Interference Fringe Pattern Research Articles

Investigation of Stress State in Plane Truss Nodes

Stress state in a plane truss node was studied in two ways: numerically using the finite element method and experimentally using the photoelasticity method. The finite element method was used to calculate plane truss model. Photoelasticityor polarization-optical method was used to research stresses of piezo-optical materials. The picture of interference fringe patterns in the model of a plane truss was obtained by the method of photoelasticity. Stresses were calculated with their help. The purpose of the work was to compare both methods. Fields of maximum tangent stresses were obtained in the sample plane using both methods. This work is a continuation of [1]. So, we obtained picture of interference fringe patterns and isocline fields in the node of the farm model, using the photoelasticity method. The field of maximum tangent stresses in the truss node was obtained by the photoelasticity method. The stress fields in the truss node were obtained by the finite element method in the software package “SCAD”. A comparative analysis of the numerical and physical experiments results was carried out and it was found that the nature of the stress distribution in both numerical and physical experiments coincides.

Study of stresses in plane truss nodes

in this paper, the stress state in a plane truss node was studied in two ways: numerically using the finite element method and experimentally using the photoelasticity method. The finite element method was used to calculate plane truss model. Photoelasticity or polarization-optical method was used to research stresses of piezo-optical materials. The picture of interference fringe patterns in the model of a planetruss was obtained by the method of photoelasticity. Stresses were calculated with their help. The purpose of the work was compared with both methods. Fields of maximum tangent stresses were obtained in the sample plane using both methods.

Evolution of the fracture mechanics parameters in the vicinity of the hole in conditions of low-cycle fatigue according to the data of modeling a crack with narrow notches

We propose a new method for studying the effect of low-cycle fatigue on the evolution of the fracture mechanics parameters in conditions of loading plane specimens with stress concentrators. Three programs of loading with a constant value of the stress range and different values of the stress ratio, as well as two programs with a constant value of the stress ratio but different stress ranges are considered. One program is common for both cases. All the programs include uniaxial tension-compression. Each program was implemented by testing a batch of the same specimens from seven to nine in each. One specimen from each batch was assigned to assess the durability. The other specimens were brought to various stages of low-cycle fatigue in each program. Experimental data were obtained for cracks of different length which were modeled by a sequence of three narrow notches launched from a through hole in a rectangular specimen. Each notch was exposed to constant external load of the same level. The deformation response to a small increment in the notch length at a constant external load was measured at different stages of low-cycle fatigue using electronic speckle pattern interferometry. The interference fringe patterns used as initial experimental data provided determination of the tangential components of in-plane displacements directly on the notch sides and the values of notch opening were thus determined from the results of direct measurements. The transition from measured displacement components to the values of the stress intensity factor and T-stress was performed using the relationships of a modified version of the crack compliance method based on Williams formulation. Distributions of the fracture mechanics parameters along the notches were obtained at various stages of cyclic loading. The dependences of the crack mouth opening displacement, the stress intensity factor and the T -stress on the number of loading cycles are constructed for the notches of a fixed length at different stages of low-cycle fatigue. It is shown that experimental distributions of the stress intensity factor values over the life time practically coincide for all four combinations of the loading cycle parameters.

Doppler coherence imaging of scrape-off-layer impurity flows in the HL-2A tokamak

A new Doppler coherence imaging spectroscopy interferometer has been developed on the HL-2A tokamak for the scrape-off-layer impurity flow measurement. Its spatial resolution is estimated to be up to ∼0.8 mm in the horizontal direction and ∼9 mm in the vertical direction, with a field of view of ∼34°. Its typical temporal resolution is about 1 ms. This salient feature allows for time-resolved 2D measurements in short-time phenomena on HL-2A, such as edge localized modes. Group delay and interference fringe pattern were calibrated with a dedicated calibration system. The robustness of group delay calibration and the feasibility of the extrapolation model for fringe pattern calibration are demonstrated. In this paper, we report the details of the optical instruments, calibration, and the initial experimental results of this Doppler coherence imaging spectroscopy interferometer.

