Ring Array Research Articles

Synthesis of Clustered Concentric Ring Arrays Through Joint Optimization of Multi-Parameters

This article proposes a novel hybrid methodology that addresses the clustering of concentric ring arrays (CRAs) through joint optimization of ring radii, clusters partitions, and clusters excitations. It takes advantage of convex programming (CP) with respect to the excitation variables due to their convex nature. For the optimization of rings radii and clusters partitions, a subproblem is formulated by mix-integer programming with linear constraints, which is effectively resolved using the developed technique of mixed-integer linear-constraint genetic algorithm (MILCGA). A set of representative numerical experiments show the effectiveness of the proposed method and illustrate its potentialities, representing a promising solution for CRAs to obtain a suitable tradeoff between costs, robustness, flexibility, and beam control performances.

Quantitative Evaluation of In Vivo Corneal Biomechanical Properties after SMILE and FLEx Surgery by Acoustic Radiation Force Optical Coherence Elastography.

The purpose of this study is to quantitatively evaluate the differences in corneal biomechanics after SMILE and FLEx surgery using an acoustic radiation force optical coherence elastography system (ARF-OCE) and to analyze the effect of the corneal cap on the integrity of corneal biomechanical properties. A custom ring array ultrasound transducer is used to excite corneal tissue to produce Lamb waves. Depth-resolved elastic modulus images of the in vivo cornea after refractive surgery were obtained based on the phase velocity of the Lamb wave. After refractive surgery, the average elastic modulus of the corneal flap decreased (71.7 ± 24.6 kPa), while the elastic modulus of the corneal cap increased (219.5 ± 54.9 kPa). The average elastic modulus of residual stromal bed (RSB) was increased after surgery, and the value after FLEx (305.8 ± 48.5 kPa) was significantly higher than that of SMILE (221.3 ± 43.2 kPa). Compared with FLEx, SMILE preserved most of the anterior stroma with less change in corneal biomechanics, which indicated that SMILE has an advantage in preserving the integrity of the corneal biomechanical properties. Therefore, the biomechanical properties of the cornea obtained by the ARF-OCE system may be one of the essential indicators for evaluating the safety of refractive surgery.

Large-Area and High-Precision Milling of Focused Ion Beam Based on the Integration of Nanoscale Machine Vision and Compensation Control

Abstract Focused ion beam (FIB) is a high-precision technology for micro/nanofabrication that can be used to fabricate micro/nanoscale structures and electronic devices, such as waveguide gratings, resonators, and photonic crystals. In this study, a novel FIB processing system was developed using machine vision coupled with a piezoelectric motor, which compensates the process periodically and automatically. The FIB system is controlled by a computer program that enables automatic processing, automatic recognition, and provides feedback to control the movement of the stage. The results show that ring arrays with a diameter of 2 μm can be detected automatically under the field of view (FOV) of 114 × 114 μm2 with relative errors of less than 6%. The FOV can be larger than 400 × 400 μm2 after the splicing function of automatic compensation control is applied to the same ring arrays. Structurally, the average splicing errors in the X- and Y-directions decreased one order of magnitude, which are from 1.49 to 0.15 μm and 1.47 to 0.37 μm, respectively. This paves the way for the mass production of nanoholes in a large area with high precision and high speed for semiconductor manufacturing and research.

LSPR Sensing of Epithelial Cell Adhesion Molecules through Sphere and Cavity Plasmons of a Composite Ring Array of Poly[2-(dimethylamino)ethyl methacrylate]/Gold Nanoparticles.

