Large Aperture Size Research Articles

Inverse design of perimeter-controlled InAs-assisted metasurface for two-dimensional dynamic beam steering.

The current commercially viable light detection and ranging systems demand continuous, full-scene, and dynamic two-dimensional point scanning, while featuring large aperture size to ensure long distance operation. However, the biasing architecture of large-area arrays with numerous individually controlled tunable elements is substantially complicated. Herein, inverse design of a perimeter-controlled active metasurface for two-dimensional dynamic beam steering at mid-infrared regime is theoretically presented. The perimeter-control approach simplifies biasing architecture by allowing column-row addressing of the elements. The metasurface consists of a periodic array of plasmonic patch nanoantennas in a metal-insulator-metal configuration, wherein two active layers of indium arsenide are incorporated into its building block. The metasurface profile facilitates wide phase modulation of on the reflected light at the individual element level through applying independent voltages to its respective columns and rows. The multi-objective genetic algorithm (GA) for optimizing user-defined metrics toward shaping desired far-zone radiation pattern is implemented. It is demonstrated that multi-objective GA yields better results for directivity and spatial resolution of perimeter-controlled metasurface by identifying the design tradeoffs inherent to the system, compared to the single-objective optimizer. A high directivity and continuous beam scanning with full and wide field-of-view along the azimuth and elevation angles are respectively maintained.

Mixed precipitants derived nanocrystalline powders and RE doped LuAG transparent ceramics

Lu3Al5O12 (LuAG) nanocrystalline powders were synthesized by using ammonium hydroxide (NH4OH, AH) and ammonium hydrogen carbonate (NH4HCO3, AHC) as mixed precipitant. In the absence of sintering aids such as TEOS, MgO or ZrO2, the obtained LuAG powders showed good sinterability in H2 atmosphere (PLSH) at low temperature. The in-line transmittance of LuAG ceramic reached 81% in the whole visible light band from 400 nm to 800 nm. The average grain size of obtained transparent ceramics was ranged in 1–6 μm at different sintering temperatures by PLSH. Various kinds of rare earth ions, such as Nd, Yb, Ce, Pr, and Tm doped RE:LuAG transparent ceramics could be prepared by PLSH technology without sintering aids and HIP post-treatment. Through PLSH technology, RE:LuAG transparent ceramics show high optical quality and large aperture size.

Modeling of Relative Intensity Noise in QD-VCSEL

In this paper, the dynamics and statics properties of a 1.3 m InAs/InGaAs Quantum-Dot (QD) vertical-cavity surface-emitting laser (VCSEL) have been investigated using a self-consistent coupled rate-thermal equations model. Results demonstrate that self-heating caused by current transition through the Bragg mirrors and active area of the laser produces temperature rise and deteriorates the performance of the laser where it is most apparent at higher temperatures. Although the minimum value of Relative intensity noise (RIN) and the turn-on delay and maximum value of the output power occurs at the same bias current, the maximum achievable 3-dB modulation bandwidth is obtained at lower bias currents. In addition, the larger aperture size and the greater number of QD layers modify the self-heating and enhance the efficiency and output characteristics of the laser where the rolled-off of the laser happens at higher bias currents.

Risk factors for the development of a parastomal hernia in patients with enterostomy: a systematic review and meta-analysis.

