Showing papers on "Guided wave testing published in 2010"

Periodic Leaky-Wave Antenna for Millimeter Wave Applications Based on Substrate Integrated Waveguide

Abstract: Substrate integrated waveguides (SIW) are built up of periodically arranged metallic via-holes or via-slots The leakage loss of SIW structures increases with the distance between the via-holes or via-slots An open periodic waveguide with a large via distance supports the propagation of leaky-wave modes and can thus be used for the design of a leaky-wave antenna In this paper, this leakage loss is studied in detail and used to design a periodic leaky-wave antenna The proposed concept represents an excellent choice for applications in the millimeter-wave band Due to its versatility, the finite difference frequency domain method for periodic guided-wave or leaky-wave structures is used to analyze the characteristics of the proposed periodic leaky-wave antenna Two modes (TE10 and TE20) are investigated and their different leaky-wave properties are analyzed Based on the proposed leaky-mode analysis method, a novel periodic leaky-wave antenna at 28-34 GHz is designed and fabricated

Minimum variance ultrasonic imaging applied to an in situ sparse guided wave array

Abstract: Ultrasonic guided wave imaging with a sparse, or spatially distributed, array can detect and localize damage over large areas. Conventional delay-and-sum images from such an array typically have a relatively high noise floor, however, and contain artifacts that often cannot be discriminated from damage. Considered here is minimum variance distortionless response (MVDR) imaging, which is a variation of delay-and-sum imaging whereby weighting coefficients are adaptively computed at each pixel location. Utilization of MVDR significantly improves image quality compared with delay-and-sum imaging, and additional improvements are obtained from incorporation of a priori scattering information in the MVDR method, use of phase information, and instantaneous windowing. Simulated data from a through-hole scatterer are used to illustrate performance improvements, and a performance metric is proposed that allows for quantitative comparisons of images from a known scatterer. Experimental results from a through-hole scatterer are also provided that illustrate imaging efficacy.

Optomechanics in an ultrahigh-Q slotted 2D photonic crystal cavity

Abstract: Optical guided wave dielectric structures with nanoscale slots are known to provide strong electric field enhancements in the slotted region, enabling strong light-matter interactions. Here we demonstrate an ultrahigh-Q slotted 2D photonic crystal cavity for the purpose of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The experimentally measured optical quality factor is Q=1.2x10^6 for a cavity with a simulated effective optical modal volume of 0.04 cubic wavelengths. Optical transduction of the thermal Brownian motion of the fundamental in-plane mechanical resonance of the slotted structure (151 MHz) is performed, from which an optomechanical coupling of 140 GHz/nm is inferred for an effective motional mass of 20 pg. Dynamical back-action of the optical field on the mechanical motion, resulting in both cooling and amplication of the mechanical motion, is also demonstrated.

Trapped rainbow storage of light in metamaterials

Abstract: We review recent theoretical and experimental in progress in the realisation of slow and stopped light by the 'trapped rainbow' principle in optical metamaterials featuring negative electromagnetic parameters (permittivity/permeability and/or refractive index). We explain how and why these structures can enable complete stopping of light even in the presence of disorder and, simultaneously, dissipative losses. Using full-wave numerical simulations we show that the incorporation of thin layers made of an active medium adjacently to the core layer of a negative-refractive-index waveguide can completely remove dissipative losses - in a slow-light regime where the effective index of the guided wave is negative.

Multi-site damage localization in anisotropic plate-like structures using an active guided wave structural health monitoring system

Abstract: A new approach for structural health monitoring using guided waves in plate-like structures has been developed. In contrast to previous approaches, which mainly focused on isotropic or quasi-isotropic plates, the proposed algorithm does not assume any simplifications regarding anisotropic wave propagation. Thus, it can be used to improve the probability of detection. In this paper the mathematical background for damage localization in anisotropic plates will be introduced. This is an extension of the widely known ellipse method. The formalism is based on a distributed sensor network, where each piezoelectric sensor acts in turn as an actuator. The automatic extraction of the onset time of the first waveform in the differential signal in combination with a statistical post-processing via a two-dimensional probability density function and the application of the expectation-maximization algorithm allows a completely automatic localization procedure. Thus, multiple damages can be identified at the same time. The present study uses ultrasonic signals provided by the spectral element method. This simulation approach shows good agreement with experimental measurements. A local linear neural network is used to model the nonlinear dispersion curves. The benefit of using a neural network approach is to increase the angular resolution that results from the sparse sensor network. Furthermore, it can be used to shorten the computational time for the damage localization procedure.

