Scan Angle Research Articles

Fast Backprojection Filtration Algorithm in Circular Cone-Beam Computed Tomography

In order to meet the heavy backprojection calculation of the backprojection filtration (BPF) algorithm in circular cone-beam computed tomography (CT), a fast backprojection method is developed, which uses the integral operator of the fixed scanning angle integral interval. The proposed method combines with Hilbert filtration and the filter of the Blackman window, and then, the fast BPF (F-BPF) algorithm is obtained. The experimental results of simulation data and real data demonstrate that the proposed algorithm is fast enough for high-quality reconstructed images only with half-circle projection data.

Cascaded 2D Micromirror with Application to LiDAR.

This paper introduced a novel approach to enhance the vertical scanning angle of a large aperture 2D electromagnetic micromirror through the utilization of a cascaded torsional beam design. The primary objective was to increase the vertical scanning angle without compromising the robustness, which was achieved by optimizing the trade-off between the rotation angle and the first mode of resonant frequency. The cascaded design provides flexibility to either increase the outer frame's rotation angle without sacrificing torsional stiffness or enhance the torsion beam's stiffness while maintaining the same rotation angle, thus elevating the first-mode resonant frequency and overall robustness. The effectiveness of the cascaded design was demonstrated through a comparative study with a non-cascaded 2D micromirror possessing the same aperture size, torque, and mass moment of inertia. Theoretical analysis and finite-element simulation are employed to determine critical parameters such as the stiffness ratio between the cascaded torsion beams, and to predict improvements in the scanning angle and primary resonant frequency brought by the cascaded design. Prototypes of both cascaded and non-cascaded designs are fabricated using a flexible printed circuit board combined with Computer numerical control (CNC) machining of a Ti-alloy thin film, confirming the superior performance of the cascaded 2D micromirror. The cascaded design achieved vertical scanning angles up to 26% higher than the traditional design when both were actuated at close resonance frequencies. Additionally, the micromirror was successfully integrated into a 3D LiDAR system. The light detection and ranging (LiDAR) system was modelled in Zemax OpticStudio to find the optimized design and assembly positions.

Preparation of chitosan/citral forward osmosis membrane via Schiff base reaction with enhanced anti-bacterial properties

In this study, hydrogels generated by the Schiff base reaction between citral and chitosan (CS) were used for the first time to improve the anti-bacterial property of forward osmosis (FO) membranes. The composite membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Water contact angle (WCA), Zeta potential and confocal laser scanning microscopic (CLSM). In the FO filtration experiment, the membrane performance of TFC-1 with 1 M sodium chloride solution as the draw solution and deionized water as the feed solution was the best, with the water flux of 25.54 ± 0.7 L m−2 h−1 and the reverse salt flux of 4.7 ± 0.4 g m−2 h−1. Although the hydrogel coating produced a certain hydraulic resistance, the flux of the modified membrane was only reduced by about 8%, compared with the unmodified membrane. However, the anti-bacterial property (Pseudomonas aeruginosa) and anti-fouling properties (bovine serum protein and lysozyme protein) of the modified membranes were improved, showing good antibacterial properties (99%) and flux recovery rate (over 90%). The modified method has the advantages of easy access to raw materials, simple operation and no risk of secondary pollution, which can effectively reduce the cost of chemical cleaning and extend the service life of the membrane. The modification of membrane by chitosan-based hydrogel is a promising option in the field of membrane anti-bacteria.

Analysis of tightly-coupled dipole phased array antennas with metasurface superstrate

Tightly coupled dipole arrays, including connected arrays, and capacitively coupled arrays, are one of the best solutions for wideband phased array antenna designs. However, to increase bandwidth and maximum scan angle, we can use a metasurface superstrate. We propose an analytical model to compute the scan impedance of a tightly coupled dipole array loaded with a metasurface. This analytical model helps us to simplify the calculation of the scan impedance of the array and speeds up the design process of these array antennas. It is shown that the metasurface superstrate improves the bandwidth and beam scanning angles of the array. Using the proposed general transmission line model, the computation of the scan impedance of tightly coupled dipole arrays is done very fast with minimum error. The semi-analytical model is about 7 times faster than a full-wave simulation.