Parastomal hernia (PSH) is a common and serious complication in patients with enterostomy, but there is no current consensus for the risk factors for PSH from previous studies. Therefore, this study systematically analyzed the risk factors for PSH to provide a reference for prevention and treatment of this condition. Seven databases and 3 registers were systematically searched from database inception to January, 2021. Study quality was assessed by Newcastle-Ottawa Scale. Review Manager 5.3 software was used for statistical analysis. The data that could not be combined quantitatively were only analyzed qualitatively. Sixteen studies with 2031 patients were included. Higher BMI (OR, 1.29; 95% CI,1.02-1.63), older age (OR, 1.04; 95% CI, 1.02-1.07), female (OR, 2.55; 95% CI,1.39-4.67), lager aperture size (OR, 2.8; 95%CI, 1.78-4.42), transperitoneal stoma creation (OR, 2.4; 95% CI, 1.33-4.35), and lager waist circumference (OR, 1.01; 95% CI,1.0-1.01) were significant risk factors for PSH. The laparoscopic approach was not a risk factor for PSH (OR, 2.09; 95% CI, 0.83-5.27). Other risk factors, including the thickness of abdominal subcutaneous fat, no mesh, a stoma not through the middle of the rectus abdominis, atrophy of left lower medial part of rectus abdominis, α1(III) procollagen expression level, emergency surgery, no preoperative stoma site marking, end colostomy, smoking, diabetes, peristomal infection, severe abdominal distention, severe cough, chronic obstructive pulmonary disease, operation time and hypertension, were significant on the multivariate analysis of each individual study. The current available evidence showed that higher BMI, older age, female, larger aperture size, the creation of a transperitoneal stoma, and a larger waist circumference were independent risk factors for PSH. For factors without exact cutoff value, further explorations are needed in the future. In addition, reference to the limited number of studies in the pooled analysis, these factors still need to be interpreted carefully.

IRS-Assisted OAM-MIMO Communication with Partial Arc Sampling Receiving(PASR) Scheme

Orbital Angular Momentum-based Multiple Inputs Multiple Outputs (OAM-MIMO) Communication has recently been explored in wireless communication to provide an alternative way of multiplexing different orthogonal OAM modes over a common medium and significantly improve reliability, capacity, and energy efficiency. Although the near-field applications of radio vortex have been successfully verified in a near-field line-of-sight scenario, perfect antenna misalignment should be required to maintain orthogonality, which is difficult to be satisfied in a multipath environment consisting of many non-line-of-sight(NLOS) paths and LOS path. In addition, beam spread and divergence reduce the transmission distance accompanied by large performance degradation, thus requiring a large aperture size receiving for efficient detection of OAM modes. This paper studies the communication performance of OAM-MIMO with the PASR (Partial Aperture Sampling Receiving) scheme by deploying an intelligent reflective surface (IRS) of a large number of reconfigurable passive elements to achieve an intelligent wireless propagation environment through software-controlled reflection and address the above issues and limitations under the Perfect Channel State Information (CSI). We analyze the concepts of PASR and OAM mode selection by preserving orthogonality according to the required aperture scale, and the influence of the Rayleigh and Rician channels on the system performance of IRS-Assisted OAM-MIMO Communication with the PASR scheme in a multipath environment. The simulation results show that the channel capacity for IRS-assisted OAM-MIMO Communication with the PASR scheme is greatly improved compared with IRS-assisted OAM-MIMO Communication, which can meet the performance requirements, and provide insights into the angular aperture needed for efficient (de)-multiplex OAM modes, and performance limit over propagation distance.

Design and Numerical Analysis of an Infrared Cassegrain Telescope Based on Reflective Metasurfaces.

Reflective imaging systems such as Cassegrain-type telescopes are widely utilized in astronomical observations. However, curved mirrors in traditional Cassegrain telescopes unavoidably make the imaging system bulky and costly. Recent developments in the field of metasurfaces provide an alternative way to construct optical systems, possessing the potential to make the whole system flat, compact and lightweight. In this work, we propose a design for a miniaturized Cassegrain telescope by replacing the curved primary and secondary mirrors with flat and ultrathin metasurfaces. The meta-atoms, consisting of SiO2 stripes on an Al film, provide high reflectance (>95%) and a complete phase coverage of 0~2π at the operational wavelength of 4 μm. The optical functionality of the metasurface Cassegrain telescope built with these meta-atoms was confirmed and studied with numerical simulations. Moreover, fabrication errors were mimicked by introducing random width errors to each meta-atom; their influence on the optical performance of the metasurface device was studied numerically. The concept of the metasurface Cassegrain telescope operating in the infrared wavelength range can be extended to terahertz (THz), microwave and even radio frequencies for real-world applications, where metasurfaces with a large aperture size are more easily obtained.