Quantitative experimental measurements of matrix cracking and delamination using acoustic emission

Abstract: Quantitative measurements of the amplitude and angular variation of acoustic emission (AE) events due to matrix cracking and delamination in large quasi-isotropic composite plate specimens are reported. A procedure for determining the minimum specimen size necessary to make quantitative measurements is presented. The amplitude of AE events is quoted as the absolute surface displacement of different guided wave modes and can therefore be used as the input to forward models of the AE process. Matrix cracking events are found to be dominated by the S0 guided wave mode and have a pronounced amplitude variation with angle. Events due to delamination growth are dominated by the A0 guided wave mode and have no clear angular dependence.

Resolution enhancement in surface plasmon resonance sensor based on waveguide coupled mode by combining a bimetallic approach.

Abstract: In this study, we present and demonstrate a new route to a great enhancement in resolution of surface plasmon resonance sensors. Basically, our approach combines a waveguide coupled plasmonic mode and a kind of Au/Ag bimetallic enhancement concept. Theoretical modeling was carried out by solving Fresnel equations for the multilayer stack of prism/Ag inner-metal layer/dielectric waveguide/Au outer-metal layer. The inner Ag layer couples incident light to a guided wave and makes more fields effectively concentrated on the outer Au surface. A substantial enhancement in resolution was experimentally verified for the model stack using a ZnS-SiO2 waveguide layer.

Guided wave diffraction tomography within the born approximation

Abstract: Detection and sizing of corrosion in pipelines and pressure vessels over large, partially accessible areas is of growing interest in the petrochemical industry. Low-frequency guided wave diffraction tomography is a potentially attractive technique to rapidly evaluate the thickness of large sections of partially accessible structures. Finite element simulations of a 64-element circular array on a plate show that when the scattering mechanism of the object to be reconstructed satisfies the Born approximation, the reconstruction of the thickness is accurate. However, the practical implementation is more challenging because the incident field is not known. This paper describes the baseline subtraction approach commonly used in structural health monitoring applications and proposes a new approach in which the measurement of the incident field is not required when using a circular array of transducers. Experimental results demonstrate that ultimately the scattering from the array of transducers is a major source of error in the tomographic reconstruction, but when there is no scattering from the array of transducers the reconstructions are very similar to the finite element simulations.

Damage Detection in Thin Composite Laminates Using Piezoelectric Phased Sensor Arrays and Guided Lamb Wave Interrogation

Abstract: Damage detection in composite laminated panels using Lamb waves is demonstrated with an innovative use of a sensor array and processing algorithm. Two models were developed to characterize the Lamb wave propagation properties of orthotropic panels. Predictions of the dispersion relations were made for a fiber-reinforced composite laminate. Experiments were conducted to empirically characterize the wave propagation behavior in a manufactured laminate. Piezoelectric patches were used as sensors and actuators in the experiments. Comparisons were made between analytical predictions and experimental results, which demonstrate that the higher order model captured essential wave propagation behavior at frequencies of interest. Sensor arrays and associated processing were used for wavenumber decomposition and filtering of the Lamb wave modes. Composite laminates were manufactured with an embedded defect to simulate inter-ply delamination. Experiments were conducted to detect the presence of delamination damage in...

Guided wave phase velocity measurement using multi-emitter and multi-receiver arrays in the axial transmission configuration.

