High-frequency tortuosity relaxation in open-cell foams.

Area of Science:

• Materials Science
• Acoustics
• Polymer Physics

Background:

• Ultrasound propagation in porous materials is complex.
• Understanding foam microstructure is key to predicting acoustic behavior.
• Previous studies lacked a complete view of ultrasound transition in foams.

Purpose of the Study:

• To investigate ultrasound propagation in open-cell polymeric foams across a wide frequency range.
• To model foam microstructure and relate it to acoustic properties.
• To explain the observed sigmoid growth in ultrasound velocity and transmission loss.

Main Methods:

• Air-coupled ultrasound and Fourier spectral analysis (0.1-6 MHz).
• Micrographic analysis for foam microstructure characterization.
• Development of a unit cell model and novel air-coupled transducers.

Main Results:

• Measured ultrasound phase velocity and transmission loss exhibit sigmoid growth with frequency.
• The sigmoid growth transition was fully observed for all studied foams.
• A probabilistic tortuous walk model with relaxation behavior accurately describes the results.

Conclusions:

• The study successfully characterized ultrasound propagation in open-cell polymeric foams.
• A novel approach using a probabilistic tortuous walk model explains the observed acoustic behavior.
• The findings provide a deeper understanding of acoustic wave interaction with foam structures.