Excitation Of Guided Waves Research Articles

SH guided wave excitation by an apparent face-shear mode (d36) piezocomposite transducer: experiments and theory

The fundamental shear horizontal (SH0) wave in plate-like structures is of practical importance in structural health monitoring (SHM) due to its non-dispersive characteristics. However, compared with Lamb waves, SH0 wave is less used in practice since it is difficult to be excited by using conventional piezoelectric transducers. In this work, an apparent face-shear mode (d36) piezocomposite transducer was proposed to excite and receive SH0 wave. The piezocomposite transducer was made up of epoxies and several hollow PZT squares of different sizes. The face-shear d36 mode was synthetized by the thickness-shear deformation of each side of the hollow PZT squares. Both finite element simulations and experimental testings showed that the apparent d36 piezocomposite transducer was capable of exciting pure SH0 wave along four main directions (0°, 90°, 180° and 270°) from 70 to 150 kHz. Moreover, the piezocomposite transducer can filter Lamb waves and receive SH0 wave only over a wide frequency range from 70 to 370 kHz. Based on Huygens’ principle and the method of solving inclusion problem, an eigenstrain-based theoretical model was then proposed to describe the SH0 wave field generated by face-shear transducers. Explicit analytical expressions for the piezocomposite transducer were successfully obtained and their accuracies were verified by both experiments and finite element simulations. Furthermore, some general guidelines based on the analytical model were presented for optimization of the transducer’s dimensions. The proposed apparent d36 piezocomposite transducer may be a good candidate for exciting and receiving low frequency SH0 wave in SHM systems, since it is lightweight and shows better surface conformability than PZT wafers.

An ultrasonic guided wave excitation method at constant phase velocity using ultrasonic phased array probes

High-order ultrasonic guided wave modes have recently been attracting interest in a variety of nondestructive testing applications, ranging from thickness gauging to bond characterization. Accurate control of the transmitted ultrasonic guided wave mode is paramount when working at frequencies above the cutoff of the first high-order mode. The high number of modes available makes this range of frequency-thickness products difficult to exploit in practice. Many papers and textbooks have showed that multielement probes, such as comb transducers, are able to target a specific wavelength which depends on the elementary pitch. This method can be enhanced by adding an elementary delay law. However, this method of excitation has major drawbacks as the areas of excitation in a dispersion curves depends on the frequency and the technique is not unidirectional. This paper demonstrate that a conventional phased array transducer for which the elementary pitch is small relative to the targeted wavelength is able to excite high order guided wave modes at a constant phase velocity (independently of the frequency). The aim is to excite different regions of the dispersion curves by controlling the input signal bandwidth and the angle of the generated beam. The paper describes the theoretical background and details the differences between the various methods of excitation of ultrasonic guided waves, especially with the comb transducer method. Finite element simulations are presented to verify the analytical predictions and quantify the unidirectional and diffraction properties of the transmitted beam. Experiments conducted on an aluminum plate show striking agreement with finite element simulations, including the possibility of exciting a single mode in a narrow region at high frequency-thickness products. Experiments conducted on a CFRP plate demonstrates that the method can be adapted to other materials.

An analytical model of transducer array arrangement for guided wave excitation and propagation on cylindrical structures

Ultrasonic guided wave (GW) inspection is one of the non-destructive testing (NDT) techniques available for the engineering structures. Compared with other NDT techniques, guided waves can propagate a long distance with a relatively high sensitivity to defects in the structure. In order to increase the performance for pipe inspections to meet higher requirements under different conditions, the optimisation of piezoelectric transducer array design is still a need, as the technique is currently subject to a complex analysis due to wide number of guided wave modes generated. This can be done by optimising the transducer array design. In this paper, it is described an analytical mode of a set of piezoelectric transducer arrays upon torsional wave mode T(0,1) excitation in a tubular structure. The proposed analytical model for predicting signal propagation is validated by using finite element analysis in ABAQUS and three-dimensional laser vibrometer experiments for transducer array characterisations. The proposed analytical model works well and very fast for simulating transducer excitation and wave propagation along cylindrical structures. This will significantly reduce the complexity of guided wave analysis, enhancing effectively the structural health of structures and subsequently reducing the industry maintenance cost.

