Charge-coupled Device Imaging Research Articles

Digital Image Sensor Evolution and New Frontiers

This article reviews nearly 60 years of solid-state image sensor evolution and identifies potential new frontiers in the field. From early work in the 1960s, through the development of charge-coupled device image sensors, to the complementary metal oxide semiconductor image sensors now ubiquitous in our lives, we discuss highlights in the evolutionary chain. New frontiers, such as 3D stacked technology, photon-counting technology, and others, are briefly discussed.

High-accuracy centroid location of CCD imaging retro-reflective targets in close-range photogrammetry

Depending on the size, shape, and gray intensity distribution of charge-coupled device (CCD) imaging retro-reflective targets (RRTs) in close-range photogrammetry, and based on conventional grayscale centroiding, this paper proposes grayscale threshold variable-index weighted centroiding (GTVIWC). The centroid location accuracy of CCD imaging RRTs was analyzed and compared using simulated and measured target images, respectively. The experimental results demonstrated that the centroid location accuracy of the algorithms used in the experiment was relatively high, reaching the subpixel level. Among them, GTVIWC has the highest location accuracy. The root mean square error (RMSE) of the centroid location for the simulated and measured CCD imaging RRTs reaches 0.0011 pixels and 0.0122 pixels, respectively. The correctness, reliability, and high accuracy of the proposed algorithm are verified.

Evolution of solid-in-hollow structured plasma bullet: Modulated by pulse repetition frequency and rising time

Plasma bullets in atmospheric pressure plasma jets have drawn much scholarly attention in the past decade, especially its shape. This Letter reports the formation and evolution mechanism of a solid-in-hollow structured bullet. At high pulse repetition frequency (≥20 kHz) and long rising time (≥200 ns), the traditional hollow ring bullet turns into the solid-in-hollow structure, and the plasma plume correspondingly appears as a purple external plume with an extra internal filamentary red core under bare eyes. An image process method based on color recognition and decoupling is designed to separate the images of the external plume and the internal filamentary core and is then used to analyze the discharge mechanism together with the intensified charge-coupled device imaging and spectrum measurement. Analyses reveal that the dominant ionization sources for external ring and internal core are N2 and He, respectively, and the internal discharge can be enhanced by increasing the pulse repetition frequency, which might be explained by the electron oscillating heating in high frequency. Finally, the evolution mechanism of the internal filamentary core is studied, and the internal discharge is initially a hollow ring as well when it just exits the tube end, making the bullet a hollow-in-hollow structure, but quickly contracts into a solid core due to the Coulomb repulsion between the two plasma rings.

PlatoSim: an end-to-end PLATO camera simulator for modelling high-precision space-based photometry

Context. PLAnetary Transits and Oscillations of stars (PLATO) is the ESA M3 space mission dedicated to detect and characterise transiting exoplanets including information from the asteroseismic properties of their stellar hosts. The uninterrupted and high-precision photometry provided by space-borne instruments such as PLATO require long preparatory phases. An exhaustive list of tests are paramount to design a mission that meets the performance requirements and, as such, simulations are an indispensable tool in the mission preparation. Aims. To accommodate PLATO’s need of versatile simulations prior to mission launch that at the same time describe innovative yet complex multi-telescope design accurately, in this work we present the end-to-end PLATO simulator specifically developed for that purpose, namely PlatoSim. We show, step-by-step, the algorithms embedded into the software architecture of PlatoSim that allow the user to simulate photometric time series of charge-coupled device (CCD) images and light curves in accordance to the expected observations of PLATO. Methods. In the context of the PLATO payload, a general formalism of modelling, end-to-end, incoming photons from the sky to the final measurement in digital units is discussed. According to the light path through the instrument, we present an overview of the stellar field and sky background, the short- and long-term barycentric pixel displacement of the stellar sources, the cameras and their optics, the modelling of the CCDs and their electronics, and all main random and systematic noise sources. Results. We show the strong predictive power of PlatoSim through its diverse applicability and contribution to numerous working groups within the PLATO mission consortium. This involves the ongoing mechanical integration and alignment, performance studies of the payload, the pipeline development, and assessments of the scientific goals. Conclusions. PlatoSim is a state-of-the-art simulator that is able to produce the expected photometric observations of PLATO to a high level of accuracy. We demonstrate that PlatoSim is a key software tool for the PLATO mission in the preparatory phases until mission launch and prospectively beyond.

