Study and comparison of different EMAT configurations for SH wave inspection
01 Dec 2011-IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control (IEEE Trans Ultrason Ferroelectr Freq Control)-Vol. 58, Iss: 12, pp 2571-2581
TL;DR: A finite element model of the elementary transducers has been developed and shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object.
Abstract: Guided wave inspection has proven to be a very effective method for the rapid inspection of large structures. The fundamental shear horizontal (SH) wave mode in plates and the torsional mode in pipe-like structures are especially useful because of their non-dispersive character. Guided waves can be generated by either piezoelectric transducers or electro- magnetic acoustic transducers (EMATs), and EMATs can be based on either the Lorentz force or magnetostriction. Several EMAT configurations can be used to produce SH waves, the most common being Lorentz-force periodic permanent magnet and magnetostrictive EMATs, the latter being directly applied on the sample or with a bonded strip of highly magnetostrictive material on the plate. This paper compares the performance of these solutions on steel structures. To quantitatively assess the wave amplitude produced by different probes, a finite element model of the elementary transducers has been developed. The results of the model are experimentally validated and the simulations are further used to study the dependence of ultrasonic wave amplitude on key design parameters. The analysis shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object. Periodic permanent magnet EMATs generate intermediate wave amplitudes and are noncontact and insensitive to the variations in properties seen across typical steels. Large signal amplitudes can be achieved with magnetostrictive EMATs with a layer of highly magnetostrictive material attached between the transducer and the plate, but this compromises the noncontact nature of the transducer.
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TL;DR: A variety of state-of-the-art MPT configurations and their applications will be reviewed along with the working principle of this transducer type.
Abstract: A magnetostrictive patch transducer (MPT) is a transducer that exploits the magnetostrictive phenomena representing interactions between mechanical and magnetic fields in ferromagnetic materials. Since MPT technology was mainly developed and applied for nondestructive ultrasonic testing in waveguides such as pipes and plates, this paper will accordingly review advances of this technology in such a context. An MPT consists of a magnetic circuit composed of permanent magnets and coils, and a thin magnetostrictive patch that works as a sensing and actuating element which is bonded onto or coupled with a test waveguide. The configurations of the circuit and magnetostrictive patch therefore critically affect the performance of an MPT as well as the excited and measured wave modes in a waveguide. In this paper, a variety of state-of-the-art MPT configurations and their applications will be reviewed along with the working principle of this transducer type. The use of MPTs in wave experiments involving phononic crystals and elastic metamaterials is also briefly introduced.
200 citations
Cites background from "Study and comparison of different E..."
...For an inspection of a non-ferromagnetic system or when a higher transduction efficiency is necessary in a ferromagnetic system, MPTs that employ magnetostrictive patches can be considered [51]....
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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.
Abstract: Shear-Horizontally (SH) polarized, ultrasonic, guided wave modes are considered in order to infer changes in the adhesive properties at several interfaces located within an adhesive bond joining two metallic plates Specific aluminium lap-joint samples were produced, with different adhesive properties at up to four interfaces when a glass–epoxy film is inserted into the adhesive bond EMAT transducers were used to generate and detect the fundamental SH0 mode This is launched from one plate and detected at the other plate, past the lap joint Signals are picked up for different propagation paths along each sample, in order to check measurement reproducibility as well as the uniformity of the adhesively bonded zones Signals measured for four samples are then compared, showing very good sensitivity of the SH0 mode to changes in the interfacial adhesive properties In addition, a Finite Element-based model is used to simulate the experimental measurements The model includes adhesive viscoelasticity, as well as spatial distributions of shear springs (with shear stiffness KT) at both metal–adhesive interfaces, and also at the adhesive–film interfaces when these are present This model is solved in the frequency domain, but temporal excitation and inverse FFT procedure are implemented in order to simulate the measured time traces Values of the interfacial adhesive parameters, KT, are determined by an optimization process so that best fit is obtained between both sets of measured and numerically predicted waveforms Such agreement was also possible by adjusting the shear modulus of the adhesive component 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 Finally, the paper considers improvements that could be made to the process, and its potential for testing the interfacial adhesion of adhesively bonded composite components
88 citations
TL;DR: This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures, and proposes an experimental research work assisted by numerical simulations to investigate the response of U GWs upon interaction with cracks in different shapes and orientations.
Abstract: Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws.
87 citations
TL;DR: In this article, a pipe screening tool for petrochemical pipelines both topside and subsea is presented, using Shear Horizontal (SH) guided waves propagating circumferentially around the pipe whilst the scanner is moved axially along the length.
