Optical Measurement Method Research Articles

Luminescence performance of Dy3+ ions incorporated modifier reliant boro-tellurite glasses for white light applications

A diverse array/unique set of Dysprosium (Dy3+) activated alkali boro-tellurite glasses were synthesized for the current study using the conventional approach of glass fabrication, and its potential for photonic applications were explored utilizing optical absorption, emission, and decay measurement methods. In the interest of assessing the Rare Earth (RE) ions bonding behavior with the neighboring metal ligand site, and to establish the glasses ionic/covalence nature, bonding parameters (δ) and Nephelauxetic ratios were computed from the absorption band locations. For the as-prepared samples, the Judd-Ofelt parameters and oscillator strengths were determined in order to scrutinize the uniformity of the ligands surrounding Dy3+ ions. The calculated JO values consistently pursue Ω2 > Ω4 > Ω6 pattern for all samples, indicating their asymptotic character. When excited at 387 nm, the emission spectra demonstrate three intense transitions; 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2. Among them, strong yellow emission was observed owing to the increased transfer of electrons to 6H13/2 level. Besides, using JO parameters, radiative parameters were determined which was followed by lifetime studies to actualize the novel applications. The photoluminescence spectra were employed to estimate the CIE coordinates (x, y) and Yellow/Blue ratio, furthermore the (x, y) values were used to calculate the colour purity followed by colour correlated temperature (CCT). This demonstrates that the prepared samples have the ability to emit neutral white light.

A High-Precision Multi-Beam Optical Measurement Method for Cylindrical Surface Profile.

To automatically measure the surface profile of a cylindrical workpiece, a high-precision multi-beam optical method is proposed in this paper. First, some successive images for the cylindrical workpiece's surface are acquired by a multi-beam angle sensor under different light directions. Then, the light directions are estimated based on the feature regions in the images to calculate surface normal vectors. Finally, according to the relationship of the surface normal vector and the vertical section of the workpiece's surface, a depth map is reconstructed to achieve the curvature surface, which can be employed to measure the curvature radius of the cylindrical workpiece's surface. Experimental results indicate that the proposed measurement method can achieve good measurement precision with a mean error of the curvature radius of a workpiece's surface of 0.89% at a reasonable speed of 10.226 s, which is superior to some existing methods.

Deep Feature Interaction Network for Point Cloud Registration, With Applications to Optical Measurement of Blade Profiles

Optical measurement methods for blade profiles attract lots of interest in industry. Due to the nature of the thin-walled and twisted spatial freeform surfaces of blades, the measurement accuracy would be significantly affected by the accumulated error associated with the geometric accuracy and motion stability of the developed multi-view system. To overcome these issues, this paper proposes a deep feature interaction network (DFINet) for fine registration of the multi-view data. In our network, we design a two-branch structure to integrate a global and a local feature extraction branch to encode point cloud features. Moreover, we propose a feature interaction module to strengthen information association between two point clouds during feature extraction. Next, an attention mechanism is used to fuse matching information between two matching matrices obtained from the global-based and the local-based features. Experimental results demonstrate the feasibility and good practical application prospect of this method.

Influence of Environment Conditions on Ultrasonic and Electrostatic Precipitation of Aerosols of Wood Flour

The risk of human exposure to finely-dispersed aerosol particles being airborne indoors is determined by the size and the number concentration of particles, the intensity of an aerosol emission source, the air filtration and ventilation efficiency, etc. The emphasis in this article is on behaviour patterns of aerosol particles when exposed to ultrasonic and electrostatic fields in different conditions of air temperature and relative humidity. Wood flour having sizes of interest (characteristic particle diameter about 10 μm) is chosen as a model aerosol. The article considers a physical and mathematical model presenting the evolution of aerosol particles in external fields, taking into account the moisture content and the temperature of a dispersive medium. The efficiency of ultrasonic and electrostatic precipitation in different relative humidity and temperature conditions in an enclosed space was studied using optical measurement methods of particle size and concentration.

Dual-ratio approach for detection of point fluorophores in biological tissue.