Proposed values for diagnostic reference levels in intraoral dental radiography in Serbia

Values for diagnostic reference levels are proposed for intraoral dental radiography in the Republic of Serbia. Proposed numbers for diagnostic reference levels were based on measurements on 119 intraoral units in clinical settings for an adult posterior bitewing X-ray. Values of 3.17 mGy, 3.11 mGy, and 1.58 mGy incident air kerma were found for image receptors film E class, charge-coupled device, and photostimulable phosphor plate, respectively. Similarly, 89.6 mGycm2, 88 mGycm2, and 44.6 mGycm2 air kerma-area products were found for the same detectors. All values are greater than those published in several other similar studies. This is especially true for charge-coupled device image receptors since this technology enables lower patient doses as reported before. This calls for urgent action to optimize intraoral dental imaging, so we present the radiographic techniques used and equipment description to help guide optimization actions.

Supra-Quantum Dot Assemblies to Maximize Color-Based Multiplexed Fluorescence Detection with a Smartphone Camera.

Photoluminescence (PL) imaging and bioanalysis with smartphone-based devices are of growing interest for point-of-care/point-of-need diagnostics. Strategies for maximizing sensitivity have been explored in this context, but color multiplexing has been very limited, with its maximum level unexplored. Here, we evaluated color multiplexing with smartphone-based PL imaging by using supra-nanoparticle assemblies of quantum dots (supra-QDs). These materials were prepared as composite colors that were tailored to the red-green-blue (RGB) color space of smartphone cameras by coassembling different ratios of R-, G-, and B-emitting QDs on a silica nanoparticle scaffold. The supra-QDs were characterized and used to label cell-sized objects that were measured under flow with a smartphone-based device. Each color followed an approximately linear trajectory in the RGB space, and training of support vector machine models enabled color classification with overall accuracies ≥87% for 10-color multiplexing and better accuracies for fewer colors. Most misclassification occurred at low signal levels, such that establishing a nonclassifiable zone near the origin of RGB color space improved the overall 10-color classification accuracy to ≥94%. Similar improvements in accuracy with greater retention of data were possible with a probabilistic rather than a radial threshold. Simulations that were parameterized by experimental data suggested that ≥14-color multiplexing with accuracies ≥90% should be possible with an optimized supra-QD color set. This study is an important foundation for advancing RGB color-based multiplexing for imaging and analyses with smartphone cameras and related charge-coupled device and CMOS color image sensor technologies.

Rotation periods and colours of 10-m-scale near-Earth asteroids from CFHT target of opportunity streak photometry

ABSTRACT The rotational properties of ∼10-m-scale asteroids are poorly understood with only a few measurements. Additionally, collisions or thermal recoil can spin their rotations to periods less than a few seconds obfuscating their study due to the observational cadence imposed by the long read-out times of charge-coupled device imagers. We present a method to measure the rotation periods of 10-m-scale asteroids using the target of opportunity capability of the Canada–France–Hawaii Telescope (CFHT) and its MegaCam imager by intentionally streaking their detections in single exposures when they are at their brightest. Periodic changes in brightness as small as ∼0.05 mag along the streak can be measured as short as a few seconds. Additionally, the streak photometry is taken in multiple g, r, and i filter exposures enabling the measurement of asteroid colours. The streak photometry method was tested on CFHT observations of three 10-m-scale asteroids, 2016 GE1, 2016 CG18, and 2016 EV84. Our three targets are among the smallest known asteroids with measured rotation periods/colours having some of the shortest known rotation periods. We compare our rotation period and taxonomic results with independent data from the literature and discuss applications of the method to future small asteroid observations.

