Charge-coupled Device Camera Research Articles

White spots noise removal of neutron images using improved robust principal component analysis

• A simple white spots removal method is proposed for degraded neutron images. • A‘detection-location-removal’ iterative strategy is introduced for the white spots detection and removal. • The qualitative and quantitative analysis are used for evaluating the performance of the mentioned methods. • The proposed method has a better performance in spots removal and details preservation than the comparison methods. Neutron radiography (NR) technology has been widely used in non-destructive investigations. However, the neutron images are always polluted by random white spots due to the interactions between the gamma rays, scattered neutron and other radiation and chip of the charge-coupled device (CCD) camera. In this paper, we propose a novel denoising method based on a ‘detection-location-removal’ iterative strategy, which adopts an improved robust principal component analysis (RPCA) in combination with the suitable threshold selection strategy and median filters for white spots noise removal of neutron images. Experimental results based on both simulation testing and real neutron images show that the proposed method is effective in improving neutron image quality in terms of numerical criteria and visual results. The comparison with the other denoising methods shows that the proposed method possesses higher robustness and effectiveness in practical denoising applications.

The Application of Electron Backscatter Diffraction on Halide Perovskite Materials

AbstractRecently, the application of electron backscatter diffraction (EBSD) in halide perovskites has enabled the correlation of the micro‐structural arrangement of polycrystalline grains with other properties (optical, electrical, mechanical, and chemical) in a “pixel‐by‐pixel” approach. Most studies so far have used an ultra‐sensitive electron beam detector that has sensitivity thousands of times higher than a traditional scintillator screen and charge coupled device camera, enabling much lower beam currents. An alternative approach has been the use of low vacuum measurement conditions to avoid charge buildup that leads to damage. This review focuses on introducing the classical EBSD technique to the halide perovskite community, where it has been highly underutilized due to beaminduced damage in these relatively unstable materials. Recent research is used to dispel some common misconceptions about grain boundaries in halide perovskites and highlight what has been learned by comparing and correlating EBSD with other techniques. Additionally, the remaining limitations, development challenges, and future of the EBSD technique for halide perovskites are discussed. Successful utilization of the EBSD technique as a common characterization tool in the halide perovskite community will enable scientists and engineers to develop maps of cross correlated properties, helping to unlock the full potential of this complex material system.

Effective solution of three-dimensional inverse radiation problem in participating medium based on RDFIEM

A novel integral equation method based on radiation distribution factor (RDFIEM) is developed for solving radiation transfer equation (RTE) to obtain radiation intensity signal in a small solid angle on a small point, which is effectively applied to reconstruct the three-dimensional (3D) temperature distribution in an absorbing, emitting and scattering medium. The spatial distribution of radiation intensity inside the medium can be derived by the reverse Monte Carlo method based on the radiation distribution factor (RDF), and source term distribution can be obtained by integration of RDFs. Consequently, according to the idea of integral equation method (IEM), the boundary exit radiation intensity with respect to the RDF and temperature can be deduced. It is worth noting that the RDF is only related to the geometry and radiation properties of the medium, which can be calculated only once to make RDFIEM be more efficient. Meanwhile, the error caused by the random number of RMC can be reduced by integrating the RDFs. As a consequence, the RDFIEM is particularly suitable for temperature field reconstruction. The directional radiation intensity signals obtained by charge-coupled device (CCD) camera are used as the known information to reconstruct the temperature distribution, the effects of CCD combinations, detection directions, optical thickness, boundary conditions, scattering type and scattering albedo, measurement and coefficient errors on the implementation of RDFIEM have been examined. The least square QR decomposition (LSQR) algorithm is introduced to solve the 3D temperature reconstruction problem. The results show that the temperature field can be reconstructed accurately and efficiently.

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages. To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition, a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages. The results show that when the discharge voltage is high, the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition; with the gradual strengthening of the ignition process, the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases. The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.