Lissajous MEMS laser beam scanner with uniform and high fill-factor projection for augmented reality display.

MEMS Laser beam scanning (LBS) has been identified as a key advancement for augmented reality (AR) displays due to its ability to create compact optical systems that generate bright, high-contrast images with minimal heat dissipation. This innovation can be attributed to the focus-free, efficient light-on-demand pixel projection mechanisms integral to LBS. The LBS, specifically in Lissajous-mode, outperforms the raster-mode in terms of larger scan angles and stability to external vibrations, by leveraging a MEMS mirror operating at bi-axial resonance. However, it tends to be hampered by small mirror aperture, low fill-factor, and inconsistent uniformity of image projection. In this research, a unique gimbal-less Lissajous MEMS scanner was proposed. It employs a bi-axial high frequency of 12,255 Hz and 7,182 Hz to achieve a resolution of 640 × 360 pixels and a video refresh rate of 57 Hz, all while maintaining a high image fill factor of 85.11%. The robust structure of the mirror is proven to sustain stable scanning under broad spectrum of external vibration disturbance up to 2,000 Hz. Furthermore, the large mirror diameter of 2 mm improves refined pixel projection and increased optical etendue for exit pupil. Mathematic model of Lissajous pixel-cells and image reconstruction simulation were established to validate the LBS's ability to generate a uniform and densely pixelated visual effect that fits for typical AR head-up display (AR-HUD). In a pioneering move, performance metric of figure-of-merit was defined to evaluate AR light-engines using varied picture-generation techniques, laying a foundation for guiding future AR system development.

Correction of scanning laser Doppler vibrometer measurements when subjected to six degree-of-freedom base motion

Scanning laser Doppler vibrometer (SLDV) measurements are affected by sensor head vibrations as though they are vibrations of the target surface itself. Previous work has established a fully general theoretical analysis which shows that the only measurement required for measurement correction is of the vibration velocity at the incident point on the final steering mirror in the direction of the outgoing laser beam. Two practical—but not quite perfect—options for measurement correction were presented (one more suitable to manufacturer implementation, one more applicable to the vibration engineer end user). In both cases, placement of the correction transducer is critical with correction working for totally arbitrary instrument vibration and scan angle. Experimental validation, employing frequency-domain based processing, has been completed for one degree-of-freedom, on-axis vibration. Simultaneously, advancements in the data processing approach have realised improved correction in practice, especially for lower frequencies and for transient, as opposed to statistically stationary, vibration. In this paper, extension of the experimental validation to six degree-of-freedom instrument vibration is presented for the first time. In combination with the latest data processing approaches, reductions in the measurement error of 29.4 and 28.2 dB for the frequency- and time-domain processing techniques, respectively, are realised.

Rosette‐scan tomographic single‐pixel imager

AbstractSpin‐scan tomographic scanning imagers utilise a reticle with a fixed number of thin slits and nutating optics, and have produced images and video at both infrared and optical wavelengths. However, the fixed nature of these systems reduces their versatility by restricting changes that can be made after manufacture. An alternative rosette‐scan tomographic scanning imager based on similar concepts is proposed to overcome this limitation. A single thin‐slit reticle is rotated to be perpendicular to the line scan angle of each rosette petal, thereby allowing tomographic reconstruction. The parameters of the proposed system can be dynamically changed to achieve different trade‐offs between resolution and frame rate. Initial results obtained from a proof‐of‐concept prototype demonstrate the feasibility of this approach.