Abstract: This paper is devoted to a method of extraction of guided waves phase velocities from experimental signals. Measurements are performed using an axial transmission device consisting of a linear arrangement of emitters and receivers placed on the surface of the inspected specimen. The technique takes benefit of using both multiple emitters and receivers and is validated on a reference wave guide. The guided mode phase velocities are obtained using a projection in the singular vectors basis. The singular vectors are determined by the singular values decomposition (SVD) of the response matrix between the two arrays in the frequency domain. This technique enables to recover accurately guided wave phase velocity dispersion curves. The SVD based approach was designed to overcome limitations of spatio-temporal Fourier transform for receiver array of limited spatial extent as in the case of clinical assessment of cortical bone in axial transmission.

Experimental investigation of reflection in guided wave-based inspection for the characterization of pipeline defects

Abstract: In guided wave-based pipeline inspection, the reflection from a defect usually includes sufficient defect-relevant information. It has been found that the reflection of guided waves at defect is the joint result of interference between reflections from both its front and back edges. However, the majority of published work has only studied and considered the overall resulting reflection signal for the inspection-related tasks. This paper reports the findings of extensive experimental investigation on the effects of a defect’s geometric parameters on the two reflection signals from the respective edge of defect. We show that the two edge reflections present different signal features, which further results in the complexity of the overall reflection signal from the defect. We accordingly propose a new strategy that considers the extraction of two edge reflection signals embedded in overall reflection signal and the use of the identified edge signals so as to enable an accurate and quantitative pipeline defect characterization.

Multiridge-based analysis for separating individual modes from multimodal guided wave signals in long bones

Abstract: Quantitative ultrasound has great potential for assessing human bone quality. Considered as an elastic waveguide, long bone supports propagation of several guided modes, most of which carry useful information, individually, on different aspects of long bone properties. Therefore, precise knowledge of the behavior of each mode, such as velocity, attenuation, and amplitude, is important for bone quality assessment. However, because of the complicated characteristics of the guided waves, including dispersion and mode conversion, the measured signal often contains multiple wave modes, which yields the problem of mode separation. In this paper, some novel signal processing approaches were introduced to solve this problem. First, a crazy-climber algorithm was used to separate time-frequency ridges of individual modes from time-frequency representations (TFR) of multimodal signals. Next, corresponding time domain signals representing individual modes were reconstructed from the TFR ridges. It was found that the separated TFR ridges were in agreement with the theoretical dispersion, and the reconstructed signals were highly representative of the individual guided modes as well. The validations of this study were analyzed by simulated multimodal signals, with or without noise, and by in vitro experiments. Results of this study suggest that the ridge detection and individual reconstruction method are suitable for separating individual modes from multimodal signals. Such a method can improve the analysis of skeletal guided wave signals by providing accurate assessment of mode-specific ultrasonic parameters, such as group velocity, and indicate different bone quality properties.

Trapped Rainbow Storage of Light in Metamaterials

Abstract: We review recent theoretical and experimental breakthroughs in the realm of slow and stopped light in structured photonic media featuring negative electromagnetic parameters (permittivity/permeability and/or refractive index). We explain how and why these structures can enable complete stopping of light even in the presence of disorder and, simultaneously, dissipative losses. Using full-wave numerical simulations we show that the incorporation of thin layers made of an active medium adjacently to the core layer of a negative-refractive-index waveguide can completely remove dissipative losses – in a slow-light regime where the effective index of the guided wave is negative.

Lamb wave tuning curve calibration for surface-bonded piezoelectric transducers

Abstract: Surface-bonded lead zirconate titanate (PZT) transducers have been widely used for guided wave generation and measurement. For selective actuation and sensing of Lamb wave modes, the sizes of the transducers and the driving frequency of the input waveform should be tuned. For this purpose, a theoretical Lamb wave tuning curve (LWTC) of a specific transducer size is generally obtained. Here, the LWTC plots each Lamb wave mode' amplitude as a function of the driving frequency. However, a discrepancy between experimental and existing theoretical LWTCs has been observed due to little consideration of the bonding layer and the energy distribution between Lamb wave modes. In this study, calibration techniques for theoretical LWTCs are proposed. First, a theoretical LWTC is developed when circular PZT transducers are used for both Lamb wave excitation and sensing. Then, the LWTC is calibrated by estimating the effective PZT size with PZT admittance measurement. Finally, the energy distributions among symmetric and antisymmetric modes are taken into account for better prediction of the relative amplitudes between Lamb wave modes. The effectiveness of the proposed calibration techniques is examined through numerical simulations and experimental estimation of the LWTC using the circular PZT transducers instrumented on an aluminum plate.