Interrogation technique analyses of a hybrid fiber optic sensor based on SPR and MMI.

This study evaluates the interrogation techniques of a hybrid fiber optic sensor based on surface plasmon resonance (SPR) and multimode interference (MMI). The sensor is based on a single mode, fiber-no core, fiber-single mode fiber (SMF-NCF-SMF) structure with a deposited gold film layer. Both SPR and MMI effects are excited in a single sensor structure without enlarging the device size. However, at the same time, the interference fringe patterns are also mixed with the SPR transmission spectra, and the traditional SPR interrogation technique becomes unavailable since the resonant wavelength is hard to be located. In this study, the fast Fourier transform and different filtering algorithms are applied, both SPR signal and interference signal with different orders are separated effectively due to their different spatial frequency distributions, and they are processed individually for refractive index (RI) sensing. The experimental results verify that the overall RI sensitivity of the hybrid sensor is significantly enhanced. This study provides an important supplement to the traditional SPR and MMI functions.

Calibration method and uncertainty for the primordial inflation explorer (PIXIE)

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure cosmological signals from both linear polarization of the cosmic microwave background and spectral distortions from a perfect blackbody. The targeted measurement sensitivity is 2–4 orders of magnitude below competing astrophysical foregrounds, placing stringent requirements on instrument calibration. An on-board blackbody calibrator presents a polarizing Fourier transform spectrometer with a known signal to enable conversion of the sampled interference fringe patterns from telemetry units to physical units. We describe the instrumentation and operations needed to calibrate PIXIE, derive the expected uncertainty for the intensity, polarization, and frequency scales, and show the effect of calibration uncertainty in the derived cosmological signals. In-flight calibration is expected to be accurate to a few parts in 106 at frequencies dominated by the CMB, and a few parts in 104 at higher frequencies dominated by the diffuse dust foreground.

Ghost Mach–Zehnder interferometry for phase measurement with spatially incoherent light

We describe a phase-measuring interferometry based on classical ghost imaging with spatially incoherent light. The setup is constructed in such a way that a conventional Mach–Zehnder (MZ) interferometer is incorporated into the test arm of a standard classical ghost imaging setup. This technique may thus be referred to as ghost MZ interferometry. It is shown theoretically that the correlation between intensity fluctuations at two detectors gives an interference fringe pattern specifying the phase of the object. The features of the interference fringe pattern vary, depending on the type of the detector in the test arm and the quantities characterizing the imperfection of the setup. As a consequence, we demonstrate that correct phase imaging is possible with this technique even when the setup has a certain imperfection. The conditions for which the proposed ghost MZ interferometry works properly are addressed.

Temperature Field Measurement in a Cutting Tool by Laser Interferometry

To increase machining efficiency, in addition to determining the temperature distribution on the tool surface, it is also necessary to determine the internal temperature distribution. The existing methods for determining the cutting tool temperature distribution and temperature field measurement have significant disadvantages, which limit their applicability and accuracy. The purpose of this study is to develop and test a novel cutting tool temperature field measurement method. The method involves recording the cutting tool thermal expansion fields by laser interferometry and calculating the tool material temperatures with its coefficient of thermal expansion (CTE). Compared with the methods employing infrared thermometry, the method developed in the present study has a higher spatial resolution and a lower achievable field of view due to its usage of light in the visible region. In addition, since the oxidation film has a higher reflection coefficient for visible light, the present method is less sensitive to the thin-film interference on an oxidized tool surface than those using infrared thermometry, eliminating the false shift of the measured temperature. Moreover, by utilizing cheaper optical components and equipment for interference fringe pattern registration, this method is more affordable. Unlike the emissivity coefficient in infrared thermometry, CTE is independent of changes in the surface quality and can be measured with high accuracy by modern dilatometry. Therefore, the developed method, which employs CTE to calculate the temperature, has a higher reliability. In the present study, the efficiency of this method is tested by the orthogonal turning of difficult-to-cut martensitic heat-treated steel with a cemented tungsten carbide tool. Through the experiment, the temperature distributions along the rake face and flank of the tool, as well as the temperature field inside the tool, were obtained. The results can improve the temperature field measurement in machining cutting tools.

