Angular Scan Range Research Articles

Better than the Total Variation Regularization

The total variation (TV) regularization is popular in iterative image reconstruction when the piecewise-constant nature of the image is encouraged. As a matter of fact, the TV regularization is not strong enough to enforce the piecewise- constant appearance. This paper suggests a different regularization function that is able to discourage some smooth transitions in the image and to encourage the piecewise-constant behavior. This new regularization function involves a Gaussian function. We use the limited-angle tomography problem to illustrate the effectiveness of this new regularization function. The limited-angle tomography situation considered in this paper uses a scanning angular range of 40°. For two-dimensional parallel-beam imaging, the required angular range is supposed to be 180°.

Widening Multi‐Beam Scan Angle of Conventional Waveguide Lens Antennas by Increasing Focal Points for Multi‐Feed Excitations

AbstractThis paper presents an alternative approach to improve the achievable beam scan angle of a traditional multi‐beam waveguide lens antenna. Due to the focusing mechanism by manipulating the geometrical curvatures of the waveguide lens, the angular scan range is limited in the conventional waveguide lens design using dual‐focal points of excitations because the geometrical curvatures of the waveguide lens only provide two design freedoms. To overcome this limitation, a solution of treating the waveguide lens as a transmit array consisting of non‐identical elements is proposed so that each element of the antenna array can be well calibrated to improve the maximum scan angular range, where a third focus point of excitation can be created by adding another design freedom from the differentiation between non‐identical elements. Each element of this new transmitting array can be well calibrated with the help of a mathematical expression to improve the maximum angular scan range. Numerical simulations show that the proposed antenna architecture exhibits better radiation characteristics than the traditional waveguide lens antenna. Radiation characteristics are studied and compared for both types of lens antennas to validate the design concept. The proposed triple‐focal point provides a higher gain than the traditional lens antenna with fewer antenna elements. The gains of the beams at ±10°, ±20°, ±30°, and ±40° are found to be 27.78, 26.94, 26.19, and 24.04 dBi, respectively. From the comparison, it is seen that the variation in gain by the proposed triple‐focal array design is more stable than the conventional dual‐focal point design.

Optimized signal of calcifications in wide-angle digital breast tomosynthesis: a virtual imaging trial.

Evaluate microcalcification detectability in digital breast tomosynthesis (DBT) and synthetic 2D mammography (SM) for different acquisition setups using a virtual imaging trial (VIT) approach. Medio-lateral oblique (MLO) DBT acquisitions on eight patients were performed at twice the automatic exposure controlled (AEC) dose. The noise was added to the projections to simulate a given dose trajectory. Virtual microcalcification models were added to a given projection set using an in-house VIT framework. Three setups were evaluated: (1) standard acquisition with 25 projections at AEC dose, (2) 25 projections with a convex dose distribution, and (3) sparse setup with 13 projections, every second one over the angular range. The total scan dose and angular range remained constant. DBT volume reconstruction and synthetic mammography image generation were performed using a Siemens prototype algorithm. Lesion detectability was assessed through a Jackknife-alternative free-response receiver operating characteristic (JAFROC) study with six observers. For DBT, the area under the curve (AUC) was 0.97 ± 0.01 for the standard, 0.95 ± 0.02 for the convex, and 0.89 ± 0.03 for the sparse setup. There was no significant difference between standard and convex dose distributions (p = 0.309). Sparse projections significantly reduced detectability (p = 0.001). Synthetic images had a higher AUC with the convex setup, though not significantly (p = 0.435). DBT required four times more reading time than synthetic mammography. A convex setup did not significantly improve detectability in DBT compared to the standard setup. Synthetic images exhibited a non-significant increase in detectability with the convex setup. Sparse setup significantly reduced detectability in both DBT and synthetic mammography. This virtual imaging trial study allowed the design and efficient testing of different dose distribution trajectories with real mammography images, using a dose-neutral protocol. • In DBT, a convex dose distribution did not increase the detectability of microcalcifications compared to the current standard setup but increased detectability for the SM images. • A sparse setup decreased microcalcification detectability in both DBT and SM images compared to the convex and current clinical setups. • Optimal microcalcification cluster detection in the system studied was achieved using either the standard or convex dose setting, with the default number of projections.