Diffuse in vivo flow cytometry (DiFC) is an emerging fluorescence sensing method to non-invasively detect labeled circulating cells in vivo. However, due to signal-to-noise ratio (SNR) constraints largely attributed to background tissue autofluorescence (AF), DiFC's measurement depth is limited. The dual ratio (DR)/dual slope is an optical measurement method that aims to suppress noise and enhance SNR to deep tissue regions. We aim to investigate the combination of DR and near-infrared (NIR) DiFC to improve circulating cells' maximum detectable depth and SNR. Phantom experiments were used to estimate the key parameters in a diffuse fluorescence excitation and emission model. This model and parameters were implemented in Monte Carlo to simulate DR DiFC while varying noise and AF parameters to identify the advantages and limitations of the proposed technique. Two key factors must be true to give DR DiFC an advantage over traditional DiFC: first, the fraction of noise that DR methods cannot cancel cannot be above the order of 10% for acceptable SNR. Second, DR DiFC has an advantage, in terms of SNR, if the distribution of tissue AF contributors is surface-weighted. DR cancelable noise may be designed (e.g., through the use of source multiplexing), and indications point to the AF contributors' distribution being truly surface-weighted in vivo. Successful and worthwhile implementation of DR DiFC depends on these considerations, but results point to DR DiFC having possible advantages over traditional DiFC.

A velocity decomposition-based 3D optical flow method for accurate Tomo-PIV measurement

A velocity decomposition-based 3D optical flow method for accurate Tomo-PIV measurement

Quantitative Determination of Surface Morphology of Red Blood Cell

In this study, the determination of the surface morphology of red blood cell (RBC) from interferogram image obtained by quantitative phase imaging (QPI) method is presented. QPI, is an optical measurement method frequently used in recent years, allows to obtain quantitative data for different samples (cell, thin film surface, etc.). Many measurement setups at the micrometer level and with nanometer precision have been designed for quantitative surface determination. Among these, white light diffraction phase microscopy (WDPM) is a design that combines the advantages of off-axis holography-specific speed and phase sensitivity associated with common path interferometry. Interferogram image of RBCs have been formed by the WDPM setup. Analysis of this image has been carried out by Fourier transform. As a result of this analysis, three-dimensional (3D), dynamic (observable from all angles) and height-known profiles of RBCs have been created. From the height profiles, the parameters related to the morphology of RBCs as the projected surface area (PSA), diameter (D), mean corpuscular volume (MCV) and total surface area occupied by the cell (SA), have been determined quantitatively. In addition, two-dimensional images, obtained by examining blood samples with light microscopy and scanning electron microscopy (SEM), have been compared with the data achieved by WDPM. The advantages and disadvantages of WDPM and light microscopy and SEM, which are commonly used in biomedical measurements, are discussed through the results. In this way, it was possible to see the difference between QPI and traditional methods used to imaging the cell surface.

Optical performance measurement methods for whole slide imaging devices employing a Bayer color imager

Whole slide imaging (WSI) is a widely used digitalization technique to record microscopic images of a whole-stained tissue sample on a glass slide. The US Food and Drug Administration (FDA) provides guidelines for methods used to evaluate various WSI devices. However, the designated evaluation methods for guidance are not always optimal. To this end, novel inspection methods are proposed, which fulfill the requirements of FDA guidance, and then deployed to evaluate the measurement accuracy of our laboratory-built WSI device that employs a 2D Bayer imager. The proposed methods demonstrably evaluate distortion, chromatic aberration, and field curvature with the required precision.

Acoustic Roughness Measurement of Railway Tracks: Running Surface Detection and Compensation of Lateral Movements for Optical Measurements on a Train.

Rolling noise is a significant contributor to railway noise. Wheel and rail roughness are decisive for the emitted noise level. An optical measurement method installed on a moving train is suitable for closer monitoring of the rail surface condition. A measurement setup based on the chord method requires the sensors to be positioned in a straight line along the direction of measurement and in a stable lateral position. Measurements should always be performed within the shiny and uncorroded running surface, even when there are lateral movements of the train. In this study, concepts for the detection of the running surface and the compensation of lateral movements are investigated in a laboratory setting. The setup consists of a vertical lathe with a ring-shaped workpiece that incorporates an implemented artificial running surface. The detection of the running surface based on laser triangulation sensors and a laser profilometer is investigated. It is shown that the running surface can be detected using a laser profilometer that measures the intensity of the reflected laser light. It is possible to detect the lateral position and the width of the running surface. A linear positioning system is proposed to adjust the lateral position of the sensors based on the running surface detection of the laser profilometer. When the lateral position of the measuring sensor is disturbed by a movement with a wavelength of 18.85 m, the linear positioning system can keep the laser triangulation sensor inside the running surface for 98.44% of the measured data points at a velocity of approximately 7.5 km h-1. The mean positioning error is 1.40 mm. By implementing the proposed system on the train, future studies can be conducted to examine the lateral position of the running surface as a function of the various operational parameters of the train.

