Characteristics Of Guided Waves Research Articles

Deep‐learning‐based guided wave detection for liquid‐level state in porcelain bushing type terminal

The structural security of civil energy equipment is significant for the steady operation of power supply system, and porcelain bushing type terminal is a typical energy equipment that needs long-term monitoring. As a nondestructive structural health monitoring method, ultrasonic guided wave (UGW) technology is extremely suitable for state detection of energy equipment. However, most current UGW methods still need to manually select the guided wave features, which rely heavily on the guidance of expert experience. This article presents a deep-learning method to directly utilize original-guided wave signals to quantitatively detect the liquid-level state. Firstly, the original signals were fed into convolutional autoencoder (CAE) to catch the low-dimension representation and realize the automatic feature extraction. Then, the low-dimension representations were orderly input into the long short-term memory (LSTM) recurrent neural network for liquid-level regression. In feature extraction step, CAE method can effectively extract the useful features and remove the interference and signal distortion. In regression step, both the accuracy and the robustness of proposed method are better than backpropagation network and convolutional neural network. Experimental results show that proposed CAE-LSTM method can accurately inspect the liquid level by original signals and implement maintenance monitoring.

Study on Guided Wave Characteristics of Waveguide Rod

Waveguide rod is currently used as an auxiliary tool in ultrasonic testing. Because the waveguide rod can isolate high-temperature workpiece from ultrasonic sensor, it is often used in monitoring of high-temperature equipment. However, there are dispersion and attenuation when ultrasonic guided wave propagates in waveguide rod, which is not conducive to the monitoring of equipment. In order to improve the monitoring accuracy, the effects of diameters and lengths on the guided wave characteristics of the waveguide rod were analyzed through numerical calculation and experimental research. The results show that the larger the diameter of the waveguide rod, the smaller the attenuation of the ultrasonic guided wave and the weaker the dispersion; the increase in the length of the waveguide rod has no effect on the dispersion of the guided wave, but it will increase the attenuation.

Bayesian dynamic modification of corrosion in a cylindrical rod quantified by guided waves technique

ABSTRACT In this study, both estimation and modification strategies of measurement uncertainty were investigated when using a guided waves (GWs) technique to quantify the corrosion level of a cylindrical rod induced by an accelerated setup, thus providing essential and reliable information for making decisions regarding necessary remedial work. First, the remnant diameters under corrosion were quantified based on the dispersion characteristics of GWs, and the measurement uncertainty derived from time-frequency analysis was specifically considered. After demonstrating the equivalence with the self-adaptive Monte Carlo method, the method in guide to the expression of uncertainty in measurement (GUM) was used as a more efficient approach for carrying out interval estimation of the corrosion level. Furthermore, a designed Bayesian dynamic linear model (BDLM) with a model monitoring mechanism was introduced to modify the measurement sequence. Thus, not only were more credible estimations achieved but discrepant sequences of measurement data could also be identified to avoid a misled judgement.

Guided wave characteristics in the functionally graded two‐dimensional hexagonal quasi‐crystal plate

AbstractDue to the limit of preparation technology, defects, such as cracks and inclusions, are inevitable in the functionally graded quasi‐crystal material. For the purpose of the guided wave non‐destructive testing on the functionally graded (FG) two‐dimensional(2‐D) hexagonal quasi‐crystal(QC) plates, Lamb and SH wave characteristics in the context of the Bak's model are investigated by means of the Legendre polynomial method. The convergence of the polynomial method applied on the FG 2‐D hexagonal QC plate is analyzed. Some new wave characteristics resulted from the phonon‐phason coupling effect are revealed. There are three Lamb‐like modes without cut‐off frequencies for the x‐y and y‐z QC plates, but four Lamb‐like modes without cut‐off frequencies for the x‐z QC plate. For phonon modes, phonon displacements and stresses are bigger than phason displacements and stresses. However, they are just opposite for phason modes. It can be utilized to distinguish phonon modes and phason modes.

