Laser ultrasonic propagation imaging method in the frequency domain based on wavelet transformation (original) (raw)
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Wavelet Transform Applied to Internal Defect Detection by Means of Laser Ultrasound
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Laser-generated ultrasound represents an interesting nondestructive testing technique that is being investigated in the last years as performative alternative to classical ultrasonic-based approaches. The greatest difficulty in analyzing the acoustic emission response is that an in-depth knowledge of how acoustic waves propagate through the tested composite is required. In this regard, different signal processing approaches are being applied in order to assess the significance of features extracted from the resulting analysis. In this study, the detection capabilities of internal defects in a metallic sample are proposed to be studied by means of the time-frequency analysis of the ultrasonic waves resulting from laser-induced thermal mechanism. In the proposed study, the use of the wavelet transform considering different wavelet variants is considered due to its multi-resolution time-frequency characteristics. Also, a significant time-frequency technique widely applied in other fields of research is applied, the synchrosqueezed transform.
Structural damage identification based on laser ultrasonic propagation imaging technology
2009
An ultrasonic propagation imaging (UPI) system consisted of a Q-switched Nd-YAG pulsed laser and a galvanometer laser mirror scanner was developed. The system which requires neither reference data nor fixed focal length could be used for health monitoring of curved structures. If combined with a fiber acoustic wave PZT (FAWPZT) sensor, it could be used to inspect hot target structures that present formidable challenges to the usage of contact piezoelectric transducers mainly due to the operating temperature limitation of transducers and debonding problem due to the mismatch of coefficient of thermal expansion between the target, transducer and bonding material. The inspection of a stainless steel plate with a curvature radius of about 4 m, having 2mm×1mm open-crack was demonstrated at 150°C using a FAWPZT sensor welded on the plate. Highly-curved surfaces scanning capability and adaptivity of the system for large laser incident angle up to 70° was demonstrated on a stainless steel cylinder with 2mm×1mm open-crack. The imaging results were presented in ultrasonic propagation movie which was a moving wavefield emerged from an installed ultrasonic sensor. Damages were localized by the scattering wavefields. The result images enabled easy detection and interpretation of structural defects as anomalies during ultrasonic wave propagation.
Wavelet filtering of signals from ultrasonic flaw detector
Russian Journal of Nondestructive Testing, 2002
The paper considers basic principles of the algorithm of wavelet filtering of signals from an ultrasonic flaw detector with the help of the fast wavelet transform. Criteria for selection of the type and order of a wavelet are formulated, and the number of decomposition levels required for the needed accuracy and reproducibility of results of ultrasonic tests are determined.
NEW DESIGN AND ALGORITHM FOR AN ULTRASONIC PROPAGATION IMAGING SYSTEM
Laser-based ultrasonic sensing generally requires the probe to have a fixed focal length or to be contact. On the other hand, such a requirement is not essential in laser-based ultrasonic generation. Based on this point, we designed a pulsed laser-based ultrasonic propagation imaging (UPI) system which included developments of a tilting mirror system (TMS) for rapid ultrasonic scanning of target and an in-line filter for real-time band-pass filtering capable of ultrasonic mode selection. For the novel UPI algorithm as well as the UPI system, 1D-temporal averaging, 2Dspatial averaging, and 3D-data structure building algorithms were developed for clearer results, hence higher damage detectability. The imaging results on a flat stainless steel plate were presented in movie and snapshot formats which showed the propagation of ultrasound visible as a concentric wavefield emerging from an installed ultrasonic sensor. An open hole of diameter 1 mm on the plate was indicated by the scattering wavefields. Even if the damage size was comparatively small, the result was clear enough for non-experts on ultrasonics not to overlook it. The results showed that this UPI system is robust and independent of focal length and reference data requirement. Therefore, the UPI system will be able to a versatile tool for on-site automatic nondestructive testing for many applications such as power plant structures, infrastructures and transportation structures.
Ultrasonic NDE of composite material structures using wavelet coefficients
NDT & E International, 2001
A wavelet-based method is proposed to perform the analysis of NDE ultrasonic signals received during the inspection of reinforced composite materials. The non-homogenous nature of such materials induces a very high level of structural noise which greatly complicates the interpretation of the NDE signals. By combining the time domain and the classical Fourier analysis, the wavelet transform provides simultaneously spectral representation and temporal order of the signal decomposition components. To construct a C-scan image from the wavelet transform of the A-scan signals, we propose a selection process of the wavelet coef®cients, followed by an interpretation procedure based on a windowing process in the time±frequency domain. The proposed NDE method is tested on cryogenic glass/epoxy hydrogen reservoir samples. q
Measurement, 2002
This paper deals with a method for the automatic analysis and characterization of defects due to encapsulation and/or surface mount processes of microelectronic devices. This method is based on digital signal processing of ultrasonic signals in the 10-100-MHz frequency range. In particular, it is used for automatic evaluation of time-of-flight between echoes received by the acoustic transducer. The signals are first pre-processed by a new algorithm, based on the Wiener filtering, and then by a numeric algorithm, based on the wavelet transform, already applied successfully to this problem. The pre-processing phase increases the sensitivity of the successive numeric algorithm. The theory underlying the pre-processor and the chosen procedure to implement it are described in detail in this paper. Furthermore, experimental results obtained by applying the proposed method on acoustic signals from an electronic structure acquired through an ultrasonic scanning system are given and discussed.
A wavelet analysis of acoustic fields and signals in ultrasonic nondestructive testing
Russian Journal of Nondestructive Testing, 2005
The use of the continuous and discrete wavelet analysis for investigation and filtering of acoustic signals and fields is considered. Special attention is paid to the application of wavelet filtering for improving the quality of the visualization of flaws. Wavelet contour plots, a new method for representing information, are introduced. This technique simplifies the determination of conventional dimensions of flaws.
Wavelet Network Approach for Structural Damage Identification Using Guided Ultrasonic Waves
IEEE Transactions on Instrumentation and Measurement, 2000
An appropriate wavelet network (WN) approach is introduced for detecting damage location and severity of structures based on measured guided ultrasonic wave (GUW) signals. An algorithm for establishing a multiple-input multiple-output fixed grid wavelet network (FGWN) is proposed. This algorithm consists of three main stages: 1) formation of wavelet latticel; 2) formation of wavelet matrix; and 3) optimizing the wavelet structure by means of orthogonal least square algorithm. Three damage-sensitive features are extracted from the GUW signals: 1) time of flight; 2) normalized damage wave amplitude; and 3) normalized damage wave area. These features are considered as the FGWN inputs and the damage location and severity are estimated. The established FGWN is used for identifying damage location and severity in a structural beam. The beam is investigated and simulated in different damaged conditions. Computed finite element method (FEM) simulation signals are used for training the FGWN. Some other FEM simulation signals, as well as measured experimental ones are used for testing. The proposed damage identification method is compared with three artificial neural network (ANN)-based algorithms. In addition to some other benefits of the proposed WN-based algorithm over ANN-based methods discussed in this paper, the results show that our approach performs better in both damage location and severity detections than other methods. Index Terms-Artificial neural network (ANN), damage identification, guided ultrasonic wave (GUW), structural health monitoring (SHM), wavelet network (WN).