Experimental Demonstration of Beam Scanning of Dual-Metasurface Antenna

Beam-scanning antennas are employed in a wide range of applications, such as in satellite communications and 5G networks. Current commercial solutions rely mostly on electronically reconfigurable phased arrays, which require complex feeding networks and are affected by high losses, high costs, and are often power-hungry. In this paper, a novel beam scanning architecture employing a pair of planar metasurfaces, for use in thin reconfigurable antennas, is presented and experimentally demonstrated. The structure consisted of a radiative passive (non-reconfigurable) modulated metasurface, and a second metasurface that controls beam pointing, operating as a variable-impedance ground plane. Unlike other existing approaches, surface impedance variation was obtained by on-plane varactor diodes, no vias and a single voltage bias. This paper presents a design procedure based on an approximate theoretical model and simulation verification; a prototype of the designed antenna was fabricated for operation in X band, and a good agreement between measured results and simulations was observed. In the presented simple embodiment of the concept, the angular scanning range was limited to 10°; this limitation is discussed in view of future applications.

Multi-scale dilated dense reconstruction network for limited-angle computed tomography

Objective. Due to the incomplete projection data, the image reconstructed by limited-angle computed tomography (CT) usually suffers from significant artifacts, by which the structural details are heavily blurred. In this study, we aim to develop a novel approach to improve the limited-angle CT reconstruction performance, especially for the narrow scanning angular range. Approach. A deep learning based iterative framework for limited-angle tomography is proposed, which is named multi-scale dilated dense reconstruction network (MSDDRNet). The MSDDRNet utilizes a multi-scale dilated dense convolution neural network (MSDD-CNN) with conventional reconstruction algorithm for predicting image from incomplete projection data. The MSDD-CNN enhances the image features in the network by merging the DenseNet-Like structure, which serves to restore invisible singularities and reduce artifacts, as well as introducing constraints on the projection domain data into the iterative process to achieve better image detail recovery. Additionally, to improve the training speed of the network, we use a strategy of pre-training and model migration. Main results. Numerical experiments demonstrate that the proposed MSDDRNet performs well in terms of artifact correction, noise reduction and structure recovery compared to existing methods with limited scan angles, and we also extend the proposed method to more general scanning condition and other application such as dental CT data. Significance. The proposed method is a general framework, which can be applied to other CT problems, such as low dose CT, sparse-data CT and spectral CT.

Near-Field Angular Scan Enhancement of Antenna Arrays Using Metasurfaces

In this publication, we continue our previous work on extending the angular scan range of phased arrays using metasurfaces. We consider in detail scan enhancement using a single metasurface lens in the near-field of a source and provide analytical expressions for source excitation to obtain a desired beam. We show that such a device suffers from the same directivity degradation as in the case of far-field lens placement. Moreover, we discuss in detail that this approach has limitations, and one cannot place the lens arbitrarily close to the source array. We then propose a two-lens near-field scan enhancer which is not subject to the same limitations, although still subject to the same directivity degradation. Finally, we propose a binary metasurface concept which theoretically achieves desired scan enhancement without directivity degradation. Some theoretical claims are then verified via full-field simulations.

ARIEL: Passive Beam-Scanning Antenna teRminal for Iridescent and Efficient LEO Satellite Connectivity

A novel low-cost high-gain beam-steering antenna terminal topology for global data connectivity with low-earth-orbit satellite constellations in the UHF 900 MHz ISM band is reported. It is shown how a simple printed-circuit-board half-width microstrip leaky-wave antenna (LWA) with passive frequency-beam scanning capacity provides an energy-efficient scanning method avoiding more power-demanding and expensive beam-steering techniques (such as electronic scanning, mechanical rotation, or beam switching). For that, iridescent channel-agile operation and cross-layer optimization are needed. As an example, two single-element LWAs and an LWA array are designed to scan the celestial vault with an angular elevation scanning range of 130° and using the available LoRaWAN protocol channels from 902 to 928 MHz. It is reported a scanned-beam peak gain above 9 dBi for the compact printed-circuit LWA array design with 55 cm × 27 cm aperture dimensions.