Diagnostic of manufacturing defects in ultrasonically welded thermoplastic composite joints using ultrasonic guided waves

This article presents research about the propagation of ultrasonic guided waves in ultrasonically welded thermoplastic composite joints. The goal of the study was to understand the effect of weld manufacturing defects on guided wave transmission across the joint. Triangular energy-directors integrated into the lower composite adherends enabled the production of defective joints in a controlled manner. The produced defect types were unwelded areas and adherend fibre bundle distortion. The reference condition corresponded to the fully welded stage which showed the highest single-lap shear strength. It was possible to detect adherend fibre bundle distortion through the increase in the negative shift of the signal characteristic frequency. Evidence of the presence of unwelded areas was found in the increase of Time-of-Flight of the maximum amplitude Lamb wave group. The sensitivity of the diagnostic parameters was found to be dependent on the ultrasonic guided wave excitation frequency.

An analytically based computer model for evaluating effective elastic properties of nitride nanowire-polymer compositions using laser-generated surface acoustic waves

The investigation of physical and mechanical properties of nitride nanowires (NWs) is a topical field of modern nanotechnological research due to a wide range of promising applications. Normally, the NWs are embedded in a host polymer (e.g., hydrogen silsesquioxane – HSQ), and it becomes necessary to determine the effective properties of polymer-NW compositions rather than of separate wires. The central idea of the present research is the evaluation of the effective elastic moduli of the anisotropic composite HSQ-NW material via the minimization of the goal function that specifies the discrepancy between the measured and calculated characteristics of laser-generated surface acoustic waves. The experimental data are obtained on the basis of transient grating spectroscopy while the theoretical dispersion curves are calculated using the analytically based computer model for elastic guided wave excitation and propagation in multilayered elastic anisotropic half-spaces. The numerical examples illustrate the validation of the developed computer model against the experimental data acquired for sandwich microstructures with known elastic moduli as well as demonstrate the restoration of the latter in the case of HSQ-NW compositions with unknown mechanical properties.

Guided wave excitation and propagation in damped composite plates

Guided wave attenuation in composites due to material damping is strong, anisotropic, and cannot be neglected. Material damping is a critical parameter in selection of a particular wave mode for long-range structural health monitoring in composites. In this article, a semi-analytical finite element approach is presented to model guided wave excitation and propagation in damped composite plates. The theoretical framework is formulated using finite element method to describe the material behavior in the thickness direction while assuming analytical expressions in the wave propagation direction along the plate. In the proposed method, the Kelvin–Voigt damping model using a complex frequency-dependent stiffness matrix is utilized to account for anisotropic damping effects of composites. Thus, the existing semi-analytical finite element approach is being extended to include material damping effect. Theoretical predictions are experimentally validated using scanning laser Doppler vibrometer measurements of guided wave propagation generated by a circular piezoelectric wafer active sensor transducer in a unidirectional carbon fiber reinforced polymer composite plate. The proposed method achieves good agreement with the experimental results.

Modeling guided wave excitation in plates with surface mounted piezoelectric elements: coupled physics and normal mode expansion

Guided waves have been extensively studied and widely used for structural health monitoring because of their large volumetric coverage and good sensitivity to defects. Effectively and preferentially exciting a desired wave mode having good sensitivity to a certain defect is of great practical importance. Piezoelectric discs and plates are the most common types of surface-mounted transducers for guided wave excitation and reception. Their geometry strongly influences the proportioning between excited modes as well as the total power of the excited modes. It is highly desirable to predominantly excite the selected mode while the total transduction power is maximized. In this work, a fully coupled multi-physics finite element analysis, which incorporates the driving circuit, the piezoelectric element and the wave guide, is combined with the normal mode expansion method to study both the mode tuning and total wave power. The excitation of circular crested waves in an aluminum plate with circular piezoelectric discs is numerically studied for different disc and adhesive thicknesses. Additionally, the excitation of plane waves in an aluminum plate, using a stripe piezoelectric element is studied both numerically and experimentally. It is difficult to achieve predominant single mode excitation as well as maximum power transmission simultaneously, especially for higher order modes. However, guidelines for designing the geometry of piezoelectric elements for optimal mode excitation are recommended.

Structural Health Monitoring of Above-Ground Storage Tank Floors by Ultrasonic Guided Wave Excitation on the Tank Wall.

There is an increasing interest in using ultrasonic guided waves to assess the structural degradation of above-ground storage tank floors. This is a non-invasive and economically viable means of assessing structural degradation. Above-ground storage tank floors are ageing assets which need to be inspected periodically to avoid structural failure. At present, normal-stress type transducers are bonded to the tank annular chime to generate a force field in the thickness direction of the floor and excite fundamental symmetric and asymmetric Lamb modes. However, the majority of above-ground storage tanks in use have no annular chime due to a simplified design and/or have a degraded chime due to corrosion. This means that transducers cannot be mounted on the chime to assess structural health according to the present technology, and the market share of structural health monitoring of above-ground storage tank floors using ultrasonic guided wave is thus limited. Therefore, the present study investigates the potential of using the tank wall to bond the transducer instead of the tank annular chime. Both normal and shear type transducers were investigated numerically, and results were validated using a 4.1 m diameter above-ground storage tank. The study results show shear mode type transducers bonded to the tank wall can be used to assess the structural health of the above-ground tank floors using an ultrasonic guided wave. It is also shown that for the cases studied there is a 7.4 dB signal-to-noise ratio improvement at 45 kHz for the guided wave excitation on the tank wall using shear mode transducers.