Response of triaxial velocity and acceleration geophones to channel waves in a 1-m thick coal seam

Intelligent coal mining techniques are developing rapidly in China and require geological transparency of the working face. Coal seam channel waves are particularly promising because they only propagate in coal seams and are sensitive to changes in seam thickness and local geological structure. Previous channel wave studies focused mostly on medium-thick coal seams, while channel wave signal characteristics in thin coal seams remain poorly understood. We have conducted experiments on the transmission of channel waves in a 1-m thick coal seam using triaxial velocity geophones and acceleration geophones embedded in the coal seam and its roof and floor rock mass to better understand guided wave characteristics in thin coal seams. We find that a wide-frequency triaxial acceleration geophone with stable amplitude-frequency characteristics enables collection of all of the 1-m thick coal seam guided wave information. However, the velocity geophones did not effectively respond to different coal seam guided waves. Signal analysis reveals that the thin coal seam channel wave features with an Airy seismic phase frequency of 570 Hz and velocity of 950 m/s. There was a high-energy and high-frequency guided wave between the P and S direct waves of the coal seam roof and floor. Combined with time-frequency analysis, polarization analysis, and numerical simulation, the guided wave is inferred to be a P-P interference wave with potential exploration value propagating in the same direction along the roof and floor of the coal seam. Acceleration geophones with a wide frequency band and stable sensitivity are therefore the key point to acquiring coal seam channel wave exploration data.

Wave isogeometric analysis method for calculating dispersive properties of guided waves in rotating damped cylinders

The reliable guided wave inspection techniques depend on the accurate understanding of dispersive properties. The classic finite element method has been proven to be very practical for modeling wave propagation in arbitrary waveguides. However, when it comes to modeling on complex geometries, it still has a major drawback: the geometric discrete errors and the high consumption of resources to improve accuracy. Recently, Isogeometric analysis has been found advantageous over the classic finite element method on geometry representation and mesh generation. Here, a wave isogeometric analysis (WIGA) method is proposed for the computation of guided wave characteristics in rotating damped cylinders, based on the Floquet’s principle. According to the linear incremental theory and the principle of virtual power, elastodynamic wave equation is established, with regard to the WIGA. To ensure its effectiveness, the convergence and accuracy of the proposed method are considered compared with that of the wave finite element method. The size of unit cell and the solvable frequency range are discussed in detail. Furthermore, dispersive behaviors are computed considering the effects of damping and rotation. The results demonstrate that flexural wave modes are very sensitive to the rotation effect. Particularly, in phase velocity spectra the characteristic frequency at the amplitude peak equals to the rotational angular speed, where wave propagating and attenuating both vanish.

Spoof plasmonic waveguide developed from coplanar stripline for strongly confined terahertz propagation and its application in microwave filters.

A novel planar terahertz (THz) plasmonic waveguide developed from coplanar stripline (CPS) is proposed for the first time to achieve strongly confined THz propagation performance based on the concept of spoof surface plasmon polaritons (SSPP). Guided-wave characteristics of the proposed plasmonic waveguide are theoretically investigated by eigen-mode simulation technique and finite-difference time-domain solutions. It is found that the waveguide propagation characteristics can be directly manipulated by designing the SSPP unit cells, which exhibit flexible tuning ability of the asymptotic frequency and strong THz field confinement. The idea has been validated through fabricated filter experiments in microwave frequency regime by scaling up the geometry size of the proposed structure. The measured results illustrate high performance of the ultra-wideband filter, in which the reflection coefficient is better than -10 dB from 3 to 13.1 GHz with the smallest and worst insertion losses of 2.2 dB and 5.6 dB, respectively. This work presents a new SSPP waveguide developed from CPS to realize the THz-wave propagation with strong field confinement, which may have promising potential applications in various integrated THz plasmonic devices.

