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Showing papers on "Guided wave testing published in 2014"


Book
11 Aug 2014
TL;DR: The semi-analytical finite element method (SAFE) has been used for guided wave modeling as discussed by the authors, which has been shown to be useful in the analysis and display of non-destructive testing.
Abstract: Preface Acknowledgments 1. Introduction 2. Dispersion principles 3. Unbounded isotropic and anisotropic media 4. Reflection and refraction 5. Oblique incidence 6. Waves in plates 7. Surface and subsurface waves 8. Finite element method for guided wave mechanics 9. The semi-analytical finite element method (SAFE) 10. Guided waves in hollow cylinders 11. Circumferential guided waves 12. Guided waves in layered structures 13. Source influence on guided wave excitation 14. Horizontal shear 15. Guided waves in anisotropic media 16. Guided wave phased arrays in piping 17. Guided waves in viscoelastic media 18. Ultrasonic vibrations 19. Guided wave array transducers 20. Introduction to guided wave nonlinear methods 21. Guided wave imaging methods Appendix A: ultrasonic nondestructive testing principles, analysis and display technology Appendix B: basic formulas and concepts in the theory of elasticity Appendix C: physically based signal processing concepts for guided waves Appendix D: guided wave mode and frequency selection tips.

823 citations


Patent
21 Oct 2014
TL;DR: In this article, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device is described, where a guiding portion guides the first wave to a junction for coupling the wave to the transmission medium and the coupling of the wave propagates via at least one first guided wave mode.
Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

281 citations


Patent
21 Oct 2014
TL;DR: In this article, a quasi-optical coupling system was proposed to launch and extract surface wave communication transmissions from a wire, where the lenses on the transmitters are focused and the reflectors positioned such that the reflected transmissions are guided waves on the surface of the cables.
Abstract: A quasi-optical coupling system launches and extracts surface wave communication transmissions from a wire. At millimeter-wave frequencies, where the wavelength is small compared to the macroscopic size of the equipment, the millimeter-wave transmissions can be transported from one place to another and diverted via lenses and reflectors, much like visible light. Transmitters and receivers can be positioned near telephone and power lines and reflectors placed on or near the cables can reflect transmissions onto or off of the cables. The lenses on the transmitters are focused, and the reflectors positioned such that the reflected transmissions are guided waves on the surface of the cables. The reflectors can be polarization sensitive, where one or more of a set of guided wave modes can be reflected off the wire based on the polarization of the guided wave modes and polarization and orientation of the reflector.

281 citations


Patent
26 Aug 2014
TL;DR: In this article, a dielectric waveguide coupling system for launching and extracting guided wave communication transmissions from a wire is proposed, where the waveguide is brought into close proximity to a wire, and the guided waves decouple from the dielectrics and couple to the wire, while continuing to propagate as guided waves about the surface of the wire.
Abstract: A dielectric waveguide coupling system for launching and extracting guided wave communication transmissions from a wire. At millimeter-wave frequencies, wherein the wavelength is small compared to the macroscopic size of the equipment, transmissions can propagate as guided waves guided by a strip of dielectric material. Unlike conventional waveguides, the electromagnetic field associated with the dielectric waveguide is primarily outside of the waveguide. When this dielectric waveguide strip is brought into close proximity to a wire, the guided waves decouple from the dielectric waveguide and couple to the wire, and continue to propagate as guided waves about the surface of the wire.

227 citations


Journal ArticleDOI
TL;DR: 3D EFIT simulations of guided wave propagation in undamaged and damaged anisotropic and quasi-isotropic composite plates are described and volumetric delamination data acquired via X-ray microfocus computed tomography is directly incorporated into the simulation.

102 citations


Journal ArticleDOI
TL;DR: This work suggests a promising use of SH-like guided modes for quantifying shear properties at adhesive interfaces, and shows that such waves can be used for inferring adhesive and cohesive properties of bonds separately.

