Amplifying Lamb Wave Detection for Fiber Bragg Grating with a Phononic Crystal GRIN Lens Waveguide

Area of Science:

• Materials Science
• Acoustics
• Structural Health Monitoring

Background:

• Guided ultrasonic wave inspection is vital for structural health monitoring.
• Achieving sufficient signal amplitude for detection remains a challenge.
• Fiber Bragg grating (FBG) sensors offer strong directional sensitivity.

Purpose of the Study:

• To demonstrate a graded-index (GRIN) phononic lens and channel waveguide can focus anti-symmetric Lamb waves.
• To investigate signal amplification for enhanced ultrasonic inspection.
• To optimize FBG sensor placement for maximum signal extraction.

Main Methods:

• Fabrication of a GRIN phononic lens and channel waveguide using a commercial 3D printer.
• Characterization of A0 mode Lamb wave focusing using 3D laser Doppler vibrometry.
• Measurement of focused energy extraction with an FBG sensor, optimizing bond location and length.

Main Results:

• Significant amplification of the ultrasonic waveform was achieved.
• The focusing capability of the GRIN lens and waveguide system was experimentally verified.
• Optimal FBG sensor placement within the waveguide channel was identified as critical for maximizing signal amplification.

Conclusions:

• A 3D-printed GRIN phononic lens combined with a channel waveguide effectively focuses Lamb waves.
• This integrated system significantly amplifies ultrasonic signals, addressing a key challenge in guided wave inspection.
• Precise FBG sensor positioning is crucial for maximizing signal extraction and improving structural health monitoring capabilities.