Small Pixel Research Articles

Application of Multiband Acoustooptical Filtering of Radiation to Solution of the Object Remote Identification Problems by the Method of Programmed Linear Separation of Multispectral Optical Signals in the Case of Reflection of a Wideband Light from Objects with A Priori Known Reflection Coefficients

A new approach to solution of the problem of remote determination of spectrally complex optical signals and identification on this base of two objects out of a set of possible spatially inseparable objects located in one small ground pixel is considered. Computer simulation is performed; it is shown that the results of measurements of the mean powers of filtered signals at the outputs of two (or more) selected reference multiband acoustooptical filters (MAOFs) can ensure subsequent programmed (digital) separation of spectrally complex optical signals and identification of the objects corresponding to these signals. By the example of an arbitrarily chosen group of ten types of objects and three types of the background, computer verification of the new method is carried out with the use of realizable parameters of modern MAOFs. It has been found that, in conditions of the actual accuracy of setting and/or measuring of the energy of the main components of the problem (~1%), this method can provide unambiguous correct decision about the type of the object located on part of a pixel with a probability of ~99.9%.

Small pitch resonator-QWIP detectors and arrays

We are developing small pixel 12-μm pitch resonator-QWIPs for infrared imaging at 8 μm and 10 μm. The materials and geometries are designed to yield 44% quantum efficiency (QE) at 1.0 × 1018 cm−3 doping and 56% at 1.2 × 1018 cm−3 for the 8 μm detectors and 47% at 1.0 × 1018 cm−3 for the 10 μm detector. Because of production variability and excess detector tunneling current at large bias, the maximum QE for the 8 μm detectors is measured to be 24.6% and 56.4%, respectively, while that for the 10 μm detector is 44%. Focal plane arrays of 1280 × 1024 resolution were produced from the lower doping, 8 μm material. Their performance is the same as the test detectors up to the maximum internal bias of the readout circuit. From the test detector I-V characteristics, the performance can be further projected to higher bias, at which the FPAs can offer 23 mK sensitivity at 3.7 ms integration time from the lower doping material and 21 mK at 3.2 ms from the higher doping material. For the 10 μm FPAs, the sensitivity is projected to be 30 mK at 3.8 ms. Therefore, we have demonstrated high sensitivity and fast R-QWIP FPAs down to 12-μm pitch. To expand the application envelope of the resonator-pixel technology, we have deigned resonant geometries for other infrared materials. Experimental efforts are underway.

CMS Pixel detector development for the HL-LHC

An upgrade program is underway to increase the luminosity of the LHC up to about 7.5×1034 cm−2s−1 in 2027, with the goal of an integrated luminosity of 3000 fb−1 by the end of 2037. This High Luminosity scenario, HL-LHC, presents new challenges of higher data rates and increased radiation hardness for the pixel detector: a non-ionizing fluence of 2.3×1016 neq/cm2 an ionizing dose of 12 MGy, is expected on the inner pixel layer for 3000 fb−1 integrated luminosity. To maintain or even improve the performance of the present system, new technologies have to be fully exploited for the so-called Phase-II upgrade. Among them is the future version of front-end chips in 65-nm CMOS by the CERN RD53 Collaboration which supports small pixel sizes of 50×50 or 25×100 μm2 lower thresholds (∼ 1000 e−). For the development of the appropriate planar pixel sensor, CMS has recently launched a submission of n+-p sensors on 6 inch wafers with an active thickness of 150 μm at Hamamatsu. The submission consists of physically thinned, directly bonded and deep diffused wafers with p-stop or p-spray isolation. A variety of sensors with and without biasing scheme is designed to match the different read-out chips (RD53A, ROC4Sens, etc.) and first hybrid modules are assembled at Fraunhofer IZM. In this document, we will present an overview of the Phase II pixel R&D program and report on preliminary results on the HPK submission.

Implementation of Rivest Shamir Adleman Cryptographic Algorithms and Techniques of Steganography First of File for Message Security

Accessing data by an unauthorized person often happens these days. Addressing this case, the techniques of cryptography and steganography was necessary. The science of cryptography use randomizes/disguise the data, whereas the science of steganography to hide data in a way. The cryptographic algorithms to be used is the Rivest Shamir Adleman (RSA) which utilizes two prime numbers to generate a public key and private key. To further enhance the security of message, the algorithm has combined with the First of File (FoF) as steganography techniques. The technique First of File (FoF) works by inserting a message at the beginning of the file image horizontally to produce a stego image that will extract to get the previous ciphertext. Then the ciphertext decrypted to be returned to the original message. By using FoF, in the cover image with large pixel size, the insertion process with FoF is entirely invisible, so the stego image and original image cannot be distinguished, whereas in small pixels there is a black line above the image. A combination of RSA and the FOF will increase data security because when a message has scrambled into a ciphertext and the ciphertext will be inserted into the image file.