Implementation of laser-induced breakdown spectroscopy technique for qualitative analysis of an austenitic steel

In this work was used laser induced breakdown spectroscopy to study and characterize a sample of austenitic, steel American Iron and Steel Institute nomenclature, 304 series, with the objective of identifying constituent elements in the material. The steel was chosen because it is an economic and multipurpose material, which due to its physical characteristics, it is of great interest in the construction industry, design of tools and mechanical equipment. The contributions of this research to the industrial and metallurgical sector is that the laser induced breakdown spectroscopy technique allows to reduce costs in the experimental execution for qualitative studies of steels. Plasma generation was performed by focusing the radiation laser on the surface of a sample of steel. Plasma radiation generated was conducted through an optical fiber to a Mechelle spectrograph attached to an Intensified charge coupled device camera. The information obtained through the spectra allowed the characterization of the plasma by means of the parameters electronic temperature and electronic density, as well as the elementary identification of constituents of the steel sample, allowing identify major elements such as chromium, nickel, manganese and silicon, being concordant with the composition of elements present in the austenitic steel.

Characterization of a transient spark micro-discharge in nitrogen using simultaneous two-wavelength diagnostics

A transient spark micro-discharge in nitrogen is investigated between two sharpened electrodes at a pressure of 0.5 bar. The plasma parameters (gas temperature, electron density and reduced electric field) are determined using optical emission spectroscopy (OES) and numerical simulations. The gas temperature of 3500 ± 100 K is determined by the comparison of the measured and simulated rotational distributions of the photoemission spectra of neutral molecular nitrogen N2(C-B,0–0). Both direct and stepwise electron impact excitation are considered in the collision-radiative model. The rate constants for electron impact excitation processes are calculated for different electric field values using the electron velocity distribution function, which is simulated by solving the Boltzmann equation. The applied broadband echelle spectrometer is absolutely calibrated in a spectral range of 200 nm to 800 nm, using two standard light sources, a deuterium lamp and a tungsten ribbon lamp, which are certificated by the Physikalisch-Technische Bundesanstalt (PTB), Germany. With the aid of this absolutely calibrated echelle spectrometer and a microwave atmospheric plasma source operated in a nitrogen flow, the intensified charge-coupled device (ICCD) camera, provided with an in-house made optical arrangement for simultaneous two-wavelength diagnostic is calibrated. The spatial resolution of this diagnostic system under the studied plasma conditions amounts to 13 µm. The accurate examination of the experimental results allows determining the dominant process of electron impact excitation of molecular nitrogen ion from ionic ground state. Applying the chosen excitation model of the nitrogen photoemission, the spatially resolved reduced electric field and the electron density are determined. This is done by using the inverse Abel transformation of the absolute intensities of molecular nitrogen bands N2(C-B,0–0) and (B-X,0–0), which were measured with the calibrated ICCD camera. The measured electric current of the micro-discharge is compared with the calculated one using the measured plasma parameters and a good coincidence is established.

A Smart Advanced Chemiluminescence-Sensing Platform for Determination and Imaging of the Tissue Distribution of Natural Antioxidants.

Antioxidants have gained marked attention owing to their ability to prevent the oxidation of biological components and to protect the body from reactive oxygen species, thereby maintaining human health. Thus, antioxidant-rich dietary supplements and natural foods can be effective against oxidative stress and can even act as chemopreventive agents. Therefore, a simple and rapid assay for evaluation of antioxidant capacity and assessment of their distribution profile in natural sources is vital. Herein, we report a rapid, innovative chemiluminescence (CL) platform for evaluation and visualization of antioxidant capacity. We found that intense and long-lasting CL was formed upon the redox reaction of quinones, e.g., menadione, with antioxidants, e.g., l-ascorbic acid, in the presence of luminol. The produced CL intensities were proportional to the antioxidants' concentrations with a detection limit of 0.18 μM for the model antioxidant, l-ascorbic acid. As the formed CL was long-lasting, it could be easily captured and detected with a charge-coupled device (CCD) camera. To evaluate the quantification ability of the CCD camera, we developed a smart and fast microplate-based assay based on photographing the generated CL with a cooled CCD camera. The photographed CL intensities were linearly proportional with the antioxidant concentrations, and then the method was applied for photographing multiple food sample extracts. Ultimately, we utilized our method for the distribution profiling of antioxidant capacity in food cut sections. Samples were dipped in luminol and then in quinone, followed by CCD camera photography, without the need for any pulverization/extraction procedure, giving precise antioxidant distribution information.

Numerical simulation analysis of the influence of ultra-fine glass fiber production process on product homogeneity

Glass fiber felt is produced by flame blowing process, in which primary glass filament splits into glass fiber through the gas jet into the diffusion duct. In the diffusion duct, the velocity difference at axial direction creates a fiber recirculating zone at some position downstream in the duct while affecting the homogeneity of the product. In order to understand the impact of diffusion duct design to the felt forming, numerical simulations with experiment-based boundary conditions were performed to investigate the movement of fiber suspension flow. In the numerical analysis, the fiber slender-body theory is introduced. A visualization method is developed to characterize the uniformity of glass fiber, through charge coupled device camera imaging demonstrating the intensity of glass fiber in the surface of the product. The proposed methodology enabled new design of the diffusion duct, which eliminated the recirculating zone in the duct, resulting in more uniform products.

