Circular Ring Array Research Articles

Generation of OAM Beams Using Circular Ring Array With In-Phase Feed

Generation of OAM Beams Using Circular Ring Array With In-Phase Feed

Effect of spatial-domain pulse width on the resolution of scattering images in ultrasound computed tomography

Full-aperture tomography (FAT) is the major image reconstruction method for a circular ring array (CRA)-based ultrasound computed tomography (USCT) system. The FAT technique requires transferring the reconstruction process from the temporal domain to the spatial domain, during which the imaging resolution of the USCT is degraded by the spatial-domain pulse width (SDPW) of backprojection areas. To tackle this challenge, this study investigates the characteristics of the SDPW and how it degrades the image resolution. We show that the SDPW depends on the frequency of the ultrasound and the position of the transmitting elements, receiving elements and the imaging point. To quantify the deterioration of image resolution associated with the position of the transmitting and receiving elements, a SDPW broadening factor (SDPWBF) is introduced. The results of numerical simulation show a smaller SDPWBF provides a better reflection image resolution, and the distribution of SDPWBF shows that a shorter distance between the receiving element and the transmitting element yields a smaller SDPWBF. The SDPWBF is therefore able to be an indicator of selecting the signals acquired from the transmitting and receiving elements to perform optimal image resolution. Single-scatterer phantom and in vivo experiments demonstrate how the SDPWBF affects the USCT image spatial resolution and signal-to-noise ratio (SNR), and the results agree well with the theoretical predictions.

COSECANT-SQUARED BEAM PATTERN SYNTHESIS OF CONCENTRIC CIRCULAR ANTENNA ARRAY IN A RANGE OF AZIMUTH PLANE USING EVOLUTIONARY ALGORITHM

This paper presents, a pattern synthesis method based on Differential Evolutionary Algorithm. A cosec2 beam pattern has been generated from different concentric circular ring arrays of isotropic elements by finding the optimum set of elements amplitude and phase using the Differential Evolution algorithm. The shaped beam pattern (cosec2) is generated in three predefined azimuth planes (φ=0°, 5° and 10°) from a Concentric Circular Antenna Array (CCAA) having two rings, three rings, and four rings. The total number or isotropic elements are equal for array geometries. The optimum excitation for array geometries is also verified for a range of arbitrarily chosen azimuth planes. The obtained main beam is similar to the desired pattern with some minor variations in peak Side Lobe Level (peak SLL) and ripple. Dynamic range ratio (DRR) is improved by using 4-bit discrete Amplitudes and 5-bit discrete Phases. These discrete excitations also simplify the design complexity of the feed networks.

Synthesis of Reconfigurable Multiple Shaped Beams of a Concentric Circular Ring Array Antenna Using Evolutionary Algorithms

The approach described in this paper uses evolutionary algorithms to create multiple-beam patterns for a concentric circular ring array (CCRA) of isotropic antennas using a common set of array excitation amplitudes. The flat top, cosec2, and pencil beam patterns are examples of multiple-beam patterns. All of these designs have an upward angle of θ = 0◦. All the patterns are further created in three azimuth planes (φ = 0◦, 5◦, and 10◦). To create the necessary patterns, non-uniform excitations are used in combination with evenly spaced isotropic components. For the flat top and cosecant-squared patterns, the best combination of common components, amplitude and various phases is applied, whereas the pencil beam pattern is produced using the common amplitude only. Differential evolutionary algorithm (DE), genetic algorithm (GA), and firefly algorithm (FA) are used to generate the best 4-bit discrete magnitudes and 5-bit discrete phases. These discrete excitations aid in lowering the feed network design complexity and the dynamic range ratio (DRR). A variety of randomly selected azimuth planes are used to verify the excitations as well. With small modifications in the desired parameters, the patterns are formed using the same excitation. The results proved both the efficacy of the suggested strategy and the dominance of DE over GA as well as FA.