Abstract: The use of guided waves is now widespread in industrial NDT for locating metal loss in pipelines, that manifests as pitting, corrosion and general wall thinning. In this paper, a screening technique is assessed in terms of defect detection and defect sizing capability. Shear Horizontal (SH) guided waves propagate circumferentially around the pipe whilst the scanner is moved axially along the length. This type of tool is preferable to other methods, being applied to the exterior of the pipe, without requiring full circumferential access, and is able to operate through thin coatings (up to 1 mm thick). It is designed to provide a pipe screening tool for petrochemical pipelines both topside and subsea, particularly for detecting defects at pipe support areas. The system's efficacy in terms of detection and sizing of defects is considered via experimental measurements on artificially induced defects and in service corrosion patches, with results compared to finite element modelling of the interaction of the guided waves with artificial defects. Finite element modelling has been used to better understand the behaviour of different wave modes when they interact with defects, focusing on the mode conversions and reflections that occur.
87 citations
Cites background from "Study and comparison of different E..."
...The Lorentz and magnetostrictive forces generated by this arrangement generate a shearing force at the surface of the sample, with the Lorentz force being the dominant mechanism in the generation of ultrasound within the sample [9,10]....
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TL;DR: An omni-directional SH magnetostrictive patch transducer that consists of an annular magnetostriction patch, a toroidal coil and a permanent magnet is proposed.
Abstract: As an effective tool to inspect large plates, omni-directional guided wave transducers have become more widely used to form phased-array inspection systems. While omni-directional Lamb wave transducers have been successfully utilized in the systems, omni-directional Shear-Horizontal (SH) wave transducers have not been investigated. In this paper, we propose an omni-directional SH magnetostrictive patch transducer that consists of an annular magnetostrictive patch, a toroidal coil and a permanent magnet. After presenting the unique configuration of the proposed transducer and its working principle, the omni-directivity of the developed transducer is verified through simulations and experiments conducted in an aluminum plate. The frequency characteristics of the proposed transducer depending on the patch size are also investigated as the underlying reference data for future construction of an SH phased-array system.
75 citations
Cites background from "Study and comparison of different E..."
...Because the amplitude of the SH wave generated by the magnetostrictive phenomenon highly depends on the applied static magnetic field strength [19,20], the permanent magnet should be properly located above the patch....
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References
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13 Dec 1990TL;DR: Magnetism in MATERIALs: MAGNETIC PHENOMENA on the MICROSCOPIC SCALE Magnetic Properties Hysteresis and Related Properties Barkhausen Effect and Related Phenomena Magnetostriction Magnetoresistance.
Abstract: ELECTROMAGNETISM: MAGNETIC PHENOMENA ON THE MACROSCOPIC SCALE Magnetic Fields Magnetic Field Magnetic Induction Magnetic Field Calculations References Further Reading Exercises Magnetization and Magnetic Moment Magnetic Moment Magnetic Poles and Amperian Bound Currents Magnetization Magnetic Circuits and the Demagnetizing Field Penetration of Alternating Magnetic Fields into Materials References Further Reading Exercises Magnetic Measurements Induction Methods Force Methods Methods Depending on Changes in Material Properties Superconducting Quantum Interference Devices References Further Reading Exercises Magnetic Materials Classification of Magnetic Materials Magnetic Properties of Ferromagnets Different Types of Ferromagnetic Materials for Applications Paramagnetism and Diamagnetism References Further Reading Exercises MAGNETISM IN MATERIALS: MAGNETIC PHENOMENA ON THE MICROSCOPIC SCALE Magnetic Properties Hysteresis and Related Properties Barkhausen Effect and Related Phenomena Magnetostriction Magnetoresistance References Further Reading Exercises Magnetic Domains Development of Domain Theory Energy Considerations and Domain Patterns References Further Reading Exercises Domain Walls Properties of Domain Boundaries Domain-Wall Motion References Further Reading Exercises Domain Processes Reversible and Irreversible Domain Processes Determination of Magnetization Curves from Pinning Models Theory of Ferromagnetic Hysteresis Dynamics of Domain Magnetization Processes References Further Reading Exercises Magnetic Order and Critical Phenomena Theories of Paramagnetism and Diamagnetism Theories of Ordered Magnetism Magnetic Structure References Further Reading Exercises Electronic Magnetic Moments Classical Model of Magnetic Moments of Electrons Quantum Mechanical Model of Magnetic Moments of Electrons Magnetic Properties of Free Atoms References Further Reading Exercises Quantum Theory of Magnetism Electron-Electron Interactions Localized Electron Theory Itinerant Electron Theory References Further Reading Exercises MAGNETICS: TECHNOLOGICAL APPLICATIONS Soft Magnetic Materials Properties and Applications of Soft Magnets Materials for AC Applications Materials for DC Applications Materials for Magnetic Shielding References Further Reading Materials Conferences Hard Magnetic Materials Properties and Applications of Hard Magnets Permanent Magnet Materials References Further Reading Materials Conferences Magnetic Recording History of Magnetic Recording Magnetic Recording Media Recording Heads and the Recording Process Modeling the Magnetic Recording Process References Further Reading Magnetic Evaluation of Materials Methods for Evaluation of Materials Properties Methods for Detection of Flaws and Other Inhomogeneities Magnetic Imaging Methods Sensitivity to Microstructure and Material Treatment References Further Reading Solutions to Exercises
1,586 citations
TL;DR: In this paper, the authors present a review of the studies of the propagation of the waves and their sensitivity to defects which have been conducted in order to provide a sound scientific basis for the method.