A hybrid time and wavenumber domain algorithm for generalized beamforming with circular synthetic aperture data

Synthetic aperture sonar systems typically scan along a linear trajectory, however autonomous underwater vehicles (AUV's) provide a useful platform for performing scans along more complicated trajectories with specific advantages. One example is the circular scan, which provides superior wavenumber coverage and resolution for images reconstructed near the circle center. A variety of approaches have been put forward for beamforming synthetic aperture data collected along a circular trajectory, but for images that span a significant fraction of the circle radius, accelerated time-domain approaches such as fast-factorized backprojection (FFBP) have been suggested. The computational requirements for generating a fully sampled image collected around a circular aperture are extremely large, however, even for FFBP. This is primarily because of the extremely small pixel size required to maintain adequate spatial sampling as larger portions of the aperture are coherently fused in the later stages of the FFBP algorithm. A method is presented for replacing the later stages of the algorithm with a series of spectral mappings, retaining the generality of the beamformer while improving computational efficiency.

Convolution Neural Network Based on Two-Dimensional Spectrum for Hyperspectral Image Classification

Inherent spectral characteristics of hyperspectral image (HSI) data are determined and need to be deeply mined. A convolution neural network (CNN) model of two-dimensional spectrum (2D spectrum) is proposed based on the advantages of deep learning to extract feature and classify HSI. First of all, the traditional data processing methods which use small area pixel block or one-dimensional spectral vector as input unit bring many heterogeneous noises. The 2D-spectrum image method is proposed to solve the problem and make full use of spectral value and spatial information. Furthermore, a batch normalization algorithm (BN) is introduced to address internal covariate shifts caused by changes in the distribution of input data and expedite the training of the network. Finally, Softmax loss models are proposed to induce competition among the outputs and improve the performance of the CNN model. The HSI datasets of experiments include Indian Pines, Salinas, Kennedy Space Center (KSC), and Botswana. Experimental results show that the overall accuracies of the 2D-spectrum CNN model can reach 98.26%, 97.28%, 96.22%, and 93.64%. These results are higher than the accuracies of other traditional methods described in this paper. The proposed model can achieve high target classification accuracy and efficiency.

Digital count summing vs analog charge summing for photon counting detectors: A performance simulation study.

Charge sharing is a significant problem for CdTe-based photon counting detectors (PCDs) and can cause high-energy photons to be misclassified as one or more low-energy events. Charge sharing is especially problematic in PCDs for CT because the high flux necessitates small pixels, which increase the magnitude of charge sharing. Analog charge summing (ACS) is a powerful solution to reduce spectral distortion arising from charge sharing but may be difficult to implement. We investigate correction of the signal after digitization by the comparator ("digital count summing"), which is only able to correct a subset of charge sharing events but may have implementation advantages. We compare and quantify the relative performance of digital and ACS in simulations. Transport of photons in CdTe was modeled using Monte Carlo simulations. Energy deposited in the CdTe substrate was converted to electrical charges of a predetermined shape, and all charges within the detector pixel are assumed to be perfectly collected. In ACS, the maximum charge received over any 2×2 block of pixels was grouped together prior to digitization. In digital count summing (DCS), the charge was digitized in each pixel, and subsequently, adjacent pixels that detected events grouped their charge to record a single, higher energy event. All simulations were performed at the limit of low flux (no pileup). The default tube voltage was 120kVp, object thickness was 20cm of water, pixel pitch was 250μm, and charge cloud modeled as a Gaussian with σ=40μm. Variation of these parameters was examined in a sensitivity analysis. Detectors that used no correction, DCS, and ACS misclassified 51%, 39%, and 15% of incident photons, respectively. For iodine basis material imaging, DCS exhibited 100% greater dose efficiency compared to uncorrected, and ACS exhibited an additional 111% greater dose efficiency compared to digital charge summing. For a nonspectral task, the dose efficiency improvement as estimated by improvement of zero-frequency detective quantum efficiency, DQE(0) was 10% for DCS compared to uncorrected and 10% for ACS compared to DCS. A sensitivity analysis showed that DCS generally achieved half the benefit of ACS over a range of conditions, although the benefit was markedly less if the charge cloud was instead modeled as a small sphere. Summing of counts after digitization may be a simpler alternative to summing of charge prior to digitization due to the relative complexity of analog circuit design. Over most conditions studied, it provides roughly half the benefit of ACS and may offer certain implementation advantages.

