In-plane and out-of-plane displacement measurement by ultrasonic speckle correlation method (USCM)

Abstract

When an object moves, ultrasonic speckles backscattered from its surface will follow the object to move. From the Kirchhoff diffraction theory and the correlation principles of random signals, the necessary condition for keeping the correlativity between the speckle fields before and after the objective displacement was deduced. Based on this condition, the formulas for the relationship between the speckle displacement and the objective displacement were obtained. Practical measurement was performed. Ultrasonic digital speckle correlation method was used to measure the in-plane displacement and out-of-plane displacement of an object. The displacements of the objective surface were evaluated after the displacements of the speckles were determined.This method can be also used to measure the displacements of an inner objective surface. A mountain-climbing search method was proposed, which enabled us to find the maximum correlation coefficient in the correlation operation quickly and efficiently. The experimental results showed good agreement with the theoretical predictions.

Strain measurement by ultrasonic speckle technique based on adaptive genetic algorithm

“…In the initial situation, R scanned a square area of the XY plane centered at point O with a step length of 0.4 mm, which equaled half the average lateral size of the speckles. 14 A total of 30 × 30 speckle signals were collected. The power spectral density of the central frequency of each point speckle signal was taken as the characteristic value to compose the pre-deform data array.…”

“…When the surface is insonified by ultrasound, the backscattered waves stack and produce ultrasonic speckles whose average lateral size can be obtained from the second-order statistic properties. 14 The average lateral size δ p can be expressed as δ p = 1 . 22 λ F / 1 . 22 λ F φ φ , where λ is the wavelength of ultrasound, F is the focal length of ultrasound probes and φ is the radius of the probe. After scanning with the ultrasound probe, the speckle signals have been collected from every point.…”

“…Therefore, as a noncontact measurement method, the ultrasonic speckle technique could measure the full-field displacements of measured surface in an nondestructive way. 14–16 Based on the ultrasonic C-scan and correlation searching algorithms, the ultrasonic speckle technique proposed in this article was applied to measure the displacements and strains of the inner surface in water.…”

In Situ Monitoring of Epoxy Resin Curing Process Using Ultrasonic Technique

“…In signal analysis, 11 a correlation function is often used to compute the distance between two similar waveforms. After A/D transformation, two signals X ( t ) and Y ( t ) become two infinite discrete sequences x ( n ) and y ( n ).…”

Effect of apertures on the speckle size from rough surfaces

“…INTRODUCTION The phenomenon known as a speckle pattern results when coherent light are scattered from rough surfaces [1]. Since the advent of lasers, many important statistical properties of the speckle have been investigated both experimentally and theoretically, and have been applied to various practical applications [2][3][4][5][6][7][8][9]. The speckle size is one of the important properties of the speckle, many researchers have discussed this problem, and based on the diffraction theory derived the speckle size [10][11][12][13].…”