Iterative parallel registration of strongly misaligned wavefront segments.

The paper presents an algorithm for the precise registration of multiple wavefront segments containing large misalignment and phase differences. The measurement of a wavefront with huge dynamics or a large aperture size can be carried out in multiple Shack-Hartmann sensor measurements of segments of the wavefront. The registration algorithm is flexible with respect to the shape of the wavefront and can reconstruct a plane as well as divergent wavefronts, making it suitable for freeform wavefronts. The algorithm enables parallel registration of the wavefront segments which is carried out in an iterative manner to compensate for large misalignment errors. A simulative analysis of the proposed algorithm compares its performance to a fast parallel registration (FPR) algorithm and the established iterative closest point (ICP) algorithm. For a sensor misalignment of up to 100 μm and 3 mrad the algorithm registers a plane and a divergent wavefront with a precision that is a factor 4 and 12 better than the registration precision of the FPR and ICP algorithm.

Simulation of Corneal imaging properties for near objects.

Using raytracing simulation to study the effect of corneal imaging metrics for different aperture sizes as a function of object distances with different schematic model eyes. This raytracing simulation determined the best focus (with the least root-mean-square (rms) ray scatter) and the best wavefront focus (with least rms wavefront error) for four schematic model eyes (Liou-Brennan (LBME), Atchison (ATCHME), Gullstrand (GULLME) and Navarro (NAVME)) with 4 aperture sizes (2-5mm) and 30 object distances in a logscale from 10cm to 10m plus infinity. For each configuration, 10,000 rays were traced through the cornea, and the aperture stop was located at the lens front apex plane as described in the model eyes. The wavefront was decomposed into Zernike components to extract the spherical aberration term. The focal distance with respect to the corneal front apex increases from around 31mm for objects at infinity to around 40mm for objects at 10cm. The best (wavefront) focus was systematically closer to the cornea compared with the paraxial focus, and the overestimation of focal length with the paraxial focus was larger for large aperture sizes and small object distances. The rms ray scatter and wavefront error were both systematically larger with large aperture and small object sizes. At best focus the rms wavefront error was systematically larger, and the rms ray scatter was systematically smaller compared to the best wavefront focus. Spherical aberration varied more with GULLME than with LBME or NAVME, and increased strongly at smaller object distances. The imaging properties of the cornea, especially spherical aberration, increase strongly as the object distance decreases. This effect should be considered, especially when considering aberration correcting lenses for near vision such as multifocal or enhanced depth of focus lenses.

Large-pore covalent organic frameworks for ultra-fast tight ultrafiltration (TUF)

Tight ultrafiltration (TUF) membranes featuring specific pore sizes are increasingly developed to bridge the gap between nanofiltration and ultrafiltration. So far, a wealth of efforts has been devoted to tackle the limitation found in TUF, but there still lacks a facile accessibility to upgrade TUF membranes with simultaneously improved permeance and selectivity. Herein, we report a large-pore covalent organic framework (LP-COF) as the building material to prepare ultra-permeable TUF membranes for fast separations. The LP-COF layers with an exceptionally large aperture size of up to ~3.6 nm are synthesized on macroporous substrates through a unidirectional diffusion method. The resultant LP-COF layers show a moderate crystallinity and low thickness down to ~60 nm, and allow ultrafast water permeation. Surprisingly, the optimal LP-COF membrane exhibits an unprecedented water permeance of ~3147 L m−2 h−1 MPa−1 with a high Congo red rejection (~92.6%), which is basically unchanged after several cycles of filtration. Moreover, the large-pore channels enable an unimpeded pass of ions, thus affording the membrane an excellent dye/salt separation competence, and largely exceeding state-of-the-art membranes. Therefore, this work opens up a new opportunity in producing high-performance TUF membranes by large-pore COFs for rapid and precise separations.

