Irregular Array Research Articles

3-D Short-Range Imaging With Irregular MIMO Arrays Using NUFFT-Based Range Migration Algorithm

3-D imaging with irregular planar multiple-input-multiple-output (MIMO) arrays is discussed. Due to signal acquisition on irregular spatial sampling grids by using these antenna arrays, the fast Fourier transform (FFT)-based imaging algorithms cannot readily be used for image formation. To avoid the application of computationally intensive coherent summation algorithms such as filtered backprojection or Kirchhoff migration, we propose a nonuniform FFT (NUFFT)-based MIMO Range Migration Algorithm (i.e., NUFFT-based MIMO-RMA) for efficient microwave imaging. The algorithm exploits NUFFT to reconstruct the wavenumber–domain spectra related to each Fourier frequency. It is generic and applicable to 3-D imaging with irregular planar MIMO arrays. The effects of irregular spatial sampling and signal bandwidth on the imaging performance and computational efficiency of the proposed algorithm are analyzed. Finally, some numerical simulations and experimental results are presented to demonstrate the performance of the proposed imaging algorithm.

Trifrequency Reconfigurable Linear Irregular Array with Beam Deflection Capability in X/Ku/Ka-Bands

This paper proposes a trifrequency reconfigurable antenna (FRA), which can work in the X-band, Ku-band, and Ka-band, by controlling only two RF MEMS switches. The antenna element has a frequency ratio beyond 3 : 1 and provides a good candidate for the frequency reconfigurable antenna array, since the size of the antenna is reduced by loading multiple metal shorting holes between the antenna radiating surface and the ground plate, and the overall size is only 0.14λX × 0.35λX (λX is the free-space wavelength at 8.6 GHz). Based on the proposed FRA element, a 1 × 16 linear irregular frequency reconfigurable antenna array (FRAA) with beam deflection ability is designed, which effectively addresses the element spacing problem in the optimization of the array. In addition, the close-coupling in X-band and the grating lobe caused by the long distance of array element spacing in Ka-band are comprehensively considered. With uniform amplitude feeding network, the sidelobe level is below −15 dB under beam deflection. Moreover, both FRA elements and FRAA prototypes have been fabricated and measured to verify their superiority. Good agreements are obtained between simulated and measured results, which indicates that the antenna has potential application in the future multifrequency wireless communication and intelligent radar anti-interference fields.

Generating the dual‐band and multimode OAM by irregular pentagonal patch antenna array

This Letter presents an irregular pentagonal patch array antenna with a multilayer structure for dual-band and multimode orbital angular momentum (OAM) generation. An irregular pentagonal patch antenna with U-shaped slots resonating at different frequencies is designed as the array's element. The proposed antenna array consists of two uniform circular microstrip antenna arrays and two phase-shifting feeding networks. It can be used to generate OAM mode l = − 1, 1 at 3 GHz and OAM mode l = −2, 2 at 6 GHz. The simulated near-field phase distributions images of different OAM modes are obtained, which have verified the OAM generation. This proposed array antenna has the possibility to generate a total of six different OAMs in three frequency bands, by changing the number of array elements and optimising the irregular pentagonal patch antenna. This design may provide a new idea for the generation multimode vortex electromagnetic wave.

Stochastic allocation strategy for irregular arrays based on geometric feature control

Irregularities in microphone distribution enrich the diversity of spatial differences to decorrelate interferences from the beamforming target. However, the large degrees of freedom of irregular placements make it difficult to analyse and optimize array performance. This article proposes fast and feasible optimal irregular array design methods with improved beamforming performance for human speech. Important geometric features are extracted to be used as the input vector of the neural network structure to determine the optimal irregular arrangements of sensors. In addition, a hyperbola design method is proposed to directly cluster microphones in the hyperbola areas to produce rich differential distance entropies and yield significant signal-to-noise ratio improvements. These methods can be easily applied to guide non-computer-aided optimal irregular array designs for human speech in acoustic scenes such as immersive cocktail party environments.