Guided wave propagation in functionally graded cylindrical structures with sector cross-sections

The differential equations governing guided waves in functionally graded cylindrical structures with sector cross-sections are solved by introducing the double orthogonal polynomial series method into the cylindrical coordinate system, and the wave characteristics are subsequently investigated. The validity of the present method is confirmed by way of the comparison with available references, and the convergence is discussed. The corresponding phase velocity dispersion curves, displacement distributions and Poynting vectors are illustrated. The influences of the variation in the radius to thickness ratio, angular measure and gradient index on the guided wave characteristics are discussed, which can be used as significant guidance on ultrasonic guided wave non-destructive testing for functionally graded cylindrical structures with sector cross-sections.

Wave propagation in functionally graded piezoelectric-piezomagnetic rectangular bars

Abstract In recent years, guided wave propagation in piezoelectric-piezomagnetic composite (PPC) structures are paid much attention for the design and optimization of PPC transducers. Previous investigations are mainly limited in horizontally infinite flat plates, axially infinite hollow cylinders, and so on. They are all one-dimensional model structures, i.e. structures having variable displacement field in only one direction, and the other two displacement fields are both constant. In this paper, a double orthogonal polynomial series approach is proposed to solve the guided wave in two-dimensional model structures, namely, a functionally graded piezoelectric-piezomagnetic (FGPP) bar with a rectangular cross section. The validity of the double polynomial approach is illustrated by the comparison with the available reference results for a pure elastic homogeneous rectangular bar. The guided wave characteristics, including dispersion curves and mechanical displacement distributions, are discussed by calculating various FGPP rectangular bars.

An adaptive guided wave-Gaussian mixture model for damage monitoring under time-varying conditions: Validation in a full-scale aircraft fatigue test

Structural health monitoring technology has gradually developed from the research in laboratory to engineering validations and applications. However, the problem of reliable damage evaluation under time-varying conditions is a main obstacle for applying structural health monitoring to real aircraft structures. Among the existing structural health monitoring methods, the guided wave–based structural health monitoring method is popular but the time-varying problem needs to be addressed. Several methods have been proposed to deal with this problem but limitations remain. In this article, an adaptive guided wave-Gaussian mixture model–based damage monitoring method is proposed. It can be used online without any structural mechanical model and a priori knowledge of damage under time-varying conditions. With this method, a baseline guided wave-Gaussian mixture model is constructed first based on the guided wave features obtained under time-varying conditions when the structure is in healthy state. When a new guided wave feature is obtained during an online damage monitoring process, the guided wave-Gaussian mixture model is updated by an adaptive updating mechanism including dynamic learning and Gaussian components split-merge. The mixture probability structure of the guided wave-Gaussian mixture model and the number of Gaussian components can be optimized adaptively. Finally, a probability damage index is proposed to measure the degree of variation between the baseline guided wave-Gaussian mixture model and the online guided wave-Gaussian mixture model to reveal the damage-induced weak cumulative variation trend of the guided wave-Gaussian mixture model so as to increase the damage evaluation reliability. The method is validated in a full-scale aircraft fatigue test, and the results indicate that the reliable crack growth monitoring of the right landing gear spar and the left wing panel under the fatigue load condition is achieved.

Crack propagation monitoring in a full-scale aircraft fatigue test based on guided wave-Gaussian mixture model

For aerospace application of structural health monitoring (SHM) technology, the problem of reliable damage monitoring under time-varying conditions must be addressed and the SHM technology has to be fully validated on real aircraft structures under realistic load conditions on ground before it can reach the status of flight test. In this paper, the guided wave (GW) based SHM method is applied to a full-scale aircraft fatigue test which is one of the most similar test status to the flight test. To deal with the time-varying problem, a GW-Gaussian mixture model (GW-GMM) is proposed. The probability characteristic of GW features, which is introduced by time-varying conditions is modeled by GW-GMM. The weak cumulative variation trend of the crack propagation, which is mixed in time-varying influence can be tracked by the GW-GMM migration during on-line damage monitoring process. A best match based Kullback–Leibler divergence is proposed to measure the GW-GMM migration degree to reveal the crack propagation. The method is validated in the full-scale aircraft fatigue test. The validation results indicate that the reliable crack propagation monitoring of the left landing gear spar and the right wing panel under realistic load conditions are achieved.