88 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented a guided wave generation, sensing, and damage detection in metallic plates using in-plane shear (d36 type) piezoelectric wafers as actuators and sensors.
Abstract: This work presents guided wave generation, sensing, and damage detection in metallic plates using in-plane shear (d36 type) piezoelectric wafers as actuators and sensors. The conventional lead zirconate titanate (PZT) based on induced in-plane normal strain (d31 type) has been widely used to excite and receive guided waves in plates, pipes or thin-walled structures. The d36 type of piezoelectric wafer, however, induces in-plane (or called face) shear deformation in the plane normal to its polarization direction. This form of electromechanical coupling generates more significant shear horizontal (SH) waves in certain wave propagation directions, whose amplitudes are much greater than those of Lamb waves. In this paper, an analysis of SH waves generated using in-plane shear electromechanical coupling is firstly presented, followed by a multiphysics finite element analysis for comparison purposes. Voltage responses of both the conventional d31 and the new d36 sensors are obtained for comparison purposes. Results indicate that this type of wafer has the potential to provide a simple quantitative estimation of damage in structural health monitoring.

80 citations


Journal ArticleDOI
TL;DR: Guided wave imaging with a distributed array of inexpensive transducers offers a fast and cost-efficient means for damage detection and localization in plate-like structures such as aircraft and spacecraft skins as discussed by the authors.
Abstract: Guided wave imaging with a distributed array of inexpensive transducers offers a fast and cost-efficient means for damage detection and localization in plate-like structures such as aircraft and spacecraft skins. As such, this technology is a natural choice for inclusion in condition-based maintenance and integrated structural health management programs. One of the implementation challenges results from the complex interaction of propagating ultrasonic waves with both the interrogation structure and potential defects or damage. For example, a guided ultrasonic wave interacts with a surface or sub-surface defect differently depending on the angle of incidence, defect size and orientation, excitation frequency, and guided wave mode. However, this complex interaction also provides a mechanism for guided wave imaging algorithms to perform damage characterization in addition to damage detection and localization. Damage characterization provides a mechanism to help discriminate actual damage (e.g. fatigue cracks) from benign changes, and can be used with crack propagation models to estimate remaining life. This work proposes the use of minimum variance imaging to perform damage detection, localization, and characterization. Scattering assumptions used to perform damage characterization are obtained through both analytical and finite element models. Experimental data from an in situ distributed array are used to demonstrate feasibility of this approach using a through-hole and two through-thickness notches of different orientations to simulate damage in an aluminum plate.

67 citations


Journal ArticleDOI
TL;DR: In this article, a mesoscale model of an ultrasonic non-destructive method has been proposed to evaluate creep deformed states based on nonlinear guided waves, which can be applicable to all precipitate stages including coherent and semi-coherent precipitates in the metallic alloy undergoing creep degradation.
Abstract: The early deformations in materials such as creep, plasticity, and fatigue damages have been proved to have a close relationship with the nonlinear effect of ultrasonic waves propagating in them. In the present paper, a theoretical mesoscale model of an ultrasonic non-destructive method has been proposed to evaluate creep deformed states based on nonlinear guided waves. The model developed here considers the nonlinear generation of Lamb waves response from precipitates variation in the dislocation network, which can be applicable to all precipitate stages including coherent and semi-coherent precipitates in the metallic alloy undergoing creep degradation. To verify the proposed model, experiments of titanium alloy Ti60 plates were carried out with different creep strains. An “increase-decrease” change of the acoustic nonlinearity of guided wave versus the creep life fraction has been observed. Based on microscopic images analyses, the mesoscale model was then applied to these creep damaged Ti60 specimens, which revealed a good accordance with the measured results of the nonlinear guided waves. It is shown that the change of the nonlinear Lamb wave depends on the variations of the α2 precipitation volume fraction, the dislocation density, the growth of the creep-voids, and the increasing mismatch of the phase velocities during the creep deformation process. The results indicate that the effect of the precipitate-dislocation interactions on the nonlinear guided wave is likely the dominant mechanism responsible for the change of nonlinear guided wave propagation in the crept materials.