Phased laser diode array permits selective excitation of ultrasonic guided waves in coated bone-mimicking tubes

This paper validates simulation predictions, which state that specific modes could be enhanced in quantitative ultrasonic bone testing. Tunable selection of ultrasonic guided wave excitation is useful in non-destructive testing since it permits the mediation of energy into diagnostically useful modes while reducing the energy mediated into disturbing contributions. For instance, it is often challenging to distinguish and extract the useful modes from ultrasound signals measured in bone covered by a soft tissue. We show that a laser diode array can selectively excite ultrasound in bone mimicking phantoms. A fiber-coupled diode array (4 elements) illuminated two solid tubes (2–3 mm wall thickness) embraced by an opaque soft-tissue mimicking elastomer coating (5 mm thick). A predetermined time delay matching the selected mode and frequency was employed between the outputs of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results suggest that this array reduces the disturbances caused by the elastomer cover and so pave way to permit non-contacting in vivo guided wave ultrasound assessment of human bones. The implementation is small, inexpensive, and robust in comparison with the conventional pulsed lasers.

The features of the guided wave excitation and propagation at testing of pipes

The generalized integral solutions of the problem connected with excitation and propagation of torsional waves by electromagnetic-acoustic transducers in unloaded pipes and under conditions of loading on contact viscoelastic media, taking into account excitation parameters (frequency and geometry of the transducers), geometry, viscosity and elastic characteristics of pipe material and surrounding media, are presented. The amplitude of angular displacements of the torsional waves in pipes is estimated from the point of choice of frequency band, scanning distance and sensitivity estimation in guided wave testing of the pipes with various types and sizes. The numerical and experimental estimation of influence of the surrounding media viscoelastic characteristics on attenuation of the torsional T(0,1), longitudinal L(0,1) and flexural F(1,1) waves in the pipe is performed. The model of acoustic path of the guided wave technique on multiple reflections for testing the pipes with fixed sizes is presented and the guided wave technique sensitivity to defects depending on quantity of the received reflections, clamping force of the acoustic transducer and unwanted mode amplitude which is restricting the sensitivity to the defects is estimated.

Influence of Ultrasonic Guided Wave Excitation Frequency on the Mode Control

Influence of Ultrasonic Guided Wave Excitation Frequency on the Mode Control

Thermosonic Testing with Phased Matched Guided Wave Excitation

Thermosonic Testing with Phased Matched Guided Wave Excitation

Thermosonic Testing with Phase Matched Guided Wave Excitation

An innovative coupling method is presented that significantly improves the distribution of ultrasonic energy of guided waves for vibrothermography non-destructive testing. While typical sources radiate ultrasound cylindrically from the point or area of contact, it’s possible to channel energy towards a specified direction, e.g. the field of view of an infrared camera, by placing periodic linear structures between the transducer and the specimen. Their distance is phase matched to the wavelength of the guided wave excited that is determined by the excitation frequency and specimen properties. This antenna-like coupling device works exceptionally well in conjunction with the local defect resonance technique, as both techniques require a frequency dependent set-up. A significant increase in the defect vibration amplitude was measured when using this ultrasonic line source. Likewise, vibrothermography testing results confirm that channeling ultrasonic energy towards a specified direction is advantageous for exciting defect vibrations while using low energy input sources.

電磁超音波探触子を用いた超音波ガイド波による鋼管内部の減肉検査

The aim of this work presented here is to demonstrate that the ultrasonic guided wave testing system using electromagnetic acoustic transducers (EMAT) is able to detect the inner corrosion of steel pipes. Both excitation and reception of the guided wave is carried out with EMAT in this system, promising the practical guided wave testing system. First of all, theoretical background of the guided wave and EMAT are reviewed. Dispersion curve of the group velocity are calculated from a set of characteristic equation. Principle of the guided wave excitation and reception with EMAT is also discussed. Second, three dimensional guided wave testing simulator is developed and details of the guided wave testing system is delivered. Finally, simulation and experimental results are compared and discussed. Steel pipes with artificial inner corrosion are tested with torsional guided wave mode and the sensitivity to the corrosion is evaluated.