A High-Speed Chip-Scale Rotary Polygon Optical Scanner Based on a Micromotor Integrated With a Micro-Polyhedron Mirror

Micro-opto-electro-mechanical systems (MOEMS) based mirrors with a suitable actuation range are often used for optical beam scanning applications. While several MOEMS scanners have been reported, they often have limitations with respect to their range of motion, field of view, mass, size and fabrication cost. In this work, we present a rotary micro-polygon scanner based on an electrostatic variable capacitance micromotor for laser beam steering applications. The miniaturized scanner consists of a hollow micro-polyhedron mirror with a base radius of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200 {\mu }\text{m}$ </tex-math></inline-formula> and a height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400 {\mu }\text{m}$ </tex-math></inline-formula> . It is mounted on the rotor of a variable capacitance micromotor using an epoxy-based adhesive. The rotor has a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$600 {\mu }\text{m}$ </tex-math></inline-formula> and is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5 {\mu }\text{m}$ </tex-math></inline-formula> thick. The micromotor was fabricated using a commercial three-layer polysilicon surface micro-machining process (PolyMUMPs) and the micro-polyhedrons were fabricated using a commercial bulk micro-machining process (PiezeoMUMPs). After fabrication of the components, the micro-scanner was assembled and operated under atmospheric conditions using a three-phase square wave excitation ranging from 0 V to 200 V and achieved rotational speeds of up to 2100 rpm. An optical laser beam with a wavelength of 632 nm was reflected off the sidewall of the rotating micro-polyhedron, achieving an experimentally measured scanning angular range of 57.88°, an angular scan rate of 220 radians per second and a scan speed of 25,200 lines per minute or 420 lines per second with a 12 sided micro-mirror. The ratio of the output power over the input optical power is measured over a scanning range of 22°, which is limited by the size of the photo-detector, yielding a ratio spanning from 0.18 to 0.22. This rotary micro-scanner can provide high scanning speeds and a wide scanning field of view with a footprint of 1.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a thickness of 0.83 mm, which is suitable to implement chip-level high-performance micro-beam steering systems for various applications. [2022-0020]

Review of Electrothermal Micromirrors.

Electrothermal micromirrors have become an important type of micromirrors due to their large angular scanning range and large linear motion. Typically, electrothermal micromirrors do not have a torsional bar, so they can easily generate linear motion. In this paper, electrothermal micromirrors based on different thermal actuators are reviewed, and also the mechanisms of those actuators are analyzed, including U-shape, chevron, thermo-pneumatic, thermo-capillary and thermal bimorph-based actuation. Special attention is given to bimorph based-electrothermal micromirrors due to their versatility in tip-tilt-piston motion. The exemplified applications of each type of electrothermal micromirrors are also presented. Moreover, electrothermal micromirrors integrated with electromagnetic or electrostatic actuators are introduced.

Low-cost electrothermally actuated MEMS mirrors for high-speed linear raster scanning

Electrothermally actuated MEMS mirrors are significantly lower in cost than their electrostatically actuated counterparts, largely due to their ability to perform well without hermetic packaging. However, their typical slower speeds, higher power requirement, and non-linear drive limit their widespread use. In this work, we address these limitations and achieve an electrothermally actuated MEMS mirror capable of reliable linear raster scanning at speeds up to 300 Hz with a large angular range of motion ( ± 40 ∘ optical). A simple pulse design technique is used to achieve ∼ 99 % scan linearity and correct for artifacts like overshoot and ringing. Furthermore, segmented polysilicon microheaters along the actuators are used for impedance matching to low-voltage electronics, resulting in lower power consumption and improved scan speed and angular range. These mirrors serve as an attractive option for low-cost and compact integrated beam-steering optical devices, and we demonstrate one such use case in an optical coherence tomography (OCT) system.

Frequency-Scanned Monopulse Antenna for RSSI-Based Direction Finding of UHF RFID Tags

A compact printed-circuit leaky-wave antenna is designed to synthesize frequency-scanned monopulse patterns in the UHF RFID band from 902 to 928 MHz. A high-permittivity ceramic substrate is used to maximize the angular scanning range in such a narrow band. Two operating modes, i.e., narrow-field and wide-field modes, can be chosen by properly selecting the frequency channels and antenna ports. This allows to adapt to different fields of view while maximizing the maximum reading distance, as demonstrated with a fabricated prototype.