Heat transfer characteristics and heat conductivity prediction model of waste steel slag–clay backfill material

The thermal performance of the backfill material used in ground source heat pump systems directly affects their heat transfer efficiency. To enhance the heat transfer efficiency, aiming at the low heat conductivity of existing backfill materials, this paper proposes a waste steel slag–calcareous clay mixture as the backfill material for buried pipes. First, the heat conductivities of 128 sets of waste steel slag–calcareous clay mixtures in different preparation states were tested by performing indoor thermal probe tests, and the influences of the steel slag mixture, moisture content, dry density, and particle gradation on the heat conductivity were investigated. Scanning electron microscopy and Charge coupled device imaging were employed to capture the microscopic morphology of the materials and to analyze their heat transfer mechanism. With the test results, a heat conductivity prediction model of the backfill material based on a back propagation neural network was developed. The incorporation of waste steel slag was found to significantly improve the heat conductivity of the mixed backfill materials, the heat conductivity of a mixture incorporated with 70% steel slag was the highest, with the value being 1.86 to 2.46 times higher than that of the clay material without steel slag. The established heat conductivity prediction model produced accurate results with an average relative error of 1.0007%. This study can provide reasonable thermal parameters for waste steel slag–clay mixtures as backfill materials in ground source pump systems, and the effective utilization of waste steel slag can improve its added value.

Large-range and high-sensitivity displacement sensing based on a SNAP microresonator by multimode encoding technique

Probe-type micro-displacement sensors with a large range and high sensitivity have important applications in both aerospace and nano-lithography. However, the state-of-the-art measurement range achieved using conventional methods such as charge coupled device imaging and fiber grating demodulation is limited to only tens of micrometers. In this study, we propose and demonstrate a displacement sensing mechanism with a large range and high sensitivity for measuring linear displacements. The mechanism is based on a multimode encoding technique implemented on a surface nanoscale axial photonics (SNAP) microcavity platform. By tracking the transmittance variations of multiple axial modes and employing encoding techniques, we can determine the rough absolute position as well as the axial mode with the highest sensitivity in each region. Moreover, the selected mode for each region is exploited to accurately measure the micro-displacement with a large range and high accuracy. As a proof-of-principle experiment, the results indicate a large sensing range about 346 μm and a high sensitivity ranging up to 0.013 μm−1. Assuming that the transmittance can be resolved by 0.1%, the resolution of the measurement is about 0.1 μm.

Improved noise performance from the next-generation buried-channel p-MOSFET SiSeROs

The Single electron Sensitive Read Out (SiSeRO) is a novel on-chip charge detector output stage for charge-coupled device (CCD) image sensors. Developed at MIT Lincoln Laboratory, this technology uses a p-MOSFET transistor with a depleted internal gate beneath the transistor channel. The transistor source-drain current is modulated by the transfer of charge into the internal gate. At Stanford, we have developed a readout module based on the drain current of the on-chip transistor to characterize the device. In our earlier work, we characterized a number of first prototype SiSeROs with the MOSFET transistor channels at the surface layer. An equivalent noise charge (ENC) of around 15 electrons root mean square (RMS) was obtained. In this work, we examine the first buried-channel SiSeRO. We have achieved substantially improved noise performance of around 4.5 electrons root mean square (RMS) and a full width half maximum (FWHM) energy resolution of 132 eV at 5.9 keV, for a readout speed of 625 kpixel/s. We also discuss how digital filtering techniques can be used to further improve the SiSeRO noise performance. Additional measurements and device simulations will be essential to further mature the SiSeRO technology. This new device class presents an exciting new technology for the next-generation astronomical X-ray telescopes requiring fast, low-noise, radiation-hard megapixel imagers with moderate spectroscopic resolution.

