Guided Wave Propagation Research Articles

A Method for Reducing Transcendental Dispersion Relations to Nonlinear Ordinary Differential Equations in a Wide Class of Wave Propagation Problems

A class of problems of wave propagation in waveguides consisting of one or several layers that are characterized by linear variation of the squared refractive index along the normal to the interfaces between them is considered in this paper. In various problems arising in practical applications, it is necessary to efficiently solve the dispersion relations for such waveguides in order to compute horizontal wavenumbers for different frequencies. Such relations are transcendental equations written in terms of Airy functions, and their numerical solutions may require significant computational effort. A procedure that allows one to reduce a dispersion relation to an ordinary differential equation written in terms of elementary functions exclusively is proposed. The proposed technique is illustrated on two cases of waveguides with both compact and non-compact cross-sections. The developed reduction method can be used in applications such as geoacoustic inversion.

Influence of Composite Thickness on Ultrasonic Guided Wave Propagation for Damage Detection.

In this paper, the propagation properties of ultrasonic guided waves (UGWs) in different-thickness composites (i.e., 2, 4 and 9 mm) were critically assessed, and their effectiveness for damage detections and localisations under varying temperatures was demonstrated. A diagnostic film with phased-array lead zirconate titanate (PZT) transducers based on the ink-jet printing technique was used in the experiments. Initially, the dispersion curves for these composites were compared. Next, the effects of the composite thickness on the A0 and S0 mode amplitudes and the group velocity were investigated by active sensing. Next, the behaviours of UGWs under varying temperatures in different-thickness plates were also investigated. Finally, surface-mounted artificial damage and impact damage were detected and located in different composites.

Damage shape recognition algorithm of composite woven fabric plate based on guided waves

Modern lightweight woven fabric composite structures play an important role in industrial field. The occurrence and accumulation of structure damages can threaten the integrity of in-service structures. With the high damage sensitivity, guided wave-based structural health monitoring has been regarded as the effective tool for damage detection. In this study, a damage shape recognition algorithm has been developed to continuously identify the damage extent in composite woven fabric structures, which is necessary for further analysis of remaining life estimation. The proposed algorithm is established relying on the accurate guided wave propagation information and precise damage scattered wave sources identification, and consists of the following stages: guided wave velocity calculation, guided wave signals collection, damage location identification, extraction of time of flight (TOF), damage boundary estimation, noise points filtering and damage shape and size recognition. The semi-analytical finite element method is presented to model guided wave propagation in multi-ply woven fabric panels. The numerical predictions are experimentally validated using the novel omnidirectional wave velocity measurement of guided wave collected by mobile PZT transducer. The precise TOF extraction and noise point elimination method are first proposed for improving effectiveness of damage identification. The approach was validated by several cases of damage at arbitrary positions. The estimated numerical and experimental results show the potential of the proposed algorithm in identifying various damage features in anisotropic composite plates, such as its location, shape and size, and achieve good agreement with the actual damage.

Phased array guided wave propagation in curved plates

For the monitoring of plate structures, phased array guided wave has great application prospects to effectively determine damage location and size. Locating damage via phased array focusing is a challenging task, especially in curved plates. Hence, a systematic understanding of the behavior of the phased array guided wave propagation in curved plates is needed. In this study, a phased array focusing method was proposed for the damage localization of curved plates. Different damage scenarios and phased array focusing schemes are investigated in the finite element plate models with different radii. A high-speed signal generation and acquisition system including PZT actuators and sensors is set up. Experimental tests are carried out on a curved aluminum plate with embedded piezoelectric elements to verify the finite element models. Parametric studies are then performed to evaluate the effect of different radii and damage scenarios on the behavior of phased array guided wave propagation in curved plates. Numerical simulations and experimental results show that the proposed PA method has the capabilities of wave focusing and damage identification in curved plates. The damage localization method using phased array guided wave has the potential to be applied to the real-time monitoring of structures with curved plates.

