Quantifying the breakdown of single scattering for ultrasonic backscatter measurements

Area of Science:

• Materials Science
• Acoustics
• Non-destructive Testing

Background:

• Diffuse ultrasonic backscatter arises from elastic wave interactions with material heterogeneity, providing microstructural insights.
• Accurate quantitative interpretation of ultrasonic scattering measurements, especially in highly scattering materials, requires sophisticated models.
• A recent double scattering model assumes energy scatters at most twice, but its applicability needs thorough investigation.

Purpose of the Study:

• To theoretically and experimentally compare the validity and significance of single and double ultrasonic scattering models.
• To explore the range of applicability for the double scattering model in material characterization.
• To provide guidelines for experimental design to ensure measurements fall within desired scattering regimes.

Main Methods:

• Theoretical analysis comparing single and double scattering models under various conditions.
• Experimental validation using steel as a strongly scattering material.
• Measurements conducted at ultrasonic frequencies of 5, 7.5, 10, and 15 MHz.

Main Results:

• Single scattering models are suitable for weakly scattering materials across diverse experimental setups.
• Stronger scattering materials exhibit significant second-order scattering influenced by transducer frequency and material path.
• Experimental data for steel identified the conditions under which double scattering becomes significant and highlighted model limitations.

Conclusions:

• The double scattering model is crucial for accurately characterizing strongly scattering materials.
• Transducer frequency and material path are key parameters influencing the significance of double scattering.
• Guidelines are provided to optimize experimental design for reliable ultrasonic scattering measurements.