A high-speed small-area pixel 16 × 16 ISFET array design using 0.35-μm CMOS process

This paper reports the design of a 16 × 16 ion-sensitive field-effect transistor (ISFET) chip with tightly arranged small pixels that can work in relatively higher speeds. During the chip design, we thoroughly considered the pixel area, speed, power consumption, and extensibility. The chip was fabricated using a conventional 4-metal 0.35-μm CMOS process. As a result, we obtained a chip's pixel area of 7.4 μm × 7.4 μm, power consumption of 3.3 V × 4 mA, and scanning rate reaching 6.25 M pixels/s. The passivation layer, mainly consisting of Si3N4, was directly treated as the sensing film. By arranging the overall layout tightly, this chip could be regarded as a module to expand the scale of ISFET arrays and can be used in applications having larger scale arrays. Initially, we obtained an average sensitivity of 20 mV/pH ±2 mV/pH and modified it up to 35 mV/pH ±2 mV/pH by rinsing it in BOE (Buffered Oxide Etch) with a volumn ratio of 1:4:4 (HF:H2O:NH4F) for 15 min.

An experimental comparison of multi-resolution segmentation, SLIC and K-means clustering for object-based classification of VHR imagery

ABSTRACTWith smaller pixel coverages from recent sensors, considering single pixels in the classification process has become ineffective and incapable for delineation of the characteristics of targeted land use land cover (LULC) types. Object-based image analysis (OBIA) has been recently applied to enhance the identification performance of the classifiers considering not only the spectral but also the contextual and textural information. In this study, three segmentation approaches having a different theoretical basis, namely multi-resolution segmentation (MRS), Simple Linear Iterative Clustering (SLIC) superpixel algorithm and K-means clustering, were utilized to produce image objects, from which thematic maps were generated using random forest classifier. The most widely used segmentation evaluation metrics were applied by considering manually digitized reference polygons to evaluate the goodness of the constructed segments. Quality analyses were performed on four specific LULC types (residential, industrial and public buildings, and coniferous trees) for analysing the effectiveness of the approaches. Overall, the MRS algorithm produced the most accurate results in terms of both segmentation quality and classification accuracy. On the other hand, the difference in classification accuracy varied by about 4% for the segmentation algorithms. Results confirmed the importance of quality metrics for evaluating the goodness of generated segments because a direct link was observed between the quality of the segments and the classification accuracy achieved. However, the NSR metric is not favoured since it solely considers the number of segments, not the congruity of reference and corresponding image objects.

A smartphone-based apple yield estimation application using imaging features and the ANN method in mature period

Apple yield estimation using a smartphone with image processing technology offers advantages such as low cost, quick access and simple operation. This article proposes distribution framework consisting of the acquisition of fruit tree images, yield prediction in smarphone client, data processing and model calculation in server client for estimating the potential fruit yield. An image processing method was designed including the core steps of image segmentation with R/B value combined with V value and circle-fitting using curvature analysis. This method enabled four parameters to be obtained, namely, total identified pixel area (TP), fitting circle amount (FC), average radius of the fitting circle (RC) and small polygon pixel area (SP). A individual tree yield estimation model on an ANN (Artificial Neural Network) was developed with three layers, four input parameters, 14 hidden neurons, and one output parameter. The system was used on an experimental Fuji apple (Malus domestica Borkh. cv. Red Fuji) orchard. Twenty-six tree samples were selected from a total of 80 trees according to the multiples of the number three for the establishment model, whereby 21 groups of data were trained and 5 groups o data were validated. The R2 value for the training datasets was 0.996 and the relative root mean squared error (RRMSE) value 0.063. The RRMSE value for the validation dataset was 0.284 Furthermore, a yield map with 80 apple trees was generated, and the space distribution o the yield was identified. It provided appreciable decision support for site-specific management.