Resonant Guided Wave Networks

Abstract: A resonant guided wave network is an optical materials design consisting of power-splitting elements arranged at the nodes of a waveguide network. The resulting wave dispersion depends on the network layout due to localized resonances at several length scales in the network. These structures exhibit both localized resonances with a Q ~ 80 at 1550 nm wavelength as well as photonic bands and band gaps in large periodic networks at infrared wavelengths.

Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers.

Abstract: This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.

A generalized approach for efficient finite element modeling of elastodynamic scattering in two and three dimensions.

Abstract: A robust and efficient technique for predicting the far-field scattering behavior for an arbitrarily-shaped defect in a generally anisotropic medium is presented that can be implemented in a commercial FE package. The spatial size of the modeling domain around the defect is as small as possible to minimize computational expense and a minimum number of models are executed. The method is based on an integral representation of a wave field in a homogeneous anisotropic medium. A plane incident mode is excited by applying suitable forces at nodes on a surface that encloses the scatterer. The scattered wave field is measured at monitoring nodes on a concentric surface and then decomposed into far-field scattering amplitudes of different modes in different directions. Example results for 2D and 3D bulk wave scattering in isotropic material and guided wave scattering are presented. Modeling accuracy is examined in various ways, including a comparison with the analytical solutions and calculation of the energy balance.

Guided wave structural health monitoring using CLoVER transducers in composite materials

Abstract: The guided wave (GW) fleld excited by piezoelectric wafers and piezocomposite transducers in carbon-flber composite materials is experimentally investigated with applications to structural health monitoring. This investigation supports the characterization of the Composite Long-range Variable-direction Emitting Radar (CLoVER) transducer introduced by the authors. A systematic approach is followed where composite conflgurations with difierent levels of anisotropy are analyzed. In particular, unidirectional, cross-ply [0/90]6S, and quasi-isotropic [0/45/-45/90]4S IM7-based composite plates are employed. A combination of laser vibrometry and flnite element analysis is used to determine the inplane wave speed and peak-to-peak amplitude distribution in each substrate considered. The results illustrate the efiect of the material anisotropy on GW propagation through the steering efiect where the wave packets do not generally travel along the direction in which they are launched. After characterizing the efiect of substrate anisotropy on the GW fleld, the performance of the CLoVER transducer to detect damage in various composite conflgurations is explored. It is found that the directionality and geometry of the device is efiective in detecting the presence and identifying the location of simulated defects in difierent composite layups.

Random Rough Surface Effects on Wave Propagation in Interconnects

Abstract: To address the rough surface effects in high-speed interconnects on printed circuit boards (PCBs) and microelectronic packages, we study the electromagnetic wave propagation in a rough surface environment. In our model, the rough surface is characterized by a stochastic random process with correlation function or spectral density. This paper reviews the analytical theory, numerical simulations and experimental results based on such a model. We describe the rough surface characterization and the extraction of roughness parameters from 3D profile measurements. Initially we study the 2D case with the rough surface height function varying in only one horizontal direction and consider the case of plane wave incidence. Analytic second-order small perturbation method (SPM2) was used to obtain simple closed-form expressions for the absorption enhancement factor. The numerical transfer matrix (T-matrix) method and the method of moments (MoM) were also used. We next consider the case of the 3D problem with the rough surface height varying in both horizontal directions. We also used SPM2 to obtain a simple closed form expression for the enhancement factor. In interconnect problems, electromagnetic (EM) waves propagate in a guided wave environment. Thus, we next considered a waveguide model to study the effects of random roughness on wave propagation and compare with results from the plane wave formulation. Analytic SPM2 and numerical finite element method (FEM) with mode matching were used to obtain the enhancement factor. We also describe experimental results and correlation with the theoretical models. Finally, we explain how the enhancement factor concept used throughout lends itself to direct inclusion of rough surface effects in a wide variety of modeling problems.