Improvements in the surface tension measurement using the capillary rise method and its application to water under external magnetic fields

Using a micro ruler and charge-coupled device image acquisition system, we have improved the capillary rise method for an easy, quick and accurate measurement of liquid surface tension. We have determined and assessed the surface tension coefficients and temperature characteristics of purified water, ethylene glycol and anhydrous ethanol. Our results demonstrate low uncertainties for stable liquids and good linearity with temperature, with a measuring percentage deviation of less than 0.1% at 20 °C for purified water. Furthermore, we exposed purified water to a series of external magnetic fields ranging from 0 to 5 T for 40 min, followed by a withdrawal of fields for 5 min and observed a drop peak of surface tension at 1.0 T and a saturating transition at approximately 1.2 T. Furthermore, we found that the surface tension coefficients rapidly decrease with increasing magnetic fields from 0 to 1.0 T, increase rapidly from 1.0 to 1.2 T and then increase slowly at fields higher than 1.2 T. The maximum reduction of surface tension affected by external fields is approximately 11%. These magnetic behaviours of water surface tension have scientific significance in the study of water molecular liquids and their potential applications in water treatments.

Homogeneous dielectric barrier discharge in CO2

This study investigates dielectric barrier discharges generated in CO2 at atmospheric pressure. According to the literature, under these conditions, discharges usually work in the filamentary regime. On the contrary, the experimental results reported in the present study demonstrate for the very first time that it is also possible to obtain a diffuse CO2 discharge under these conditions. The diffuse regime appears to be related to a memory effect mechanism occurring at the dielectric surface. Both the filamentary and diffuse regimes were compared in this work based on electrical measurements coupled with intensified charged coupled device (iCCD) imaging and optical emission spectroscopy. The clear difference between both regimes is discussed.

ISTD-PDS7: A Benchmark Dataset for Multi-Type Pavement Distress Segmentation from CCD Images in Complex Scenarios

The lack of large-scale, multi-scene, and multi-type pavement distress training data reduces the generalization ability of deep learning models in complex scenes, and limits the development of pavement distress extraction algorithms. Thus, we built the first large-scale dichotomous image segmentation (DIS) dataset for multi-type pavement distress segmentation, called ISTD-PDS7, aimed to segment highly accurate pavement distress types from natural charge-coupled device (CCD) images. The new dataset covers seven types of pavement distress in nine types of scenarios, along with negative samples with texture similarity noise. The final dataset contains 18,527 images, which is many more than the previously released benchmarks. All the images are annotated with fine-grained labels. In addition, we conducted a large benchmark test, evaluating seven state-of-the-art segmentation models, providing a detailed discussion of the factors that influence segmentation performance, and making cross-dataset evaluations for the best-performing model. Finally, we investigated the effectiveness of negative samples in reducing false positive prediction in complex scenes and developed two potential data augmentation methods for improving the segmentation accuracy. We hope that these efforts will create promising developments for both academics and the industry.

Fringing Analysis and Simulation for the Vera C. Rubin Observatory’s Legacy Survey of Space and Time

The presence of fringing in astronomical Charge-Coupled Device (CCD) images will have an impact on photometric quality and measurements. Yet its impact on the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) has not been fully studied. We present a detailed study on fringing for CCDs already implemented on the Rubin Observatory LSST Camera’s focal plane. After making physical measurements and knowing the compositions, we developed a model for the e2v CCDs. We present a method to fit for the internal height variation of the epoxy layer within the sensors based on fringing measurements in a laboratory setting. This method is generic enough that it can be easily modified to work for other CCDs. Using the derived fringing model, we successfully reproduce comparable fringing amplitudes that match the observed levels in images taken by existing telescopes with different optical designs. This model is then used to forecast the expected level of fringing in a single LSST y-band sky background exposure with Rubin telescope optics in the presence of a realistic time-varying sky spectrum. The predicted fringing amplitude in LSST images ranges from 0.04% to 0.2% depending on the location of a CCD on the focal plane. We find that the predicted variation in surface brightness caused by fringing in LSST y-band sky background images is about 0.6 , which is 40 times larger than the current measurement error. We conclude that it is necessary to include fringing correction in the Rubin’s LSST image processing pipeline.