Study of in-plane wave propagation in 2-D polycrystalline microstructure

In this paper, a numerical and experimental study on in-plane guided wave propagation in polycrystalline microstructure is presented. For numerical study, Voronoi tessellation is used to generate the microstructure considering the concept of regularity parameter. It helped in producing equiaxed grains of microstructure, which resembles the texture of natural polycrystalline structure. In-plane guided wave propagation, resulting in simultaneous P and S wave transmission in two-dimensional (2-D) microstructure is simulated using a commercial finite element (FE) package, using graphics processing unit (GPU) based computing. Experimental verification of the in-plane guided wave propagation model is performed in the Rayleigh regime. The in-house experiments are performed on Inconel-600 plate using piezoelectric wafers as transducers. Though considerable work has been reported on P-wave characterization in a polycrystalline material, the study of in-plane guided waves is limited. It is found that within Rayleigh regime, the attenuation behavior of the in-plane guided wave shows a frequency dependency that is substantially less compared to the bulk wave in the 2-D polycrystalline microstructure. The model is first validated with the existing literature, particularly for the attenuation characterization in the Rayleigh regime. For in-plane guided waves, firstly, the numerical and experimental time-domain responses showing P and S waves are presented for different excitation frequencies. Within Rayleigh regime, the experimental and numerical group velocities and attenuation are in good agreement. Next, the attenuation characteristics are studied in the frequency range corresponding to the Rayleigh regime for different grain sizes. A new attenuation coefficient is proposed that relates the attenuation of bulk and in-plane guided waves. The study of in-plane guided wave in polycrystalline material will help in the ultrasonic investigation of defects and flaws in such materials.

Acoustic emission monitoring of wood materials and timber structures: A critical review

• Different NDE methods applied to wood and timber structures were explained. • Concept of AE and its experimentation was introduced. • Impact of wood characteristics on AE wave (velocity, attenuation) was discussed. • Applications of AE in monitoring of wood materials were critically reviewed. • Opportunities, challenges, and outline of future research were discussed. The growing interest in timber construction and using more wood for civil engineering applications has given highlighted importance of developing non-destructive evaluation (NDE) methods for structural health monitoring and quality control of wooden construction. This study, critically reviews the acoustic emission (AE) method and its applications in the wood and timber industry. Various other NDE methods for wood monitoring such as infrared spectroscopy, stress wave, guided wave propagation, X-ray computed tomography and thermography are also included. The concept and experimentation of AE are explained, and the impact of wood properties on AE signal velocity and energy attenuation is discussed. The state-of-the-art AE monitoring of wood and timber structures is organized into six applications: (1) wood machining monitoring; (2) wood drying; (3) wood fracture; (4) timber structural health monitoring; (5) termite infestation monitoring; and (6) quality control. For each application, the opportunities that the AE method offers for in-situ monitoring or smart assessment of wood-based materials are discussed, and the challenges and direction for future research are critically outlined. Overall, compared with structural health monitoring of other materials, less attention has been paid to data-driven methods and machine learning applied to AE monitoring of wood and timber. In addition, most studies have focused on extracting simple time-domain features, whereas there is a gap in using sophisticated signal processing and feature engineering techniques. Future research should explore the sensor fusion for monitoring full-scale timber buildings and structures and focus on applying AE to large-size structures containing defects. Moreover, the effectiveness of AE methods used for wood composites and mass timber structures should be further studied.

Shear elastic waves in bi-material multi-layered waveguide

This analytical study demonstrates shear elastic wave propagation in stratified waveguide with emphasis on wave localisation effects using the propagator matrix method. The stratified waveguide consists of two-phase piecewise homogeneous periodically arranged finite number sub-layers along waveguide thickness. Analytical solutions are carried out for traction free waveguide. The existence of two modal types of guided waves is established: i) a localised surface mode occurring in “stopband” and ii) normal modes arising in a “passband” of frequencies.

Integration of GaAs waveguides on a silicon substrate for quantum photonic circuits.

We report a method for integrating GaAs waveguide circuits containing self-assembled quantum dots on a Si/SiO2 wafer, using die-to-wafer bonding. The large refractive-index contrast between GaAs and SiO2 enables fabricating single-mode waveguides without compromising the photon-emitter coupling. Anti-bunched emission from individual quantum dots is observed, along with a waveguide propagation loss <7 dB/mm, which is comparable with the performance of suspended GaAs circuits. These results enable the integration of quantum emitters with different material platforms, towards the realization of scalable quantum photonic integrated circuits.