Abstract: The detection of corrosion in insulated pipes is of major importance to the oil and chemical industries. Current methods involving point-by-point inspection are expensive because of the need to remove the insulation. An alternative method which is being developed at Imperial College is to propagate guided waves in the walls of the pipes, and to look for reflections from defects. The test configuration is essentially pulse-echo; the insulation is removed at just one location on a pipe and the signals are then transmitted and received using a single transducer unit. The technique is currently undergoing field trials. This paper presents a review of the studies of the propagation of the waves and their sensitivity to defects which have been conducted in order to provide a sound scientific basis for the method. Issues of importance were the selection of the optimum guided wave modes and the establishment of relationships between the defect size and the strength of wave reflection. Analytical and numerical studies were conducted in parallel with an extensive experimental programme.
581 citations
"Study and comparison of different E..." refers background in this paper
...moreover, the driving frequency is representative of experimental conditions found in practice: frequencies in the range 10 to 250 kHz are often used [8], [33], [34], depending on the thickness of the test object and other experimental considerations....
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Book•
01 Jan 1999
TL;DR: The physics of giant magnetostriction and its application in magnetostrictive thin-film technologies are discussed in this paper, where the authors present a model of the giant magneto-strictive material.
Abstract: Physics of Giant Magnetostriction. Modelling of Giant Magnetostrictive Materials. Magnetostrictive Design. Magnetostrictive Material and Actuator Characterization. Device Application Examples. Giant Magnetostrictive Thin Film Technologies.
563 citations
"Study and comparison of different E..." refers background in this paper
...The microscopic explanation of magnetostriction of a polycrystalline metal lies in the motion of magnetic domain walls and the rotation of domains to align with the applied magnetic field (depending on the intensity of the field), which results in a mechanical deformation [17], [18]....
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Book•
03 Dec 2010
TL;DR: In this paper, the authors present a survey of EMAT techniques and their applications in the industrial domain, including on-line texture monitoring of steel sheets and in-situ monitoring of Dislocation Mobility.
