Visualization Of Wavefronts Research Articles

Excitation and Propagation of Guided Waves in Multilayer Hollow Cylinders Using PWAS Transducers: A Theoretical and Experimental Study

In this paper, the excitation and propagation of guided waves in multilayer hollow cylinders with piezoelectric wafer active sensor (PWAS) transducers were modeled with the normal mode expansion (NME) method using the semi-analytical finite element (SAFE) formulation. The theoretical development of SAFE for hollow cylindrical structures was introduced and used to obtain guided-wave mode shapes and dispersion curves of multilayer hollow cylinders. The SAFE discretization was applied across the thickness. The layers present in the cylinder were modeled by grouping the elements in the region corresponding to the respective layers. Each finite element region was given the property of the layer that it represented. The number of elements in a layer was determined through convergence studies. The PWAS excitation effect, introduced using the ideal-bonding assumption, was represented by a line-force acting on the PWAS boundary. The SAFE-NME solution obtained in the wavenumber domain was resolved in the physical domain through inverse Fourier transform and residue theorem. Experimental validation of theoretical prediction was performed by comparison with scanning laser Doppler vibrometer (SLDV) measurements from a “6-inch schedule-40” pipe of 11 mm thickness installed with a 7-mm square PWAS transducer for wave excitation. Numerical prediction of the guided wave propagation emanating from the PWAS was first performed and wavefront visualization was obtained. An SLDV area scan of the guided waves generated by the PWAS was then performed and compared with numerical predictions. A good match between experiment and prediction was observed.

Underwater Acoustic Wavefront Visualization by Scanning Laser Doppler Vibrometer for the Characterization of Focused Ultrasonic Transducers.

The analysis of acoustic wave fields is important for a large number of engineering designs, communication and health-related reasons. The visualization of wavefronts gives valuable information about the type of transducers and excitation signals more suitable for the test itself. This article is dedicated to the development of a fast procedure for acoustic fields visualization in underwater conditions, by means of laser Doppler vibrometer measurements. The ultrasonic probe is a focused transducer excited by a chirp signal. The scope of this work is to evaluate experimentally the properties of the sound beam in order to get reliable information about the transducer itself to be used in many kinds of engineering tests and transducer design.

Acoustic wave-front visualization by use of a Kösters prism in the optical Fresnel diffraction region

A simple method for visualizing the wave fronts of a progressive acoustic wave is explained. The Kosters prism works by folding the acoustically phase-modulated optical wave front at its bisecting semitransparent plane. The same temporal frequency components in the folded optical field can interfere with each other in space. Interference fringes spaced by half the acoustic wavelength are obtained over the observation area; the edges of the Kosters prism do not give appreciable diffraction effects. The fringe visibility attains a maximum of 0.54 at the Raman–Nath parameter v = 1.92. Theoretical predictions are fully verified experimentally. The frequency range of acoustic waves to be visualized is discussed; a high-frequency limit is almost nonexistent, but the lowest frequency is limited by the aperture size of the Kosters prism used. This aperture size must be at least four times as large as one acoustic wavelength in the propagation direction of the acoustic wave. Visualization can be made at any planes in the optical Fresnel diffraction region.