Self-organization facilitates the formation of specific structures as a result of constituent interactions. In this study, the bottom of a 600 nm hole array photoresist template, which was deposited with a hydrophobic atom transfer radical polymerization (ATRP) initiator, was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) was grafted from the ring array of the initiator to immobilize gold nanoparticles (AuNPs) as a uniform ring array on a silicon substrate via repeated swelling/shrinking cycles. The localized surface plasmon resonance (LSPR) peak of the PDMAEMA-AuNP hybrid ring (PAHR) red-shifted after 12 swelling/shrinking cycles. In comparison to gold nanoparticles, scalable gold nanorings can effectively develop a variety of nanostructures to design LSPR-based sensors and optimize the sensing accuracy and stability. To detect epithelial cell adhesion molecules (EpCAM) during the structural change from a ring to a disk, antiEpCAM was anchored onto the PAHR as a biosensor during swelling/shrinking. The coupling of antiEpCAM and EpCAM led to asymptotical convergence from rings to disks as well as blue shifts of the LSPR peaks. Linear correlation between the blue shift and EpCAM concentration showed a limit of detection of ∼27 pg mL-1 and a linear range of 25-200 pg mL-1 for the detection of EpCAM within 30 min. The simple method of combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of AuNPs for highly sensitive and selective biosensing.

Coherently Radiating Periodic Structures for Feeding Concentric Rings Array with Reduced Number of Phase Shifters

This paper presents the application of CORPS (coherently radiating periodic structures) for feeding CRA (concentric rings array) with a reduced number of phase shifters. The proposed design technique for the structure of concentric rings provides a better scanning capability with respect to other existing configurations. This design technique utilizes 2 × 3 or 4 × 7 CORPS networks depending on the configuration or the number of antenna elements in the phased array system. These CORPS networks are set strategically in the feeding network to provide several advantages with respect to others in the scanning capability and the reduction of the number of phase shifters of the array system. The contribution of this paper is the full antenna system design of phased CRA for analyzing scanning and the reduction of phase shifters. The proposed phased array reduces the number of phase shifter devices in CRA for a scanning range of ±25° in the elevation plane. Differential evolution (DE) was applied to optimize the amplitudes of the proposed system. Several design cases were analyzed using full-wave simulation results to verify the phased array model and to take mutual coupling into account. Full-wave simulation results provide radiation patterns with low SLL in all scanning directions. The proposed phased array was validated by experimental measurements of the full antenna system prototype.

Concentric-ring arrays for forward-viewing ultrasound imaging.

Current ultrasound (US)-image-guided needle insertions often require an expertized technique for clinicians because the performance of tasks in a three-dimensional space using two-dimensional images requires operators to cognitively maintain the spatial relationships between the US probe, the needle, and the lesion. This work presents forward-viewing US imaging with a ring array configuration to enable needle interventions without requiring the registration between tools and targets. The center-open ring array configuration allows the needle to be inserted from the center of the visualized US image, providing simple and intuitive guidance. To establish the feasibility of the ring array configuration, the design parameters causing the image quality, including the radius of the center hole and the number of ring layers and transducer elements, were investigated. Experimental results showed successful visualization, even with a hole in the transducer elements, and the target visibility was improved by increasing the number of ring layers and the number of transducer elements in each ring layer. Reducing the hole radius improved the region's image quality at a shallow depth. Forward-viewing US imaging with a ring array configuration has the potential to be a viable alternative to conventional US image-guided needle insertion methods.

Vari-focal liquid microlens array using an electrically responsive fluid actuated by a ring array patterned electrode.

A transparent fluid dibutyl adipate (DBA) is suitable for fabricating the adaptive lens due to its unique deformation under a direct current (DC) electric field. In this report, a DBA liquid microlens array (LMA) with a tunable focal length is demonstrated. A hydrophobic layer deposited in the ring array patterns on the electrode induced the formation of the DBA liquid microdroplets array self-assembly. The electronegative DBA liquid tends to move to the anode at a DC voltage. The proposed DBA LMA with a diameter of 100µm can change its focal length from 0.92 to 1.42mm when the voltage changes from 0 to 200V. The response time is relatively fast (∼790m s). Due to the high optical transmittance (∼91%) and good thermal stability in the temperature range of -24.8-161.5∘C, our DBA LMA shows good focusing properties and has potential applications in the field of image processing, portable electronic devices, beam steering, ophthalmology, and 3D displays.