Application of ultrasonic guided waves for non-destructive testing of defective CFRP rods with multiple delaminations

Abstract: One of the most important parts of gliders is a lightweight longeron reinforcement made of carbon fibre reinforced plastic (CFRP) rods. During manufacturing, in order to build the arbitrary spar profile, these small diameter (few millimetres) rods are glued together into epoxy filled matrix. Still, defects present in the rods, such as break of fibres, multiple delaminations due to lack of bonding and reduction in density affect construction strength markedly and are extremely complicated to eliminate. Therefore, appropriate non-destructive testing techniques intended for carbon fibre rods should be applied prior to gluing them together. The aim of the present paper is to analyse development possibilities of NDT technique based on application of ultrasonic guided waves and intended for CFRP rods that are used for aerospace applications and are defective with multiple delaminations. The regularities of ultrasonic guided wave propagation in a defective CFRP circular-shape rod with multiple delaminations have been investigated using 3D numerical simulations, finite difference and finite element models. The corresponding experiments have been conducted as well. Based on leaky wave suppression over a defective region due to the weak vertical component of particle displacements, the mechanism of guided wave interaction with the region of multiple delaminations is explained from the ultrasonic NDT viewpoint.

Ultrasonic guided waves for nondestructive evaluation/structural health monitoring of trusses

Abstract: Ultrasonic guided waves (UGWs) are particularly effective in those nondestructive evaluation and structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a method to detect cracks in large trusses that combines the advantages of UGWs with the extraction of defect-sensitive features to perform a multivariate diagnosis of damage. The proposed algorithm was applied to the guided waves propagating along one of the main chords of a dismantled overhead sign support structure. The probing hardware consisted of a data acquisition system that controlled the generation and detection of ultrasonic signals by means of piezoelectric transducers made of lead zirconate titanate. The effectiveness of the proposed approach to diagnose the presence of an artificial defect around the welded joint between one main chord and a diagonal member of the truss structure is explained.

Configuration optimization of magnetostrictive transducers for longitudinal guided wave inspection in seven-wire steel strands

Abstract: The configuration of magnetostrictive transducers for both transmitter and receiver was optimized for the generation and reception of ultrasonic longitudinal guided waves in seven-wire steel strands in a pitch catch arrangement. Three axisymmetric permanent magnets significantly improved the capability of magnetostrictive transducers compared to two permanent magnets, and effectively increased the amplitude of the longitudinal guided wave mode, L(0, 1) at 160 kHz. Experimental results show that the maximum amplitude of a received guided wave signal could be obtained by using a receiver with a three-layer coil in parallel and a transmitter with a three-layer coil in series. The amplitudes of the defect-reflected signal increased by as much as 50% or more as compared with those when both transducers used a single layer coil. As a result, magnetostrictive transducers with an optimized configuration, including permanent magnet distribution and multilayer coil connection, could be efficiently used for the inspection of seven-wire steel strands by using ultrasonic guided waves in a pitch catch arrangement.

Finite-element simulations of Stoneley guided-wave reflection and scattering at the tips of fluid-filled fractures

Abstract: The reflection and scattering of Stoneley guided waves at the tip of a crack filled with a viscous fluid was studied numerically intwodimensionsusingthefinite-elementmethod.Therocksurrounding the crack is fully elastic and thefluidfilling the crack is elastic in its bulk deformation behavior and viscous in its shear deformation behavior. The crack geometry, especially the crack tip, is resolved in detail by the unstructured finite-element mesh. Atthetipofthecrack,theStoneleyguidedwaveisreflected.The amplitude ratio between reflected and incident Stoneley guided wave is calculated from numerical simulations, which provide valuesrangingbetween43%andcloseto100%dependingonthe type of fluid filling the crack water, oil or hydrocarbon gas, the crack geometry elliptical or rectangular, and the presence of a small gas cap at the cracktip.The interference of incident and reflectedStoneleyguidedwavesleadstoanodezeroamplitudeat the tip of the crack.At other positions along the crack, this interferenceincreasestheamplitude.However,theexponentialdecay awayfromthecrackmakestheStoneleyguidedwavedifficultto detectatarelativelyshortdistanceawayfromthecrack.Thepart oftheStoneleyguidedwavethatisnotreflectedisscatteredatthe crack tip and emitted into the surrounding elastic rock as body waves. For fully saturated cracks, the radiation pattern of these elastic body waves points in every direction from the crack tip. TheemittedelasticbodywavescanallowthedetectionofStoneley guided wave-related resonant signals at distances away from thecrackwheretheamplitudeoftheStoneleyguidedwaveitself istoosmalltobedetected.

