Transport parameters for an ultrasonic pulsed wave propagating in a multiple scattering medium

Area of Science:

• Acoustics and wave propagation in disordered media.
• Materials characterization using ultrasonic techniques.

Background:

• Key parameters for wave propagation in disordered media include elastic (l(s)), transport (l*), and absorption (l(a)) mean free paths, and the diffusion constant (D).
• These parameters are widely used in optics but less established in acoustics.
• Characterizing multiple scattering media is crucial for understanding wave behavior.

Purpose of the Study:

• To develop and validate ultrasonic experimental methods for characterizing multiple scattering media.
• To determine elastic, transport, and absorption mean free paths and the diffusion constant in acoustics.
• To explore applications in materials like coarse-grain stainless steels.

Main Methods:

• Development of ultrasonic experimental methods based on the expansion of the average solution for the heterogeneous Green's function equation.
• Time-resolved measurements of transmitted amplitude through a prototype sample of randomly located steel rods.
• Varying sample thickness to distinguish between ballistic and coherent wave regimes and follow the transition.
• Utilizing coherent backscattering effect to estimate diffusion constant (D) and transport mean free path (l*).
• Inferring absorption mean free path (l(a)) from average time-resolved intensity measurements.

Main Results:

• Successfully characterized a multiple scattering medium using ultrasonic methods.
• Determined elastic mean free path (l(s)) by varying sample thickness and observed the transition from coherent to diffusive regimes.
• Demonstrated a method to estimate diffusion constant (D) and transport mean free path (l*) via coherent backscattering.
• Enabled inference of absorption mean free path (l(a)) through intensity measurements.

Conclusions:

• The developed ultrasonic methods provide a robust framework for characterizing wave propagation in disordered media.
• The study successfully determined key parameters (l(s), l*, l(a), D) in acoustics, analogous to optical studies.
• Potential applications for characterizing materials like coarse-grain stainless steels were discussed.