Real-Time 3D Liver Tumor Localization via Combined Optical Surface Imaging and an X-Ray Projection from Arbitrary Imaging Angles

A deep learning (DL)-based, deformable registration-driven liver tumor localization technique was developed for onboard deformable motion tracking. The technique (Surf-X360-Bio) uses in-room optical surface imaging and an x-ray projection at an arbitrary scan angle to solve volumetric liver and liver tumor motion in real-time. Surf-X360-Bio solves the volumetric motion of the liver and localizes the liver tumor, through deforming liver and liver tumor meshes segmented on prior 4D-CTs/CBCTs. It uses real-time onboard information from an optical surface image and a simultaneously-acquired x-ray projection (from an arbitrary scan angle). Surf-X360-Bio localizes tumors via two steps: liver boundary motion estimation and intra-liver motion derivation. Surf-X360-Bio first estimates liver boundary motion by a patient-specific surface imaging model (Surf), utilizing the correlation between the external body surface motion and the internal liver boundary motion. As the correlation can be imperfect, the residual motion estimation errors were corrected by a patient-specific, angle-agnostic x-ray imaging model (X360). X360 deformed the liver boundary to match motion-related imaging features encoded in an arbitrarily-angled x-ray projection, using the Surf output for initialization. X360 adopted a geometry-aware learning module to extract and adapt to angle-varying features of arbitrarily-angled x-ray images, by calculating the projection system matrix of each x-ray image on-the-fly during model training and inference. After the liver boundary motion estimation by Surf and X360, intra-liver deformation was solved by a biomechanical model (Bio) to propagate the liver boundary motion inside to localize the tumors. The DL-based Bio model used domain knowledge of tissue biomechanics and finite element analysis (FEA) to solve intra-liver motion, with a much faster speed than conventional FEA methods to meet the real-time constraint. Surf-X360-Bio was evaluated using a dataset of 34 liver patients. Liver tumor localization accuracy was evaluated by the Dice similarity coefficient (DSC), the 95-percentile Hausdorff distance (HD95), and the center-of-mass error (COME). Using 3,306 motion scenarios spanning the 360 degree x-ray scan angles for each testing patient, Surf-X360-Bio localized the liver tumors to 0.81 (mean) ± 0.16 (s.d.) in DSC, 2.5 ± 1.7 mm in HD95, and 2.1 ± 1.8 mm in COME. In comparison, the prior reference image without deformable registration-driven localization yielded 0.42 ± 0.29 in DSC, 8.1 ± 5.2 mm in HD95, and 8.5 ± 5.2 mm in COME. Via Surf-X360-Bio, the overall inference time was below 230 ms for each case. Combining optical surface imaging and x-ray imaging, Surf-X360-Bio achieved fast (<250 ms inference time), accurate (mean error < 2.1 mm), and robust liver tumor localizations at arbitrary x-ray scan angles for real-time, marker-less 3D deformable motion tracking.

Experimental realization of an ultra-thin and continuous scanning metasurface mimicking a Luneburg lens

Luneburg lens is traditionally a spherical dielectric with centro-symmetric and graded refractive index, which has been widely applied in civilian and military fields due to its outstanding abilities of focusing or collimating electromagnetic waves. However, the existing designs of Luneburg lens generally suffer from the disadvantages of bulkiness, complex fabrication process, and limited scanning angles, etc. Herein, a planar metasurface that could mimic the planar Luneburg lens is designed by utilizing the addition theorem. It has been experimentally verified that the Luneburg-like lens has large and continuous scanning angles from −52° to 52° at a frequency of 10 GHz if an excitation antenna is moved along a straight line. Besides, the total thickness of the proposed lens is only 3 mm and it has the advantages of low cost, ease of fabrication, as well as being isolated from the feeder. As a result, the proposed Luneburg-like lens has great potential values of being flexibly applied in numerous fields.

Real-time hybrid angular-interrogation surface plasmon resonance sensor in the near-infrared region for wide dynamic range refractive index sensing

Herein, we integrated angle-scanning surface plasmon resonance (SPR) and angle-fixed SPR as a hybrid angular-interrogation SPR to enhance the sensing performance. Galvanometer-mirror-based beam angle scanning achieves a 100-Hz acquisition rate of both the angular SPR reflectance spectrum and the angle-fixed SPR reflectance, whereas the use of near-infrared light enhances the refractive index (RI) sensitivity, range, and precision compared with visible light. Simultaneous measurement of the angular SPR reflectance spectrum and angle-fixed SPR reflectance boosts the RI change range, RI resolution, and RI accuracy to 10–1–10–6 RIU, 2.24 × 10−6 RIU, and 5.22 × 10−6 RIU, respectively. The proposed hybrid SPR is a powerful tool for wide-dynamic-range RI sensing with various applications.