Abstract: Preface. Introduction: Noncontact Ultrasonic Measurements. Brief Historical Sketch of EMAT. Electromagnetic Acoustic Resonance - EMAR. Part I: Development of EMAT Techniques. 1: Coupling Mechanism. 1.1. Background. 1.2. Generation Mechanism. 1.3. Receiving Mechanisms. 1.4. Comparison with Measurements. 2 : Available EMATS. 2.1. Bulk-Wave EMATs. 2.2. Longitudinal-Guided-Wave EMAT for Wires and Pipes. 2.3. PPM EMAT. 2.4. Meander-Line Coil SH-Wave EMAT. 2.5. SH-Wave EMAT for Chirp Pulse Compression. 2.6. Axial-Shear-Wave EMAT. 2.7. SH-Wave EMAT for Resonance in Bolt Head. 2.8. Rayleigh-Wave EMAT. 2.9. Line-Focusing EMAT. 2.10. Trapped-Torsional-Mode EMAT. 2.11. EMATs for High Temperature Measurements. 3: Brief Instruction To Build EMATs. 3.1. Coil. 3.2. Magnets. 3.3. Impedance Matching. Part II: Resonance Spectroscopy with EMATs -EMAR-. 4: Principles of EMAR for Spectral Response. 4.1. Through-Thickness Resonance. 4.2. Spectroscopy with Analog Superheterodyne Processing. 4.3. Determination of Resonance Frequency and Phase Angle. 5: Free-Decay Measurement For Attenuation And Internal Friction. 5.1. Difficulty of Attenuation Measurement. 5.2. Isolation of Ultrasonic Attenuation. 5.3. Measurement of Attenuation Coefficient. 5.4. Correction for Diffraction Loss. 5.5. Comparison with Conventional Technique. Part III: Physical-Acoustics Studies. 6: In-Situ Monitoring Of Dislocation Mobility. 6.1. Dislocation-Damping Model for Low Frequencies. 6.2. Elasto-Plastic Deformation in Copper. 6.3. Point-Defect Diffusion toward Dislocations in Deformed Aluminum. 6.4. Dislocation Damping after Elastic Deformation in Al-Zn Alloy. 6.5. Recovery and Recrystallization in Aluminum. 7: Elastic Constants and Internal Friction of Advanced Materials. 7.1. Mode Control in Resonance Ultrasound Spectroscopy by EMAR. 7.2. Inverse Calculation for Cij and Qij-1. 7.3. Monocrystal Copper. 7.4. Metal-Matrix Composites (SiCf/Ti-6Al-4V). 7.5. Lotus-Type Porous Copper. 7.6. Ni-Base Superalloys. 7.7. Thin Films. 7.8. Piezoelectric Material (Langasite: La3Ga5SiO14). 8: Nonlinear Acoustics. Part IV: Industrial Applications. 9: On-Line Texture Monitoring Of Steel Sheets. 9.1. Texture of Polycrystalline Metals. 9.2. Mathematical Expressions of Texture and Velocity Anisotropy. 9.3. Relation between ODCs and r-Values. 9.4. On-Line Monitoring with Magnetostrictive-Type EMATs. 10: Acoustoelastic Stress Measurements. 10.1. Nonlinear Elasticity. 10.2. Acoustoelastic Response of Solids. 10.3. Birefringence Acoustoelasticity. 10.4. Practical Stress Measurements with EMAR. 10.5. Monitoring Bolt Axial Stress. 11: Measurements On High-Temperature Steels. 11.1. Velocity Variation at High Temperatures. 11.2. Solidification-Shell Thickness of Continuous Casting S
287 citations
"Study and comparison of different E..." refers background in this paper
...another attractive feature of EmaTs is their capability of generating a wide range of ultrasonic wave modes, by careful design of their geometric configuration [6], [7], including shear horizontal (sH) waves in plate-like structures or torsional waves in pipe-like components—wave modes which are not easily excited by traditional piezoelectric transducers....
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...Hirao and ogi [6] have shown that within the strong bias approximation, d has only two independent components: d22, proportional to the derivative of the magnetostriction curve at the operation point, and d61, proportional to the ratio of magnetostrictive strain over magnetic bias field....
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TL;DR: A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10-300 kHz has been carried out, finite element predictions being validated by experiments on selected cases.
Abstract: A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10-300 kHz has been carried out, finite element predictions being validated by experiments on selected cases. Both cracklike defects with zero axial extent and notches with varying axial extents have been considered. The results show that the reflection coefficient from axisymmetric cracks increases monotonically with depth at all frequencies and increases with frequency at any given depth. In the frequency range of interest there is no mode conversion at axisymmetric defects. With nonaxisymmetric cracks, the reflection coefficient is a roughly linear function of the circumferential extent of the defect at relatively high frequencies, the reflection coefficient at low circumferential extents falling below the linear prediction at lower frequencies. With nonaxisymmetric defects, mode conversion to the F(1,2) mode is generally seen, and at lower frequencies the F(1,3) mode is also produced. The depth and circumferential extent are the parameters controlling the reflection from cracks; when notches having finite axial extent, rather than cracks, are considered, interference between the reflections from the start and the end of the notch causes a periodic variation of the reflection coefficient as a function of the axial extent of the notch. The results have been explained in terms of the wave-number-defect size product, ka. Low frequency scattering behavior is seen when ka 1.
264 citations
"Study and comparison of different E..." refers background in this paper
...moreover, the driving frequency is representative of experimental conditions found in practice: frequencies in the range 10 to 250 kHz are often used [8], [33], [34], depending on the thickness of the test object and other experimental considerations....
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...Furthermore, these wave modes do not show any out-of-plane particle displacement, thus they are not affected by the presence of (nonviscous) liquids in contact with the waveguide [8]....
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