Showing papers on "Guided wave testing published in 2016"

Guided wave based structural health monitoring: A review

Abstract: The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

Guided-wave transmission device with non-fundamental mode propagation and methods for use therewith

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes a transmitter that generates a first electromagnetic wave to convey data. A coupler couples the first electromagnetic wave to a single wire transmission medium having an outer surface, to forming a second electromagnetic wave that is guided to propagate along the outer surface of the single wire transmission medium via at least one guided wave mode that includes an asymmetric or non-fundamental mode having a lower cutoff frequency. A carrier frequency of the second electromagnetic wave is selected to be within a limited range of the lower cutoff frequency, so that a majority of the electric field is concentrated within a distance from the outer surface that is less than half the largest cross sectional dimension of the single wire transmission medium, and/or to reduce propagation loss. Other embodiments are disclosed.

Repeater and methods for use therewith

Abstract: Aspects of the subject disclosure may include, for example, a repeater device having a first coupler to extract downstream channel signals from first guided electromagnetic waves bound to a transmission medium of a guided wave communication system. An amplifier amplifies the downstream channel signals to generate amplified downstream channel signals. A channel selection filter selects one or more of the amplified downstream channel signals to wirelessly transmit to the at least one client device via an antenna. A second coupler guides the amplified downstream channel signals to the transmission medium of the guided wave communication system to propagate as second guided electromagnetic waves. Other embodiments are disclosed.

Communication system, guided wave switch and methods for use therewith

Abstract: Aspects of the subject disclosure may include, for example, a guided wave switch that selectively aligns an end of the first dielectric core of a first conductorless guided wave cable with an end of a selected one of a plurality of second dielectric cores of at least one second conductorless guided wave cable to facilitate coupling of the first guided waves from the first dielectric core to a selected one of the plurality of second dielectric cores Other embodiments are disclosed

Launcher and coupling system for guided wave mode cancellation

Abstract: Aspects of the subject disclosure may include, for example, a coupling module that includes a waveguide that guides a first electromagnetic wave conveying data from a transmitting device. A dielectric coupler receives the first electromagnetic wave from the waveguide to form a second electromagnetic wave, and that guides the second electromagnetic wave along the dielectric coupler adjacent to a transmission medium, and wherein the dielectric coupler has a length that supports a cancellation of at least one cancelled wave mode from a coupling of the second electromagnetic wave to the transmission medium.

Anomalous Refraction of Acoustic Guided Waves in Solids with Geometrically Tapered Metasurfaces.

Abstract: The concept of a metasurface opens new exciting directions to engineer the refraction properties in both optical and acoustic media. Metasurfaces are typically designed by assembling arrays of subwavelength anisotropic scatterers able to mold incoming wave fronts in rather unconventional ways. The concept of a metasurface was pioneered in photonics and later extended to acoustics while its application to the propagation of elastic waves in solids is still relatively unexplored. We investigate the design of acoustic metasurfaces to control elastic guided waves in thin-walled structural elements. These engineered discontinuities enable the anomalous refraction of guided wave modes according to the generalized Snell's law. The metasurfaces are made out of locally resonant toruslike tapers enabling an accurate phase shift of the incoming wave, which ultimately affects the refraction properties. We show that anomalous refraction can be achieved on transmitted antisymmetric modes (A_{0}) either when using a symmetric (S_{0}) or antisymmetric (A_{0}) incident wave, the former clearly involving mode conversion. The same metasurface design also allows achieving structure embedded planar focal lenses and phase masks for nonparaxial propagation.

Client node device with frequency conversion and methods for use therewith

Abstract: Aspects of the subject disclosure may include, for example, a repeater device having a first coupler to extract downstream channel signals from first guided electromagnetic waves bound to a transmission medium of a guided wave communication system. An amplifier amplifies the downstream channel signals to generate amplified downstream channel signals. A channel selection filter selects one or more of the amplified downstream channel signals to wirelessly transmit to the at least one client device via an antenna. A second coupler guides the amplified downstream channel signals to the transmission medium of the guided wave communication system to propagate as second guided electromagnetic waves. Other embodiments are disclosed.