Physical Design and Experimental Verification of a Huygens’ Metasurface Two-Lens System for Phased-Array Scan-Angle Enhancement

Over the past decades, many radome designs to extend the angular scan range of phased-array antennas have been devised by utilizing dielectric materials and metamaterials. More recently, metasurface technology such as planar lenses and beam deflectors have been applied to phased arrays, enabling scan-angle enhancers to have a low profile. In this work, a physical Huygens’ metasurface (HMS) two-lens system for scan-angle doubling of a phased array is presented. For the HMS unit cells, the wire-loop topology is deployed to achieve high transmission for the required phase-angle shift. The proposed two-lens system is analyzed by full-wave simulations and experiments. The simulation results demonstrate that the scan angle doubles when the incident angle is below 15° in accordance to the design specification. Furthermore, the directivity degradation of the refracted beams by the two-HMS lenses is in good agreement with theory. Finally, a fabricated two-lens system with two 15λ long by 15λ wide metasurface lenses and a 16 × 16-element patch antenna array as a source is experimentally verified at 10 GHz. The experimental results are in good agreement with the simulated results by showing angle-doubling performance with ±2° scan errors.

3D-Printed frequency-scanned slot array in grating waveguide

In this work, a linearly-polarized frequency-scanned slot-antenna linear array fed by a travelling wave in grating waveguide is designed at 17 GHz. Additionally, the insertion of periodic gratings in the bottom broad-wall of the feeding waveguide reduces the guided wavelength of the fundamental propagating mode. Therefore, steering angles around broadside can be attained in the radiation pattern, contrary to conventional travelling-wave designs where grating lobes would inevitably appear. Furthermore, tuning posts are included in the radiating element design to mitigate the mismatch provoked by uniform phase feeding. A 16-element array is fabricated to validate the design, which experimentally shows a continuous angular scanning range of ±10°around broadside in the band from 16 to 18 GHz, with a peak gain of 18 dBi and a maximum gain drop of 4 dB.

Dielectric Gratings Enhancing the Field of View in Low Dielectric Permittivity Elliptical Lenses

Low relative permittivity plastic elliptical lenses in combination with integrated focal plane arrays are a promising solution to be used in the future mm- and sub-mm-wave systems. Their appeal lies in the availability of materials with moderate loss and lightweight, and the possibility to use cost-effective manufacturing techniques. However, the achievable scanning angular range is relatively small with low permittivity lenses. In this article, we explore the use of dielectric gratings with modulated height integrated in the lens material, with the aim of enlarging the steering angle. The dielectric gratings synthesize a tilted feed pattern, reducing the reflection loss and spillover when illuminating the lens off-focus. A quasi-analytic approach based on the Floquet mode analysis of the gratings is used to synthesize the grating profile. This method is combined with an analysis in reception of the lens antenna. A wideband prototype in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G$ </tex-math></inline-formula> -band (140–220 GHz) has been fabricated, achieving a field of view of ±25° with gain >30 dBi.

TM-polarized angle-dispersive metasurface for axisymmetric extension of beam steering angles.

Axisymmetric extension of beam steering angles by metasurfaces is of great interest due to its potential application in extending the angular scan range of existing phased arrays. This angle-multiplexed manipulation functionality requires anti-symmetrically angle-dispersive phase gradient, as well as anti-symmetric angular phase dispersion over continuous incident angles, which is difficult to be implemented by existing metasurfaces. In this work, a series of meta-atoms with asymmetric structures are developed to achieve the required phase response. Based on the asymmetric meta-atoms, an angle-dispersive metasurface for axisymmetric beam steering of transmitted transverse-magnetic (TM) wave is designed, fabricated and tested, whose simulation and experimental results demonstrate the axisymmetric extension capability of beam steering angles from -53° ≤ θi ≤ 53° to almost -90° ≤ θt ≤ 90°.