Illumination spot profile correction in digital holographic microscopy for overlay metrology

BackgroundPrecise, accurate, and fast overlay (OV) metrology is an important step in semiconductor device manufacturing. With the increasing demand for better OV over a larger range of different process layers, the optics used in OV metrology tools become more complex, bulky, and expensive. OV, which is to be measured with sub-nanometer precision, is susceptible to many small imperfections in the measurement system.AimWe present a dark-field digital holographic microscope (DHM) that measures the complex field of the OV targets using simple optics, followed by computational algorithms to correct for hardware imperfections. With the setup, we aim to correct the effects of the absolute intensity of the illumination beam as well as the spatial profile.ApproachThe spatial profiles of two oblique illumination beams for diffraction based OV metrology are calibrated using large gratings as calibration targets using DHM, and thereafter OV target images are corrected by the calibrated illumination spot profiles.ResultsOVs are calculated for test targets with known OV values, and illumination spot correction removes errors originating from intensity imbalance and intensity variation.ConclusionWe present an optical OV measurement method that is more robust against non-uniform illumination beams using simple calibration steps.

Double Optical Fiber Temperature Compensation Method for Measurement of Interface Pressure Between Simulated Cable and Accessory at High Temperatures

Reliable interface pressure between cables and accessories is closely associated with the safe operation of a power cable system. Using an external optical fiber Bragg grating temperature-compensating curvature sensor, a new method for online measurement of the interface pressure between a cable and an accessory at high temperatures is proposed. On the basis of the sensing principle of a fiber Bragg grating, a mathematical pure bending model, and a model of a thick-walled cylinder, a fiber Bragg grating temperature-compensating curvature sensor is fabricated using Dow Corning Sylgard-184 silicone rubber. The interface pressures of 10 kV cable accessories with different expansion rates at different temperatures are measured. The results of the measurements show that the temperature-compensated deviation of wavelength measurements made by the fiber grating curvature sensor ranges from -2.59% to 5.50%. The interface pressure between the cable and the accessory gradually increases with an increase in temperature from 30 to 60 °C. The results are consistent with the results of measurements made using a traditional piezoelectric sensor. This method is expected to evaluate the long-term reliability of the interface pressure of cable accessories in actual complex-temperature environments.

Temperature tracing test and numerical simulation study during leakage of earth-rock dam

The leakage of earth rock dams exhibits characteristics of space-time randomness, concealment, and significant destructiveness. Prompt detection and identification of dam leakage are critical to ensuring the structural safety of these constructions. The distributed optical fiber temperature measurement method, which is based on optical frequency domain reflection (OFDR) technology, possesses attributes such as high spatial resolution, minimal temperature error, short response time, and real-time monitoring. As a result, it is an ideal technique for experimental research on leakage monitoring of earth rock dams. In this study, a model test was conducted on a clay core rockfill dam to investigate the feasibility of utilizing distributed optical fiber for identifying dam leakage. The variation pattern of partial distributed optical fiber temperature measurements in the dam body under the leakage state was compared and analyzed using the gradient method and the thermal pulse method. Furthermore, the heat flow coupled numerical simulation method was employed to verify and expand the findings of the indoor tests. The results of this study indicate that the OFDR distributed optical fiber leakage monitoring method using the thermal pulse approach can entirely reflect the temperature changes that occur during leakage, thereby providing strong reliability and exhibiting considerable potential for leakage location. The study offers valuable insights and a reference for the practical use of distributed optical fiber to monitor earth rock dam leakage.

Recent Progress of Optical Imaging Approaches for Noncontact Physiological Signal Measurement: A Review

In recent years, optical imaging techniques have gained wide recognition for the measurement of vital signals, such as heart rate, respiratory rate, oxygen saturation, and blood pressure, which are crucial indicators for evaluating human health conditions in clinical examinations. There is a wide range of optical imaging methods for remote physiological signal monitoring, including RGB imaging, thermal imaging, hyperspectral imaging, depth imaging, and multimodal imaging, which provide spatial information compared to other noncontact measurement approaches, thereby allowing extensive applications in this area. In this survey, some fundamental knowledge about optical imaging methods for vital signal measurement is reviewed, including principles of various optical imaging techniques, processing methods for data analysis, discussion on advantages and disadvantages, application summary, and future prospects. This is a comprehensive overview of the noncontact physiological signal measurement of optical imaging approaches.

Optimizing a two-layer method for hybrid diffuse correlation spectroscopy and frequency-domain diffuse optical spectroscopy cerebral measurements in adults.