Three-dimensional time-domain full-waveform inversion for ring-array-based ultrasound computed tomography

Ultrasound computed tomography (USCT) is a promising imaging technique for breast cancer diagnosis. Full-waveform inversion (FWI)-based image reconstruction methods based on the acoustic wave equation can produce quantitatively accurate images of acoustic properties with higher spatial resolution compared to ray-based methods. One common USCT design employs a circular ring-array of elevation-focused ultrasonic transducers that can be translated orthogonally to the imaging plane to achieve volumetric scanning. Currently, slice-by-slice (SBS) reconstruction methods are often used in this setting. Such methods use a 2D wave physic model to reconstruct a cross-sectional image for each position of the ring-array and vertically stack them together to render the 3D volume. However, this approach neglects the 3D wave propagation physics and transducer’s focusing properties, leading to out-of-plane scattering artifacts and degraded spatial resolution. To address this, a 3D time-domain FWI method that utilizes measurement data acquired at multiple adjacent ring-array locations is proposed. The reconstruction method was investigated using virtual imaging studies of ring-array-based USCT that employed realistic 3D numerical breast phantoms. The results demonstrated improved spatial resolution (both in-plane and off-plane) and reduced image artifacts compared to the SBS approach. Additionally, the impact of the number of ring-array locations on image quality is assessed.

Highly Directive Array Pattern Synthesis in Different phi Planes of a Large CCRAA Using Array Thinning Technique

This paper presents a pattern synthesis method of a sizeable concentric circular ring array (CCRAA) of isotropic antennas using Evolutionary Algorithms. In this method, the array is thinned using the optimum set of binary excitations to achieve the desired highly directive pencil beam patterns with lower peak side lobe level(SLL). The half-power beam width and first null beam width is kept constant to obtain such highly directive beam patterns with lower peak SLL. This pattern is not synthesized to a particular azimuth plane rather in four different ' planes from entire azimuth planes. The isotropic elements are uniformly spaced in the concentric ring. The achieved set of optimum amplitudes are constructed with either 1 or 0 using Differential Evolutionary Algorithm(DE), Genetic Algorithm (GA), and Particle Swarm Optimization Algorithm (PSO). These excitations show the state of the elements. The elements are in “ON” state or in “OFF” state depending upon the excitation ‘1’ or ‘0’. It is also helpful to reduce the complexity of the feed networks. The excitations are also verified in the whole range (0o <phi<360o) of ' planes by selecting four phi planes arbitrarily. The outcomes established the superiority of GA and DE over PSO and also the effectiveness of the proposed method.

Controlling Graphene Sheet Resistance for Broadband Printable and Flexible Artificial Magnetic Conductor-Based Microwave Radar Absorber Applications

Current artificial magnetic conductor (AMC) designs use metallic patterns on rigid substrates and focus on shapes and sizes of AMC structures, rather than on material performance, which has hindered operation bandwidth and design flexibility. Here, we introduce printed graphene AMC-based broadband and flexible microwave radar absorbers, which not only redirect but also absorb the incident wave so to broaden the operation bandwidth. Contrasting to other reported works, the phase characteristics of the AMCs are realized through the control of the surface resistance provided by printed graphene laminates. We produced a variety of AMC structures, composed of printed graphene circular ring arrays with exactly the same shape and size, but different sheet resistances. By carefully designing the sheet resistance of printed graphene laminates, the optimized anti-phase reflection cancellation between AMCs can be achieved. With printed graphene AMCs and flexible dielectric substrate, the absorber presented in this work has a broadband effective absorption (above 90% absorptivity) from 7.58 GHz to 18, is polarization insensitive under normal incident, and can work at relatively wide incident angles. Furthermore, this absorber is capable of bending easily with notable performance, which makes it ideal for applications with irregular and uneven shapes.

Angularly stable frequency selective surface for the gain enhancement of isolated multiple input multiple output antenna

AbstractA metasurface is highly useful for improving the performance of patch antennas and reducing their size due to their inherent and unique electromagnetic properties. In this research work, we design a wideband bandstop reflector‐based frequency selective surface (FSS). It consists of a periodic array of circular shape metallic rings with four stubs. The FSS unit cell resonates over a frequency band from 7.2 to 9.2 GHz and has excellent stability under different polarizations and incident angles. A microstrip patch‐based isolated multiple input multiple output (MIMO) antenna is designed that operates over a frequency band of 7.9GHz to 8.7 GHz. The MIMO antenna and FSS are printed on the one face of a substrate. The radiation performance such as gain and directivity of the antenna is improved due to parasitic radiation of the surface and coherent‐ superposition of energy in the far‐field, between the antenna and FSS unit cells. Where the other parameters such are efficiency, radiation pattern and isolation are well preserved. The designed structure shows low complexity during fabrication. The simulated and experimental results confirm the predicted antenna performance and gain enhancement.