66 citations


Journal ArticleDOI
TL;DR: In this paper, a general inversion method that extends the range of insonification angles by exploiting the information carried by the signals that wrap around the pipe multiple times before reaching the receive array, thus resulting in superior image resolution and increased depth estimation accuracy.
Abstract: The transmission of guided ultrasonic waves across corrosion or erosion damage encodes information about the defect depth. Tomography maps the depth profile from multiple transmission experiments performed under different insonification angles by solving the so-called inverse problem; the accuracy of the depth estimation being dependent on the range of angles available for the inversion. Practical application of tomography to tubular structures, such as pipes and bends, requires the use of two ring arrays of ultrasonic transducers at the two ends of the pipe section to be inspected. However, such a configuration leads to an insufficient angular coverage when considering the signals that travel along the shortest temporal path between a pair of transducers. This paper introduces a general inversion method that extends the range of insonification angles by exploiting the information carried by the signals that wrap around the pipe multiple times before reaching the receive array, thus resulting in superior image resolution and increased depth estimation accuracy. In addition, to address typical thermal fluctuations encountered during continuous monitoring, a strategy that combines a temperature compensation scheme with the intrinsic thermal stability of electromagnetic acoustic transducers (EMATs) is developed and tested with full-scale experiments performed on a schedule of 40, 8″ diameter steel pipe instrumented with two ring arrays of EMAT transducers. It is shown that for an irregularly shaped defect the proposed inversion method yields maximum depth estimations that are as accurate as single point ultrasonic thickness gaging measurements and over a wide temperature range up to 175 °C. The results indicate that advanced inversion schemes in combination with EMAT transduction offer great potential for continuously monitoring the progression of corrosion or erosion damage in the oil and gas industry.

62 citations


Journal ArticleDOI
TL;DR: This study describes leaky Lamb wave calculation with the SAFE and formulated a new solution using a feature that a single Lamb wave mode generates a harmonic plane wave in leaky media.

Journal ArticleDOI
TL;DR: In this article, a full derivation of Lamb wave equations for n-layered monoclinic composite laminates based on linear 3D elasticity by considering the displacement fields in all three directions using the partial wave technique in combination with the Global Matrix (GM) approach is presented.

Journal ArticleDOI
TL;DR: In this article, the dispersive properties of guided waves are exploited to enable thickness maps to be produced from wave speed reconstructions, where Ray tomography, diffraction tomography and a hybrid algorithm combining their features were investigated to reconstruct wave speed.
Abstract: Accurate inversion is vital for quantitative imaging, including ultrasonic guided wave tomography, where thickness maps of plate-like structures are reconstructed to quantify corrosion damage. The dispersive properties of guided waves are often exploited to enable thickness maps to be produced from wave speed reconstructions. Ray tomography, diffraction tomography and a hybrid algorithm combining their features were investigated to reconstruct wave speed. Test data produced from simple defects of different sizes using a realistic full elastic guided wave model and the equivalent idealized acoustic model were passed to the imaging algorithms, generating wave speed maps, and, from these, thickness maps. For both datasets, ray tomography exhibited poor resolution. Diffraction tomography performed better, but was limited to shallow, small defects. The hybrid algorithm achieved the best results, giving a resolution around 1.5–2 wavelengths from the realistic test data compared to half wavelength from the idealized case. These results were validated with experimental data, and also extended to a realistic corrosion patch confirming the trends demonstrated with simple defects. The resolution loss with realistic data compared with idealized data indicates the acoustic model cannot accurately capture guided wave scattering and an alternative approach is necessary for better resolution reconstructions.

Journal ArticleDOI
TL;DR: In this article, a Bayesian approach is proposed to quantitatively identify damages in beam-like structures using experimentally measured guided wave signals, which treats the damage location, le...
Abstract: A Bayesian approach is proposed to quantitatively identify damages in beam-like structures using experimentally measured guided wave signals. The proposed methodology treats the damage location, le...

Journal ArticleDOI
TL;DR: Two-dimensional in-plane imaging is investigated, based on propagation of the single S0 Lamb mode, and despite very high dispersion of that mode, scatterers are accurately located and the spatial resolution is equal to about one wavelength.