Composite-structured-light profilometry using greyscale expansion

In traditional composite-structured-light profilometry, the N-frame carrier gratings and modulated phase-shifting sinusoidal gratings must share a 256-greyscale dynamic range, which is the standard for commercial digital light projectors (DLPs). Additionally, each of the demodulated phase-shift gratings must possess a 43-greyscale dynamic range. This decreases the greyscale dynamic range for each of the demodulated gratings and compresses the phase information. Consequently, measurement accuracy is a challenge, even for incomplete reconstructions. To solve this problem, we propose a new composite-structured-light profilometry using greyscale expansion. Specifically, a composite video is synthesised using three different purposefully designed patterns, each possessing a 256-greyscale dynamic range. These patterns are used as the composite-structured-light to replace the traditional static composite grating. After projecting the repetitive video onto a measured object and controlling the exposure time of the charge-coupled device camera, the deformed composite 766-greyscale pattern can be stably captured. Furthermore, after demodulation, the dynamic range of the deformed demodulated patterns can be expanded up to 229. Numerical and experimental results indicate that the proposed method can be used to divide the single 256-greyscale DLP standard and accurately reconstruct measured objects.

On optical sensing of surface roughness of flat and curved microplastics in water

The growth of microplastic (MP) pollution is of increasing concern and represents a global challenge. In situ detection of these small particles is difficult because of their sizes, shapes, transparency or translucency, surface texture and ambient conditions. We propose and demonstrate the use of a prototype optical sensor to detect flat, nearly flat, curved and rough MPs prepared from commercial polyethylene terephthalate (PET) plastics and PET bottles in water. The prototype measures the specular reflection of a laser radiation incident on MPs, with a photodiode, and the transmitted laser speckle pattern, with a charge-coupled device (CCD) camera. The presence of the MPs as well as the optical surface roughness are determined from the specular reflection. Additionally, the so-called speckle contrast calculated from the speckle pattern, as a promising tool, is used to rank the rough MPs according to the different average surface roughness, to approximately twice the wavelength of the probing light. The novel application of laser speckle contrast and the optical roughness estimation allows the description of MP surface roughness in water. Moreover, in combination with earlier studies, these results, therefore, pave a way for the complete and a relatively easier description of MPs properties optical and also advances our step towards the development of simple and robust optical monitoring techniques for micro and nanoplastics in open and wastewater.

Soft x-ray laser beamline for surface processing and damage studies.

We have developed a soft x-ray laser (SXRL) beamline equipped with an intensity monitor dedicated to ablation study such as surface processing and damage formation. The SXRL beam having a wavelength of 13.9 nm, pulse width of 7 ps, and pulse energy of around 200 nJ is generated from Ag plasma mediums using an oscillator-amplifier configuration. The SXRL beam is focused onto the sample surface by the Mo/Si multilayer coated spherical mirror. To get the correct irradiation energy/fluence, an intensity monitor composed of a Mo/Si multilayer beam splitter and an x-ray charge-coupled device camera has been installed in the beamline. The Mo/Si multilayer beam splitter has a large polarization dependence in the reflectivity around the incident angle of 45°. However, by evaluating the relationship between reflectivity and transmittance of the beam splitter appropriately, the irradiation energy onto the sample surface can be derived from the energy acquired by the intensity monitor. This SXRL beamline is available to not only the ablation phenomena but also the performance evaluation of soft x-ray optics and resists.

Photon-counting 3D integral imaging with less than a single photon per pixel on average using a statistical model of the EM-CCD camera

We investigate photon-counting 3D integral imaging (PCII) with an electron multiplying charged-coupled device (EM-CCD) camera using dedicated statistical models. Using conventional integral imaging reconstruction methods with this camera in photon-counting conditions may result in degraded reconstructed image quality if multiple photons are detected simultaneously in a given pixel. We propose an estimation method derived from the photon detection statistical model of the EM-CCD to address the problems caused by multiple photons detected at the same pixel and provide improved 3D reconstructions. We also present a simplified version of this statistical method that can be used under the correct conditions. The imaging performance of these methods is evaluated on experimental data by the peak signal-to-noise ratio and the structural similarity index measure. The experiments demonstrate that 3D integral imaging substantially outperforms 2D imaging in degraded conditions. Furthermore, we achieve imaging in photon-counting conditions where, on average, less than a single photon per pixel is detected by the camera. To the best of our knowledge, this is the first report of PCII with the EM-CCD camera employing its statistical model in 3D reconstruction of PCII.