Research on impact localization method based on passive tomography of piezoelectric sensors

Impact monitoring of plate structures has always been a hot spot in structural health monitoring research. In order to improve the accuracy of impact monitoring, this paper proposes a beam-focusing impact localization algorithm based on passive tomography using a sensor arrangement method in a ring array. The impact damage monitoring of large-sized structures in different directions is performed by each linear array of the ring array and the impact damage localization distribution maps of the corresponding linear arrays are generated. The localization accuracy of the linear arrays in different directions is obtained experimentally to assign the weights of each linear array to achieve image reconstruction of the impact damage. The experimental results show that the method can achieve a more accurate visualization of the impact location, and the reconstructed impact laminar image can well reflect the impact location distribution information. It can be used for the localization of impact damage and extended monitoring.

Fabrication of scalable poly(N-isopropylacrylamide)/gold nanoparticles composite ring array as LSPR sensor for label-free biosensor application

Self-organization facilitates the formation of specific structures as a result of constituent interaction. In this study, the bottom of a 500-nm hole array photoresist template, which was deposited with a hydrophobic atom transfer radical polymerization (ATRP) initiator, was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted from the ring array of the initiator to immobilize gold nanoparticles (AuNPs) as a uniform ring array on the silicon substrate via repeated swelling/shrinking cycles. The localized surface plasmon resonance (LSPR) peaks of the biotin-anchored AuNP–PNIPAAm composite ring (APCR) were employed to detect streptavidin as biosensors. The coupling of biotin and streptavidin led to asymptotical convergence from rings to disks as well as blue-shifts of the LSPR peaks. Linear correlation between the blue-shift and streptavidin concentration showed a limit of detection of ∼10 nM and a linear range of 10–150 nM for the detection of streptavidin within 30 min. The simple method of combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of AuNP for highly sensitive and sensitive biosensing.

Research on the Multi-Element Synthetic Aperture Focusing Technique in Breast Ultrasound Imaging, Based on the Ring Array.

As a widely clinical detection method, ultrasonography (US) has been applied to the diagnosis of breast cancer. In this paper, the multi-element synthetic aperture focusing (M-SAF) is applied to the ring array of breast ultrasonography (US) imaging, which addresses the problem of low imaging quality due to the single active element for each emission and the reception in the synthetic aperture focusing. In order to determine the optimal sub-aperture size, the formula is derived for calculating the internal sound pressure of the ring array with a 200 mm diameter, and the sound pressure distribution is analyzed. The ring array with 1024 elements (1024 ring array) is established in COMSOL Multiphysics 5.6, and the optimal sub-aperture size is 16 elements, according to the sound field beam simulation and the directivity research. Based on the existing experimental conditions, the ring array with 256 elements (256 ring array) is simulated and verified by experiments. The simulation has a spatial resolution evaluation in the k-Wave toolbox, and the experiment uses nylon rope and breast model imaging. The results show that if the sub-aperture size has four elements, the imaging quality is the highest. Specifically, the spatial resolution is the best, and the sound pressure amplitude and signal-to-noise ratio (SNR) are maintained at a high level in the reconstructed image. The optimal sub-aperture theory is verified by the two kinds of ring arrays, which also provide a theoretical basis for the application of the multi-element synthetic aperture focusing technology (M-SAF) in ring arrays.

Expediting Image Acquisition in Reflection Ultrasound Computed Tomography.

Reflection ultrasound computed tomography (RUCT) attains optimal image quality from objects that can be fully accessed from multiple directions, such as the human breast or small animals. Owing to the full-view tomography approach based on the compounding of images taken from multiple angles, RUCT effectively mitigates several deficiencies afflicting conventional pulse-echo ultrasound (US) systems, such as speckle patterns and interuser variability. On the other hand, the small interelement pitch required to fulfill the spatial sampling criterion in the circular transducer configuration used in RUCT typically implies the use of an excessive number of independent array elements. This increases the system's complexity and costs, and limits the achievable imaging speed. Here, we explore acquisition schemes that enable RUCT imaging with the reduced number of transmit/receive elements. We investigated the influence of the element size in transmission and reception in a ring array geometry. The performance of a sparse acquisition approach based on partial acquisition from a subset of the elements has been further assessed. A larger element size is shown to preserve contrast and resolution at the center of the field of view (FOV), while a reduced number of elements is shown to cause uniform loss of contrast and resolution across the entire FOV. The tradeoffs of achievable FOV, contrast-to-noise ratio, and temporal and spatial resolutions are assessed in phantoms and in vivo mouse experiments. The experimental analysis is expected to aid the development of optimized hardware and image acquisition strategies for RUCT and, thus, result in more affordable imaging systems facilitating wider adoption.