An Improved Gaussian Mixture Model for Damage Propagation Monitoring of an Aircraft Wing Spar under Changing Structural Boundary Conditions.

Structural Health Monitoring (SHM) technology is considered to be a key technology to reduce the maintenance cost and meanwhile ensure the operational safety of aircraft structures. It has gradually developed from theoretic and fundamental research to real-world engineering applications in recent decades. The problem of reliable damage monitoring under time-varying conditions is a main issue for the aerospace engineering applications of SHM technology. Among the existing SHM methods, Guided Wave (GW) and piezoelectric sensor-based SHM technique is a promising method due to its high damage sensitivity and long monitoring range. Nevertheless the reliability problem should be addressed. Several methods including environmental parameter compensation, baseline signal dependency reduction and data normalization, have been well studied but limitations remain. This paper proposes a damage propagation monitoring method based on an improved Gaussian Mixture Model (GMM). It can be used on-line without any structural mechanical model and a priori knowledge of damage and time-varying conditions. With this method, a baseline GMM is constructed first based on the GW features obtained under time-varying conditions when the structure under monitoring is in the healthy state. When a new GW feature is obtained during the on-line damage monitoring process, the GMM can be updated by an adaptive migration mechanism including dynamic learning and Gaussian components split-merge. The mixture probability distribution structure of the GMM and the number of Gaussian components can be optimized adaptively. Then an on-line GMM can be obtained. Finally, a best match based Kullback-Leibler (KL) divergence is studied to measure the migration degree between the baseline GMM and the on-line GMM to reveal the weak cumulative changes of the damage propagation mixed in the time-varying influence. A wing spar of an aircraft is used to validate the proposed method. The results indicate that the crack propagation under changing structural boundary conditions can be monitored reliably. The method is not limited by the properties of the structure, and thus it is feasible to be applied to composite structure.

Numerical De-Embedding of Effective Wave Impedances of Substrate Integrated Waveguide With Varied Via-to-Via Spacings

SIW is considered as an effective rectangular waveguide with periodically loaded vias on its two side walls instead of vertical plates. Effective wave impedances of substrate integrated waveguide (SIW) with varied via-to-via spacings are for the first time numerically de-embedded from three-dimensional (3-D) full-wave algorithm by virtue of a short-open-load (SOL) calibration approach. Full-wave simulation is at first conducted to model a finite-cell SIW with two feeding uniform waveguides. Afterwards, three calibration standards are formed and modeled to de-embed the two-port ABCD matrix of the finite-cell SIW section. In addition to propagation constant, effective wave impedance of the SIW can be accurately derived without any prior assumption. After numerical convergence versus unit cells is studied, these parameters are gained to give the complete view on guided-wave characteristics along the SIW.

Highly-confined and low-loss spoof surface plasmon polaritons structure with periodic loading of trapezoidal grooves

In this paper, we propose an ultra-thin spoof surface plasmon polaritons (SPPs) structure, periodically loaded with trapezoidal grooves. Compared to the reported SPPs with rectangular grooves, the proposed SPPs structure can support the guided surface SPP wave with enlarged propagation constant, which implies an enhanced confinement of surface wave along the spoof SPPs structure. Guided-wave characteristics of the proposed SPPs structure are theoretically investigated by virtue of a numerical short-open calibration (SOC) technique. The results show that the loss of spoof SPPs is lower than that in other reported spoof SPPs structures. Experiment on prototype in microwave frequency regime is carried out which validates the theoretical findings. It is believed that the proposed structure could be scaled to THz frequencies, and is very promising in developing the miniaturized planar surface plasmonic devices and circuitry.