A Novel Demultiplexing Scheme for Vortex Beams in Radio Communication Systems

The orbital angular momentum (OAM) based communication is a promising technology in the wireless communication system for its improving spectrum efficiency. However, for the OAM demultiplexing, it requires a very large aperture size in the receiving end due to the OAM beam divergence and the amplitude null in the beam center, which restricts the full development of OAM based communication. In this paper, we propose a novel partial arc sampling receiving (PASR) scheme based on the augmented dynamic mode decomposition (ADMD) to solve this issue. We explore the use of the phase delay coordinates in the conventional DMD to sort the arbitrary OAM modes with arc sampling receiving. Simulation results demonstrate the accuracy and robustness of the proposed approach in sorting both integral and fractional OAM modes with the PASR scheme. Our work offers a practical approach for demultiplexing OAM beams in radio communication systems with fewer receiving devices, especially for the long-distance transmission case.

Spatially variant autofocus for circular synthetic aperture sonar.

Circular synthetic aperture sonar (CSAS) is a method for improving the resolution and target detection capabilities of a synthetic aperture sonar system. CSAS data are difficult to focus because of their large aperture sizes and elevation sensitivity. This difficulty has sometimes been addressed by using transponders or distributing isotropic scatterers in the field of view of the system; however, this comes at the cost of reduced practicality. As an alternative, map-drift based multipoint autofocus ("multilateration") was proposed by Cantalloube and Nahum [IEEE Trans. Geosci. Remote Sens. 49, 3730-37 (2011)] for autofocusing analogous circular synthetic aperture radar data. Multilateration also solves the problem of aberration spatial variance by providing a three-dimensional navigation correction. In circular synthetic aperture focusing problems, though, correcting aberrations is a joint navigation and elevation estimation problem, and the present work extends the multilateration approach to simultaneously solve both a navigation solution and coordinate corrections for the multilateration control patches. Additionally, methods for addressing the stability and behavior of the inverse problem are addressed, and an adaptive weighting scheme for reducing the influence of outliers is presented. The field results demonstrate near optimal point-spread functions on distributions of natural isotropic scatterers and robustness in regions with bathymetric variability.

Regulatable pervaporation performance of Zn-MOFs/polydimethylsiloxane mixed matrix pervaporation membranes

Pervaporation (PV) is an emerging separation technique for liquid mixture. Mixed matrix membranes (MMMs) often demonstrate trade-off relationship between separation factor and flux. In this study, by changing the organic linkers (2-methyl imidazolate, imidazole-2-carboxaldehyde, 2-ethyl imidazolate), ZIF-8, ZIF-90 and MAF-6 were prepared and filled in polydimethylsiloxane (PDMS) membranes for dealcoholization of 5% (mass) n-butanol solution, and the membranes properties and pervaporation performances were adjusted. Compared with the pure PDMS membrane, the addition of ZIF-8 resulted in a 9% increase in flux (1136 g·m−2·h−1) and a 22.5% increase in separation factor (28.3), displaying anti-trade-off effect. For the MAF-6/PDMS MMMs (2.0% mass loading), the pervaporation separation index (PSI) and separation factor were 32347 g·m−2·h−1 and 58.6 respectively (increased by 34% and 154% in contrast with that of the pure PDMS membrane), and the corresponding permeation flux was 552 g·m−2·h−1, presenting great potential in the removal butanol from water. It was deduced that the large aperture size combined with moderate hydrophobicity of metal–organic frameworks (MOFs) favor the concurrent increase in permeability and selectivity.

Advances in Transparent Planar Optics: Enabling Large Aperture, Ultrathin Lenses

AbstractUnlike electronics, optics do not follow Moore's law. This statement, expressed by Microsoft's Bernard Kress, refers to the hard challenges to solve in augmented reality hardware. While light sources have undergone numerous revolutions from candles to light emitting diodes, the evolution in transparent optics has been much slower. For transparent materials, variation of the shape, bulk refractive index, and/or its distribution leads to control of the transmitted beam in an optical system. An alternative, the control of the optical axis orientation in an anisotropic material in transparent micrometer‐thin films on a variety of substrates, is explored here. In contrast to metamaterials, these diffractive waveplates have a continuous structure allowing multilayer/multifunctional planar optical systems with close to 100% efficiency across broad bands of wavelengths (ultraviolet to infrared) with customizable spectra. The low‐cost and fast fabrication technology of this fourth generation of optics is scalable to very large aperture sizes. In addition to wearable adaptive optics, the technology enables thin and compact non‐mechanical fast beam steering systems for light detection and ultralight space telescopes. This review will first serve as an introduction to these unique transparent, planar optical films, and then recent advances enabled by specific optical designs will be presented.