Magnetic moiré effects and two types of topological transition in a twisted-bilayer hyperbolic metasurface with double-split ring arrays.

Moiré configurations have recently attracted much attention due to their ability to enhance photonic responses and manipulate surface waves in the subwavelength ranges. However, previous studies have usually been focused on natural hyperbolic materials with limitations on patterning procedures, controlling rotation angles, and merely manipulating electric surface plasmons. Here, we theoretically and numerically investigate a novel magnetic moiré hyperbolic metasurface in the terahertz region, which enables two types of topological transition and a plethora of unusual magnetic moiré effects (magnetic surface wave manipulation, dispersion engineering, magic angles, spacer-dependent topological transition, and local field enhancement). This work extends twistronics and moiré physics to the terahertz region and magnetic polaritons, with potential applications in quantum physics, energy transfer, and planarized magnetic plasmonic devices.

Design and Simulation of a Ring Transducer Array for Ultrasound Retinal Stimulation.

Argus II retinal prosthesis is the US Food and Drug Administration (FDA) approved medical device intended to restore sight to a patient’s blind secondary to retinal degeneration (i.e., retinitis pigmentosa). However, Argus II and most reported retinal prostheses require invasive surgery to implant electrodes in the eye. Recent studies have shown that focused ultrasound can be developed into a non-invasive retinal prosthesis technology. Ultrasound energy focused on retinal neurons can trigger the activities of retinal neurons with high spatial-temporal resolution. This paper introduces a novel design and simulation of a ring array transducer that could be used as non-invasive ultrasonic retinal stimulation. The array transducer is designed in the shape of a racing ring with a hemisphere surface that mimics a contact lens to acoustically couple with the eye via the tear film and directs the ultrasound to avoid the high acoustic absorption from the crystalline lens. We will describe the design methods and simulation of the two-dimensional pattern stimulation. Finally, compared with other existing retinal prostheses, we show that the ultrasound ring array is practical and safe and could be potentially used as a non-invasive retinal prosthesis.

Quantifying the computational capability of a nanomagnetic reservoir computing platform with emergent magnetisation dynamics

Devices based on arrays of interconnected magnetic nano-rings with emergent magnetization dynamics have recently been proposed for use in reservoir computing applications, but for them to be computationally useful it must be possible to optimise their dynamical responses. Here, we use a phenomenological model to demonstrate that such reservoirs can be optimised for classification tasks by tuning hyperparameters that control the scaling and input-rate of data into the system using rotating magnetic fields. We use task-independent metrics to assess the rings’ computational capabilities at each set of these hyperparameters and show how these metrics correlate directly to performance in spoken and written digit recognition tasks. We then show that these metrics, and performance in tasks, can be further improved by expanding the reservoir’s output to include multiple, concurrent measures of the ring arrays’ magnetic states.

Generating a multi-mode vortex beam based on spoof surface plasmon polaritons.

The vortex beam provides a promising alternative for next-generation wireless communication, but it is a long-standing challenge to generate a multi-mode and robust vortex beam. In this Letter, a multi-mode vortex beam emitter is introduced and experimentally verified based on spoof surface plasmon polaritons (SSPP). The SSPP on a helical grating carries multi-mode orbital angular momentum and can be converted into a high-purity vortex beam via the diffraction of a ring array. The operation frequency and topological charge are determined by that of the SSPP. This emitter can achieve the function of beam-scanning in each radiation band. The beam-scanning and vortex characteristics are experimentally verified. The designed emitter is compact and robust, and we are confident that this work will have great application prospects in communication systems.