Journal ArticleDOI
TL;DR: A prototype plasmonic nanocircuit composed of four v-groove waveguides in an evenly spaced 2 × 2 configuration functions as a simple, compact optical logic device at telecommunication wavelengths, routing different wavelengths to separate transmission ports due to the resulting network resonances.
Abstract: Composed of optical waveguides and power-splitting waveguide junctions in a network layout, resonant guided wave networks (RGWNs) split an incident wave into partial waves that resonantly interact within the network. Resonant guided wave networks have been proposed as nanoscale distributed optical networks (Feigenbaum and Atwater, Phys. Rev. Lett. 2010, 104, 147402) that can function as resonators and color routers (Feigenbaum et al. Opt. Express 2010, 18, 25584–25595). Here we experimentally characterize a plasmonic resonant guided wave network by demonstrating that a 90° waveguide junction of two v-groove channel plasmon polariton (CPP) waveguides operates as a compact power-splitting element. Combining these plasmonic power splitters with CPP waveguides in a network layout, we characterize a prototype plasmonic nanocircuit composed of four v-groove waveguides in an evenly spaced 2 × 2 configuration, which functions as a simple, compact optical logic device at telecommunication wavelengths, routing diff...

Journal ArticleDOI
TL;DR: The results of the study suggest that the high-resolution RT is a valuable imaging tool to extract dispersive guided wave energies under limited aperture.
Abstract: Multichannel analysis of dispersive ultrasonic energy requires a reliable mapping of the data from the time-distance (t-x) domain to the frequency-wavenumber (f-k) or frequency-phase velocity (f-c) domain. The mapping is usually performed with the classic 2-D Fourier transform (FT) with a subsequent substitution and interpolation via c = 2πf/k. The extracted dispersion trajectories of the guided modes lack the resolution in the transformed plane to discriminate wave modes. The resolving power associated with the FT is closely linked to the aperture of the recorded data. Here, we present a linear Radon transform (RT) to image the dispersive energies of the recorded ultrasound wave fields. The RT is posed as an inverse problem, which allows implementation of the regularization strategy to enhance the focusing power. We choose a Cauchy regularization for the high-resolution RT. Three forms of Radon transform: adjoint, damped least-squares, and high-resolution are described, and are compared with respect to robustness using simulated and cervine bone data. The RT also depends on the data aperture, but not as severely as does the FT. With the RT, the resolution of the dispersion panel could be improved up to around 300% over that of the FT. Among the Radon solutions, the high-resolution RT delineated the guided wave energy with much better imaging resolution (at least 110%) than the other two forms. The Radon operator can also accommodate unevenly spaced records. The results of the study suggest that the high-resolution RT is a valuable imaging tool to extract dispersive guided wave energies under limited aperture.

Journal ArticleDOI
TL;DR: Finite element simulations were used to show that by exciting multiple guided wave modes simultaneously and identifying which modes are received by a sensor array it is possible to estimate the minimum remaining thickness along the propagation path.

Journal ArticleDOI
TL;DR: Guided wave structural health monitoring shows potential for practical use as it allows detection of sma... as discussed by the authors. But it is not suitable for the monitoring of large-scale industrial assets, such as power plants.
Abstract: Industrial interest in structural health monitoring of safety-critical assets is increasing. Guided wave structural health monitoring shows potential for practical use as it allows detection of sma...

Journal ArticleDOI
TL;DR: The experimental results demonstrate that the proposed method can improve the resolution of adjacent defects and the accuracy of defect location in the propagation direction of the magnetostrictive guided wave.
Abstract: As a rapid, noncontact, and nondestructive technology, magnetostrictive guided waves have been widely used for the quality inspection of pipes and stay cables. Traditionally, a single-frequency signal with a high amplitude and a long pulse duration is used to increase the excitation energy and detection distance. However, the longer the pulse duration of a single-frequency signal is, the lower the resolution of adjacent defects and the accuracy of defect location will be. A novel method of addressing this problem is proposed in this paper. An encoded multifrequency excitation signal, whose frequency range is selected from a calculated dispersion curve, is used to excite the guided wave. After passing through the signal-conditioning board, the detected defect signals are sampled, averaged, and then filtered using a matched filter. In this manner, the pulse width of echoes can be greatly compressed. Our experimental results demonstrate that our proposed method can improve the resolution of adjacent defects and the accuracy of defect location in the propagation direction of the magnetostrictive guided wave.