Spatially resolved edge currents and guided-wave electronic states in graphene

Abstract: Experiments show that electron waves can be confined to and guided along the edges of monolayer and bilayer graphene sheets, analogous to the guiding of light waves in optical fibres.

Guided Wave Tomography Based on Full Waveform Inversion

Abstract: In this paper, a guided wave tomography method based on full waveform inversion (FWI) is developed for accurate and high-resolution reconstruction of the remaining wall thickness in isotropic plates. The forward model is computed in the frequency domain by solving a full-wave equation in a two-dimensional (2-D) acoustic model, accounting for higher order effects such as diffractions and multiple scattering. Both numerical simulations and experiments were carried out to obtain the signals of a dispersive guided mode propagating through defects. The inversion was based on local optimization of a waveform misfit function between modeled and measured data, and was applied iteratively to discrete frequency components from low to high frequencies. The resulting wave velocity maps were then converted to thickness maps by the dispersion characteristics of selected guided modes. The results suggest that the FWI method is capable to reconstruct the thickness map of a irregularly shaped defect accurately on a 10-mm-thick plate with the thickness error within 0.5 mm.

Method and apparatus for adjusting a field of a guided wave to mitigate interference

Abstract: Aspects of the subject disclosure may include, for example, a system that performs operations including detecting a signal degradation of guided electromagnetic waves bound to a transmission medium without utilizing an electrical return path, the guided electromagnetic waves having a non-optical frequency range, and adjusting an alignment of at least a portion of fields of the guided electromagnetic waves to mitigate the signal degradation. Other embodiments are disclosed.

A design of active elastic metamaterials for control of flexural waves using the transformation method

Abstract: The ability to control flexural wave propagation is of fundamental interest in many areas of structural engineering and physics. Metamaterials have shown a great potential in subwavelength wave propagation control due to their inherent local resonance mechanism. In this study, we propose a transformation method to derive the material properties of a flexural waveguide and implement the functionality based on a design of active elastic metamaterials. The numerically demonstrated flexural waveguide can not only steer an elastic wave beam as predicted from the transformation method but also exhibit various unique properties including extraordinary wave beam deflection and tunabilities over a broad frequency range and various steering directions. The waveguide is equipped with an array of active elastic metamaterials composed of the electrorheological elastomer subjected to adjustable electric fields. Such metamaterial-based waveguides provide a new design methodology for guided wave signal modulation devices...

Rapid guided wave delamination detection and quantification in composites using global-local sensing

Abstract: This paper presents a rapid guided ultrasonic wave inspection approach through global inspection by phased array beamforming and local damage evaluation via wavenumber analysis. The global-local approach uses a hybrid system consisting of a PZT wafer and a non-contact laser vibrometer. The overall inspection is performed in two steps. First, a phased array configured by a small number of measurements performs beamforming and beamsteering over the entire plate in order to detect and locate the presence of the damage. A local area is identified as target damage area for the second step. Then a high density wavefield measurement is taken over the target damage area and a spatial wavenumber imaging is performed to quantitatively evaluate the damage. The two-step inspection has been applied to locate and quantify impact-induced delamination damage in a carbon fiber reinforced polymer composite plate. The detected delamination location, size and shape agree well with those of an ultrasonic C-scan. For the test case studied in this work the global-local approach reduced the total composite inspection (damage detection and characterization) time by ~97% compared to using a full scan approach.

Hybrid local FEM/global LISA modeling of damped guided wave propagation in complex composite structures

Abstract: This paper presents a new hybrid modeling technique for the efficient simulation of guided wave generation, propagation, and interaction with damage in complex composite structures. A local finite element model is deployed to capture the piezoelectric effects and actuation dynamics of the transmitter, while the global domain wave propagation and interaction with structural complexity (structure features and damage) are solved utilizing a local interaction simulation approach (LISA). This hybrid approach allows the accurate modeling of the local dynamics of the transducers and keeping the LISA formulation in an explicit format, which facilitates its readiness for parallel computing. The global LISA framework was extended through the 3D Kelvin–Voigt viscoelasticity theory to include anisotropic damping effects for composite structures, as an improvement over the existing LISA formulation. The global LISA framework was implemented using the compute unified device architecture running on graphic processing units. A commercial preprocessor is integrated seamlessly with the computational framework for grid generation and material property allocation to handle complex structures. The excitability and damping effects are successfully captured by this hybrid model, with experimental validation using the scanning laser doppler vibrometry. To demonstrate the capability of our hybrid approach for complex structures, guided wave propagation and interaction with a delamination in a composite panel with stiffeners is presented.