DESIGN OF A METALENS FOR CORRECTING THE PHASE DISTORTIONS OF A HEMISPHERIC DIELECTRIC RADOME IN THE KA BAND

A semianalytical approach based on an equivalent circuit representation is proposed to calculate the microwave transmission through metasheets consisting of two-dimensional periodic arrays of planar circular metal rings on a dielectric substrate. In the semianalytical approach, the impedances of the equivalent circuit are parameterized and fitted to match the values of transmission coefficients obtained by full-wave simulations at selected frequency points. As dimensional parameters, the outer radius and the width of the ring are considered. A metalens with four concentric zones is designed by using this semianalytical approach to correct the phase distortions due to a polypropylene hemispheric radome at frequencies around 28 GHz in the Ka band. It is shown that the designed metalens works well for 27 GHz, 28 GHz and 29.5 GHz, implying the bandwidth of approximately 2.5 GHz. The field transmitted through the metalens and the radome is calculated by Physical Optics (PO). The electrically large integration area is divided into small square facets to calculate the PO integral. The calculated and measured results are shown to agree well.

Comparison of Passive 2-D and 3-D Ring Arrays for Medical Telemetry Focusing

In this letter, we investigate the performance of subdermal ring designs for focusing electromagnetic fields inside the body for next-generation implantable medical devices. We will concentrate on the Medical Implant Communications Service band $(\text{402} \text{--}\text{405 MHz})$ , but prepare our design at $\text{433 MHz}$ , the nearest Industrial, Scientific, Medical band. The designs include two-dimensional (2-D or coplanar) and 3-D arrays of circular rings and 3-D arrays of ellipses. The 3-D ring and ellipse arrays focus the fields more effectively than 2-D designs, through constructive coupling between the rings. Compared to the case where no rings are used, the power available from the focused field 20 mm below the skin is 2.24 times and 3.12 times larger if 3-D rings and 3-D ellipses are utilized, respectively. Rings can be used for circular polarization applications, and ellipses are more optimal for linear polarization applications.

Design and Optimization of a Coherent Beamforming Network for an Aperiodic Concentric Ring Array

In this work, a flexible and reconfigurable feeding network design for a nonuniform aperture on circular concentric ring arrays is proposed and analyzed. The network subsystem delivers coherent in-phase outputs with a Gaussian-like amplitude distribution, in a modular and basic topology based on sets of alternated power combiners and dividers. A complete antenna system in a monobeam configuration with a coherent network based on grouped inputs (blocks) per ring for an aperiodic concentric ring array with beam scanning and beam shaping properties is synthesized and analyzed. Additionally, a comparative analysis based on nonuniform and uniform concentric ring arrays fed by the proposed coherent network configuration is conducted and assessed. The optimization of the aperiodic layout on the antenna aperture (radii and interelement antenna spacings) is done by the differential evolution algorithm. Numeric experimentation demonstrates the performance advantages and capabilities of the proposed coherent network configuration with a nonuniform aperture over its uniform counterpart, with an improvement in average equal to −8.7 dB of side lobe level and 3.9 dB of directivity. Furthermore, the numeric examples show a complexity reduction on the coherent feeding network configuration based on the number of control signal inputs compared with a conventional phased antenna array; in the proposed configuration, the main beam is steered and shaped with N-1 control feeding ports per ring in this antenna system.

