Electronic Speckle Pattern Interferometry Image Research Articles

BM3D adaptive TV filtering-based convolutional neural network for ESPI image denoising.

Image denoising is a fundamental part of image processing. The real electronic speckle pattern interferometry (ESPI) contains a large amount of speckle noise, which affects the image quality and adversely affects subsequent studies. In this paper, a method based on an improved denoising convolutional neural network (CNN) has been proposed, with the goal of reducing noise while maintaining accurate information. The block matching 3D-based adaptive TV denoising CNN can protect the valid information while preventing the information of the original image itself from being corrupted. A two-channel model is used to improve the noise reduction effect of real images. The proposed method is compared with the conventional denoising algorithms and the deep-learning denoising algorithms. Experimental results show that the proposed method can maintain accuracy, integrity, and stability while preserving the details, texture, and edge information of the stripe pattern.

In situ and dynamic observation of coating failure behavior

In this study, the failure behavior of epoxy coating in 3.5% (mass fraction) NaCl solution was investigated by electronic speckle pattern interferometry (ESPI) and electrochemical impedance spectroscopy (EIS). We found that ESPI images changed with the diffusion of corrosion products and the appearance of defects such as blistering. Direct information can be obtained from the images taken at different times. The relation between impedance characteristics and ESPI images was investigated. Experimental results showed that ESPI is an effective technique to detect coating degradation, and it provides a comprehensive approach to studying the process of coating degradation and under-film corrosion.

Denoising for variable density ESPI fringes in nondestructive testing by an adaptive multiscale morphological filter based on local mean.

Analysis of speckle images with variable density fringes is a challenging task when electronic speckle pattern interferometry (ESPI) is used for nondestructive testing of defects. In this paper, an adaptive multiscale morphological filter based on local mean is proposed. First, the image is segmented, and the regions are divided into different density levels using local mean. Then, the structural elements that adapt to different density levels are designed, and the proper size of the structural elements is determined by an iterative procedure. Finally, the morphological open-closing filtering is conducted, and the block edges are smoothed by averaging. The proposed method was applied to computer-simulation fringes and fringes experimentally obtained from a prefabricated defect specimen under thermal loading and then compared with the commonly used methods, i.e., discrete cosine filter, wavelet filter, Lee filter, and nonlocal mean filter. The experimental results showed that the proposed method had the best performance in terms of noise reduction and edge preservation. With the capability of noise reduction for ESPI images of variable density fringes, the proposed method will be helpful to build a quantitative relationship between fringes and defects in the cases of nonuniform deformation of speckle interferometry, such as nondestructive defect detecting, thermal structural analysis, and heterogeneous materials mechanical analysis.

Observing Deformation and Fracture of Rock with Speckle Patterns

The high resolution technique of electronic speckle pattern interferometry (ESPI) can be very useful in determining deformation of laboratory specimens and identifying initiation of failure. The in-plane ESPI theory is described and the fringe pattern of the processed ESPI image is analyzed to determine deformation and crack opening displacement. Fringes on the ESPI image represent lines of equal intensity, which relate to surface displacement. An ESPI system was constructed and calibrated for measuring uni-directional displacements. Several types of the experiments, such as uniaxial compression and fracture testing, were conducted to demonstrate the utility of ESPI.

Initiation of tensile and mixed-mode fracture in sandstone

Initiation of failure under three-point bending was observed in sandstone specimens with and without a stress concentrator. Acoustic emission (AE) and electronic speckle pattern interferometry (ESPI) were used to quantify the fracture phenomena through AE locations and ESPI images of an intrinsic damage zone. To investigate mixed mode fracture, beam tests with off-center notches were studied as well. Before about 95% of peak load, the locations of AE were somewhat random for beams with a smooth boundary (no notch). From 96–100% of peak, microcrack hypocenters indicated localization in the form of an intrinsic zone, which was also identified by the high resolution technique of ESPI. The discrete element technique was used to mimic the failure process. A synthetic rock was composed of rigid circular particles that interact through normal and shear springs, and the particles were glued to each other using normal and shear bonds. A microcrack forming in tension or shear was simulated by breakage of the bond between two particles in contact. The synthetic rock was calibrated for elastic properties, unconfined compressive strength, and bending tensile strength. The beam strength with and without notches and the fracture path were studied in the numerical experiments, and the results compared favorably with those obtained from the laboratory experiments.

Drum tuning: An experimental analysis of membrane modes under slightly nonuniform tension.

Results of an experimental study of normal mode vibrations in single-headed musical drums under nonuniform tension will be presented. Although uniform tension is often assumed in theoretical treatments, in practice the musical drum only approximates this condition, even after careful tuning by the drummer. This study investigates the behavior of normal mode shapes and frequencies under (slightly) nonuniform tension, as they relate to the tuning process. In particular, the role of the (1,1) mode will be described. Experimental results include electronic speckle pattern interferometry images of modal shapes along with the associated frequencies. A finite element model will be used for comparison with the experimental results.

Technique for the removal of speckle phase in electronic speckle interferometry

It is shown that the speckle nature of electronic speckle pattern interferometry images can be reduced in quasireal time with the use of only three consecutive video images. By use of additive-subtractive phase modulation processing the technique is essentially insensitive to environmental noise, and distortion of fringes does not occur. By further removing the random speckle phase we show, using speckle statistics, that the number of dark speckles in the resulting fringe pattern is close to zero.