Meander Line Nanoantenna Absorber for Subwavelength Terahertz Detection

The detection of terahertz electromagnetic waves is crucial for emerging applications within this frequency band, such as spectroscopy, imaging, and communication. Extending the well-developed uncooled infrared focal plane array technology to terahertz frequency regime would be very attractive, but high absorption in the terahertz region with a subwavelength pixel is necessary. In this paper, we proposed a meander line nanoantenna (MLNA) absorber with a metal-insulator-metal structure for subwavelength terahertz absorption. 89% absorption is achieved at the wavelength of 155 μm with a 10 μm pitch size. The MLNA absorber is polarization insensitive and can maintain a high absorption when the incident angle is within 40°. We expect that the proposed MLNA absorber can be integrated with the small pixels of uncooled infrared focal plane array for terahertz detection.

New Updates on the ATLAS ROD Board Implementation for Pixel Layers 1 and 2

This paper intends to briefly overview the new technological updates on the large hadron collider (LHC) A Toroidal LHC ApparatuS (ATLAS) acquisition system of the Pixel Detector. The herein presented Read-Out Driver (ROD) is a Versa Module Europa (VME) board devoted to data processing, configuration, and control. It is designed to provide data formatting, front-end specific error handling, and calibration. This board was initially designed to interface the data sensed by the insertable B-layer (IBL) with the ATLAS Trigger and Data AcQuisition system (TDAQ). IBL is the innermost sensing layer of the ATLAS Pixel Detector, added during the 2013/2014 LHC long shutdown, to withstand higher luminosity and feature higher throughput performance. To read out the new layer of pixels with a smaller pixel size with respect to the other outer layers, a front-end ASIC (FE-I4) was designed. Because of its optimal performance, it was decided to adopt the IBL ROD also for pixel Layers 1 and 2. Among the several advantages, one of the most important is the reduction of link occupancy due to the increased bandwidth (80 Mb/s, two times the previous one); 40 ROD boards, fabricated and tested in 2015, were installed in the Layer 2 acquisition system featuring outstanding performance, while 45 RODs for Layer 1 are still under test and will be installed by the end of 2016.

Prototype High Angular Resolution LEKIDs for NIKA2

The current resolution of the NIKA2 260 GHz arrays is limited by the $1.6\times 1.5 mm^2$ inductor size on the individual pixels. In view of future updates of the instrument, we have developed a prototype array with smaller pixels that is experimentally compared to the current pixel design. We find an in-lab improvement increase of the angular resolution of 8%, promising an on-sky FWHM resolution of 10.2" using this new pixel design.

A study on back irradiation flat panel detector with crystal silicon based x-ray CMOS image sensor

In order to find an image of small-sized defects in a subject that consists of a high Z-number material, the X-ray image sensor should have a high spatial and a high radiometric resolutions for the high energy X-ray imaging. Because the sensors based on thin film transistors cannot make small size pixels, the sensors based on CMOS technology have been considered. Moreover, in order to overcome the degradation of the spatial resolution with a thick scintillator, the back irradiation (BI) method was proposed. In this study, we verified the combination of the BI method and the sensor based on the CMOS technology. From the results of the light yield, which is related to the radiometric resolution, the thin wafer is one of the important factors for enhancing the collection efficiency of the BI method, especially in the collection of the soft X-ray. In addition, the high voltage on the tube helps improve the efficiency of the BI method. From the results of the modulation transfer function, which is related to the spatial resolution, the BI method has a better result compared with the conventional method, which is called front irradiation, no matter the thickness of the scintillators.

Electrically tunable transmission-type beam deflector using liquid crystal with high angular resolution.

Highly efficient transmission-type beam deflectors that have high angular resolution have been widely used for various applications. Continuously tunable beam deflectors have also been needed for many purposes. An indium-tin-oxide (ITO), widely used for transparent electrodes, was placed on the upper and lower glass substrate. The ITO layer on the lower substrate was patterned by the contact mask aligner for relatively wide input and output pad compared to main grating ITO patterns in the active area. These input and output pads on the lower substrate are connected to each driving integrated circuit (IC), which has 360 channels for continuous control. A small pixel pitch of grating patterns of 6 μm (the electrode width is 3 μm with a 3 μm spacing) was developed, and the maximum diffraction angle is calculated and measured at 2.541° with a wavelength of 532 nm. A minimal cell gap of 2.5 μm was applied for the full 2π phase modulation by using a high-birefringence liquid crystal. A driving module for continuous beam steering is also developed and applied to the beam deflector system. A diffraction efficiency of about 50.9% is observed at an angle of diffraction about 2.541°.