Coupled-Mode Parabolic Equations for the Modeling of Sound Propagation in a Shallow-Water Waveguide with Weak Elastic Bottom

In this work, a mode parabolic equation method with interacting modes accounting for the weak elasticity at the bottom is developed. An important feature of the proposed method is that computations of elastic modes are avoided and that the solution is obtained in the form of expansion over acoustic modes. A numerical technique for solving resulting mode parabolic equations is developed, and the accuracy and efficiency of the resulting solution is validated by a direct comparison against source image solutions in the 3D wedge benchmark problem. Satisfactory agreement of the two solutions is achieved for sufficiently small values of shear wave speed that are typical for soft sediments of the sea bottom. The developed approach may be used for solving 3D problems of sound propagation with the elastic properties of bottom sediments taken into account.

A modelling technique to investigate the effects of quasi-static loads on guided-wave based structural health monitoring systems

Guided wave-based methods for damage detection have been widely investigated as techniques to identify damages and their dimensions in structures. Most of the research activities presented in literature have been performed focusing on simple case studies in a laboratory environment, whereas Structural Health Monitoring systems should be investigated under operational loading conditions. When subjected to an operational load, propagation mechanisms can change, suffering from the interaction between propagating signal and scattered waves due to an initial stress-strain state, and so leading to errors in damage sites estimation. In this work, a numerical model, based on Finite Element approach, is proposed to investigate the effects of an initial stress-strain state, induced by a quasi-static load, on guided-wave propagation mechanisms. The case study consists of a real structure, a blended winglet of a general aviation aircraft. The methodology was assessed with reference to different scenarios.

Ultrafast pulse propagation in graphene-comprising nanophotonic waveguides considering nonperturbative electrodynamic nonlinearity

We outline a comprehensive model for ultrafast optical pulse propagation along nonlinear graphene-comprising integrated photonic waveguides. An electrodynamic graphene hot-electron model (GHEM) is used to capture the temporal dynamics and intertwined absorptive and refractive nonlinearity to explore a strongly nonperturbative photoconductivity regime that transcends third-order phenomena. We propose a formalism to abstract the 2D material-related modal properties of the waveguides in the static/continuous-wave regime that can also be plugged into a generalized nonlinear Schrödinger equation (NLSE) framework. Our model of optical pulse propagation consists of a coupled NLSE along with the nonlinear equation system of the GHEM. We demonstrate pulsed applications pertinent to integrated photonic components, namely, improvement of the extinction ratio (ER) of a nonreturn-to-zero (NRZ)-modulated bitstream, pulse shaping, spectral broadening, and optical-shock formation leading to pulse breaking and soliton formation. Our NLSE-GHEM extracts graphene nonlinearity from fundamental physics without resorting to phenomenological correction terms or fitted parameters, shows good agreement with recent experiments, and can potentially be used in the study of high-power on-chip applications such as pulsed lasers and frequency combs.

Performance analysis of slotted rectangular photonic crystal fiber structures in terahertz waveguidance

For an efficient and reliable transmission of data beyond 5G and 6G technologies, proper waveguide structures are needed. We present a rectangular solid-core slotted cladding photonic crystal fiber (PCF) and analyze its signal transmission capability in the terahertz (THz) regime. The proposed PCF performances have been investigated numerically using the finite element method. Various parameters, such as birefringence, core power fraction, effective material loss, effective area, mode-field diameter, beat length, dispersion, confinement loss, etc., have been studied by varying the geometry of the PCFs. The obtained simulation results exhibit dispersion of the order 2 ns / THz / cm, high birefringence of 0.0983, low confinement loss of the order 10 − 19 mm − 1, the effective area of 0.073 mm2, and high core power fraction of 99.8% in 0.2 to 2 THz range. All the parameters have been optimized among six different structures of the proposed PCF. This analysis will be helpful for the researchers to predict the transmission capability of THz waves in a rectangular PCF waveguide, which assures the boost in communication beyond 5G toward 6G evolution.

