Moire Fringe Patterns Research Articles

Application of Moire Profilometry in Three-Dimensional Profile Reconstruction of Key Parts in Railway.

Moire profilometry (MP) is one of the three-dimensional (3D) topography measurement methods of structured light, which has the advantages of single frame reconstruction, high speed, no contact and high precision, and is suitable for dynamic measurement scenes. In this article, the digital MP is applied to the wheel tread measurement, the virtual grating is generated by computer to project to the object surface, the moire fringe pattern of the object is obtained by filtering, and finally the continuous phase pattern is obtained by phase unwrapping. The 3D shape reconstruction of the wheel tread is realized, and a new method of wheel tread detection is provided. At the same time, in this paper, the results of using different filters are compared, and the significance of the frequency domain filtering to MP is proved. It is necessary to choose a suitable filtering method according to different environmental conditions. At present, digital MP can be used in industrial static detection, and it can be extended to the dynamic detection of rolling wheels in the future, so as to improve the detection efficiency and realize the automatic detection of trains.

Implementation of Talbot–Lau x-ray deflectometry in the pulsed power environment using a copper X-pinch backlighter

A Talbot–Lau x-ray deflectometer can map electron density gradients in high energy density plasmas, as well as provide information about plasma elemental composition through single-image x-ray refraction and attenuation measurements. A new adaptation to a pulsed power environment used backlighting from copper X-pinches, allowing for electron density mapping of a low-Z object. Even though the X-pinch backlighter is not properly optimized for emitting x-rays in terms of source size and photon fluence, Moire fringe patterns with contrast up to 14% and fringe shift due to refraction on a beryllium object are obtained. Due to the proximity of the deflectometer with the X-pinch (∼6 cm), it is shown that a protective filter is required to avoid damage in the closest (i.e., source) grating due to both plasma debris and mechanical shock. Regarding grating survival, these did not show any damage due to the intense magnetic field or heating induced by plasma radiation. Electron density on beryllium was measured with a difference lower than 16%. The areal electron density mapping of the sample was limited by source size characteristics, in similarity to transmission radiography. These results show the potential of plasma electron density as well as material mapping through Talbot–Lau x-ray deflectometry in a pulsed power environment.

Fourier transform phase retrieval for x-ray phase-contrast imaging based on cascaded Talbot–Lau interferometers

Long exposure time is one of the major limitations in x-ray phase-contrast imaging (XPCI). Therefore, we demonstrate a promising alternative method for grating-based XPCI coupled with cascaded Talbot–Lau interferometers (TLIs). A Fourier analysis of the moire fringe patterns generated by the interferometers was used to obtain the multicontrast images (such as absorption, differential phase-contrast, and normalized visibility-contrast images) with a single exposure. The cascaded configuration with TLI and inverse TLI using large-period absorption gratings was established to verify the effectiveness of the algorithm and three multicontrast images of a polytetrafluoroethylene (PTFE) tube were obtained experimentally. The groove structures in the PTFE can be clearly identified in the differential phase-contrast image. This method shows potential for application of cascaded TLI in medical imaging.

3-DOF measurement method for non-diffracting Moiré fringes based on CGH

Aiming at the motion errors of the linear stage, a measurement method for the determination of three-degree-of-freedom (3-DOF) error motions is proposed based on non-diffracting Moire fringes produced by computer-generated holograms (CGHs). A liquid crystal spatial light modulator (SLM) is used to generate non-diffracting beams, and two non-diffracting beams form Moire fringes. A 3-DOF measuring optical path of non-diffracting Moire fringes is designed. Meanwhile, a 3-DOF mathematical model of motion errors is established, and three kinds of motion errors (yaw angle, roll angle and pitch angle) are separated by geometric analysis method. A rotary table is used to simulate the 3-DOF motion errors on different conditions. The NDB and non-diffracting Moire fringe patterns are obtained by CCD1 and CCD2 respectively. Experimental results show that the motion errors calculated by the positions of the central points agree well with the theoretical value with the error less than 0.0104°, which can verify the feasibility and correctness of the 3-DOF measurement system for non-diffracting Moire fringes.