Journal ArticleDOI
TL;DR: In this article, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field of periodic permanent magnet(PPM) EMATs.
Abstract: The fundamental shear horizontal(SH0) wave has several unique features that are attractive for long-range nondestructive testing(NDT). By a careful design of the geometric configuration, electromagnetic acoustic transducers(EMATs) have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal(SH) waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet(PPM) EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SH0-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern of PPM EMATs, and can be used for their parameter optimization.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the leaky and non-leaky behaviors of guided waves, between the composite skin and the core in CF/EP sandwich structures, focusing on the fundamental symmetric like and anti-symmetric like guided wave modes and Rayleigh waves.

Journal ArticleDOI
TL;DR: In this paper, the application of the guided wave (GW) method and Spectral Element Method (SEM) has been proposed as an efficient simulation technique for structural health monitoring.
Abstract: Among many structural health monitoring (SHM) methods, guided wave (GW) based method has been found as an effective and efficient way to detect incipient damages. In comparison with other widely used SHM methods, it can propagate in a relatively long range and be sensitive to small damages. Proper use of this technique requires good knowledge of the effects of damage on the wave characteristics. This needs accurate and computationally efficient modeling of guide wave propagation in structures. A number of different numerical computational techniques have been developed for the analysis of wave propagation in a structure. Among them, Spectral Element Method (SEM) has been proposed as an efficient simulation technique. This paper will focus on the application of GW method and SEM in structural health monitoring. The GW experiments on several typical structures will be introduced first. Then, the modeling techniques by using SEM are discussed.

Journal ArticleDOI
TL;DR: In this article, a Capacitive micromachined ultrasonic transducers (cMUTs) have been used for axial transmission measurement of long bones such as the radius or tibia.
Abstract: A wide range of ultrasound methods has been proposed to assess the mechanical strength of bone. The axial transmission technique, which consists of measuring guided elastic modes through the cortical shell of long bones such as the radius or tibia, has recently emerged as one of the most promising approaches of all bone exploration methods. Determination of dispersion curves of guided waves is therefore of prime interest because they provide a large set of input data required to perform inverse process, and hence to evaluate bone properties (elastic and geometric). The cortical thickness of long bones ranges from approximately 1 to 7 mm, resulting in wide inter-individual variability in the guided wave response. This variability can be overcome by using a single probe able to operate with a tunable central frequency, typically within the 100 kHz to 2 MHz frequency range. However, there are certain limitations in the design of low-frequency arrays using traditional PZT technology; these limitations have triggered active research to find alternative solutions. Capacitive micromachined ultrasonic transducers (cMUTs) have the potential to overcome these limitations and to improve axial transmission measurement significantly. The objective of this study was to design and construct a new cMUT-based axial transmission probe and to validate the approach. We report all the steps followed to construct such a prototype, from the description of the fabrication of the cMUT (based on a surface micromachining process) through probe packaging. The fabricated device was carefully characterized using both electrical and optical measurements to check the homogeneity of the device, first from cMUT to cMUT and then from element to element. Finally, axial transmission measurements carried out with the prototype cMUT probe are shown and compared with results obtained with a PZT-based array.

Journal ArticleDOI
TL;DR: An explicit expression for the group velocity of wave packets, propagating in a laminate anisotropic composite plate in prescribed directions, is proposed, based on the cylindrical guided wave asymptotics derived from the path integral representation for wave fields generated in the composites by given localized sources.
Abstract: An explicit expression for the group velocity of wave packets, propagating in a laminate anisotropic composite plate in prescribed directions, is proposed. It is based on the cylindrical guided wave asymptotics derived from the path integral representation for wave fields generated in the composites by given localized sources. The expression derived is theoretically confirmed by the comparison with a known representation for the group velocity vector of a plane guided wave. Then it is experimentally validated against laser vibrometer measurements of guided wave packets generated by a piezoelectric wafer active sensor in a composite plate.

