Direct measurement of SAW dispersion relations in the k-ω domains; numerical and experimental studies

Abstract

We evaluate the dispersion relation of surface acoustic waves by temporally and spatially modulated laserultrasound in the presented work. Experimental data are acquired by the combined application of intensity modulated laserdiodes and a spatial light modulator. Numerical simulations obtained from the solution of the coupled heat and wave equations using the finite difference time domain method with a combination of implicit and explicit temporal integration techniques.

Guided ultrasonic waves propagation imaging: a review

“…Sometimes the detection of damage can only be done by optimally narrowing the bandwidth to a specific frequency or wavenumber. In this case, although never been reported for G-UPI application, waves with a specific wavenumber can be generated using a beam shaping technique in order to acquire a periodic spatial modulation using a spatial light modulator, transient grating, slits, or masks, for example [26,122,123], and waves at a specific frequency can be generated using temporal modulation of the laser [123,124]. For G-UPI, it is common to merely control the wave frequency during DAQ using an analog frequency filter, and if needed, further narrowing of the frequency or wavenumber could be achieved using the software during result processing.…”

“…Using a pulsed laser for generation has many interesting potentials; for example, the laser can be split into multiple beams for simultaneous multi-ROI inspection [9,162] for large structures, significantly reducing downtime for structural inspection. The generation laser beam can also be focused into different shapes, which can be manipulated for purposes such as beam forming of wavefront [122,163] not unlike those used by phased-array transducers [164,165] or for the generation of wavefield at a specific wavelength using spatial light modulator [122,123]. Generation of ultrasound using a 'plasma shock' configuration is possible too [166], which might be useful if irradiation of laser on the specimen should be avoided.…”

“…Among these, Fourier transformation is widely used to generate dispersion curves from 3D wavefield data (time history of areal scan) [145,146], 2D data (time history of line scan) [151,230,288,289], or minimally from two waves which are measured from two spatially separated points [290,291]. Other methods, such as the dispersion compensation method [292], sparse recovery method [293], and searching of wavenumber-frequency space using spatial-temporal modulation of the laser during ultrasound generation [123], are available too.…”