A robust and effective phase-shift fringe projection profilometry method for the extreme intensity

The structured-light with phase-shift fringe projection profilometry (PFPP) plays a significant role in non-contact 3D surface measurement. The multi-frequency heterodyne (MFH) phase unwrapping algorithm is widely used in PFPP because of its high precision and noise-isolation features. However, measuring the over-dark and over-bright surfaces is a headache of the MFH algorithm due to its limit intensity tolerance in decoding phases. We provide a new method named as Moire Fringe Patterns Sequence (MFPS) algorithm to avoid the phase error enlargement, so as to increase the robustness of the decoding algorithm. In the MFPS algorithm, we project the synthetic patterns to the object directly, which doubles the tolerance of phase error. The MFPS algorithm has the same accuracy as the MFH. It can successfully decode the phase of the extreme pixel intensity (as low as 10 or saturated at 255), but require no more hardware or additional work. The theoretical, simulation and experimental studies verify that the MFPS algorithm is robust and effective in measuring the over-dark and over-bright object.

Electron microscopy determination of crystallographic polarity of aluminum nitride thin films

Aluminum nitride (AlN) crystallizes usually in the wurtzite structure (P63mc) and it has a crystallographic polarity. In this work, the polarity in AlN was characterized by using several methods of transmission electron microscopy (TEM) in order to examine their applicability. AlN was deposited by metalorganic vapor phase epitaxy (MOVPE), followed by annealing at 1550 °C. TEM samples were prepared by using a focused ion beam (FIB) mill. Observation was performed with microscopes of JEM-2100, JEM-ARM200 F and FEI Titan Cubed G2 at Kyushu University (Japan), and the following results were obtained. (1) Conventional TEM imaging: Under a diffraction condition with hkil = 0002, inversion domains or an inversion domain boundary (IDB) was observed. (2) Scanning TEM (STEM) High-Angle Annular Dark Field (HAADF) imaging: Even when atomic column images of Al and N are not resolved completely from each other, the polarity was determined from the shape of atomic column images. (3) Scanning moire fringe imaging: The moire fringe pattern indicated the position of IDB and determine the direction of polarity. (4) Convergent beam electron diffraction (CBED): CBED was applicable for determination of the polarity in AlN at the acceleration voltage of 120 kV. Hence the polarity, direction of polarity and inversion domain boundary was determined using advanced TEM methods.

Single shot multiple phase retrieval in digital holographic interferometry using subspace processing

The article presents a method to estimate multiple phases from a single moire fringe pattern in digital holographic interferometry. The proposed method relies on analysing the holographic moire signal using subspace rotational invariance approach and offers feasibility for single shot multi-component estimation without multiple frames or spatial carrier and high performance against severe noise. Simulation and experimental results demonstrate the applicability of the proposed method.

Demodulation of moire fringes in digital holographic interferometry using an extended Kalman filter.

This paper presents a method for extracting multiple phases from a single moire fringe pattern in digital holographic interferometry. The method relies on component separation using singular value decomposition and an extended Kalman filter for demodulating the moire fringes. The Kalman filter is applied by modeling the interference field locally as a multi-component polynomial phase signal and extracting the associated multiple polynomial coefficients using the state space approach. In addition to phase, the corresponding multiple phase derivatives can be simultaneously extracted using the proposed method. The applicability of the proposed method is demonstrated using simulation and experimental results.

Short-time Fourier transform method for online glass ream inspection

In the float glass defect inspection system based on machine vision, the common defects can be detected and classified correctly. However, the online glass ream inspection is still a problem to be solved, and the accuracy cannot fulfill the requirement of glass grading. As the glass ream is a rather slight optical distortion in most cases, it should be amplified so that it can be checked out easily. A Moire method based on the theory of superposition shadow is proposed, which can magnify the distortion effectively without increasing the system complexity, and a STFT method is presented to analyze the distortion according to the characteristics of Moire fringe pattern. With this method, the vision interference angle of glass ribbon can be calculated out accurately in real time, which makes it suitable for online glass ream inspection.