Tunable depth of focus of acoustical pupil masked Soret Zone Plate

In acoustical lenses both resolution and depth of focus are determined by diffraction and the smaller the lens aperture the worse the resolution and the greater the depth of focus. Diffraction-limited resolution has a Soret Zone Plate, but a long depth of focus has an axicon. Nevertheless, these are two different devices each of which requires its own independent design. In this paper, we have shown that the transition from focusing to a diffraction limited spot to a quasi-diffraction free beam can be realized in the same focusing device without changing its topology. It has been shown that using a classical planar Soret Zone Plate lens made of a concentric array of circular aperiodical rings with an amplitude pupil mask placed closely to the surface of lens allows to form a quasi-Bessel beams under specific conditions, part of a diffracted wave collimates, producing an elongated focus. Experiments are performed in water tanks in order to verify the simulation results. Experimental verification shown that the depth of focus of a pupil-masked Soret Zone Plate increases 1.63 times and resolution increases 1.2 times (with minimal beam waist about of 0.67 of wavelength and depth of focus about 5.72 of wavelength). By dynamically controlling the size of the amplitude pupil mask, it is possible to quickly control the depth of focus of an acoustic lens.

Planar Ultrasonic Lenses Formed by Concentric Circular Sandwiched‐Ring Arrays

AbstractAn underwater ultrasonic planar lens is numerically and experimentally developed with a small thickness and maintains a highly efficient transmission. The lens is formed by an array of concentric circular resin rings sandwiched between two identical silicone rings. Since the velocity of the water is closely in between that of the resin and silicone, a 2π phase variation can be achieved by changing the thickness ratios of the resin to the silicone ring within a thin sandwiched structure. Based on this principle, both single‐point and multipoint focusing lenses with high transmission in the axial direction are realized, which are believed to have potential applications in underwater imaging and detection.

Thermal-Aware Synthesis of 5G Base Station Antenna Arrays: An Overview and a Sparsity-Based Approach

Heat removal capabilities and radiation performances of several sparse antenna array topologies are studied for cooling enhancement in 5G millimeter-wave base station antennas. Both electromagnetic (EM) and thermal aspects are jointly considered for the first time in array layout optimization, and a novel connection between layout sparsity and thermal management is presented. Two types of active electronically scanned arrays (AESAs), based on the traditional and planar approaches, are examined. Thermal management in AESAs is discussed, with a focus on cooling challenges at millimeter waves. Being relatively low cost and low profile while supporting flexible beamforming, passively cooled planar AESAs with fanless CPU coolers are proposed, for the first time, to be used in 5G base stations. Additional cooling for such arrays is achieved by increasing the inter-element distances in the layout. Linear irregular arrays, spiral arrays, thinned arrays, circular ring arrays, and heat sink antenna arrays are revisited with a critical discussion on their EM and thermal performance. The results are compared with regular and square layouts that are used as benchmarks throughout this paper.

A SEMI-ANALYTICAL APPROACH FOR FAST DESIGN OF MICROWAVE METASHEETS WITH CIRCULAR METAL RINGS ON DIELECTRIC SUBSTRATES

Metasheets are ultra-thin sheets built from sub-wavelength resonators designed in order to achieve certain frequency-dependent transmission behaviour. A semi-analytical approach based on an equivalent circuit representation is proposed to calculate the microwave transmission through metasheets which consist of 2D periodic arrays of planar circular metal rings with and without substrate. The electromagnetic response of the metasheet can be controlled by changing the radius and the periodicity of the circular rings. In the semi-analytical approach, the equations for the impedances of the equivalent circuit are parametrized and fitted to match the values of transmission coefficients obtained by full-wave simulations at selected frequency points. Such an approach permits an optimization of the metasheet design with a very small number of full-wave numerical simulations. It is shown that the results of the semi-analytical approach match well with full-wave simulations and measurements within a reasonable range of radius and periodicity values.

Two-Dimensional Direction of Arrival Estimation for Improved Archimedean Spiral Array With MUSIC Algorithm

Direction-of-Arrival (DOA) estimation capability of sensor arrays is greatly influenced by geometric configuration of arrays. We proposed a new type 2-D planar array, improved Archimedean spiral array (IASA), to arrange sensor elements and enhance the array performance through Archimedean curves. The 2-D MUSIC algorithm is used to estimate the spatial spectrum of signals. The analysis is complemented with numerical simulations. By comparing the root mean square error, the IASA has better 2-D DOA estimation results than circular array, rectangular array, and concentric ring array.