Excitation of Single-Mode Lamb Waves at High-Frequency-Thickness Products

Abstract: Guided wave inspection is used extensively in petrochemical plants to check for defects such as corrosion. Long-range low-frequency inspection can be used to detect relatively large defects, while higher frequency inspection provides improved sensitivity to small defects, but the presence of multiple dispersive modes makes it difficult to implement. This paper investigates the possibility of exciting a single-mode Lamb wave with low dispersion at a frequency thickness of around 20 MHz-mm. It is shown by finite element (FE) analysis backed up by experiments that a signal dominated by the A1 mode can be generated, even in a region where many modes have similar phase velocities. The A1 mode has relatively little motion at the plate surface which means that only a small reflection is generated at features such as T-joints; this is verified numerically. It is also expected that it will be relatively unaffected by surface roughness or attenuative coatings. These features are very similar to those of the higher order mode cluster (HOMC) reported by other authors, and it is shown that the A1 mode shape is very similar to the deflected shape reported in HOMC.

Guided Wave Based Crack Detection in the Rivet Hole Using Global Analytical with Local FEM Approach

Abstract: In this article, ultrasonic guided wave propagation and interaction with the rivet hole cracks has been formulated using closed-form analytical solution while the local damage interaction, scattering, and mode conversion have been obtained from finite element analysis. The rivet hole cracks (damage) in the plate structure gives rise to the non-axisymmetric scattering of Lamb wave, as well as shear horizontal (SH) wave, although the incident Lamb wave source (primary source) is axisymmetric. The damage in the plate acts as a non-axisymmetric secondary source of Lamb wave and SH wave. The scattering of Lamb and SH waves are captured using wave damage interaction coefficient (WDIC). The scatter cubes of complex-valued WDIC are formed that can describe the 3D interaction (frequency, incident direction, and azimuth direction) of Lamb waves with the damage. The scatter cubes are fed into the exact analytical framework to produce the time domain signal. This analysis enables us to obtain the optimum design parameters for better detection of the cracks in a multiple-rivet-hole problem. The optimum parameters provide the guideline of the design of the sensor installation to obtain the most noticeable signals that represent the presence of cracks in the rivet hole.

Scattering of guided waves at delaminations in composite plates

Abstract: Carbon fiber laminate composites are increasingly employed for aerospace structures as they offer advantages, such as a good strength to weight ratio. However, impact during the operation and servicing of the aircraft can lead to barely visible and difficult to detect damage. Depending on the severity of the impact, fiber and matrix breakage or delaminations can occur, reducing the load carrying capacity of the structure. Efficient nondestructive testing and structural health monitoring of composite panels can be achieved using guided ultrasonic waves propagating along the structure. The scattering of the A0 Lamb wave mode at delaminations was investigated using a full three-dimensional (3D) finite element (FE) analysis. The influence of the delamination geometry (size and depth) was systematically evaluated. In addition to the depth dependency, a significant influence of the delamination width due to sideways reflection of the guided waves within the delamination area was found. Mixed-mode defects were simulated using a combined model of delamination with localized material degradation. The guided wave scattering at cross-ply composite plates with impact damage was measured experimentally using a non-contact laser interferometer. Good agreement between experiments and FE predictions using the mixed-mode model for an approximation of the impact damage was found.

Longitudinal mode magnetostrictive patch transducer array employing a multi-splitting meander coil for pipe inspection