Finite element analysis of two total knee joint prostheses

Aim of this work is to compare two different total knee prostheses that differ mainly in the shape of the polyethylene (PE) component inserted between the femoral and tibial plates. The best solution between them has been originally reshaped in order to reduce stress peaks. The study procedure has been divided into the following steps. First step is the digitalisation of the shape of the prostheses by means of a 3D laser scanner. The morphology of two prototypes of the prostheses has been acquired by elaborating multiple Moire fringe patterns projected on their surfaces. Second step consisted on the manipulation of these data in a CAD module, that is the interpolation of raw data into NURBS surfaces, reducing singularities due to the typical scattering of the acquiring system. Third step has been the setting up of FEM simulations to evaluate the prostheses behaviour under benchmark loading conditions given in literature. The CAD model of the prostheses has been meshed into solid finite elements. Different flexion angles configurations have been analysed, the load being applied along the femoral axis. FEM analyses have returned stress fields in the PE insert and, in particular, in the stabilizing cam which function is to avoid dislocation. Last step has been the integrated use of CAD and FEM to modify the shape of the stabilizing cam of the best prosthesis, in order to reduce the stress peaks in the original prosthesis without affecting kinematics of the joint. Good results have been obtained both in terms of stress and contact pressure peaks reduction.

Displacement and Strain Distribution Measurement by Sampling Moire Method

Moire method is a useful method to measure deformation and strain distribution of structures. Moire fringe patterns are analyzed quantitatively and speedy by image processing using a computer. In this paper, the theory of moire method and sampling moire method is introduced. Since the sampling moire method is useful to analyze phases of a moire fringe and a grating from one image of a grating pattern, it is possible to analyze dynamic deformation accurately. Some applications of the sampling moire method to displacement measurement of a beam, and shape and strain measurement of a rubber structure are shown.

A Versatile Cell Contractility Mapping Transducer Utilizing Moiré-Based Technique

The mapping of contraction forces developed from cells to their extracellular matrix is crucial to understanding how cells regulate their physiological function to adapt to their living environment and cellular processes. This paper reports a novel cell contractility mapping transducer utilizing moire patterns as a visual and quantitative tool. Coherent light diffracted from two closely placed microfabricated periodic substrates is capable of mapping cell contraction forces via mapping the in-plane displacement on the sample substrate. By integrating cell culture environment and automated Fourier-based fringe analysis, the moire pattern generated through microfabricated periodic substrates enables the mapping of cell contraction force distribution through phase changes encoded in carrier moire fringe patterns. We demonstrated utilizing the transducer to map cardiac myocyte contraction under electric stimulation and vascular smooth muscle cell contractility evolutions triggered by agonist. Given the unique properties of optical moire techniques (i.e., their automatic displacement and strain contouring and their magnification effect for small displacements), this new approach would be an improvement over existing techniques since it can be integrated with the existing engineered substrates and provide a direct contour of cell forces and fast detection of abnormal cell contractions.

2-D crack growth measurement using circular grating moiré fringes and pattern matching

A two-dimensional (2-D) crack growth measurement method that uses moire fringes generated by circular gratings and pattern matching was developed in this work for application in structural health monitoring. The moire fringe patterns were extracted by transforming the circular gratings into linear gratings using polar-radius transformation and applying a one-dimensional average filter. The filtered image was inversely transformed to recover the moire fringes. Pattern matching was performed by comparing the absolute difference between an input fringe pattern caused by an unknown displacement and a series of reference fringe patterns of known displacements in one direction. The matching of the moire fringes caused by displacement at 90° to that in the reference patterns and combination of the two orthogonal directions was carried out after applying a rotational angle search algorithm. Demonstration using a crack model showed the applicability of the proposed system for the measurement of relative displacement of crack development along two directions with a sensitivity of 0.02 mm. The measured displacements were found to have high correlation with the actual displacements with a R2 value of 0.9985. Copyright © 2010 John Wiley & Sons, Ltd.

X-ray phase imaging of a packaged IC chip using X-ray array source

We have developed a novel configuration of an X-ray grating interferometer for the phase imaging of a packaged IC chip. A square source grating is used, and a beam splitter and an analyzer grating are positioned downstream of the investigated sample. In the proposed method, the period of source grating is smaller than the last of two gratings, the configuration of which could be implemented for phase imaging. Phase images retrieved using the principle of in-line phase contrast imaging and phase detection are the phase stepping method used in the X-ray grating interferometer. The wrapped phase images of the packaged IC chip are obtained from nine Moire fringe patterns, using an exposure time of 34ms for each scan.

