A diffraction-based optical method for the detection of in-plane motion of lamb waves

Area of Science:

• Optics
• Materials Science
• Acoustics

Background:

• Lamb waves are crucial for non-destructive testing and material characterization.
• Detecting in-plane motion of Lamb waves is challenging, especially in microscale structures.
• Existing optical techniques may lack sensitivity or require complex setups for in-plane motion detection.

Purpose of the Study:

• To introduce a new laser optical technique for detecting in-plane motion of Lamb waves.
• To demonstrate the technique's applicability on a brass plate and potential for microelectromechanical (MEMS) systems.

Main Methods:

• An interference-based laser optical method utilizing a small square indentation (approx. 30 micron width) on the sample surface.
• A simplified optical arrangement for measuring wave propagation.
• Application to a 70-micron thick brass plate to detect Lamb wave in-plane motion.

Main Results:

• Successful detection of in-plane motion of Lamb waves, specifically the So mode, in a brass plate.
• Demonstrated effectiveness in the low frequency-thickness (fd) regime.
• Validated the technique's potential for MEMS structures by replacing the indentation with a microreflector.

Conclusions:

• The developed laser optical technique provides a viable method for measuring in-plane Lamb wave motion.
• The technique is adaptable for microscale applications, including MEMS devices.
• Offers a simpler and potentially more sensitive approach for in-plane motion detection in various materials.