Search results for "Guided wave"
showing 10 items of 48 documents
Noncontact Air-Coupled Guided Wave Ultrasonics for Detection of Thinning Defects in Aluminum Plates
2001
Ultrasonic guided waves are gaining increasing attention for the inspection of platelike and rodlike structures. At the same time, inspection methods that do not require contact with the test piece are being developed for advanced applications. This paper capitalizes on recent advances in the areas of guided wave ultrasonics and noncontact ultrasonics to demonstrate a superior method for the nondestructive detection of thinning defects simulating hidden corrosion in thin aluminum plates. The proposed approach uses micromachined gas (air)-coupled capacitive transducers for the noncontact generation and detection of guided plate waves. Interesting features in the dispersive behavior of select…
Guided Wave Propagation in a Plate Edge and Application to NDI of Rail Base
2012
The analysis of guided wave propagation in a plate edge can be useful for some applications, such as for the inspection of the rail base. Here guided waves generated by a laser beam hitting, on the inclined surface, a solid media with trapezoidal cross-section have been studied. We have found that, for the geometry investigated, two guided waves propagate along both free surfaces of the plate, with same velocity and frequency. The analysis of the trajectories of the two material points, due to waves propagation, shows that the wave packets can be identified as Rayleigh waves. The presence of S0 Lamb mode, with low frequency and low amplitude, has been revealed too. As an example of a possib…
Improved global-local model to predict guided-wave scattering patterns from discontinuities in complex parts
2019
Ultrasonic guided-wave testing can greatly benefit from (1) an ability to provide quantitative information on the damage that is being detected, and (2) an ability to select the best mode-frequency combination for maximum sensitivity to a given type of damage. Achieving these capabilities in complex structures (e.g. nonprismatic structures such as a stiffened panel in aerospace fuselages) is a nontrivial task. This paper will discuss an improved Global-Local (GL) method where the geometrical “local” discontinuity (e.g. the stiffener) is modelled by traditional FE discretization and the rest of the structure (“global” part) is modelled by Semi-Analytical Finite Element (SAFE) cross-sectional…
Coded Excitation of the Fundamental Flexural Guided Wave in Coated Bone Phantoms
2017
There is an increasing interest of using ultrasonic guided waves to assess long cortical bones. In particular, a method of ultrasonic estimation of cortical thickness based on the fundamental flexural guided wave (FFGW), generally consistent with the A0 Lamb mode, has proven to be promising in vitro and modeling studies. Soft-tissue coating on top of the bone makes, however, the related in vivo application challenge. Visibility of FFGW on top of the soft tissue is not good due to the characteristic displacement profile of this mode, and due to its relatively high attenuation in the bone and surrounding tissue. Moreover, the soft tissue provides a direct propagation path for ultrasonic modes…
Obstructing propagation of interfering modes improves detection of guided waves in coated bone models
2014
Interference due to wave propagation in soft tissue that covers the bone is a major challenge to in vivo assessment of the fundamental flexural guided wave (FFGW) in bone. To improve signal-to-interference ratio (SIR) we propose to obstruct the propagation of interfering modes by locally deforming the coating by external mechanical compression. This approach was modeled by 2D finite-element transient domain (FEMTD) simulations in a fluid-coated (7 mm) solid plate (3 mm). The fluid layer mimics the soft tissue that covers the bone. A single emitter or a 6-element phased array excited ultrasound pulses at 50 kHz on the surface of the coating, and a receiver array was placed on the surface, 20…
2D Waveguided Bessel Beam Generated Using Integrated Metasurface-Based Plasmonic Axicon.
2020
International audience; Near-field imaging of the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide is reported. The operation of the axicon lens with a footprint as small as 11 μm2 is based on local engineering of the effective index of the silicon waveguide with plasmonic nanoresonators. This generic approach, which can be adapted to different types of planar lightwave circuit platforms, offers the possibility to design nano-engineered optical devicesbased on the use of plasmonic resonators to control light at the nanoscale.
Global–local model for three-dimensional guided wave scattering with application to rail flaw detection
2021
This study presents a three-dimensional global–local formulation for the prediction of guided wave scattering from discontinuities (e.g. defects). The approach chosen utilizes the Semi-Analytical Finite Element method for the “global” portion of the waveguide, and a full Finite Element discretization for the “local” portion of the waveguide containing the discontinuity. The application of interest is the study of guided wave scattering from transverse head defects in rails. Theoretical scattering results are impossible to obtain in this case for a wide-frequency range. While three-dimensional Semi-Analytical Finite Element–Finite Element models for guided wave scattering studies have been …
Detection of disbonds in multilayer structures by laser-based ultrasonic technique
2008
Adhesively bonded multi-layer structures are frequently used, mostly in the aerospace industry, for their structural efficiency. Nondestructive evaluation of bond integrity in these types of structures, both after manufacturing and for periodic inspection during service, is extremely important. A laser-based ultrasonic technique has been evaluated for non-contact detection of disbonds in aluminum multi-layer structures. Two configurations have been used to detect disbonded areas: pitch-catch with unidirectional guided wave scan and through-transmission with bidirectional scan. Guided wave scanning was done with a laser line source and air-coupled transducer sensing at 500 kHz, 1 ;MHz, and 2…
Photo-acoustic excitation and optical detection of fundamental flexural guided wave in coated bone phantoms.
2013
Abstract Photo-acoustic (PA) imaging was combined with skeletal quantitative ultrasound (QUS) for assessment of human long bones. This approach permitted low-frequency excitation and detection of ultrasound so as to efficiently receive the thickness-sensitive fundamental flexural guided wave (FFGW) through a coating of soft tissue. The method was tested on seven axisymmetric bone phantoms, whose 1- to 5-mm wall thickness and 16-mm diameter mimicked those of the human radius. Phantoms were made of a composite material and coated with a 2.5- to 7.5-mm layer of soft material that mimicked soft tissue. Ultrasound was excited with a pulsed Nd:YAG laser at 1064-nm wavelength and received on the s…
Assessment of the cortical bone thickness using ultrasonic guided waves: Modelling and in vitro study
2007
Determination of cortical bone thickness is warranted, e.g., for assessing the level of endosteal resorption in osteoporosis or other bone pathologies. We have shown previously that the velocity of the fundamental antisymmetric (or flexural) guided wave, measured for bone phantoms and bones in vitro, correlates with the cortical thickness significantly better than those by other axial ultrasound methods. In addition, we have introduced an inversion scheme based on guided wave theory, group velocity filtering and 2-D fast Fourier transform, for determination of cortical thickness from the measured velocity of guided waves. In this study, the method was validated for tubular structures by usi…