In brief

PAGE 476 Chinese researchers present an irregular pentagonal patch array antenna, featuring a multilayer structure to enable dual-band and multi-mode orbital angular momentum (OAM) generation. The proposed array has the potential generate 6 different OAMs in 3 frequency bands and may provide new ideas for generating multi-mode vortex electromagnetic waves. PAGE 482 A multiplier design technique for stochastic computing is presented. The proposed design offers exact output and latency in the order of 2N, where N = the input precision. Compared to state of the art deterministic methods, the proposed design is faster by a factor of 2N. The technique is verified by mathematical analysis and simulation. Schematic diagram of proposed antenna array's element PAGE 501 Researchers from the Republic of Korea demonstrate integrated one-dimensional optical phase arrays (OPAs) for wide-angle, two-dimensional beam-steering in a 26.5 mm2 area. The 2-D OPA consists of 16 1-D transversal steering OPAs, whose radiators have different grating periods – allowing assignment of different longitudinal angles. Carry save adder in proposed design for N = 3. Full adder and half adder are denoted by fa and ha respectively. PAGE 510 Chinese researchers present an edge-attention-based geodesic distance which can be applied to the simple linear iterative clustering (SLIC) framework for PolSAR image superpixel segmentation, improving performance without an increase in computational expense. Experiments show the superiority of the proposed distance both qualitatively and quantitatively. Structure and design parameters of the grating radiator. PAGE 490 A collaboration of Chinese researchers propose two schemes to help prevent unwanted sideslip by wheeled mobile robots when turning. A controller is proposed combining robust control and model predictive control. Together the longitudinal velocity can be adjusted according to the state of the robot, whilst the model predictive control is used to achieve path tracking. Superpixel segmentation on PolSAR images over Changle using SLIC with the proposed distance. Fuzzy-NMPC system structure.

A comparison of compressive equivalent source methods for distributed sources.

Sparse sound-field reconstruction methods based on compressive sensing and the equivalent source method have gained a lot of interest in recent years, offering a wide frequency range. An irregular array must be employed, and the sound field must be representable by a sparse vector of source-model amplitudes. With few and concentrated physical sources, the sparsity assumption can be fulfilled, but distributed sources cause problems. Several methods have therefore been introduced to support sparse representation of distributed sources. One set of such methods represents the amplitude vector as a linear combination of modal amplitude distributions. In that case, the coefficient vector just has to be sparse. The present paper gives an overview of such methods, and the performance of the methods is compared based on a set of simulated measurements. Overall the modal representations work well if the true source distribution can be represented by relatively few modes. The results show that even for a vibrating plate this may not be the case if the source model size does not match the plate size and/or if a non-central plate excitation is applied. If, in addition, there are also compact sources, then the basic method without modes may be the best choice.

Plasma-Texturing Surface Treatment of Grey Cast Iron for Friction Reduction

A new surface texturing technique, based on liquid plasma discharging in an aqueous electrolyte, is proposed to modify the surface morphology of grey cast iron. During the process, a grey cast iron sample serves as a cathode where the reduction of hydrogen from the aqueous electrolyte occurs and consequently plasma discharging is generated on the sample surface under applied high voltages (up to 480V). The formed hydrogen bubbles are exploded during the electrical discharging, leaving an irregular array of craters on the sample surface due to the high temperature and shockwaves of the plasma micro-arc discharging. After polishing the crater-like textured surface, surface roughness and oil retention are measured by a profilometer. Reciprocating tribotests are utilized to determine the coefficients of friction. The surface morphology of the polished and tested surface is studied by SEM. The same tests are also conducted for the cast iron with a cross-hatched surface. These two set of results are compared to determine the effects of the texturing and polishing on friction. The results show that the polishing of textured surface can decrease the roughness and coefficients of friction significantly at starved lubricating conditions. This method has potential to be applied on the cylinder bore surface of a cast iron liner for the internal combustion engine (ICE). By honing the textured bore surface, the friction between piston and cylinder bore is expected to decrease and the ICE efficiency to increase for environmental benefits.

Wind turbine partial wake merging description and quantification

AbstractIndividual turbine location within a wind plant defines the flow characterisitcs experienced by a given turbine. Irregular turbine arrays and inflow misalignment can reduce plant efficiency by producing highly asymmetric wakes with enhanced downstream longevity. Changes in wake dynamics as a result of turbine position were quantified in a wind tunnel experiment. Scale model turbines with a rotor diameter of 20 cm and a hub height of 24 cm were placed in symmetric, asymmetric, and rotated configurations. Simultaneous hub height velocity measurements were recorded at 11 spanwise locations for three distances downstream of the turbine array under two inflow conditions. Wake interactions are described in terms of the time‐average streamwise velocity and turbulence intensity as well as the displacement, momentum, and energy thicknesses. The effects of wake merging on power generation are quantified, and the two‐point correlation is used to examine symmetry in the mean velocity between wakes. The results indicate that both asymmetric and rotated wind plant arrangements can produce long‐lasting wakes. At shallow angles, rotated configurations compound the effects of asymmetric arrangements and greatly increase downstream wake persistence.

