Broadband leaky Lamb waves excited by optical breakdown in water

Area of Science:

• Acoustics
• Materials Science
• Non-destructive Testing

Background:

• Lamb waves are crucial for inspecting thin structures like plates.
• Generating and detecting Lamb waves efficiently is key for effective material characterization.
• Non-contact methods offer advantages in accessibility and avoiding surface contamination.

Purpose of the Study:

• To investigate the use of optical breakdown of water as a non-contact sound source.
• To characterize the excitation of leaky Lamb waves and guided modes in submerged aluminum plates.
• To analyze the relationship between mode properties and excitation conditions for sensing applications.

Main Methods:

• Utilizing laser-induced optical breakdown in water to generate acoustic waves.
• Submerging aluminum plates in water to study wave propagation.
• Measuring the broadband response of guided modes using techniques sensitive to wave propagation.
• Analyzing the frequency and wavenumber spectra of the excited waves.

Main Results:

• Successfully excited a broad range of leaky Lamb wave modes (0.1–5 MHz, 0–0.8 mm⁻¹).
• Observed strong coupling to both symmetric and antisymmetric guided modes.
• Demonstrated that peak responses occur when mode phase velocity matches the plate's compressional wave velocity.
• Validated experimental results against theoretical dispersion curves.

Conclusions:

• Optical breakdown of water is an effective non-contact source for broadband Lamb wave generation.
• The interplay of sensing geometry, wave speeds, and signal processing influences excitation.
• This technique holds significant potential for non-contact material inspection and characterization.