Multiobjective Optimization Design of Time-Modulated Concentric Circular Ring Arrays

A multiobjective approach based on the third evolution step of generalized differential evolution (GDE3) algorithm is proposed for optimizing the time-modulated array (TMA) in this paper. Different from the single-objective optimization, which optimizes a weighted sum of the peak sidelobe level (PSLL) and the peak sideband level (PSBL) of the array, the multiobjective algorithm treats the PSLL and the PSBL as two distinct objectives that are to be optimized simultaneously. Furthermore, not only one outstanding optimization result can be acquired but also a set of solutions known as Pareto front is obtained by using the GDE3 algorithm, which will guide the design of time-modulated array more effectively. Users can choose one appropriate outcome which has a suitable tradeoff between the PSLL and the PSBL. This approach is illustrated through a time-modulated concentric circular ring array (CCRA). The optimal parameters and the corresponding radiation patterns are presented at last. Experimental results reveal that the multiobjective optimization can be an effective approach for the TMA synthesis problems.

A Sidelobe and Energy Optimization Array Node Selection Algorithm for Collaborative Beamforming in Wireless Sensor Networks

The beam pattern of the virtual node antenna array (VNAA) in wireless sensor networks has a high maximum sidelobe level (SLL), thereby causing communication interference because of the uncontrollable node positions. A sidelobe and energy optimization array node selection (SEOANS) algorithm is proposed for optimally selecting the sensor nodes to form a VNAA that optimizes the beam pattern of VNAA and reduces the average energy consumption of nodes. SEOANS uses a calculation method to determine the optimal number of array nodes, proposes a node location selection optimization method based on concentric circular ring array and a novel swarm intelligence optimization algorithm called cuckoo search chicken swarm optimization (CSCSO) to optimize the excitation current of each array node. CSCSO uses chaos theory, introduces the inertia weight Levy flight, and adopts the grade mechanism in chicken swarm optimization to improve the performance of the cuckoo search algorithm. In addition, the scheduling and fault tolerance mechanisms are designed and implemented in SEOANS. Simulation results show that the node position selection optimization method and the excitation current optimization based on CSCSO can effectively reduce the maximum SLL. Furthermore, compared with traditional clustering routing algorithms, SEOANS has advantages in the communication delay and average energy consumption of nodes, thus effectively improving network lifetime.

Enhanced Terahertz Absorption of Graphene Composite Integrated with Double Circular Metal Ring Array

Graphene-based terahertz (THz) devices, such as modulators, detectors, and absorbers, play important roles in terahertz applications due to graphene’s effectively tunable terahertz absorption. The features of these terahertz devices are greatly related to the THz absorption of graphene. However, the monolayer graphene shows limited absorption to terahertz waves. In this paper, we demonstrated a new graphene composite with a double circular metal ring array deposited on graphene to enhance the absorption. The graphene composite consists of a double circular metal ring array, a monolayer graphene, silicon dioxide, and silicon substrates. The double circular metal ring array locally enhances the electromagnetic field on graphene and further increases graphene’s absorption. It shows that the peak absorption of the proposed graphene composite is increased to 95% for graphene Fermi level 0 eV at room temperature, which is more than seven times larger than that of the graphene composite without the double circular metal ring array. The enhanced terahertz absorption of the proposed graphene composite shows the potential ability of improving modulation depth and insertion loss of a THz reflection modulator.

Wide-Angle Polarization-Independent Broadband Absorbers Based on Concentric Multisplit Ring Arrays

We theoretically propose a wide-angle, polarization-independent, and broadband nearly perfect absorber, which consists of an array of concentric multisplit circular rings on top of dielectric spacer and a metallic mirror. The numerical simulation results show that the average absorption reaches 97.2% over the wavelength range from 585 to 800 nm whatever the polarization angle is. Meanwhile, the absorber keeps high absorption efficiency when the incidence angle is below 45°. The physical mechanism is analyzed by calculating the absorbed power spectra and electromagnetic field distribution. The broadband and the high absorption mainly result from the strong electromagnetic resonance and overlapping of resonant frequencies. Our proposed plasmonic absorbers have potential applications in spectral imaging, photodetector, solar energy, and so on.