Magnetic ring chains with vertex coupling of a preferred orientation

We discuss spectral properties of a periodic quantum graph consisting of an array of rings coupled either tightly or loosely through connecting links, assuming that the vertex coupling is manifestly non-invariant with respect to the time reversal and a homogeneous magnetic field perpendicular to the graph plane is present. It is shown that the vertex parity determines the spectral behavior at high energies and the Band–Berkolaiko universality holds whenever the edges are incommensurate. The magnetic field influences the probability that an energy belongs to the spectrum in the tight-chain case, and also it can turn some spectral bands into infinitely degenerate eigenvalues.

Angle-dependent spin wave spectra of permalloy ring arrays

We investigated the angle-dependent spin wave spectra of permalloy ring arrays with the fixed outer diameter and various inner diameters by ferromagnetic resonance spectroscopy and micromagnetic simulation. When the field is obliquely applied to the ring, local resonance mode can be observed in different parts of the rings. And the resonance mode will change to perpendicular spin standing waves if the magnetic field is applied along the perpendicular direction. The simulation results demonstrated this evolution and implied more resonance modes that maybe exist. And the mathematical fitting results based on the Kittel equation further proved the existence of local resonance mode.

Sensitive Detection of Aspartame and Vanillin by Combining Terahertz Fingerprinting With a Metamaterial

In this study, a terahertz (THz) metamaterial based on THz fingerprint is proposed for simultaneous measurement of aspartame and vanillin. The metamaterial consists of an array of concentric aluminum rings on a polyimide substrate. A three-dimensional full-wave electromagnetic field simulation is performed using the finite integral method. The metamaterial transmission spectrum contains two dips at 0.39 THz and 0.61 THz. These two frequencies correspond to the characteristic absorption peaks of aspartame and vanillin in the THz band. According to the hybrid induced transparency (HIT) principle, introducing an additive on the metamaterial surface results in the appearance of a narrow transmission peak at the corresponding transmission dip, where the peak intensity increases with the additive thickness. The calculated sensitivity of the proposed metamaterial sensor is 30.76 dB/(ng/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) for aspartame and 63.91 dB/(ng/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) for vanillin. Specific detection is realized because the characteristic absorption peaks of different additives appear at different positions in the transmission spectrum. Therefore, the proposed THz metamaterial sensor has high application value in the field of food additive detection.

Polarization-Independent Broadband Angular Selectivity Based on Anisotropic Diamagnetic Metamaterial

Achieving broadband angular selectivity has been attracting much interest from both scientists and engineers in recent years. Previous experimental demonstrations have been limited to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> -polarized incidence. Here, we propose a universal approach to achieve polarization-independent broadband angular selectivity by introducing electrically and magnetically anisotropic diamagnetic medium into multiple 1-D photonic crystal stacks. Such stacks have a broadband angular photonic bandgap for both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$s$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> -polarized waves. The anisotropic diamagnetic medium is artificially constructed with periodically arranged close metallic ring arrays, which exhibits a negligible frequency dispersion in an ultrawide band. As a proof of principle, one stack of photonic structures for the normal-incidence-selective case is fabricated and measured in the microwave region. The proposed approach is simple, robust, and scalable from near-zero frequencies to terahertz frequencies, showing promising practical applications such as spatial filters and anti-jamming communications.

Generating high-energy densities by sidelobe suppression in the far-field of phase-locked lasers

Laser beams with high-energy densities are desired for both fundamental research and applied applications. We present a numerical study on the generation of high-energy densities by sidelobe suppression in the far-field intensity distribution of phase-locked lasers. The method relies on modifying the combined field distribution of phase-locked lasers to obtain uniform amplitude and phase distributions in a near-field plane, which enables the formation of a high-energy density main central lobe (zeroth order) in the far field. The method is applied to various one-dimensional (1D) and two-dimensional (2D) array geometries, such as square, triangular, Kagome, random, and 1D ring. The results show that for in-phase-locked lasers in 2D array geometries, the diffraction efficiency of the high-energy density region (zeroth-order lobe) can be increased in the range of 90%–95%. For in-phase-locked lasers in a 1D ring array, the maximum diffraction is found to be ∼ 75 % . Further, the effects of the range of phase locking, system size, as well as topological defects are examined on diffraction efficiency. The method is also applied to an out-of-phase-locked laser in the square array, and a high-energy density output beam is obtained.