Phase estimation of a 2D fringe pattern using a monogenic-based multiscale analysis.

In this paper, a multiscale monogenic analysis is applied to 2D interference fringe patterns. The monogenic signal was originally developed as a 2D generalization of the well-known analytic signal in the 1D case. The analytic and monogenic tools are both useful to extract phase information, which can then be directly linked with physical quantities. Previous studies have already shown the interest in the monogenic signal in the field of interferometry. This paper presents theoretical and numerical illustrations of the connection between the physical phase information and the phase estimated with the monogenic tool. More specifically, the ideal case of pure cosine waves is deeply studied, and then the complexity of the fringe patterns is progressively increased. One important weakness of the monogenic transform is its singularity at the null frequency, which makes the phase estimations of low-frequency fringes diverge. Moreover, the monogenic transform is originally designed for narrowband signals, and encounters difficulties when dealing with noised signals. These problems can be bypassed by performing a multiscale analysis based on the monogenic wavelet transform. Moreover, this paper proposes a simple strategy to combine the information extracted at different scales in order to get a better estimation of the phase. The numerical tests (synthetic and real signals) show how this approach provides a finer extraction of the geometrical structure of the fringe patterns.

Dual wavelength digital holographic imaging of layered structures

We present a dual wavelength digital holographic technique for three-dimensional microscopic imaging of layered structures, where layers are separated from one another by the axial distances exceeding the wavelength of imaging light. Our methodology not only provides the three-dimensional structure of each layer, but also allows the height differentiation of distinct layers. We have also implemented a technique suppressing low intensity signal when no reliable phase information can be extracted, based on the quality of the interference fringe pattern. We utilize a dual wavelength setup, where the combination of two overlapping interferometers enables simultaneous acquisition of two phase profiles. We demonstrate that this imaging modality is particularly well-suited for imaging of multilayered electrode structures embedded in glass.

Initial Results of Microwave Radiometric Imaging With Mirrored Aperture Synthesis

The concept, principle, and method of microwave radiometric imaging with mirrored aperture synthesis (MAS) were proposed by the Huazhong University of Science and Technology (HUST), Wuhan, China. MAS can achieve higher spatial resolution without extending the size of the antenna array. However, the MAS principle has not been sufficiently validated by practical experiments. To solve this problem, an innovative experiment system of MAS at the V-band (MAS-V) has been developed by HUST. Experiments on the interference fringe pattern, spatial resolution, as well as the imaging of an electric warmer and the absorbing material in the styrofoam box filled with liquid nitrogen are performed. The initial experimental results demonstrate that MAS can achieve higher spatial resolution with the same antenna array compared with the conventional AS. For MAS, the experimental results are consistent with theory and simulation results.

The effect of low-cycle fatigue parameters on damage accumulation near a hole

A new destructive method for the quantitative determination of damage accumulation in the stress concentration zone has been proposed and verified. Damage accumulation in the vicinity of the hole was created by means of preliminary low-cycle fatigue loading of specimens with holes. After that, consecutive narrow notches, emanating from the hole, are performed under the constant external load for each specimen to estimate the effect of damage accumulation on fracture mechanics parameters. A measurement of deformation response, caused by local material removing in the form of a notch, is carried out by electronic speckle-pattern interferometry (ESPI). In this case, the initial experimental data has a form of interference fringe patterns, which are essential for deriving of in-plane displacement components in the vicinity of the notch. The transition from in-plane displacement components to values of the stress intensity factor (SIF) and the T-stress follows from the relationships of modified version of the crack compliance method. The curves of the crack mouth opening displacement, the stress intensity factor and the T-stress versus of notch length and number of cycles for notches emanating from open holes at different stages of low-cycle fatigue are constructed to analyse the effect of the stress range and the stress ratio on fatigue damage accumulation. The damage accumulation function is expressed in an explicit form on a base of distributions of the normalized stress intensity factor as a function of the number of cycles.