Dispersion of Guided Waves in Complex Waveguides: A Hybrid Modeling Technique Combining Gauss–Lobatto–Legendre Node Collation and Semi-Analytical Finite Element Method

Guided waves (GW) are massively used for structural health monitoring and defect evaluation in plate, pipe, and rail structures. To accurately and efficiently calculate the dispersive natures of GW in complex waveguides, this study proposes a novel Gauss–Lobatto–Legendre-based high-order semi-analytical finite element method (GLL-SAFE). Combining the GLL node collation and Lobatto quadrature into SAFE, the mass matrix in the developed GLL-SAFE is diagonal, which enables a faster solution speed and a reduced error of matrix inversion. Firstly, the GWs in the single-layer isotropic material, composite lamina, and composite laminates are calculated with both GLL-SAFE and the conventional Gauss-SAFE featuring an equidistant node collation and Gaussian quadrature. Before reaching the convergence limit, the calculated average relative errors for GLL-SAFE are smaller than those for Gauss-SAFE, and can reach an order of 10[Formula: see text] and 10[Formula: see text] for the phase and group velocity, respectively. Then a novel mesh automatic reconstruction with arbitrary element polynomial order is developed to calculate GW propagation in waveguides of complex cross section. As a hollow cylinder for validation, the calculated average relative errors reach below [Formula: see text] and [Formula: see text] for the phase and group velocity, respectively. Finally, with a complex rail track as the waveguide, the calculated dispersion characteristics with GLL-SAFE show an excellent match with those from the time-domain finite element analysis, and GLL-SAFE shows its higher calculation efficiency over Gauss–SAFE.

Shallow-water waveguide acoustic analysis in a fluctuating environment.

The Acoustic Laboratory for Marine Applications (ALMA) is a deployable and autonomous acoustic system, designed by DGA Naval Systems, to address problems in underwater acoustics, such as sound propagation in fluctuating environments. In this article, data from the ALMA-2016 at-sea campaign are used to analyze the ocean fluctuation's influence on sound propagation in a shallow-water waveguide. The experiment took place on the continental shelf of the island of Corsica in November 2016. A source and a receiver array were 9.3 km apart in a nearly constant water depth of 100 m. The source emitted a variety of signals from which the chirp (1-13 kHz) is used to extract the waveguide eigenrays. To do so, a time-domain beamforming is performed on the match-filtered received signals with an automatic detection of local maxima in the time of arrival/direction of arrival (TOA/DOA) domain. A 2 min acquisition period of more than 13 h duration shows significant fluctuations in eigenray TOAs/DOAs. Qualitative comparisons with synthetic signals obtained from simulations in two and three dimensions permit reproduction of the observed eigenray fluctuations without including range dependence of the sound-speed profile.

Ultrasonic Waveguides for Quench Detection in HTS Magnets

High-temperature superconductors (HTS) are expected to have a major impact on the development of future particle accelerators and fusion energy systems. One of key challenges associated with HTS is a slow propagation of the normal zone that complicates early detection of thermal runaway (quench) in an HTS magnet using voltage-based techniques. Furthermore, fusion systems require field ramping rates up to several T/s under strong time-varying ac magnetic fields imposed on the conductor which makes voltage-based quench detection difficult or impractical. We propose an alternative non-voltage quench detection solution based upon monitoring ultrasonic wave propagation in a solid fiber-like flexible waveguide. The latter can be co-wound with the superconducting cable and carry acoustic waves over long distances. Acoustic waveguides allow for measuring local variation of strain or temperature in a way similar to optical fibers. However, unlike fiber-optic sensors, mechanical waveguides are constructed of robust materials and eliminate the need for expensive and complex signal receivers and data processing equipment. We will present our early developments in cryogenic ultrasonic waveguide technology, and discuss preliminary experiments conducted towards validating it for future use in practical HTS magnets.