Initial stage sintering of polycrystalline spheres: A model and experiments

Conventional models for initial stage sintering consider sintering to occur between two single crystal spheres, although most powder particles are polycrystalline in reality. The conventional Coble model is modified to take into account multiple grain boundaries intersecting a neck in sintering between polycrystalline particles. The exponents N and M in the rate equation (x/R)N α (t/RM), for polycrystals were found to be 4 and 2, respectively, in contrast to 6 and 4 in single crystals; here x, R and t are the neck radius, particle radius and time, respectively. In addition there is a 1/d2 dependence, where d is the grain size. Analysis reveals that initial stage sintering will be enhanced in polycrystalline particles when the neck is large and there are a large number of grains within a particle. Accompanying experiments on close packed irregular 2D arrays of polycrystalline zirconia spheres showed that the neck growth rate was higher for the particles containing a large number of grains, compared to those with only a few grains.

Capsular contracture around silicone miniimplants following bacterial contamination: an in vivo comparative experimental study between textured and polyurethane implants

Capsular contracture remains a problem following breast implant surgery. Although impact of biofilm and implant surface on capsule formation has been demonstrated, interaction of microorganisms with different surface types has not been clarified yet. We aimed to compare the ability of biofilm formation of implants with different surfaces, under standard conditions and to demonstrate its impact on capsular contracture. Twenty-four rats were divided into four groups. Mini-implants with three different surfaces (fine-textured, rough-textured and polyurethane) were placed on the dorsum of each rat. In Group-1, sterile implants were placed in submuscular pockets. In Group-2, implants were incubated in Staphylococcus epidermidis medium before implantation. In Group-3, before implantation, implants were immersed in Rifamycin solution following bacterial contamination. In Group-4, sterile implants were immersed in Rifamycin solution before implantation, and served as the control group. Rats were sacrificed at three months. Clinical, microbiological, histological and immunohistochemical evaluations were performed. Capsule contracture developed only on infected rough-textured implants. Rough-textured and polyurethane implants showed more biofilm formation than fine-textured implants. Capsule thickness and inflammatory cell density were higher on rough-textured implants compared to fine-textured implants (p = 0.004). Actin sequence was parallel and concentric on fine-textured and rough-textured implants; but was in irregular array on polyurethane implants. In presence of bacterial contamination, rough-textured implants have the most propensity of developing capsular contracture comparing to fine-textured and polyurethane implants at three months after implantation. Despite high bacterial load and biofilm formation, polyurethane implants are resistant to capsule contracture due to surface characteristics.

Three-Dimensional and In Situ-Activated Spinel Oxide Nanoporous Clusters Derived from Stainless Steel for Efficient and Durable Water Oxidation.

Developing cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts based on earth-abundant elements is vital to hydrogen production from electrocatalytic water splitting. Herein, a three-dimensional and in situ-activated electrocatalyst derived from stainless steel is successfully fabricated via a two-step laser direct writing strategy. The electrocatalyst appears in the form of nanoparticle-stacked porous clusters on the multiscale stainless steel with irregular microcone arrays and microspheres, which exposes more active sites and facilitates the mass transport. Especially, the clusters undergoe a self-optimizing morphological and compositional reconfiguration induced by the leaching of Cr species under OER conditions for favorable charge transfer and enhanced intrinsic catalytic activity. As a result, the in situ-activated, Ni/Cr-doped Fe3O4 electrocatalyst exhibits an outstanding OER performance with a small overpotential of 262 mV to reach 10 mA cm-2, a low Tafel slope of 35.0 mV dec-1, and excellent long-term stability of 120 h, among the best spinel Fe-rich OER electrocatalysts. Finally, we also verify the feasibility of the affordable and efficient electrocatalyst coupled with the commercial Ni cathode in the practical water electrolysis. This work may open up a new avenue to design nanostructured metal oxides for various energy applications and beyond.

