Laser Ultrasound Inspection Based on Wavelet Transform and Data Clustering for Defect Estimation in Metallic Samples

Abstract

Laser-generated ultrasound is a modern non-destructive testing technique. It has been investigated over recent years as an alternative to classical ultrasonic methods, mainly in industrial maintenance and quality control procedures. In this study, the detection and reconstruction of internal defects in a metallic sample is performed by means of a time-frequency analysis of ultrasonic waves generated by a laser-induced thermal mechanism. In the proposed methodology, we used wavelet transform due to its multi-resolution time frequency characteristics. In order to isolate and estimate the corresponding time of flight of eventual ultrasonic echoes related to internal defects, a density-based spatial clustering was applied to the resulting time frequency maps. Using the laser scan beam’s position, the ultrasonic transducer’s location and the echoes’ arrival times were determined, the estimation of the defect’s position was carried out afterwards. Finally, clustering algorithms were applied to the resulting geometric solutions from the set of the laser scan points which was proposed to obtain a two-dimensional projection of the defect outline over the scan plane. The study demonstrates that the proposed method of wavelet transform ultrasonic imaging can be effectively applied to detect and size internal defects without any reference information, which represents a valuable outcome for various applications in the industry.

Directional Ultrasound Source for Solid Materials Inspection: Diffraction Management in a Metallic Phononic Crystal

“…Figure 11 shows a schematic representation of the defect embedded in the target material. We simulate the ultrasound propagation and we detect the transmitted ultrasound waves at the opposite side of the target (transmission NDT mode).This topology is used in many NDT analyses in the literature as well as beam forming for NDT applications [35][36][37][38][39][40].We compare the results obtained in the case of a healthy sample (shown in Figure 8) with those corresponding to a sample with an elliptical crack (elliptical trigonometric orthogonal axes' parameters a, b = 1, 2 cm respectively) and simulated as an air filled crack at a horizontal distance of 80 cm from the left border of the aluminium target specimen and vertically positioned at 20 cm in the middle of the specimen with and without using the ultrasound lens formed by the PC. Figure12 a show the surface plot of magnitude of the displacement field, abs(u), in the case of a normal diverging beam with no crystal, for a sample with an embedded elliptical crack.…”

Numerical simulations of infected-grain detection based on laser�ultrasonic technique

“…We have an ultrasound excited due to a thermo-elastic effect. Being widely used for non-destructive detection in many fields, it has been studied extensively [17][18][19]. In the recent years, numerical simulations of laser-ultrasonic propagation have been developed rapidly, using the finite-element method.…”

Application and Optimization of Wavelet Transform Filter for North-Seeking Gyroscope Sensor Exposed to Vibration

“…The high-frequency coefficients are limited according to the corresponding threshold criteria, and then reconstructed with low-frequency coefficients to achieve the purpose of de-noising and correction [13,14]. With the development of the WT filter, the application field has been greatly expanded to include biomedicine [15,16,17], geophysics [18,19], image processing [20,21], tracking detection [22,23,24], and feature extraction [25,26,27]. The wavelet filter also has precedents for signal processing of gyroscope sensors of the strapdown inertial navigation system (SINS) used for attitude determination, such as the fiber optic gyroscope (FOG) [28,29] and micro electro mechanical system (MEMS) gyroscopes [30,31], for which good application results have been achieved in previous studies [32,33,34,35].…”