Radiation temperature measuring method with high dynamic range via fast double-exposure image fusion

The CCD (Charge-coupled device) image sensor can invert the surface temperature of the object by collecting the radiation signal of the high-temperature object. It is a non-contact temperature measurement method, which has the characteristics of fast response without affecting the surface distribution of the tested object. Due to the restriction of the development level of CCD, the exposure tolerance of imaging is low. As a result, the temperature field measurement range is low. In order to solve the problem of low exposure tolerance caused by dark current and saturation in CCD, this paper proposes a radiation temperature measuring method with high dynamic range via fast double-exposure image fusion technology, and a high temperature field measurement system based on LabVIEW and visible light industrial camera is developed. The method proposed in this study is suitable for the stationary objects in temperature range from 750 to 1200 ℃. By correcting the non-impulse response of the sensor, the temperature measurement error is better than 2%. By fusing two images with different exposure duration, the dynamic temperature measurement range is increased to 59.2%, which significantly improves the adaptability of the CCD in the measurement of high temperature field.

Atmospheric pressure plasma jet impinging on fiber arrays: Penetration pattern determined by fiber spacing

Atmospheric pressure cold plasmas have great potential for surface functionalization, and the interaction between the plasmas and fibers is essential to understand the underlying physics. In this Letter, the penetration pattern and mechanism of an atmospheric pressure plasma jet (APPJ) interacting with different spacing fiber scaffolds were studied by both experiment and modeling. The intensified charge coupled device images showed that APPJ induced a radial surface streamer on the windward side of the scaffold and another axial forward streamer on the opposite side. Propagation distance of both the radial and axial streamers diminished as the spacing decreased. Similar trends were predicted by a 2D fluid model. The simulation results indicated that the high electrical field carried by the streamer head in APPJ was allowed to pass through the gap for large spacing scaffold, while it was blocked by high intensity charges at small spacing. Instead, one axial streamer was generated in the latter case. The physical insight on the penetration mechanism of plasma jet interacting with fiber array in this Letter may contribute to improve treatment uniformity of plasma technology.

A Morphing Point-to-Point Displacement Control Based on Long Short-Term Memory for a Coplanar XXY Stage.

In this study, visual recognition with a charge-coupled device (CCD) image feedback control system was used to record the movement of a coplanar XXY stage. The position of the stage is fedback through the image positioning method, and the positioning compensation of the stage is performed by the image compensation control parameter. The image resolution was constrained and resulted in an average positioning error of the optimized control parameter of 6.712 µm, with the root mean square error being 2.802 µm, and the settling time being approximately 7 s. The merit of a long short-term memory (LSTM) deep learning model is that it can identify long-term dependencies and sequential state data to determine the next control signal. As for improving the positioning performance, LSTM was used to develop a training model for stage motion with an additional dial indicator with an accuracy of 1 μm being used to record the XXY position information. After removing the assisting dial indicator, a new LSTM-based XXY feedback control system was subsequently constructed to reduce the positioning error. In other words, the morphing control signals are dependent not only on time, but also on the iterations of the LSTM learning process. Point-to-point commanded forward, backward and repeated back-and-forth repetitive motions were conducted. Experimental results revealed that the average positioning error achieved after using the LSTM model was 2.085 µm, with the root mean square error being 2.681 µm, and a settling time of 2.02 s. With the assistance of LSTM, the stage exhibited a higher control accuracy and less settling time than did the CCD imaging system according to three positioning indices.

Effects of particle type on the particle fluidization and distribution in a liquid–solid circulating fluidized bed boiler