Abstract: Recently, a magnetostrictive patch transducer (MPT) by means of the highly magnetostrictive (such as nickel or iron–cobalt alloy) patch attached on the specimen has been applied in nondestructive ultrasonic testing in waveguides. In the study, we proposed a new MPTs array employing a multi-splitting meander coil (MSMC) for generating and receiving longitudinal guided waves in pipes. In the suggested configuration, the directions of the static magnetic field produced by the permanent magnets and the dynamic magnetic field produced by the MSMC are in the axial direction of the pipe. Two finite element models were established to simulate the distribution of the static and dynamic magnetic fields in the patch, respectively. The proposed MSMC was made of flexible printed circuit (FPC), so it could be easily installed on pipe surface. The performance of the proposed MPTs array was experimentally studied. Firstly, it was experimentally verified that the axisymmetric longitudinal guided wave mode, L(0,2), could be effectively generated and received in pipes with the developed MSMC-MPTs array. Secondly, the frequency response characteristics of the developed MSMC-MPTs array were related to D (the distance between adjacent belts of the MSMC). Thirdly, we demonstrated the ability of the developed MSMC-MPTs array for the identification and location of a crack defect in pipes. Finally, we compared the performances of the MSMC-MPTs array and conventional meander coil-MPTs and proved that the signals of the longitudinal guided wave mode could be enhanced by using the developed MSMC-MPTs array.

Linear and Nonlinear Guided Wave Imaging of Impact Damage in CFRP Using a Probabilistic Approach.

Abstract: The amount and variety of composite structures that need to be inspected for the presence of impact damage has grown significantly in the last few decades. In this paper, an application of a probabilistic ultrasonic guided wave imaging technique for impact damage detection in carbon fiber-reinforced polymers (CFRP) is presented. On the one hand, a linear, baseline-dependent, technique utilizing the well-known correlation-based RAPID method and an array of piezoelectric transducers is applied to detect impact-induced damage in plate-like composite structures. Furthermore, a baseline-independent nonlinear extension of the standard RAPID method is proposed, and its performance is demonstrated both numerically and experimentally. Compared to the conventional RAPID, the baseline-free version suffers from a somewhat lower imaging quality. However, this drawback is compensated by the fact that no damage-free (intact) baseline is necessary for successful imaging of damage.

Independent Component Analysis for Improved Defect Detection in Guided Wave Monitoring

Abstract: Guided wave sensors are widely used in a number of industries and have found particular application in the oil and gas industry for the inspection of pipework. Traditionally this type of sensor was used for one-off inspections, but in recent years there has been a move towards permanent installation of the sensor. This has enabled highly repeatable readings of the same section of pipe, potentially allowing improvements in defect detection and classification. This paper proposes a novel approach using independent component analysis to decompose repeat guided wave signals into constituent independent components. This separates the defect from coherent noise caused by changing environmental conditions, improving detectability. This paper demonstrates independent component analysis applied to guided wave signals from a range of industrial inspection scenarios. The analysis is performed on test data from pipe loops that have been subject to multiple temperature cycles both in undamaged and damaged states. In addition to processing data from experimental damaged conditions, simulated damage signals have been added to “undamaged” experimental data, so enabling multiple different damage scenarios to be investigated. The algorithm has also been used to process guided wave signals from finite element simulations of a pipe with distributed shallow general corrosion, within which there is a patch of severe corrosion. In all these scenarios, the independent component analysis algorithm was able to extract the defect signal, rejecting coherent noise.

Damage Detection Based on Power Dissipation Measured with PZT Sensors through the Combination of Electro-Mechanical Impedances and Guided Waves.

Abstract: The use of piezoelectric ceramic transducers (such as Lead-Zirconate-Titanate—PZT) has become more and more widespread for Structural Health Monitoring (SHM) applications. Among all the techniques that are based on this smart sensing solution, guided waves and electro-mechanical impedance techniques have found wider acceptance, and so more studies and experimental works can be found containing these applications. However, even though these two techniques can be considered as complementary to each other, little work can be found focused on the combination of them in order to define a new and integrated damage detection procedure. In this work, this combination of techniques has been studied by proposing a new integrated damage indicator based on Electro-Mechanical Power Dissipation (EMPD). The applicability of this proposed technique has been tested through different experimental tests, with both lab-scale and real-scale structures.

