Quantitative theory for laser ultrasonic waves in a thin plate

Spicer, James B.; McKie, A. D. W.; Wagner, James W.

doi:10.1063/1.103999

Cited by 65 publications

(27 citation statements)

References 11 publications

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“…8͑a͒ is the theoretical transient response of the material to a 3 ns Gaussian laser source. 25,26 The spot size of the laser source is taken as 12.6 m FWHM to match that used in the experiment. Although the experimental wave form appears to have lower frequency content, perhaps due to attenuation and scattering, the general shape of the reconstructed wave form agrees well with that predicted for a pulsed source.…”

Section: Signal To Noise Ratio Considerationsmentioning

confidence: 99%

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

Balogun

Murray

2006

Journal of Applied Physics

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A high-sensitivity frequency domain laser based ultrasonic system is presented which uses a low power, amplitude modulated continuous wave (cw) laser source for acoustic wave generation. The acoustic signals are detected using a path stabilized Michelson interferometer coupled to a rf lock-in amplifier. The modulation frequency of the generation laser is scanned over the bandwidth of interest, and transient acoustic signals are reconstructed from the frequency domain data. The effects of measurement frequency resolution, bandwidth, and time domain aliasing on the reconstructed transient response are discussed. Experimental results on thin plates, where diffuse acoustic wave fields lasting several hundred microseconds are seen as a result of multiple reflections off of sample boundaries, demonstrate that the time domain signal can be unambiguously reconstructed through appropriate selection of frequency resolution. Time domain reconstructions of acoustic signals over a bandwidth of 200MHz demonstrate the utility of the approach for acoustic microscopy; individual acoustic transients can be detected with extremely high signal to noise ratio and time gated for analysis.

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Section: Signal To Noise Ratio Considerationsmentioning

confidence: 99%

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

Balogun

Murray

2006

Journal of Applied Physics

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“…The theory of pulsed laser generation of ultrasound in plates has been detailed in the literature [19,20]. In this section, an outline of the theory used to predict the steady state response of thin plates to an amplitude modulated laser excitation source is given.…”

Section: Theorymentioning

confidence: 99%

Theory and Applications of Laser Generated Zero-Group Velocity Lamb Mode Resonance

Murray

Balogun

Prada³

et al. 2008

AIP Conference Proceedings

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Lamb modes exhibit a resonant behavior at frequencies where the group velocity vanishes while the phase velocity remains finite. This type of zero group velocity (ZGV) point exists in most isotropic materials at the minimum frequency-thickness product of the first order symmetric (S 1 ) Lamb mode. Laser sources couple efficiently into this resonance and a sharp peak is observed with source and receiver on epicentre. A model for the laser generation of ultrasound in thin plates using an amplitude modulated laser source is presented. Lamb wave displacement spectra are measured using an amplitude modulated laser source for excitation and a Michelson interferometer coupled to an RF lockin amplifier for detection. The displacement spectra of Lamb waves generated in micron scale plates show good agreement with theoretical predictions. Experimental results are presented demonstrating excitation of the S 1 ZGV resonance in a 4μm thick membrane using a high frequency (700 MHz) amplitude modulated laser source. Subsurface features below the membrane are detected by tracking the S 1 ZGV resonance peak as the sample is scanned.

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“…Among the limited theoretical studies is that of Spicer et al [6], who investigated Lamb waves in a thin isotropic plate using Laplace-Hankel transforms. Normal mode technique was used by Weaver and Pao [7] to study the isothermal displacement generated by a point load applied to a plate.…”

Section: Introductionmentioning

confidence: 99%

Laser-Generated Thermoelastic Waves in an Anisotropic Infinite Plate: FEM Analysis

Al‐Qahtani

Datta

Mukdadi

2005

Journal of Thermal Stresses

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In recent years, the study of thermoelastic waves generated by focused laser beams has been undertaken by several researchers because the technique provides a means for noncontact generation of ultrasonic waves. Laser-generated ultrasonic waves have diverse applications ranging from material characterization to nondestructive testing of defects. Transient ultrasonic guided waves generated in an anisotropic infinite plate by a pulsed laser beam are investigated in this study. A semi-analytical finite element method (SAFEM) is adopted for this purpose. In this method, the plate is divided into parallel layers through its thickness and the displacement and temperature in each layer are approximated by quadratic polynomials in the thickness direction (z). They are assumed to be continuous functions of time and in-plane cartesian coordinates (x, y). Transient response is calculated using Fourier transformations in time and space variables (x, y). The analysis technique is applicable to a generally anisotropic plate. Results for dispersion of guided waves and transient displacement in infinite silicon nitride (Si 3 N 4 ) plates are presented. Numerical results show that for the assumed form of heat deposition by the laser mainly the lowest Lamb modes, namely, the lowest symmetric (S 0 ) and antisymmetric (A 0 ) modes, are excited. They also show that the transient response is dominated by the antisymmetric mode A 0 , which shows characteristic dispersion. This study provides a quantitative model for laser-generated thermoelastic waves in an anisotropic plate and can be used for nondestructive evaluation.

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Quantitative theory for laser ultrasonic waves in a thin plate

Cited by 65 publications

References 11 publications

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

Theory and Applications of Laser Generated Zero-Group Velocity Lamb Mode Resonance

Laser-Generated Thermoelastic Waves in an Anisotropic Infinite Plate: FEM Analysis

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