Shrinkage Measurement in Concrete Materials using Cure Reference Method

This paper describes the details of using Cure Reference Method (CRM) to determine the shrinkage that develops in concrete materials. The technique involves the replication of diffraction grating on the concrete specimen during curing. After demolded, the specimen is stored in a chamber where a specific drying condition is maintained for 6 days. Every day in this period, the specimen is removed from the chamber and a set of the consecutive moire fringe patterns are recorded with the help of a specially-designed stage. An automated fringe analysis program is developed to obtain the full-field displacement and strain information. Shrinkage as a function of location, time, and drying conditions is measured. A numerical method is developed in order to obtain material properties from the complex geometry used in the tests. The test in different drying condition and the ring test are performed, and their results are compared with FEA to validate the constructed model.

Alignment measurement method for imprint lithography using moiré fringe pattern

A simple and high-accuracy alignment measurement method based on a moire fringe pattern is proposed. It involves relative rotation positioning and relative linear displacement measurement. Taking full advantage of the magnification effect of moire fringe in angular and linear displacement, the relative rotation between the template and the wafer is determined first by measuring the inclination of the moire fringe, and then the relative linear displacement between them is acquired by evaluating the spatial phase shift of two matched moire fringes. The frequency components in the orthogonal directions of the fringe image obtained by a fast Fourier transform (FFT) and zooming process are used to measure the inclination of the moire fringe. By selecting different orthogonal directions, a moire fringe with any inclination can be measured accurately. When gratings are adjusted to parallel, a frequency-domain analysis is also used to extract the spatial phase of fringes at a given frequency. According to the relationship between spatial phase and linear displacement, the misalignment is detected. In experiments, the repeatability for the misalignment measurement has reached 4.8 nm (3).

An electron moiré method for a common SEM

In the electron moire method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moire fringe pattern for the scanning electron microscope (SEM). Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moire method is limited. In this study, an electron moire method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moire pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moire method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moire patterns can also be correctly generated.

Fourier and wavelet transform analysis of moire fringe patterns in electronic packaging

In this paper, two transform methods, the Fourier transform (FT) and the wavelet transform (WT) methods, are utilized to process moiré fringes for the strain analysis of electronic packaging. With the introduction of fringe carriers, those transform techniques need only one fringe pattern for each deformation state. The strain modulation to the carrier frequency can be subtracted by filtering as the pattern is transformed into spectrum domain by the fast‐FT processing, and the deformation field can thus be restored by the inverse FT transform after spectral shifting. The WT method expands the pattern information involved in the fringe carrier in both spatial domain and spectral domain to analyze the deformation distribution in this combined space. By changing the transform scales in the processing, the wavelet transform offers multi‐resolution analysis for the deformation field with high gradients.

Nanometre moire fringes in scanning tunnelling microscopy of surface lattices

A novel class of moire fringe patterns in scanning tunnelling microscope (STM) imaging ispresented and analysed in this paper. The moire fringe is generated from the interference ofthe atomic lattice of the specimen and STM scanning lines. Both parallel and rotationalSTM moire fringes of the surface of highly oriented pyrolytic graphite (HOPG) areinvestigated. The formation principle and experimental techniques of STM moire fringesare discussed. Nanometre scale resolution and sensitivity are found in the moire fringepatterns. They precisely magnify the STM image of lattice irregularities. A potentialapplication—measuring surface deformation and defects in the nanometre range—isproposed.

무아레 간섭계를 이용한 WB-PBGA 패키지의 온도변화 및 굽힘하중에 대한 거동해석

Thermo-mechanical and flexural behavior of a wire-bond plastic ball grid array (WB-PBGA) package are characterized by high sensitive moire interferometry. Moire fringe patterns are recorded and analyzed Cor several bending loads and temperatures. At the temperature higher than 100℃, the inelastic deformation in solder balls become more dominant, so that the bending of the molding compound decreases while temperature increases. The deformation caused by thermally induced bending is compared with that caused by mechanical bending. The strain results show that the solder ball located at the edge of the chip has largest shear strain by the thermal load while the maximum average shear strain by the bending moment occurs in the end solder.