High field X-ray laser physics

High field X-ray laser physics

Deep learning approach to improve tangential resolution in photoacoustic tomography.

In circular scan photoacoustic tomography (PAT), the axial resolution is spatially invariant and is limited by the bandwidth of the detector. However, the tangential resolution is spatially variant and is dependent on the aperture size of the detector. In particular, the tangential resolution improves with the decreasing aperture size. However, using a detector with a smaller aperture reduces the sensitivity of the transducer. Thus, large aperture size detectors are widely preferred in circular scan PAT imaging systems. Although several techniques have been proposed to improve the tangential resolution, they have inherent limitations such as high cost and the need for customized detectors. Herein, we propose a novel deep learning architecture to counter the spatially variant tangential resolution in circular scanning PAT imaging systems. We used a fully dense U-Net based convolutional neural network architecture along with 9 residual blocks to improve the tangential resolution of the PAT images. The network was trained on the simulated datasets and its performance was verified by experimental in vivo imaging. Results show that the proposed deep learning network improves the tangential resolution by eight folds, without compromising the structural similarity and quality of image.

Impact of Aperture, Depth, and Acoustic Clutter on the Performance of Coherent Multi-Transducer Ultrasound Imaging.

Transducers with a larger aperture size are desirable in ultrasound imaging to improve resolution and image quality. A coherent multi-transducer ultrasound imaging system (CoMTUS) enables an extended effective aperture through the coherent combination of multiple transducers. In this study, the discontinuous extended aperture created by CoMTUS and its performance for deep imaging and through layered media are investigated by both simulations and experiments. Typical image quality metrics—resolution, contrast and contrast-to-noise ratio—are evaluated and compared with a standard single probe imaging system. Results suggest that the image performance of CoMTUS depends on the relative spatial location of the arrays. The resulting effective aperture significantly improves resolution, while the separation between the arrays may degrade contrast. For a limited gap in the effective aperture (less than a few centimetres), CoMTUS provides benefits to image quality compared to the standard single probe imaging system. Overall, CoMTUS shows higher sensitivity and reduced loss of resolution with imaging depth. In general, CoMTUS imaging performance was unaffected when imaging through a layered medium with different speed of sound values and resolution improved up to 80% at large imaging depths.

Range-Angle Coupling and Near-Field Effects of Very Large Arrays in mm-Wave Imaging Radars

In order to improve the resolution of imaging radars, electrically large arrays and a high absolute modulation bandwidth are needed. For radar systems with simultaneously high range resolution and very large aperture, the difference in path length at the receiving antennas is a multiple of the range resolution of the radar, in particular for off-boresight angles of the incident wave. Therefore, the radar response of a target measured at the different receiving antennas is distributed over a large number of range cells. This behavior depends on the unknown incident angle of the wave and is, thus, denoted as range-angle coupling. Furthermore, the far-field (FF) condition is no longer fulfilled in short-range applications. Applying conventional signal processing and radar calibration techniques leads to a significant reduction of the resolution capabilities of the array. In this article, the key aspects of radar imaging are discussed when radars with both large aperture size and high absolute bandwidth are employed in short-range applications. Based on an initial mathematical formulation of the physical effects, a correction method and an efficient signal processing chain are proposed, which compensate for errors that occur with conventional beamforming techniques. It is shown by measurements that with an appropriate error correction an improvement of the angular resolution up to a factor of 2.5 is achieved, resulting in an angular resolution below 0.4° with an overall aperture size of nearly 200λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> .