Camera-based sample-position detection and control for microgravity electrostatic levitation.

This paper presents a method for high-speed sample detection and position control in an electrostatic levitator. The algorithm uses images acquired from two charge coupled device cameras and allows for robust and reliable detection of the sample position under various process conditions. The results show improvements over position sensitive detector systems especially under harsh environments and during autonomous operation under microgravity conditions. The position of samples with a radius from 0.6 mm to 1.1 mm is detected in three dimensions with an accuracy of ±40 μm inside a 7 mm × 7 mm × 7 mm levitation area. The two orthogonally arranged cameras, recording images at a resolution of 260 px × 260 px, are used to calculate the position every 5 ms. The control model and the corresponding position controller for the three axes are presented as well. The system was successfully tested in the laboratory and under microgravity conditions at the drop tower, during parabolic flights, and on the MAPHEUS sounding rocket.

Optimization of Adaptive Lighting Technology Based on Varying-Frequency Sinusoidal Grating Projection

In order to enhance the image quality of multi-reflective 3D scenes during machine vision analysis, an active self-adaptive illumination system to solve the overexposure and underexposure problems is introduced. Based on projector-camera system, adaptive illumination was achieved by modulating the projection brightness at each pixel to be proportional to the pixel brightness of the target scenes, which should firstly establish the accurate pixel correspondence between the projector and camera. In this paper, the performance of adaptive illumination is improved by optimizing the correspondence stage compared with previous research. Different grating patterns with different frequency components are projected and compared to acquire the most effective correspondence, which improves the accuracy of corresponding depth map and the experiment results can achieve higher lighting accuracy reducing the number of iterations as well as the computing time. The image quality indexes, image contrast and number of saturated or dark pixels, are combined to analyze and judge the optimized lighting result. The results demonstrate that the developed technology in this research can achieve a rate of 20 frames per second by using a standard commercial CCD (charge coupled device) camera, where it can run in real time and becomes a viable solution for the industry.

Effect of Pulse Currents on Weld Geometry and Angular Distortion in Pulsed GTAW of 304 Stainless Steel Butt Joint

In this research, the effect of pulse currents on the weld geometry and angular distortion in pulsed GTAW (PGTAW) process in 3 mm thick SS-304 autogenous butt weld joint was investigated. Welding method uses pulse current and continuous current. The mean current and welding speed were kept constant with the peak current and base current were varied. During pulsed GTAW process, the arc condition was captured directly using a charge-coupled device (CCD) camera. Weld geometry was carried out using a digital microscope. Distortion was measured using Coordinate Measuring Machine (CMM). The results show that the peak current and base current have an influence on weld geometry and angular distortion. The weld geometry on pulsed GTAW was produced wider of weld bead width than continuous GTAW. However, angular distortion on continuous GTAW was higher than pulsed GTAW. Pulsed GTAW can widen the weld bead by 0.57% - 25.09%, but can reduce distortion by 15.15%-88.17%. As compared with weld geometry to the continuous GTAW, the widest result occurs at peak current 212A and base current 40A. The smallest of distortion on pulsed GTAW was achieved at peak current 138A and base current 80A.

Vibration distribution measurement using downsampling phase-shifting interferometer

Vibration distribution measurements using interferometers have been evaluated by many researchers. We have used a laser diode interferometer to measure two-dimensional vibration distributions using a combination of phase-shifting and downsampling techniques. Our system simultaneously measured nanometer-order sinusoidal vibration distributions of two objects vibrating at different frequencies, using a charged coupled device camera with a slower frame rate than either of the two harmonic frequencies being measured. This is a cost-efficient and compact system capable of successfully measuring high-frequency vibrations without requiring expensive high-frame-rate cameras.

Confocal microscopy with a microlens array.