MmWave Zero Order Resonant Antenna with Patch-Like Radiation Fed by a Butler Matrix for Passive Beamforming.

A small zero-order resonant antenna based on the composite right-left-handed (CRLH) principle is designed and fabricated without metallic vias at 30 GHz to have patch-like radiation. The mirror images of two CRLH structures are connected to design the antenna without via holes. The equivalent circuit, parameter extraction, and dispersion diagram are studied to analyze the characteristics of the CRLH antenna. The antenna was fabricated and experimentally verified. The measured realized gain of the antenna is 5.35 dBi at 30 GHz. The designed antenna is free of spurious resonance over a band width of 10 GHz. A passive beamforming array is designed using the proposed CRLH antenna and the Butler matrix. A substrate integrated waveguide is used to implement the Butler matrix. The CRLH antennas are connected to four outputs of a 4×4 Butler matrix. The scanning angles are 12∘, -68∘, 64∘, and -11∘ for excitations from port 1 to port 4 of the 4×4 Butler matrix feeding the CRLH antenna.

Low Power Compact 3D-Constructed AlScN Piezoelectric MEMS Mirrors for Various Scanning Strategies.

In this paper, the newly developed 3D-constructed AlScN piezoelectric MEMS mirror is presented. This paper describes the structure and driving mechanism of the proposed mirror device, covering its driving characteristics in both quasi-static and resonant scan modes. Particularly, this paper deals with various achievable scan patterns including 1D line scan and 2D area scan capabilities and driving methods to realize each scanning strategy. Bidirectional quasi-static actuation along horizontal, vertical, and diagonal scanning directions was experimentally characterized and even under a low voltage level of ±20 V, a total optical scan angle of 10.4° was achieved. In addition, 1D line scanning methods using both resonant and non-resonant frequencies were included and a total optical scan angle of 14° was obtained with 100 mVpp under out-of-phase actuation condition. Furthermore, 2D scan patterns including Lissajous, circular and spiral, and raster scans were realized. Diverse scan patterns were realized with the presented AlScN-based MEMS mirror device even under a low level of applied voltage. Further experiments using high voltage up to ±120 V to achieve an enhanced quasi-static scan angle of more than 20° are ongoing to ensure repeatability. This multi-functional MEMS mirror possesses the potential to implement multiple scanning strategies suitable for various application purposes.

Wide-Angle Scanning Microstrip Patch Antenna Array for mmWave Applications with High Gain

This paper presents a modified rectangular microstrip patch antenna (MRMPA) array conforming to the hemisphere for wide-angle beam scanning. Two different conformal antenna array designs are presented in this work. The first of these designs, a 13-element MRMPA array conformal to the surface of a circular arc, and the second one, a 9-element array conformal to the surface of a hemisphere, are designed and optimized. The geometrical approach of calculating the phase value is used to calculate the phase value of each antenna. The simulated results show that the 13-element conformal MRMPA array is achieving a beam scanning angle of ±84° with a gain of 13.89 dBi with low side lobe levels, and further, the gain of the array is enhanced by a dielectric superstrate that improved the gain by ∼2 dBi at all the scanning angles. Second, an MRMPA array conformal to a hemisphere with nine elements is designed with beam scanning ability from φ = 0°−360° and θ = ±30° with a gain of 15.69 dBi, and further, the gain is enhanced by ∼3 dBi with the dielectric superstrate. Full-wave simulations have proven both designs to be accurate and aligned with theoretical calculations.