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m Pixels

A 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described. The image sensor was fabricated using a wafer process and incorporates back-illumination and an antireflection layer to minimize optical flaring and ghosting problems. In testing, the sensor achieved a polarization transmittance of 63.3% and an extinction ratio of 85 at 550 nm, thereby outperforming conventional polarization sensors. The proposed sensor also exhibited good oblique-incidence characteristics, even with small polarization pixels of $2.5~\mu \text{m}$ . Based on these results, the proposed image sensor is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition-robust surveillance.

Wideband performance analysis of ground-plane cloak designed with polarization-independent randomly patterned metamaterial

A ground-plane cloak is designed based on the quasi-conformal mapping method to hide a perfectly conducting object. It is fabricated with a metamaterial, a mixture of a dielectric and air. Using the dielectric mixing formula, the required volume fraction is calculated for a designed refractive index of the cloak. To guarantee the statistical isotropy of the cloak structure, many small pixels are randomly connected to form the metamaterial. A three-dimensional printing machine is used to implement the whole designed cloak structure. The performance of the cloak is experimentally analyzed over a wide frequency range for both independent polarizations. The measurement is also validated by numerical full-wave simulations. Because the quasi-conformal mapping generates unrealistic refractive indices, less than unity, those are removed. The effect of the truncation is experimentally observed and theoretically analyzed by the ray-tracing method.

An Investigation of Intracluster Light Evolution Using Cosmological Hydrodynamical Simulations

Abstract Intracluster light (ICL) in observations is usually identified through the surface brightness limit (SBL) method. In this paper, for the first time we produce mock images of galaxy groups and clusters, using a cosmological hydrodynamical simulation to investigate the ICL fraction and focus on its dependence on observational parameters, e.g., the SBL, the effects of cosmological redshift-dimming, point-spread function (PSF), and CCD pixel size. Detailed analyses suggest that the width of the PSF has a significant effect on the measured ICL fraction, while the relatively small pixel size shows almost no influence. It is found that the measured ICL fraction depends strongly on the SBL. At a fixed SBL and redshift, the measured ICL fraction decreases with increasing halo mass, while with a much fainter SBL, it does not depend on halo mass at low redshifts. In our work, the measured ICL fraction shows a clear dependence on the cosmological redshift-dimming effect. It is found that there is more mass locked in the ICL component than light, suggesting that the use of a constant mass-to-light ratio at high surface brightness levels will lead to an underestimate of ICL mass. Furthermore, it is found that the radial profile of ICL shows a characteristic radius that is almost independent of halo mass. The current measurement of ICL from observations has a large dispersion due to different methods, and we emphasize the importance of using the same definition when observational results are compared with theoretical predictions.

Effect of Spectral Degradation and Spatio-Energy Correlation in X-Ray PCD for Imaging.

Charge sharing, scatter, and fluorescence events in a photon counting detector can result in counting of a single incident photon in multiple neighboring pixels, each at a fraction of the true energy. This causes energy distortion and correlation of data across energy bins in neighboring pixels (spatio-energy correlation), with the severity depending on the detector pixel size and detector material. If a "macro-pixel" is formed by combining the counts from multiple adjacent small pixels, it will exhibit correlations across its energy bins. Understanding these effects can be crucial for detector design and for model-based imaging applications. This paper investigates the impact of these effects in basis material and effective monoenergetic estimates using the Cramér-Rao Lower Bound. To do so, we derive a correlation model for the multi-counting events. CdTe detectors with grids of pixels with side length of $250~\mu \text{m}$ , $500~\mu \text{m}$ , and 1 mm were compared, with binning of $4\times4$ , $2\times2$ , and $1\times1$ pixels, respectively, to keep the same net 1 mm2 aperture constant. The same flux was applied to each. The mean and covariance matrix of measured photon counts were derived analytically using spatio-energy response functions precomputed from Monte Carlo simulations. Our results show that a 1 mm2 macro-pixel with $250\times 250\,\,\mu \text{m}^{\textsf {2}}$ sub-pixels shows 35% higher standard deviation than a single 1 mm2 pixel for material-specific imaging, while the penalty for effective monoenergetic imaging is <10% compared with a single 1 mm $^{\textsf {2}}$ pixel. Potential benefits of sub-pixels (higher spatial resolution and lower pulse pile-up effects) are important but were not investigated here.

63‐4: Q‐View Technology ‐ Approach to Achieving High Resolution and Low Power in Small Pixel Micro‐Display

This paper presents our Q‐View 4K resolution, 0.55‐inch backplane. The Q‐View technology will be described along with the results from the 4K resolution backplane. The Q‐View technology can be mapped to any base resolution and enhance resolution with little to no additional power consumption.