Retracted: Elastic Guided Wave Propagation in the Prestressed Helical Multiwire Waveguide

Retracted: Elastic Guided Wave Propagation in the Prestressed Helical Multiwire Waveguide

Expanding the quantum photonic toolbox in AlGaAsOI

Aluminum gallium arsenide-on-insulator (AlGaAsOI) exhibits large χ2 and χ3 optical nonlinearities, a wide tunable bandgap, low waveguide propagation loss, and a large thermo-optic coefficient, making it an exciting platform for integrated quantum photonics. With ultrabright sources of quantum light established in AlGaAsOI, the next step is to develop the critical building blocks for chip-scale quantum photonic circuits. Here we expand the quantum photonic toolbox for AlGaAsOI by demonstrating edge couplers, 3 dB splitters, tunable interferometers, and waveguide crossings with performance comparable to or exceeding silicon and silicon-nitride quantum photonic platforms. As a demonstration, we de-multiplex photonic qubits through an unbalanced interferometer, paving the route toward ultra-efficient and high-rate chip-scale demonstrations of photonic quantum computation and information applications.

Study on Bond Defect Detection in Grouted Rock Bolt Systems under Pullout Loads

In grouted rock bolt systems, bond defects often occur, which seriously affects the safety of rock mass structures. Therefore, in this study, based on the existence of bond defects, laboratory tests were conducted to detect the location and length of bond defects and study the guided wave propagation in grouted rock bolt systems under different pullout loads. The guided wave signal was analysed in the time domain and frequency domain. In addition to the laboratory test, a numerical simulation of the effect of different bond defect locations on ultrasonic guided wave propagation in rock bolts was conducted using a damage-based model. The influence mechanism of bond defects on guided wave propagation under different pullout loads was explored. The study confirmed that there existed a stress platform in the rock bolt at the bond defect under a pullout load. The location and length of the bond defect could be detected by the stress platform and guided wave. The debonding length increased exponentially with the amplitude ratio (Q) of low frequency to high frequency, and the Q value could be used as the quantitative index of debonding length. As the pullout load increased, the impedance mismatch between the rock bolt and cement mortar (defect) increased, and the guided wave propagation in grouted rock bolt systems was irregular. The pullout load weakened the guided wave propagation law. The larger the pullout load is, the greater the weakening effect is.

Experimental and Numerical Studies on Bond Quality of Fully Grouted Rockbolt under Confining Pressure and Pull-Out Load

In mining engineering, the in situ stress changes with the stress induced by the surrounding mining activities. It positively or negatively affects the propagation of ultrasonic guided waves in rockbolts. Therefore, the effect of in situ stress in rockbolt support was determined by applying confining pressure and pull-out load in a laboratory test and using ultrasonic guided waves to test the rockbolt. Furthermore, the propagation law of ultrasonic guided waves and bond quality of the rockbolt under the interaction of the pull-out load and confining pressure were studied. Numerical simulations were performed to deduce the guided wave propagation process in grouted systems, and the influencing mechanism of the pull-out load and confining pressure on the guided wave propagation was discussed. The laboratory test and numerical simulation results show that the confining pressure weakens the guided wave propagation without pull-out load. Under the same pull-out load, the guided wave propagation gradually strengthens with increasing confining pressure. A larger confining pressure weakens the weakening effect of the pull-out load and suppresses the discreteness of the guided wave propagation. Under the same confining pressure, the guided waves did not diffract well into the cement mortar and concrete with increasing pull-out load, the confining pressure restricted the radial vibration of the guided waves, and the guided wave propagation law weakened. Thus, the pull-out load plays a weakening role in the propagation law of ultrasonic guided waves.

Tunable asymmetric transmission of Lamb waves in piezoelectric bimorph plates by electric boundary design

The multi-mode and dispersion natures of elastic guided waves bring big challenges for wave manipulation, and also provide more possibilities for smart device design. In this study, a piezoelectric bimorph plate connected to a periodic arrangement of electric circuits is proposed, and both propagating and evanescent guided Lamb waves are investigated through the complex band structure resulting form using different shunting capacitor or inductor distributions. Results show that keeping and breaking the symmetry of the electric boundary condition can, respectively, lead to decoupling or hybridizing of multi-mode Lamb waves. Accordingly, the asymmetric transmission at a desired frequency can be realized by combining the symmetric and asymmetric electric boundary conditions. Harmonic analysis shows that numerical results are in good agreement with the prediction of complex band structure. Actively changing the electric boundary conditions can be used for guided wave propagation in piezoelectric bimorph plates to easily control the system without changing the structure’s geometry. The framework presented herein offers enhanced capabilities for controlling guided wave propagation for engineering applications and to develop nondestructive testing techniques.