A Neural Network for Denoising Fringe Patterns with Nonuniformly Illuminating Background Noise

There are many interference fringe patterns with nonuniformly illuminating background noise. Nonuniformly illuminating background noise may arise from diverse sources, such as scratches, small interfering concentric circles, gaussian noise, etc. with a nonuniform light source. In this work, we propose a practical fringe pattern denoising method using a simple neural network. However, nonuniform illumination prevents us from comparing the denoised images with the ground truths. The verification of the proposed method is shown indirectly using the uniformized results obtained from a nonuniform illumination correcting process.

Automated classification of dry eye type analyzing interference fringe color images of tear film using machine learning techniques

The unstable balance in secretions of lipids and aqueous fluid to tear film is a significant cause of dry eye disease (DED). Arita et al. demonstrated a simple but very effective method that classifies dry eye types to the aqueous deficient dry eye (ADDE) and the evaporative dry eye (EDE) by focusing on the dry eye type-unique appearances of interference fringe colors and patterns of tear films. We thought this simple classification is very helpful for diagnoses and treatments. However, diagnostic bias by unskilled observers remains an issue to be solved.
 The artificial intelligence (AI)-based support for diagnosis is one of the hottest topics in the field of ophthalmology research. We expected that the AI-based model would reduce bias in DED-type diagnoses. Many studies have been reported targeting retinal diseases like age-related macular degeneration and/or diabetic retinopathy. Most of the works established AI-based predicting models using images taken by fundus cameras and/or optical coherence tomography (OCT) devices to capture disease-related structural disorders. In contrast, the interference fringes dynamically change the colors and patterns spatiotemporally. To the best of our knowledge, there is no AI-based model studied for distinguishing ADDE and EDE using interference fringe images. However, an AI-based study classifying the condition of the tear lipid layer by analyzing the textures of interference fringes compared to the device-unique grades has been reported. This suggested the possibility of using the unstructured characteristics, such as colors and/or complexities of interference fringes, as the numerical image features when building AI-based prediction models. In this study, we first examined several types of image characteristics extracted from the colors and patterns of fringes to obtain effective image features for the DED-type classification. We then evaluated whether the AI-based models would have sufficient abilities for this type of prediction by comparing their diagnoses with those made by an ophthalmologist skilled in this classification (the founder of this type classification).

Commercial polycarbonate track-etched membranes as substrates for low-cost optical sensors

Porous materials have become one of the best options for the development of optical sensors, since they maximize the interaction between the optical field and the target substances, which boosts the sensitivity. In this work, we propose the use of a readily available mesoporous material for the development of such sensors: commercial polycarbonate track-etched membranes. In order to demonstrate their utility for this purpose, we firstly characterized their optical response in the near-infrared range. This response is an interference fringe pattern, characteristic of a Fabry–Pérot interferometer, which is an optical device typically used for sensing purposes. Afterwards, several refractive index sensing experiments were performed by placing different concentrations of ethanol solution on the polycarbonate track-etched membranes. As a result, a sensitivity value of around 56 nm/RIU was obtained and the reusability of the substrate was demonstrated. These results pave the way for the development of optical porous sensors with such easily available mesoporous material.

Under-Sampled Phase Retrieval of Single Interference Fringe Based on Hilbert Transform

Phase retrieval from single interference fringe is important and effective method in obtaining the real phase distribution. The original phase can be retrieved by the line integral of its gradient expressed as sine and cosine components, which were gained by the Hilbert transform twice from a single interference fringe pattern. However, this method fails when the phase transformation of the interference fringe is too fast. In this paper, a novel method to recover the continuous phase of the whole field is proposed to solve the above problems. The shear interference technique is introduced into the phase retrieval method to build an exponential 2-D complex light field of natural base for the phase slope obtained by the Hilbert transform. Then, the expressions of phase slopes in x- and y-directions are constructed as a discrete Poisson equation. Therefore, the calculation of phase retrieval is equivalent to solve the discrete Poisson equation mathematically. Finally, the real phase is gotten by the weighted discrete cosine transform (WDCT) of the discrete Poisson equation. The simulation results verify the validity of this method and show that the proposed method can achieve the phase retrieval of the phase discontinuity in x- and y-directions, which leads to the under-sampled problem. It can restore the whole field phase distribution rapidly and accurately. Moreover, this method is applied to phase retrieval of interferometric synthetic aperture radar (InSAR) with the under-sampled problem in this paper. The experimental results show that this method can recover the phase of InSAR with the under-sampled problems caused by terrain abrupt change and so on. Compared with other commonly used methods, it achieved satisfactory results. This method provides a new idea for solving the under-sampled problem in the phase retrieval from a single-frame interference fringe.