The sensitivity to extracerebral tissues is a well-known confounder of diffuse optics. Two-layer (2L) head models can separate cerebral signals from extracerebral artifacts, but they also carry the risk of crosstalk between fitting parameters. We aim to implement a constrained 2L head model for hybrid diffuse correlation spectroscopy (DCS) and frequency-domain diffuse optical spectroscopy (FD-DOS) data and to characterize errors in cerebral blood flow and tissue absorption with the proposed model. The algorithm uses the analytical solution of a 2L cylinder and an a priori extracerebral layer thickness to fit multidistance FD-DOS (0.8 to 4cm) and DCS (0.8 and 2.5cm) data, assuming homogeneous tissue reduced scattering. We characterized the algorithm's accuracy for simulated data with noise generated using a 2L slab and realistic adult head geometries and for in vitro phantom data. Our algorithm recovered the cerebral flow index with 6.3 [2.8, 13.2]% and 34 [30, 42]% (median absolute percent error [interquartile range]) for slab and head geometries, respectively. Corresponding errors in the cerebral absorption coefficient were 5.0 [3.0, 7.9]% and 4.6 [2.4, 7.2]% for the slab and head geometries and 8 [5, 12]% for our phantom experiment. Our results were minimally sensitive to second-layer scattering changes and were robust to cross-talk between fitting parameters. In adults, the constrained 2L algorithm promises to improve FD-DOS/DCS accuracy compared with the conventional semi-infinite approach.

Implementation of an Optical Measurement Method for Monitoring Mechanical Behaviour

There is a gap between mechanical measurement methods under laboratory conditions and those under real conditions of structural monitoring. This paper proposes a method that applies well-established computer vision developments to photomechanics in difficult conditions. It is therefore a technique that is flexible and versatile while maintaining satisfying accuracy. It consists in marker tracking using ArUco fiducial markers as measurement points. It allows locating markers in non-optimal conditions of camera orientation and position. A homography process was used to analyse pictures taken with a view angle. The accuracy of the method was estimated, especially in case of out-of-plane motions, and the impact of the view angle and of the distance between camera and markers on the location error was studied. The method was applied in creep tests to measure crack parameters as well as the transverse expansion of wooden beams. In the application example presented, it enabled to compute distances between markers with only 0.28% of relative error and hence to measure the crack parameters and the long-term shrinkage-swelling of the wooden beams. However, the impacts of brightness variations and camera parameters have not been estimated. This method is very promising when experimental conditions are variable and when multiple measurements are necessary.

Study on fracture characteristics of anchored sandstone with precast crack based on double K criterion

Fracture toughness is an important fracture mechanics parameter of rocks, the double K criterion can reasonably explain the fracture mechanism of rocks. To investigate the fracture mechanics behavior of the anchored rock with a pre-crack, three-point bending test was performed to analyze the mode I fracture process of the rock. A series of pre-cracked sandstone beams of the same size, strength, and different anchor parameters were tested. The evolution characteristics of deformation field and crack tip propagation during the entire fracture process were investigated using a non-contact optical measurement method, and rock fracture mechanics parameters corresponding to different anchoring conditions were obtained. The toughening mechanism of anchor bolt was discussed based on stress intensity factor theory. The double K criterion can be used to describe the fracture failure characteristics of rocks. By regarding the anchored rock as the composite material of bolt and rock, the anchoring composite fracture toughness can be obtained, and the stability of the anchored rock can be determined using the double K criterion. The toughening mechanism of the anchor bolt increases the threshold of crack initiation and instability of the entire anchored rock by increasing the stress intensity factor at the crack tip of the rock. The crack arrest mechanism of the bolt retards crack propagation via the transverse closing force. Investigating the anchoring effect of different anchoring parameters allows, the rock anchoring control mechanism to be revealed from the perspective of fracture mechanics, which can provide a reference for mining and tunnel engineering support.

Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

In the search of an adequate real time strain measurement method in aluminum casting, the use of Fiber-Bragg-Grating (FBG) is being investigated with great interest. In order to do so, the behaviour of glass fiber sensors in a liquid aluminium alloy at temperatures up to 750°C is experimentally analysed in a laboratory environment. For better process understanding a simulation of the fiber alloy composite is conducted. FBG is an optical measurement method, which uses engraved Bragg reflectors in a 125 µm in diameter thick glass fiber. This reflector transmits most of the wavelengths but only reflects one specific wavelength. This specific wavelength can be measured and changes due to the axial strain on the grating by the fluid alloy reaction and by the changes in temperature. Using a so-called mirror furnace, several experiments with the fiber alloy composite are evaluated. These measurements are also the basis for the further understanding of hot tearing. The data gathered during the measurement campaign - both numerical and experimental - is used to parameterize a simulation. As a result, the understanding of the fiber alloy composite behaviour is expanded and a digital twin is modeled with MATLAB’s partial differential equation toolbox.