Infrasound Observations of Atmospheric Disturbances Due to a Sequence of Explosive Eruptions at Mt. Shinmoedake in Japan on March 2018

Thirty infrasound sensors have been operated over Japan since 2015. We developed the irregular array data processing in order to detect and estimate the parameters of the arrival source waves by using infrasound data related to the sequence of the volcanic eruption at Mt. Shinmoedake in March 2018. We found that the apparent velocity at the ground was equal to the acoustic velocity at particular reflection levels. The results were confirmed through a comparison of the findings of the apparent velocity with a wave propagation simulation on the basis of the azimuth, infrasound time arrivals, and the state of the atmospheric background using global atmospheric models. In addition, simple ideas for estimating horizontal wind speeds at certain atmospheric altitudes based on infrasound observation data and their validation and comparison were presented. The calculated upper wind speed and wind observed by radiosonde measurements were found to have a qualitative agreement. Propagation modeling for these events estimated celerities in the propagation direction to the sensors that were consistent with the tropospheric and stratospheric ducting. This study could inspire writers, in particular, and readers, in general, to take advantage of the benefits of infrasound wave remote-sensing for the study of the Earth’s atmospheric dynamics.

A Sound Source Identification Algorithm Based on Bayesian Compressive Sensing and Equivalent Source Method

Near-field acoustic holography (NAH) based on equivalent source method (ESM) is an effective method for identifying sound sources. Conventional ESM focuses on relatively low frequencies and cannot provide a satisfactory solution at high frequencies. So its improved method called wideband acoustic holography (WBH) has been proposed, which has high reconstruction accuracy at medium-to-high frequencies. However, it is less accurate for coherent sound sources at low frequencies. To improve the reconstruction accuracy of conventional ESM and WBH, a sound source identification algorithm based on Bayesian compressive sensing (BCS) and ESM is proposed. This method uses a hierarchical Laplace sparse prior probability distribution, and adaptively adjusts the regularization parameter, so that the energy is concentrated near the correct equivalent source. Referring to the function beamforming idea, the original algorithm with order v can improve its dynamic range, and then more accurate position information is obtained. Based on the simulation of irregular microphone array, comparisons with conventional ESM and WBH show that the proposed method is more accurate, suitable for a wider range of frequencies, and has better reconstruction performance for coherent sources. By increasing the order v, the coherent sources can be located accurately. Finally, the stability and reliability of the proposed method are verified by experiments.

Multiple Beam Synthesis of Passively Cooled 5G Planar Arrays Using Convex Optimization

An extended-feature, system-driven convex algorithm for the synthesis of uniform-amplitude, irregular planar phased arrays with simultaneous multi-beam optimization for mm-wave 5G base station applications in multi-user scenarios is presented. The inter-user interferences are suppressed by minimizing the maximum sidelobe level (SLL) for a beam scanned freely inside a given sector. The aperture size is restricted to the size of the heatsink baseplate dimensions. A minimum guaranteed inter-element spacing in the final layout is pre-defined, which prevents element overlapping, eases the thermal problem and helps reduce the effects of high mutual coupling (MC). The algorithm performance is tested via the synthesis of a 64-element integrated array with at least half a wavelength inter-element spacing. The optimized array results show that, compared to their regular counterparts, significant reduction in the SLLs is achieved for a beam scanned inside the defined sector, while keeping the maximum temperature of the array at a reliable level. The effect of MC on the results is also investigated via full-wave simulations and it is explained how embedded element patterns can potentially be included in the optimization. Superior capabilities of the proposed method are illustrated by comparing the algorithm output to those reported in the state-of-the-art literature.

Initial Stage Sintering of Polycrystalline Spheres: A Model and Experiments

Conventional models for initial stage sintering consider sintering to occur between two single crystal spheres, although most powder particles are polycrystalline in reality. The conventional Coble model is modified to take into account multiple grain boundaries intersecting a neck in sintering between polycrystalline particles. The exponents N and M in the rate equation (x/R)^N α (t/ R^M), for polycrystals were found to be 4 and 2, respectively, in contrast to 6 and 4 in single crystals; here x, R and t are the neck radius, particle radius and time, respectively. In addition there is a 1/d^2 dependence, where d is the grain size. Analysis reveals that initial stage sintering will be enhanced in polycrystalline particles when the neck is large and there are a large number of grains within a particle. Accompanying experiments on close packed irregular 2D arrays of polycrystalline zirconia spheres showed that the neck growth rate was higher for the particles containing a large number of grains, compared to those with only a few grains.