Journal ArticleDOI
TL;DR: It will be shown, that acoustic emissions are successfully localized even on anisotropic structures and in the case of geometrical complexities such as notches, which lead to reflections, and cross sectional changes, which affect the wave speed.

Patent
29 Oct 2014
TL;DR: In this paper, a pipeline defect detection method based on electromagnetic ultrasonic longitudinal guided waves is proposed. But the method is not suitable for the detection of pipeline defects. And it requires a large number of annular magnet arrays and solenoid coils.
Abstract: The invention discloses a pipeline defect detection method based on electromagnetic ultrasonic longitudinal guided waves. The method comprises the following steps: arranging a plurality of annular magnets coaxial with a pipeline, so as to generate a radial static magnetic field on the surface of the pipeline; coaxially sleeving two sides of each annular magnet array with solenoid coils, so as to generate circumferential inducing vortex in the to-be-detected pipeline; and stimulating longitudinal-mode guided waves under the combined action of the circumferential inducing vortex and the radial static magnetic field, wherein when encountering a defect, the longitudinal-mode guided waves are reflected, and reflection echoes cause change of sensing voltage of a sensing coil when passing through a sensing coil, so as to judge that whether the defect exists in the pipeline or not. The invention further discloses a detection device and a sensor for detecting the pipeline by virtue of the device and the method. According to the method, the radial magnetic fields at the edges of the magnet arrays are adequately utilized, and the uniform radial magnetic field does not need to be generated, so that the complexity of the sensor is reduced; meanwhile, a single longitudinal-mode guided wave signal can be obtained, so that the defect signal analysis difficulty is reduced, and the detection process is rapid and efficient.

Journal ArticleDOI
TL;DR: An application of the Radon transform to enhance signal-to-noise ratio and separate wave fields in ultrasonic records is presented, presenting a powerful signal-enhancement tool to process guided waves for further analysis and inversion.
Abstract: Multichannel ultrasonic axial-transmission data are multimodal by nature. As guided waves are commonly used in nondestructive material testing, wave field filtering becomes important because the analysis is usually limited to a few lower-order modes and requires their extraction. An application of the Radon transform to enhance signal-to-noise ratio and separate wave fields in ultrasonic records is presented. The method considers guided wave fields as superpositions of plane waves defined by ray parameters (p) and time intercepts (τ) and stacks the amplitudes along linear trajectories, mapping time-offset (t−x) data to a τ−p or Radon panel. The transform is implemented using a least-squares strategy with Cauchy-norm regularization that serves to enhance the focusing power. The method was verified using simulated data and applied to an uneven spatially sampled bovine-bone-plate data set. The results demonstrate the Radon panels show isolated amplitude clusters and the Cauchy-norm constraint provides a more...

Journal ArticleDOI
Zenghua Liu1, Xu Qinglong1, Gong Yu1, Cunfu He1, Bin Wu1 
TL;DR: A new phenomenon is exhibited in this paper that defect scattered wave packet appears just before the right boundary of truncation window after time reversal, which can be used as the theoretical basis in the determination of defect scattered waves in time reversal response signal.

Journal ArticleDOI
TL;DR: In this paper, the detection and localization of damage using an array of closely spaced transducers is investigated theoretically and experimentally using single and multiple-mode guided wave active sensing models, assuming that amplitude, absolute phase and source location of a scattered wave are unknown, while frequency, group velocity, and phase velocity are known.
Abstract: The detection and localization of damage using an array of closely spaced transducers is investigated theoretically and experimentally using single- and multiple-mode guided wave active sensing models. Detectors are derived using a generalized likelihood ratio approach assuming that amplitude, absolute phase, and source location of a scattered wave are unknown, while frequency, group velocity, and phase velocity are known. Theoretical detection performance for processing with each detector is derived and related to the energy-to-noise ratio of a scattered mode as a metric of determining when processing with multiple modes provides increased performance over processing with a single mode. Experimentally, detectors are implemented to detect scattering from a small mass glued to the surface of an aluminum plate with a 7 × 7 array of transducers. Relative detection and localization performance is compared through receiver operating characteristic curves and histograms of distance from true damage location for...