• Circulating fluidized bed technology is combined with boiler. • Effects of particle type on particle fluidization and distribution are investigated. • Particles accumulation exists at the bottom of the drum for all types of particles. • Particle properties obviously affect the fluidization and distribution of particles. • The non-uniform degree decreases with increased feedwater flow rate. A liquid–solid circulating fluidized bed boiler is designed and built for visualization research by applying the fluidized bed heat transfer and fouling prevention technology to the water side of the boiler. Four types of engineering plastic particles with different physical properties are selected as the solid working media. The effect of particle types on the fluidization and distribution of particles in the boiler is investigated under different feedwater flow rates and amount of added particles by using the charge couple device image measurement and acquisition system. The results show that all kinds of particles can’t be normally fluidized and accumulate in the drum at low amount of added particles and feedwater flow rate. The particles with great density and low sphericity are more likely to accumulate. The average solid holdup in the riser tubes increases with the increase in feedwater flow rate and the amount of added particles. The non-uniform degree of particle distribution in the riser tubes generally decreases with the increase in feedwater flow rate and the amount of added particles. The particles with small density and settling velocity have high average solid holdup in the riser tubes under close sphericity. In generally, the smaller the density and settling velocity, the more uniform the particle distribution in the riser tubes. Three-dimensional diagrams of the non-uniform degree of particle distribution in the riser tubes of the boiler are established.

Kinetic Properties of CO2 Hydrate Formation in the Wax-Containing System at Different Concentrations

Precipitation of wax crystals and hydrate formation during deep-sea multiphase pipeline transportation would limit pipeline transportation flow and even trigger accidents. It is necessary to study the hydrate formation behavior in the wax-containing system. This paper utilized a mixture of number 60 Kunlun paraffin wax and number 2 industrial white oil to simulate the wax-containing system, and the CO2 hydrate was formed in the wax-containing system. The morphology of CO2 hydrate formation was captured by the microscope and the charge-coupled device imaging system. In this study, the influences of the wax crystal concentrations on the induction time and cumulative gas consumption of hydrate formation were investigated, and the effects of wax crystal precipitation on the CO2 hydrate nucleation mechanism were discussed. The experimental results indicated that, for the wax crystal concentrations of 1.50 and 2.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was reduced by 29.23 and 69.23% compared to that in the pure water system, respectively. However, for the wax crystal concentration of 0.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was increased by 130.77% compared to that in the pure water system. The reason for this was that the precipitation of wax crystals at high concentrations increased the chance of heterogeneous nucleation and the probability of heterogeneous nucleation increased with the increase of wax crystal concentrations. However, for the wax crystals at low concentrations, it not only lowered the chance of cross nucleation but also increased the mass transfer resistance for gas diffusion, thereby resulting in the increase of the induction time of hydrate formation. It was also found that, with the increase of the wax crystal concentrations, the cumulative gas consumption during hydrate formation decreased gradually. When the wax crystal concentration increased to 2.50 wt %, the cumulative gas consumption was reduced by 32.96% compared to that of the pure water system. The experimental results obtained in this study were helpful for understanding the kinetic characteristics of hydrate formation in the wax-containing system, which is meaningful for the pipeline flow assurance, safety, and economic security of pipeline transportation as well as the development of carbon capture and storage.

Repetitive pulsed gas-liquid discharge in different atmospheres: from discharge characteristics to plasma-liquid interactions.

Gas-liquid discharges enable efficient plasma-liquid interactions and thus have promising applications, but many concerns remain unanswered regarding working gas, an important influencing factor. Investigations of a pulsed needle-to-water gas-liquid discharge in Ar, He, and N2 are carried out in this study. Voltage-current waveforms and intensified charge-coupled device (ICCD) images were combined to explore discharge modes and evolution processes. Experimental results demonstrate that the Ar tip spark discharge develops all the way to liquid compared with the He and N2 discharges concentrated in the tube, considerably increasing the plasma-liquid interaction efficiency. According to the optical emission spectra (OES), plasma properties are found to be strongly influenced by interactions between gas particles and interfering particles (H2O, etc.). For instance, excess water vapor causes quenching of excited species, resulting in OH (A-X) in Ar and NO (A-X) in N2 concentrated in the middle region with weak discharge. By adding dimethyl sulfoxide, it is demonstrated that OH dominates H2O2 production in Ar and contributes to both NO2- and NO3- generation in Ar and He, whereas in N2 it only affects NO3- generation. This study advances the "bridge building" between practical application and gas-liquid discharge employing different working gases.