Advanced Signal Processing Algorithms in Structural Integrity Monitoring

Abstract Damage detection using Lead-Zirconate-Titanate (PZT) transducers for exciting guided waves was investigated. The analytical model for guided wave excitation using PZT transducers was used in a Finite Element Model for simulating guided waves in a thin aluminum plate with various defect depths. The fundamental symmetric ( S0 ) mode was excited, and four sensors were placed for detecting both the reflected and transmitted waves from defects. The model was used to conduct a parametric study of the effect of the PZT adhesive bonding on the measured signal and hence probability of detection (POD).The model was also used for optimizing signal analysis algorithms, particularly for the case of multiple overlapping modes due to mode conversion from defects. A mode decomposition algorithm is proposed for separating the reflected/transmitted S0 mode from the mode converted antisymmetric mode ( A0 ). The signal processing algorithms were optimized to maximize the POD.

Pipe Structure Detection Based on Broadband Guided Wave Excitation

Pipe Structure Detection Based on Broadband Guided Wave Excitation

A rigorous theoretical model of guided waves excitation in a plane dielectric layer under electromagnetic diffraction by a conducting strip

An exact solution of two-dimensional problem of plane electromagnetic wave scattering by a perfectly conducting strip in the presence of a parallel plane dielectric layer is presented. The given solution is constructed using the mode-matching technique in the form of diffraction integrals over propagation parameter, i.e. in the form of superposition of a large number of homogeneous and inhomogeneous plane waves with continuous spectrum of spatial frequencies. These integrals have poles, which are caused by the presence of a transparent dielectric layer and correspond to its waveguide modes. Because of this, diffraction integrals need the procedure of regularization with explicit extraction of pole terms and smoothing of integrands, whereupon the residual diffraction integrals are computed using simple numerical methods. They describe usual scattered field of a bounded obstacle, which is determined by regularized diffraction integrals and decreases in all directions from an obstacle. Besides, the total diffraction field contains a discrete finite sum of waveguide fields of guided modes of a plane dielectric layer, which correspond to the extracted pole terms of initial diffraction integrals. These fields correspond to pairs of guided waves, which move apart from the region of their excitation near a strip, propagating parallel to the boundaries of a layer and conserving finite amplitude at infinity.

Interaction of whispering gallery modes in integrated optical microring or microdisk circuits: hybrid coupled mode theory model

Whispering gallery modes supported by open circular dielectric cavities are embedded into a nonparametric two-dimensional frequency domain hybrid coupled mode theory framework. Regular aggregates of these cavities, including straight access channels, are investigated. The model enables convenient studies of the guided wave scattering process, the response of the circuit to guided wave excitation. Transmission resonances can be characterized directly in terms of resonance frequency and linewidth by computing supermodes of the entire composite circuits, comprising both cavities and bus waveguides. Examples of single ring and disk filters, a coupled-resonator optical waveguide, and a three-cavity photonic molecule in a reflector configuration allow the approach to be assessed.

Design of Ultrasonic Guided Wave Excitation Signal Generator for Rotating Shafts

Ultrasonic guided wave detection technology has mangy special characteristics. It can spread very far along the components in the distance and it can throughout the whole thickness of components, so we can make use of ultrasonic guided wave to test component of internal and surface defects. The rotating shafts are the organizations widely used in the modern production but they are very easy to be dangerous faults. If we can realize the rotating shaft in time, it can reduce the danger. It is significant to design an affordable generator which produces signals to drive magnetostrictive probe that produces ultrasonic guided wave. In this paper, we choose the torsional wave as example to design signal generator. We will introduce the way to select the appropriate guided wave mode and frequency of excitation. Design signal generator with ATmega32, AD9851 and DAC0832.

Coupled piezo-elastodynamic modeling of guided wave excitation and propagation in plates with applied prestresses

Plate-like aerospace engineering structures are prone to mechanical/residual preloads during flight operation. This article focuses on the quantitative characterization of applied prestress effects on the piezoelectrically-induced guided wave propagation, which has been widely used in structural health monitoring systems. An analytical model considering coupled piezo-elastodynamics is developed to study dynamic load transfer between a surface-bonded thin piezoelectric actuator and a prestressed plate. The accuracy of the analytical prediction is evaluated by the comparison with the finite element analysis. Based on the developed model, the load-dependent guided wave signal variation in both time-of-flight and amplitude is determined, and its dependence on loading frequency and host material properties is also discussed. It is found that the guided wave signal variation due to the prestress could be significant under some circumstances. A signal difference coefficient is finally proposed to quantitatively assess the signal variation caused by different prestresses. This study can serve as a theoretical foundation for the development of the real-time piezo-guided wave–based structural health monitoring system in a realistic loading environment.