Phytochemical Constituents Isolated From Distichochlamys citrea M.F. Newman Rhizomes and Their Antioxidant and α-glucosidase Inhibitory Activities

Objective/Background: Distichochlamys citrea M.F. Newman (Zingiberaceae) is an endemic plant of Vietnam and has been used as a folk medication for treatments of infection-related diseases, diabetes, and used as spice. This study aimed to characterize the antioxidant and α-glucosidase inhibitory activities of isolated compounds from D. citrea rhizomes. Methods: Compounds have been isolated from D. citrea rhizomes by different chromatographic techniques. Their chemical structures were determined based on mass spectrometry and nuclear magnetic resonance spectroscopy in comparison with those reported in the literature. The antioxidant effect was evaluated by 2,2-diphenyl-1-picrylhydrazyl-free radical neutralization whereas α-glucosidase inhibitory activity was determined by using the method of optical density measurement. Results: Seven compounds including 5-hydroxy-3,7,4'-trimethoxyflavone (1), kaempferol (2), platyphyllone (3), 5- O-caffeoylquinic acid (4), a mixture of phytosterols ( β-sitosterol (5) and stigmasterol (6)), and glycerol monostearate (7) were isolated and identified from D. citrea rhizomes. Compounds 1 and 2 simultaneously exhibited antioxidant activities (IC50 = 794.71 ± 2.68 µM, 14.08 ± 5.60 µM, respectively) and α-glucosidase inhibitory effects (IC50 = 189.40 ± 1.55 µM, and 31.86 ± 5.38 µM, respectively). Meanwhile, compound 3 and the mixture of 5 and 6 singly inhibited the enzyme α-glucosidase (IC50 = 69.41 ± 6.11 µM, 1204.82 µM, respectively), and showed weak antioxidant effects. On the contrary, compound 4 only had antioxidant activity (IC50 = 30.20 ± 1.86 µM). Compound 7 did not exhibit either antioxidant or enzymatic inhibitory effects. Conclusion: This is the first time that all of the seven compounds (1-7) and their biological activities were reported from D. citrea. Moreover, the α-glucosidase inhibitory effect of platyphyllone (3) is reported for the first time in the literature. This study revealed that flavonoids, phenolics, sterols, and monoglycerides in D. citrea rhizomes could be responsible for the antioxidant property and α-glucosidase inhibitory effect of this Vietnamese endemic medicinal plant.

Laser triangulation measurement of blade oscillation in a transonic compressor cascade

The paper describes a method for optical measurement of oscillation of blades in a linear cascade designed for flutter research. The method uses laser triangulation, which measures the distance between the sensor and the oscillation object. The distance can be recalculated to angular displacement of the blade. However, the relation is nonlinear due to the curvature of the blade. The nonlinear dependence between the distance and angular displacement is derived and quantified analytically. The paper further analyzes the influence of light refraction in the optical window, surface quality and sensor inclination. A procedure for the nonlinear calibration is proposed and used during wind tunnel measurements in a blade cascade with forced oscillation of the middle blade.

Role of optical measurement systems in analysing the surface topography of an industry standard component

An optical measurement system is a device that does not require any physical contact and instead relies on images to accomplish the measurements. In this work, three different optical measurement methods such as focus variation, coherence scanning interferometry, and confocal microscopy were used to calibrate the topography data at an industrial scale. Due to its reliability in operation, the cutting-edge confocal fusion method was also incorporated. It was determined that the optical methods under investigation provided the most stable amplitude parameters (Sa, Sq, Sv, Sp, Sz,) when compared to the Mahr standard. When comparing the Sz and Sa parameters, the largest differences were found for the former. For the amplitude parameters, the Flexbar standard yielded the largest deviations, while the Sa parameter yielded only 34% and the Sz parameter yielded about 43%. When comparing several measurement methods, confocal fusion appears to be the most adaptable. Specifically, it fills a gap in knowledge that is typically filled by a hybrid approach involving the confocal technique and the focus variation approaches. The use of multiple measuring methods increases the reliability of optical methods and permits more accurate calibration of surface morphology.