Optimum design of phononic crystal perforated plate structures for widest bandgap of fundamental guided wave modes and maximized in-plane stiffness

Abstract: This paper presents a topology optimization of single material phononic crystal plate (PhP) to be produced by perforation of a uniform background plate. The primary objective of this optimization study is to explore widest exclusive bandgaps of fundamental (first order) symmetric or asymmetric guided wave modes as well as widest complete bandgap of mixed wave modes (symmetric and asymmetric). However, in the case of single material porous phononic crystals the bandgap width essentially depends on the resultant structural integration introduced by achieved unitcell topology. Thinner connections of scattering segments (i.e. lower effective stiffness) generally lead to (i) wider bandgap due to enhanced interfacial reflections, and (ii) lower bandgap frequency range due to lower wave speed. In other words higher relative bandgap width (RBW) is produced by topology with lower effective stiffness. Hence in order to study the bandgap efficiency of PhP unitcell with respect to its structural worthiness, the in-plane stiffness is incorporated in optimization algorithm as an opposing objective to be maximized. Thick and relatively thin Polysilicon PhP unitcells with square symmetry are studied. Non-dominated sorting genetic algorithm NSGA-II is employed for this multi-objective optimization problem and modal band analysis of individual topologies is performed through finite element method. Specialized topology initiation, evaluation and filtering are applied to achieve refined feasible topologies without penalizing the randomness of genetic algorithm (GA) and diversity of search space. Selected Pareto topologies are presented and gradient of RBW and elastic properties in between the two Pareto front extremes are investigated. Chosen intermediate Pareto topology, even not extreme topology with widest bandgap, show superior bandgap efficiency compared with the results reported in other works on widest bandgap topology of asymmetric guided waves, available in the literature. Finally, steady state and transient frequency response of finite thin PhP structures of selected Pareto topologies are studied and validity of obtained bandgaps is confirmed.

Guided waves in a stiffened composite laminate with a delamination

Abstract: The integrity of safety-critical structural composites can be enhanced by the use of innovative ultrasonic nondestructive evaluation techniques. Among the various existing techniques, guided wave methods provide a good promise in terms of sensitivity to a variety of damage types or defects and the extent of the area that can be monitored, given the ability of these waves to travel relatively long distances within the structure under investigation. In comparison with isotropic metallic structures, wave propagation in composite structures presents additional complexity for effective damage identification. The material inhomogeneity, anisotropy, and the multilayered construction of composite materials lead to significant dependence of wave modes on laminate layup configurations, direction of propagation, frequency, and interface conditions. In this article, a specific structure will be analyzed with different levels of complexities in an effort to determine the propagation characteristics of the waves. The i...

Nonlinearity-induced PT-symmetry without material gain

Abstract: Parity-time symmetry has raised a great deal of attention in optics in recent years, yet its application has been so far hindered by the stringent requirements on coherent gain balanced with loss. In this paper, we show that the conditions to enable parity and time symmetry can be simultaneously satisfied for a pair of modes with mixed frequencies interacting in a nonlinear medium, without requiring the presence of material gain. First, we consider a guided wave structure with second order nonlinearity and we derive the PT-symmetric Hamiltonian that governs the interaction of two waves of mixed frequencies when accompanied by a high intensity pump beam at the sum frequency. We also extend the results to an array of coupled nonlinear waveguide channels. It is shown that the evolution dynamics of the low-frequency waves is associated with a periodic PT-symmetric lattice while the phase of the pump beams can be utilized as a control parameter to modify the gain and loss distribution, thus realizing different PT lattices by design. Our results suggest that nonlinear wave mixing processes can form a rich platform to realize PT-symmetric Hamiltonians of arbitrary dimensions in optical systems, without requiring material gain.

Guided-wave Brillouin scattering in air

Abstract: Photonic-bandgap fibers have had major impact from fundamental studies of photon–atom interactions to new applications in nonlinear optics. While much is known about the optical properties of these fibers, relatively little is known about their optomechanical properties. Here we identify a new form of optomechanical coupling in gas-filled hollow-core fibers. We show that forward Brillouin scattering is produced by air in the core of a photonic bandgap fiber. A single Brillouin resonance is identified at 35 MHz, which corresponds to a guided sound wave within the center of an air-filled hollow-core fiber. A simple analytical model, refined by numerical simulations, is developed that accurately predicts the Brillouin coupling strength and frequency from the gas and fiber parameters, revealing that this optomechanical interaction is highly tailorable. This new mechanism could become the basis for new types of sensing and spectroscopy. Moreover, this previously unknown nonlinearity within hollow core fibers represents a power and noise limitation that requires further consideration.