Warped basis pursuit for damage detection using lamb waves

Abstract: This paper presents a novel time-frequency procedure based on the warped frequency transform (WFT) to process multi-mode and dispersive Lamb waves for structural health monitoring (SHM) applications. The proposed signal processing technique is applied to time waveforms recorded at an array of scan points after waveguide excitation. The WFT is combined with a basis pursuit algorithm to extract the distance traveled by the ultrasonic waves even in the case of multi-modal dispersive propagation associated with broadband excitation of the waveguide. This is obtained through a decomposition of the acquired signals using dictionaries composed by optimized atomic functions which are designed to match the spectro-temporal structure of the various propagating modes. The warped basis pursuit (W-BP) analysis of several acquired waveforms results in distance signals that can be combined through classical beamforming techniques for acoustical source imaging purposes. A masking procedure is also proposed to suppress imaging noise. This approach is tested on experimental data obtained by broadband guided wave excitation in a 1-mm-thick aluminum plate with an artificially introduced through crack and tiny holes, followed by multiple waveguide displacement recording through a scanning laser Doppler vibrometer. Dispersion compensation, high-resolution source, and defect imaging are demonstrated even in domain regions that are not directly accessible for measurement.

Guided lamb wave electroacoustic devices on micromachined AlN/Al plates

Abstract: An electroacoustic micro-device based on the propagation of guided acoustic Lamb waves in AlN/Al plate is described. The AlN thin film is deposited by sputtering technique, optimized to achieve a high degree of orientation (rocking curve full-width at half-maximum ? 3.5°) of the c-axis perpendicular to the plate surface. The AlN plate is micromachined using anisotropic reactive ion etching (RIE), followed by isotropic RIE to remove the silicon underlayer. Simulation results for the dispersion phase velocity curves and the electromechanical coupling coefficient (K2) are obtained by the matrix method and by the finite element method and compared with experimental data. A delay line is implemented on the structure and tested for the propagation of the first symmetrical Lamb mode (s0) at the frequency of 1.22 GHz. Measurements have shown that the structure is suitable for implementation of arrays of electroacoustic devices on a single chip for application to both sensing devices and signal processing systems.

Efficient detection of delamination in multilayered structures using ultrasonic guided wave EMATs

Abstract: This paper presents an efficient method for the detection of delamination using a combined technology of ultrasonic guided wave and electromagnetic acoustic transducer (EMAT). The material for inspection studied in this paper is a three-layered brass/copper/brass metal composite for coin stocks. We first observed a cyclic behavior of wave sensitivity to delamination width in the experiment. This observation is then confirmed with finite element simulation. We found out that the cyclic behavior is related to the phase velocity of the converted wave modes in the two subsystems after delamination. To compensate for the cyclic behavior, two wave modes are used in an industrial inspection system to ensure effective detection of delamination in the composite sample. The inspection speed achieved with this EMAT inspection system is 1.8 m2/s.

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Abstract: Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.

Megahertz-range guided pure torsional wave transduction and experiments using a magnetostrictive transducer

Abstract: This work is concerned with high-frequency guided torsional wave experiments in the range of 1 to 2 MHz in a cylindrical waveguide. A specially configured meander coil-magnetostrictive patch transducer was developed and successful experimental results of generation and measurement of guided pure torsional waves of up to 2 MHz were achieved. The usefulness of the developed method was demonstrated through a case study to detect a small-sized crack which would be otherwise difficult to identify with a lower-frequency torsional wave.