortuosity and characteristic lengths for periodic microlattices with varying porosity (75%-90%) and pore size (~200 microns).
• Demonstrated applicability to computed tomography (CT) scans of open-cell foams with unknown structures.
• Parametric sensitivity analysis highlighted the impact of errors in Nr2 on Johnson-Champoux-Allard parameters and acoustic absorption.

Conclusions:

• The proposed ultrasonic simulation technique provides a cost-effective and reliable method for determining key parameters of porous foams.
• The simulation approach overcomes experimental limitations, offering improved accuracy and applicability to complex foam structures.
• Understanding parameter sensitivity is vital for accurate acoustic absorption predictions in rigid porous materials.