Minimum Corneal Diameter and Anterior Steep Axis Curvature Share the Same Meridian: A Novel Finding

To define the external scleral sulcus (ESS) on a Scheimpflug image and use it for a morphometric analysis of corneal diameter (CD). Retrospective, cross-sectional study of pediatric Asian-Indian eyes. One random eye of 353 subjects between 5 and 18 years underwent 25-scan Pentacam HR imaging. For all scans, densitometry values along the anterior corneal edge were recorded and differentiated. The peaks on the differentiated curve were chosen as the ESS points, and this distance between them was called CD. Vertical (vCD), maximum (maxCD), minimum (minCD) CD and their meridians were defined. Multiple regression models (MRMs) with CD and other Pentacam parameters were built to predict astigmatism and its axis, mean keratometry (Kmean), and Belin/Ambrósio enhanced ectasia display deviation (BAD-D). MRMs were validated using intraclass correlation coefficient (ICC). Estimated horizontal CD (hCD) was validated against digital caliper measurement using ICC. The ICC (95% CI) between caliper and hCD was 0.96 (0.93, 0.97). MRM predictions (P < .001) used CD parameters, anterior chamber depth, corneal volume and distance from the corneal thinnest location to apex. These predictions achieved an ICC of 0.34 (0.18, 0.46), 0.82 (0.78, 0.86), 0.87 (0.84, 0.89), and 0.81 (0.76, 0.84), respectively. The astigmatism axis prediction depended on the minCD and maxCD meridians. Its within-subject SD (4.97°) was less than 2 consecutive Pentacam scan angles (7.2°). The CD metric strongly correlated with the astigmatism axis, keratometry, and BAD-D. Its spatial description may be significant in corneal treatment planning and disease diagnoses.

High-Scanning-Rate and Wide-Scanning-Angle Leaky-Wave Antenna Based on Double-Layer Slow-Wave Structure

In this letter, a leaky-wave antenna (LWA) based on double-layer (DL) slow-wave structure, possessing high scanning rate and wide scanning angle features is investigated. The DL unit structure consists of a top layer structure with cross-shaped unit and a bottom layer structure with slot-shaped unit. The DL units realize the property of controlling the cut-off frequency and slope of dispersion curves independently by independently changing the unit slow-wave property of top and bottom layers. The radiation of LWA is achieved by triangularly modulating the cross-shaped units of top layer. Due to the existence of the slot-shaped units of bottom layer, strong slow-wave property is introduced to increase the growth rate of period phase shift, thus achieving high scanning rate. Meanwhile, the n = −2 space harmonic (SH) of the LWA is separated from the fast-wave region of n = −1 SH, thus enlarging scanning angle in forward quadrant. A prototype of the proposed LWA is fabricated and measured. The LWA can achieve a wide scanning angle from −68 ° to +74 ° in a narrow frequency band of 9 to 10.75 GHz.

Two-Bit Planar Coding Reconfigurable Array Antenna for Dual-Polarized Wide-Angle Beam Scanning

In this communication, a dual-polarized coding reconfigurable array antenna with the characteristics of being low-profile, low-cost, relatively low-sidelobe and wide-angle beam scanning is proposed. By exciting the array via different feeding ports, horizontal and vertical polarized scanning beams can be generated. By adjusting the PIN diodes integrated on the feeding lines, the element presents four different phase states of -270°, -180°, -90°, and 0°, labeled as “00”, “01”, “10”, and “11”. An eight elements array antenna is designed based on the element. With the introduction of elaborately designed two groups of fixed phase delay, the sidelobe level at different scanning angles can be effectively reduced in two polarized directions and the gain are also improved. The simulated and measured results of the fabricated prototype indicate that dual-polarized ±60° wide-angle beam scanning, moderate array gain, relatively low sidelobe level, and low cross polarization level can be achieved. The proposed array antenna, which according to our best knowledge, is the first dual linear polarized wide angle beam scanning coding reconfigurable array without the feeding horn, might have good applications in base station and fully polarimetric radar.

A robust lateral shift free (LSF) electrothermal micromirror with flexible multimorph beams

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide (SiO2) as the electrothermal isolation material. However, due to the brittle nature of SiO2, such micromirrors may be incapable to survive even slight collisions, which greatly limits their application range. To improve the robustness of electrothermal micromirrors, a polymer material is incorporated and partially replaces SiO2 as the electrothermal isolation and anchor material. In particular, photosensitive polyimide (PSPI) is used, which also simplifies the fabrication process. Here, PSPI-based electrothermal micromirrors have been designed, fabricated, and tested. The PSPI-type micromirrors achieved an optical scan angle of ±19.6° and a vertical displacement of 370 μm at only 4 Vdc. With a mirror aperture size of 1 mm × 1 mm, the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments. In the drop test, the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm. In the standard frequency sweeping vibration test, the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations, respectively. In all these tests, the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO2-type micromirrors fabricated in the same batch.