Experiments with Stand-Alone Sand-Screen Specimens for Thermal Projects

Summary Most of the test protocols developed to evaluate sand-screen designs were based on scaled-screen test coupons. There have been discussions regarding the reliability of such tests on scaled test coupons. This paper presents the results of tests on wire-wrapped screen (WWS) and slotted liner (SL) test coupons for typical onshore Canada McMurray formation sand. A unique sand control evaluation apparatus has been designed and built to accommodate all common stand-alone screens that are 3.5 in. in diameter and 12 in. in height. This setup provides the capability to have a radial measurement of pressure across the sandpack and screen for three-phase flow. Certain challenges during testing such as establishing uniform radial flow and measuring the differential pressure are outlined. Produced sand is also measured during the test. The main outputs of the test are to assess the sand control performance and the mode of sanding in different flow directions, flow rates, and flow regimes. It was possible to establish uniform radial flow in both high- and low-permeability sandpacks. However, the establishment of radial flow in sandpacks with very high permeability was challenging. The pressure measurement at different points in the radial direction around the screen indicated a uniform radial flow. Results of the tests on a representative particle size distribution (PSD) from the McMurray Formation on the WWS and SL test coupons with commonly used specifications in the industry (aperture sizes of 0.012, 0.014, and 0.016 in. for WWS and 0.012, 0.016, 0.018, and 0.020 in. for SL) have shown similar sanding and flow performances. We also included aperture sizes smaller and larger than the common practice. Similar to previous tests, narrower apertures are proven to be less resistant to plugging than wider slots for both WWS and SL. Accumulation of fines close to the screen causes significant pore plugging when conservative aperture sizes were used for both WWS and SL. In contrast, using the test coupon with a larger aperture size than the industry practice resulted in excessive sanding. The experiments under linear flow seem more conservative because their results show more produced sand and smaller retained permeability in comparison to the testing under radial flow. This work discusses the significance, procedure, challenges, and early results of physical modeling of stand-alone screens in thermal operation. It also provides insight into the fluid flow, fines migration, clogging, and bridging in the vicinity of sand screens.

A High-Efficiency Conformal Transmitarray Antenna Employing Dual-Layer Ultrathin Huygens Element

A high-efficiency conformal transmitarray with ultrathin dual-layer Huygens element is developed. The element consists of “I” shape patches for magnetic response and “T” shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /60 at 10 GHz). By tuning the magnetic and electric responses, the transmitting phase of the element can be changed. Eight elements are designed to cover quantized 360° phase range with a maximal 1.67 dB loss. Then, the proposed elements are employed in a small conformal transmitarray design. To improve the antenna efficiency, the elements' dimensions are calculated by considering the oblique incidence effects. Finally, a cylindrically conformal transmitarray with a larger aperture size is simulated, fabricated, and measured. It can achieve a measured gain of 20.6 dBi with a 47% aperture efficiency.

A 10 240-Element Reconfigurable Reflectarray With Fast Steerable Monopulse Patterns

A large-scale 1-bit reconfigurable reflectarray with the feature of fast steerable monopulse patterns has been designed and tested at X-band. The reflectarray element integrates one PIN diode to reconfigure the reflective phase between 0° and 180°. The entire reflectarray is composed of 160 × 64 elements, with a total size of 2.56 m × 1.024 m. Critical design issues, including element modeling, subarray optimization, and feed horn selection, are investigated to achieve good radiation performance. For the purpose of realizing fast beam steering, 160 field-programmable gate arrays (FPGAs) are adopted to control “ON/OFF” states of every p-i-n diodes in parallel. Digital beam forming methods have been applied to scan both the sum and difference beams. The reflectarray has been fabricated and measured in an anechoic chamber, and a high gain (37.4 dBi) with relatively good aperture efficiency (17.1%) has been realized in such a large-aperture size. Precise monopulse beam steering within ±60° azimuth range has been achieved with the switching time of only 2 μs. This largeaperture reflectarray shows promising applications for tracking and detecting systems.