Low-Cost Subarrayed Sensor Array Design Strategy for IoT and Future 6G Applications

The low-cost sensor array, an effective way to provide sufficient degrees of freedom (DoFs) and affordable costs, is one of the most important foundation devices for large-scale applications of the Internet of Things (IoT) and sixth-generation (6G) spaceborne communication systems. In this article, we propose an irregular subarray-based low-cost sensor array design strategy, which decomposes the practical application problem into two subproblems according to the scene scale. For the small-size cases, a user-defined DoF control strategy is presented, which is flexibly defined and establishes an effective tradeoff between the sensor array radiation performance and manufacturing cost. Moreover, for large-size cases, a hierarchical subarray design strategy is presented. A module panel structure composed of subarray tiles is proposed to avoid both the convergence problem in high-dimensional optimization and engineering complexity. Both design strategies are able to ensure good sensor radiation performance while maintaining engineering convenience. The effectiveness and potential of the proposed method are verified by various numerical examples.

Intensity Based Spatial Soundfield Reproduction Using an Irregular Loudspeaker Array

Sound intensity is an acoustic quantity closely linked with human perception of sound location, and it can be controlled to create a high level of realism to humans in soundfield reproduction systems. In this article, we present an intensity matching technique to optimally reproduce sound intensity over a continuous spatial region using an irregular loudspeaker array. This avoids several known limitations in the previous works on intensity based soundfield reproduction, such as a single sweet spot for the listener and a regular loudspeaker geometry that is difficult to implement in real-world applications. In contrast to the previous works, the new technique uses a cost function we built to optimize sound intensity over space by exploiting spatial sound intensity distributions. The spatial sound intensity distribution is represented by spherical harmonic coefficients of sound pressure, which are widely used to describe a spatial soundfield. Compared to the conventional spatial soundfield reproduction method of pressure matching in the spherical harmonic domain and the HOA $max$ - $r_E$ decoding method optimizing sound intensity at a single position, we show that the intensity matching technique has better overall performance with two different irregular loudspeaker layouts through simulations. The impact of microphone noise on reproduction performance is also assessed. Finally, we carry out perceptual localization experiments to validate the proposed method.

Efficient Simulation of Large Irregular Arrays on a Finite Ground Plane

An efficient method is presented to take into account the radiation pattern deformation due to the presence of a finite ground plane lying under an antenna array and above a layered dielectric medium. The interactions between the antennas and the ground plane are computed using two main algorithms: on one hand, the near-field interactions are carried out using inhomogeneous plane waves, and on the other hand, a new formulation based on an analytical Hankel transform is derived to handle the intermediate-field interactions. This formulation expresses the electric field as a finite series of Hankel functions and associated Anger–Weber functions. The method is validated here for the second version of the square kilometer array (SKA) log-periodic Antenna (SKALA2) and then applied to an SKA low-frequency station (SKA1-LOW).

Preparation and characterization of vertical regular arrayed and needle-shaped irregular titanium dioxide nanotubes for dye-sensitized solar cells

This study investigated the effect of surface modification on the photovoltaic characteristics of TiO2 electrodes. The modification was done by increasing the TiO2 nanoparticles in order to increased dye absorption. The crystal phase features, morphology, and topography were assessed through such techniques as XRD, SEM, and AFM. This addition was done with several methods including ultrasonic bathing, spin-coating and immersing in an autoclave that among these techniques autoclave has the highest efficiency. Furthermore, TiO2 nanotubes (TNTs) and needle-shaped irregular nanotubes were designed on Ti sheet and Ti layer deposited on FTO glass. The characterization results point to a maximum efficiency of 1.3% that belongs to the solar cells composed of TiO2 nanotube photoanodes in TNTs on Ti layer sputtered on FTO glass. In the sample of solar cells with TiO2 nanotubes photoanode, which TNTs were designed on Ti sheet, the efficiency was 25%. Finally, for solar cells composed of TiO2 nanotube photoanodes with needle-shaped irregular nanotube arrays designed on Ti layer sputter upon FTO glass and TiO2 nanotube photoanodes with a needle-shaped irregular nanotube array designed on Ti sheet, the efficiencies were respectivly 0.54% and 0.44%.

Widening the Length Distributions in Irregular Arrays of Self-Catalyzed III–V Nanowires

Widening the Length Distributions in Irregular Arrays of Self-Catalyzed III–V Nanowires