A dual-band dual-polarized frequency beam-scanning antenna based on HMSIW and PC

A dual-band dual-polarized frequency beam-scanning (FBS) antenna based on half-mode substrate integrated waveguide (HMSIW) and photonic crystal (PC) is proposed. HMSIW can decrease the width of the substrate, and each eigenmode of PC has own unique electric-field distribution, which can be good for generating different polarization types. Therefore, the proposed antenna not only has a narrow substrate, but also has the characteristic of circularly polarized (CP) and linearly polarized (LP) radiation, which can be used for overcoming effectively the multipath fading and enhancing the channel capacity. For increasing the bandwidth of 3 dB axial ratio (AR), the slots on top surface are not perfectly symmetrical in the improved unit cell. The asymmetrical antenna based on the improved unit is manufactured and measured. The antenna can accomplish 33° scanning angle with the realized gains of 7.9–10.6 dBi in the CP working band (7.2 to 8.2 GHz), and can also achieve 24° beam-scanning for the LP radiation (8.8 to 9.6 GHz), whose realized gains are from 9.5 to 11.5 dBi. In addition, the experimental results are highly consistent with the simulated results, verifying that the design is feasible.

A Resonant Pulley Rotary Actuator for Scanning Capsule Endoscopy

We present a compact electromagnetically actuated 3D-printed rotary actuator for use in Scanning Capsule Endoscopy. The actuator comprises two cantilevers connected to a rotating body via nylon strings. External coils and the magnets placed on the cantilevers create an electromagnetic force with which the rotation can be initiated. Opposite coils are driven out-of-phase to enable resonant actuation. An electrical circuit model and finite element simulation results of the fundamental mode frequency are provided for the designed device. The design is manufactured via fused deposition modeling using polylactic acid (PLA) and thermoplastic polyurethane (TPU). Experimental results reveal a 98 ° total scan angle at 21 Hz resonance for the TPU actuator and a 19.7 ° total scan angle at 237 Hz resonance for the PLA actuator. Overall, the presented rotary actuator compares favorably over i) micromotor counterparts in terms of form factor (having a diameter of 13 mm and a total height of 7 mm) and ii) MEMS counterparts in terms of total scan angle. Manufacturing cost and duration are yet other benefits of the presented device, owing to 3D printing technique. With further development, the presented device can serve within a disposable capsule endoscopy unit for clinical use.

Quantification of 1.75 MeV Xe5+ induced defects in zirconia doped ceria (Ce0.8Zr0.2O2)

This study investigates the structural stability of the CeO2-ZrO2 system when subjected to high doses of irradiation (a few hundred displacements per atom). The goal is to explore their potential use in safe immobilization of spent nuclear fuel and development of accident-tolerant fuels for next-generation nuclear reactors. Highly dense pellets were synthesized using a solid-state reaction and then irradiated with 1.75 MeV Xe5+ ions at ion fluences ranging from 1 × 1015 to 1 × 1017 ions/cm2. Structural and microstructural analyses were conducted using glancing angle x-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy. The results indicate that Ce0.8Zr0.2O2 has a high tolerance against irradiation-induced phase transformation or amorphization but does generate irradiation-induced point defects. Each energetic ion produced a deformed region with a voluminous swelling of ∼0.61 ± 0.09 nm and a damaged zone of ∼0.09 ± 0.02 nm, as calculated from the irradiation-caused peak broadening that is explained by a three-step damage accumulation model. The electron microscopy studies show that grain boundaries serve as a sink for defects, and an increase in grain size was observed due to defect accumulation inside the grain's volume. Overall, the study shows that polycrystalline fluorite-structured Ce0.8Zr0.2O2 is a promising nuclear material for advanced energy systems as it did not show significant structural damage such as amorphization and grain fragmentation, even on irradiation at a high dose of ∼428 dpa.