Effect of Dimensional Degradation on Ultrasonic Guided Waves in Bone System

This paper investigates the feasibility of using ultrasonic guided waves for assessing the mechanical properties of human bone towards realizing a safe and economical non-invasive method for the detection of conditions such as osteoporosis. Effects of dimensional (changes in thickness) degradation in the cortical bone on guided wave characteristics are studied using numerical simulation and analysis. Guided wave propagation in tubular multi-layered waveguides mimicking the bone system is studied using the Semi Analytical Finite Element (SAFE) method. Uniform tri-layered structures consisting of bone-like tubes filled with marrow and surrounded by tissue are considered for the models. The results show that geometric condition strongly impacts the velocity of guided waves supported in the bone system. The impact of underlying assumptions in these models and identification of suitable guided wave modes for practical assessment of bone condition are also discussed.

Wave propagation in graded rings with rectangular cross-sections

In this paper, a double orthogonal polynomial series method is proposed to investigate the guided wave propagation in a two-dimensional (2-D) structure, namely, a FGM ring with a rectangular cross-section. Two kinds of graded rings are considered: material gradient directions being in the radial direction and in the axial direction respectively. Numerical comparison with available reference results for a straightly homogeneous rectangular bar illustrates the validity of the proposed method. The dispersion curves and displacement distributions of various FGM rings, which have different radius to thickness ratios, different material gradient directions and different thickness to height ratios, are calculated to reveal the guided wave characteristics.

Guided wave characteristics in functionally graded piezoelectric rings with rectangular cross-sections

For the purpose of design and optimization of functionally graded piezoelectric material (FGPM) transducers, wave propagation in FGPM structures has received much attention in the past twenty years. But previous research efforts have been focused essentially on semi-infinite structures and one-dimensional structures, i.e., structures with a finite dimension in only one direction, such as horizontally infinite flat plates and axially infinite hollow cylinders. This paper proposes a double orthogonal polynomial series approach to solving the wave propagation problem in a two-dimensional FGPM structure, namely an FGPM ring with a rectangular cross-section. By numerical comparison with the available reference results for a purely elastic homogeneous rectangular rod, the validity of the extended polynomial approach is illustrated. The dispersion curves and the electric potential distributions of various FGPM rectangular rings with different material gradient directions, different polarization directions, different radius to thickness ratios, and different width to thickness ratios are calculated to reveal the guided wave characteristics.

Guided waves in general anisotropic layered rectangular rods: An extended orthogonal polynomial approach

The orthogonal polynomial approach has been used to solve the guided wave propagation in structures for about 20 years, but was limited until now to one-dimensional structures, that is, structures with a finite dimension in only one direction, such as horizontally infinite flat plates and axially infinite hollow cylinders. This paper extends the orthogonal polynomial approach to two-dimensional structures, that is, structures with finite dimensions in two directions, with illustration on the multilayered rectangular rod. Through numerical comparison with the available results, the validity of the extended polynomial approach is illustrated. The dispersion curves and displacement distributions of various layered rectangular rods are obtained to show their guided wave characteristics.

Feasibility of MFC (Macro-Fiber Composite) Transducers for Guided Wave Technique

Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.

Dynamics and guided waves in a smart Timoshenko beam with lateral contraction

Surface-bonded wafer-type piezoelectric transducers (PZTs) have been widely used to excite or measure ultrasonic guided waves for the structural health monitoring of thin-walled structures. For successful prediction of the dynamics and ultrasonic guided waves, it is essential to use very reliable computational models for the PZT-bonded multi-layer smart structures. In this paper, the spectral element model is developed for two-layer smart beams which consist of a metallic base beam layer and a PZT layer. Axial-bending-shear-contraction coupled equations of motion and boundary conditions are derived by using Hamilton’s principle with Lagrange multipliers based on the Timoshenko beam theory and Mindlin–Herrmann rod theory. The high accuracy of this spectral element model is verified in due course and the effects of a lateral contraction on the dynamics and guided wave characteristics of the example smart beams are investigated by using this spectral element model. In addition, the constraint forces at the interface between the base beam and the PZT layer are also investigated via Lagrange multipliers.