Waveguide Superlattice-Based Optical Phased Array

High-density low-crosstalk waveguide superlattices can potentially help shrink the pitch of an optical phased array to half-wavelength, which may lead to superior beam characteristics. While a superlattice's longitudinal coherence is exploited to create phase mismatch and reduce crosstalk, its transverse coherence is also modified and will inevitably disturb the beam forming of the optical phased array. Our theory shows that the transverse and longitudinal coherence can be balanced in a nontrivial superlattice such that superlattice-induced disturbance of the beam can be suppressed without compromising crosstalk. Large supercells less restrained by symmetry offer more degrees of freedom for finding a desirable superlattice structure. The supercell configuration order and structural modulation strength are crucial to balancing coherence and approaching the ideal characteristics of a half-wavelength pitch optical phased array. Experimental results show a high main-beam energy ratio, low sidelobe levels, and a wide angular scanning range. Such optical phased arrays may potentially open up further opportunities for light detection and ranging (LIDAR), wireless optical communications, and biomedical scanning imaging.

Linear programming-based reconstruction algorithm for limited angular sparse-view tomography

The reconstruction of high-quality images from limited angular sparse-view tomography data is desired in many fields, including low-dose computed tomography and nondestructive detection. In this study, two regularization terms based on the assumptions of image continuity and nonzero pixels are utilized to reconstruct an image from incomplete data. By transforming the original nonlinear reconstruction model into a linear programming, the proposed method can obtain the optimal solution rather than the local minimum point, which helps to accurately reconstruct the images. To demonstrate the effect of the proposed method, we designed a simulation experiment under limited angle, few-view, and limited angular sparse-view conditions, and evaluated the reconstruction results using the structural similarity index, peak signal-to-noise ratio, and cosine distance. The experimental results show that our method can effectively overcome the adverse effects of sparse-view conditions and a limited scanning range. In the tomographic results of our method, streak artifacts do not appear, even when using projection data from 20 views of a 180° scanning angular range.

A sequential regularization based image reconstruction method for limited-angle spectral CT

In spectral computed tomography (CT), the object is respectively scanned under different x-ray spectra. Multiple projection data can be collectively used for reconstructing basis images and virtual monochromatic images, which have been used in material decomposition, beam-hardening correction, bone removal, and so on. In practice, projection data may be obtained in a limited scanning angular range. Images reconstructed from limited-angle data by conventional spectral CT reconstruction methods will be deteriorated by limited-angle related artifacts and basis image decomposition errors. Motivated by observations of limited-angle spectral CT, we propose a sequential regularization-based limited-angle spectral CT reconstruction model and its numerical solver. Both simulated and real data experiments validate that our method is capable of suppressing artifacts, preserving edges and reducing decomposition errors.

Linearly Sweeping Leaky-Wave Antenna With High Scanning Rate

Leaky-wave antenna (LWA) is known as a type of traveling antenna with dispersive frequency responses, which has found important applications in modern communication, imaging, and radar systems. The beam scanning rate is a key consideration in some applications since it can minimize the bandwidth requirement of the system, during the scanning in broad angular regions. However, the sweeping linearity, namely the scanning angular range per unit frequency, is seldom considered at the same time in the published literature. In this article, we propose a waveguide-type LWA working from 11.1 to 12 GHz. By loading periodical pins with glide symmetry in the waveguide, it is possible to manipulate the dispersion properties of the fast wave mode, hereby giving rise to a good balance between the scanning rate and the sweeping linearity. This scenario has been validated by numerical simulation and experiment with excellent agreement. The measurement results reveal that the scanning angles have been increased to a range from 16.7°~67.5° varying the frequency from 11.1 to 12.1 GHz. The relative average scanning rate is enhanced up to 589.3°, with high sweeping linearity.

Theory and Simulation of Metasurface Lenses for Extending the Angular Scan Range of Phased Arrays

Recent metasurface developments have led to their consideration for extending the angular scan range of phased arrays. This paper considers the use of Huygens' metasurfaces as lenses to accomplish the task. Ray optics is used to uncover how a single lens can extend the scan range. It is shown that a single scan extending lens leads to a broadside directivity degradation of the original beam. This directivity degradation is quantitatively characterized as a function of the desired angular scan-range expansion. A method of simulating phase boundaries is presented and used to verify the theoretical claims. A Huygens' metasurface lens design is presented and simulated to further validate the theoretical predictions and show that such lenses are physically realizable.