Confocal laser scanning microscopy (CLSM) is a preferred method for obtaining optical images with submicrometer resolution. Replacing the pinhole and detector of a CLSM with a digital camera [charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS)] has the potential to simplify the design and reduce cost. However, the relatively slow speed of a typical camera results in long scans. To address this issue, in the present investigation a microlens array was used to split the laser beam into 48 beamlets that are focused onto the sample. In essence, 48 pinhole-detector measurements were performed in parallel. Images obtained from the 48 laser spots were stitched together into a final image.

Circumnutation and Growth of Inflorescence Stems of Arabidopsis thaliana in Response to Microgravity under Different Photoperiod Conditions.

Circumnutation is a periodic growth movement, which is an important physiological mechanism of plants to adapt to their growth environments. Gravity and photoperiod are two key environmental factors in regulating the circumnutation of plants, but the coordination mechanism between them is still unknown. In this study, the circumnutation of Arabidopsis thaliana inflorescence stems was investigated on board the Chinese recoverable satellite SJ-10 and the Chinese spacelab TG-2. Plants were cultivated in a special plant culture chamber under two photoperiod conditions [a long-day (LD) light: dark cycle of 16:8 h, and a short-day (SD) light: dark cycle of 8:16 h]. The plant growth and movements were followed by two charge-coupled device (CCD) cameras. The parameter revealed a daily (24 h) modulation on both TG-2 and SJ-10, under both the LD and the SD conditions. The inhibition of circumnutation was more apparent by microgravity under the SD in comparison with that under the LD condition, suggesting the synergistic effects of the combined microgravity and photoperiod on the circumnutation in space. In addition, an infradian rhythm (ca. 21 days long) on the TG-2 was also observed.

End-to-end test to evaluate the comprehensive geometric accuracy of a proton rotating gantry using a cone-shaped scintillator screen detector.

In this study, we aim to evaluate the comprehensive geometric accuracy of proton rotating gantries by performing an end-to-end test using a cone-shaped scintillator screen detector, known as XRV-124. The XRV-124 comprises a cone-shaped sheet-like scintillator and charge-coupled device camera that detects the scintillation light. First, the results of the Winston-Lutz and end-to-end XRV-124 tests performed on a conventional linear accelerator were compared to confirm the reliability of the XRV-124, and the snout position dependency of the geometric accuracy was evaluated for the proton rotating gantry as a pre-verification process. Thereafter, an end-to-end test including computed tomography imaging and irradiation in 30° steps from 0° to 330° for two proton rotating gantries, which have the same specifications, was performed. The results of the pre-verification indicated that sufficient accuracy was obtained for the end-to-end test of the proton rotating gantry. The end-to-end test results showed a peak-to-peak deviation of up to 2mm for some of the coordinate axes. The two gantries exhibited almost similar results in terms of the absolute quantity; however, a few trends were different. Thus, the beam axis deviations were confirmed to be within the safety margin, as expected in clinical practice. Based on the results of this study, the XRV-124 can be used as a comprehensive end-to-end constancy test tool, as it enables a comparative verification of multiple rotating gantries and geometric accuracy verification of different treatment modalities.

Bio-Inspired Breastfeeding Simulator (BIBS): A Tool for Studying the Infant Feeding Mechanism.

This work introduces a bio-inspired breastfeeding simulator (BIBS), an experimental apparatus that mimics infant oral behavior and milk extraction, with the application of studying the breastfeeding mechanism in vitro. The construction of the apparatus follows a clinical study by the authors that collects measurements of natural intra-oral vacuum, the pressure from infant's jaw, tongue and upper palate, as well as nipple deformation on the breast areola area. The infant feeding mechanism simulator consists of a self-programmed vacuum pump assembly simulating the infant's oral vacuum, two linear actuators mimicking the oral compressive forces, and a motor-driven gear representing the tongue motion. A flexible, transparent and tissue-like breast phantom with bifurcated milk duct structure is designed and developed to work as the lactating human breast model. Bifurcated ducts are connected with a four-outlet manifold under a reservoir filled with milk-mimicking liquid. Piezoelectric sensors and a CCD (charge-coupled device) camera are used to record and measure the in vitro dynamics of the apparatus. All mechanisms are successfully coordinated to mimic the infant's feeding mechanism. Suckling frequency and pressure values on the breast phantom from the experimental apparatus are in good agreement with the clinical data. Also, the change in nipple deformation captured by BIBS matches with those from in vivo clinical ultrasound images. The fully-developed breastfeeding simulator provides a powerful tool for understanding the bio-mechanics of breastfeeding and formulates a foundation for future breastfeeding device development.