Absolute interferometric angle measurement

A new method of absolute angle measurement based on analysis of interference fringe patterns is proposed. This approach is a bridge between interferometry, offering high accuracy, and other methods that are using position sensors or amplitude effects, which can give information about absolute value of angle. Utilisation of quadrature signals makes it possible to achieve better stability, with comparison to some other methods, thanks to reduced influence of thermal expandability. Usage of special signal processing algorithms facilitates wide measurement range and high resolution. Simulations and experiments show the possibility of achieving the range of 1 deg with arc-sec accuracy. Using commercially available optical and electronic components makes it possible to create lightweight, battery operated device that could be applied in CNC machine alignment process.

Residual stress determination by optical interferometric measurements of hole diameter increments

The main questions, related to the residual stresses determination in thin welded plates by the general approach, are considered. The values of hole diameter increments in principal stress directions, obtained by both reflection hologram interferometry and electronic speckle-pattern interferometry, serve as the initial experimental information. The analytical basis shows that the formulae, which connect experimental data with residual stress components, represent unequivocally solution of the properly posed inverse problem. Simultaneous measurements of the local deformation response on the opposite faces of thin-walled object under study, when a single probe hole is drilled, is the essential condition of the general approach implementing. To do this, an optical system of combined interferometer is developed. The main feature of this optical set-up resides in a capability of simultaneous recording fringe patterns inherent in electronic speckle-pattern interferometry (ESPI) and reflection hologram interferometry on opposite specimen faces for the same through hole. The accuracy of the proposed method with respect to the residual stress components determination has been assessed by three different ways. It is shown that ESPI based interference fringe patterns of high density provides a fast and reliable way of determining residual stress values of the order 160–180 MPa at the weld seam proximity. Residual stress evolution due to cyclic loading is described through the use of ESPI data.

Interference method for mosaicking echelles using double-angle incident light and a mirror-echelle structure

A method of eliminating echelle mosaicking errors using a single-interferometer system combined with a mirror-echelle structure and double-angle incident light is proposed. Coplanar and in-plane mosaicking errors are, respectively, removed using interference fringes at zero order and diffraction order, and double-angle incidence light is exploited to erase the longitudinal offset. Two mirror-echelle structures, both with aluminum reserved for a mirror on the echelle plane to receive the double-angle incident light, are designed. The relationship between mosaicking error and the optical path difference is established. The evolution of the interference fringe pattern of mosaicking process is simulated, and a mosaicking experiment is then conducted following the simulation.

Transparent conducting properties of Mg and Al co-doped ZnO thin films deposited by spray pyrolysis technique

The oxides and their interplay with metals are of central importance in solar energy, solar cells and environmental as well as in technological applications. Doping of Mg and Al into ZnO offers an interesting way to alter various electronic, optical and structural properties. In this work, Mg doped (Zn0.98Al0.02O) films with different Mg concentrations (0, 1, 2, 4 and 6%) were grown by spray pyrolysis technique and characterized by X-ray diffraction (XRD), UV/VIS optical transmission spectroscopy and electrical measurement. XRD analysis of all samples indicates the presence of hexagonal crystal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate and the absence of any other secondary phase. All samples exhibited interference fringe patterns in the visible region of transmittance spectra with an average transmission of >60% indicating a good optical quality of the deposited films. The optical studies demonstrate also that Mg-doping induces an increase of the band gap energy. The dark electrical resistivity decreases with increasing Mg doping amount due to the increase of the grain size and the low electronegativity of Mg2+ than Zn2+.