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Selective generation of Lamb modes by a moving continuous-wave laser.
Optics Letters
|January 13, 2018
Summary
This study demonstrates a new laser ultrasonic method for generating specific Lamb wave modes in plates. A moving continuous-wave laser selectively excites single narrowband modes by matching its speed to the wave
Area of Science:
- Materials Science
- Acoustics
- Laser Ultrasonics
Background:
- Conventional laser-generated Lamb waves often result in multiple modes, complicating analysis and application.
- Pulsed lasers typically excite broadband Lamb waves with several coexisting modes.
- Precise control over Lamb wave mode generation is crucial for advanced material characterization and NDT.
Purpose of the Study:
- To introduce a novel method for the selective, non-contact generation of single Lamb wave modes.
- To demonstrate the capability of a moving continuous-wave laser for controlled Lamb wave excitation.
- To enable direct acquisition of Lamb wave dispersion curves.
Main Methods:
- Utilized a continuous-wave (CW) laser scanning along the surface of a plate.
- Adjusted the laser scanning speed to match the phase velocity of specific Lamb wave modes.
- Analyzed the power spectrum of time-domain signals to identify generated modes and dispersion characteristics.
Main Results:
- Achieved selective excitation of single narrowband Lamb wave modes, including A0 and S0 modes, by controlling CW laser scanning speed.
- Observed successive excitation of different modes and coupled resonance phenomena as scanning speed varied.
- Demonstrated the feasibility of generating a pure single S0 mode, suitable for liquid-loading environments.
Conclusions:
- The CW laser scanning method offers a groundbreaking approach for selective Lamb wave mode generation.
- This technique provides a direct route to obtaining Lamb wave dispersion curves.
- This novel method advances laser ultrasonic excitation capabilities for material inspection and research.
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