Plane Array Research Articles

High Resolution 2.5D PIV Measurements of the Flow Fields Generated by Small Fans

Abstract The free jets of an axial and a centrifugal fan have been scanned by a specialized particle image velocimetry (PIV) set-up, which allows for volumetric scans of the time-averaged velocity field. Both of these fans have similar dimensions of approximately 70 mm x 70 mm x 25 mm. A classic PIV set-up was combined with a precise linear stage to move the fans through the laser fan beam in small steps, creating a dense array of measurement planes. Two components of the time-averaged velocity field are captured by the first 2.5D scan. Another scan, with the fan rotated by 90° about its outlet surface normal, captures the missing third velocity component. This article describes the details of the measurement set-up, and mentions measures concerning seeding, reflections, and calibration. In the signal processing stage, two independent sets of gathered image data have to be processed, producing two sets of velocity image frames. These are subsequently combined using gridded interpolation in order to obtain a 3D velocity field. Specifically devised software tools allow for a CFD-like analysis and visualization of the flow field. Typical parameters of the generated jets, like the spreading and rotation rates, are calculated from the measurement data and details of the outlet flow fields are investigated. The interpolated data are also used to analyze the influence of an assumed coarser measurement grid resolution on the results for the obtained outlet flow fields.

A Wide-Beam Antenna for Wide-Angle Scanning Linear Phased Arrays

In this letter, a wide-beam (at two main planes) antenna is proposed. To broaden the 3 dB beamwidth of the original antenna, a pair of parasitic patches with metallic vias is creatively arranged on either side of the original radiation patches. Based on the proposed antenna element, two linear phased arrays are fabricated and measured. Measured results reveal that the wide-angle scanning capability of both H -plane and E -plane arrays can be obtained. The scanning beam of the former can cover territories ranging from −90° to 90°, with gain loss within 3 dB (8 GHz–11 GHz). The scanning beam of the latter can cover territories ranging from −70° to 70°, with gain loss of 3–5 dB (8 GHz–10 GHz).

Mutual Coupling Reduction of Closely E/H-Plane Coupled Antennas Through Metasurfaces

In this letter, a simple metasurface superstrate structure is proposed to reduce mutual coupling of both E -plane and H -plane coupled patch antennas. The proposed metasurface consists of periodic ring slots arranged on one side of the substrate. The metasurface can suppress the surface wave and partly change the coupling mode, which can achieve isolation enhancement of more than 40 dB at resonant frequency in both E / H -plane coupled patch antennas. The edge-to-edge spacing between antenna elements is 2 mm (0.023 λ0). The prototypes of E -plane and H -plane arrays with metasurfaces are fabricated, and the experimental measurements and the simulation results are in good agreement.

Modeling of the Acoustic Field Produced by Diagnostic Ultrasound Arrays in Plane and Diverging Wave Modes.

Recent advances in ultrafast contrast imaging have facilitated innovations, such as superresolution imaging and ultrafast contrast-enhanced Doppler imaging. Combining plane and diverging wave imaging (PWI/DWI) with tissue harmonic imaging (THI) may offer improvements in image quality in applications such as 3-D THI and harmonic color flow. However, no studies have reported simulations of the nonlinear acoustic fields produced by diagnostic arrays in either plane or diverging wave mode. The aim of this study is to model three typical diagnostic arrays that are used in clinical practice and research, Verasonics L11-4v linear array, C5-2v convex array, and P4-2v phased array with the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. We have two specific objectives: first, to investigate whether there is increased bubble destruction due to the nature of the plane and diverging fields in contrast imaging; and second, to investigate the feasibility of combining PWI/DWI and THI by quantifying the second harmonic generated by these fields. We showed in linear simulations that using such arrays for ultrafast contrast imaging produced pressures that are greater in the near field and lower in the far field than those of focused beams and thus may induce more near-field bubble destruction. In nonlinear simulations, the second harmonic produced by ultrafast THI was found to be 2-16 dB lower than that of focused beams for all arrays considered when operated at the same MI. This moderate difference of the second harmonic between PWI/DWI and focused ultrasound suggests that it is feasible to combine PWI/DWI and THI.

Three-dimensional target localization method based on the tensor subspace FDS-MIMO radar with a co-prime frequency offset

Target localization utilizing frequency diversity array (FDA) is one of the most popular research directions in the study of radars. Considering the problems of range ambiguity and localization accuracy, this paper investigates the issue of three-dimensional (3D) target localization based on the proposed frequency diverse-subaperturing multiple-input multiple-output (FDS-MIMO) radar. First, a fifth-order tensor signal model is established by exploiting the inherent multidimensional structure of the matched filter output. To alleviate the difficulty of range ambiguity, the idea of employing co-prime frequency offsets along the two directions in the planer array is provided. This strategy can resolve the contradiction between the range resolution and maximum unambiguous range in beam domain. The tensor-based complex- and real-valued rotational invariance technique (tensor- and unitary tensor-ESPRIT) algorithms are developed based on frequency offset structure. Given that the inherent multidimensional structure is utilized, the proposed methods can resolve range ambiguity with improved localization performance as compared with the existing ESPRIT algorithm and frequency offset manner. Theoretical analysis and numerical results demonstrate the effectiveness of the proposed approaches.

Camera array-based digital image correlation for high-resolution strain measurement.

Digital image correlation (DIC) is a well-known technique for non-contact, non-destructive, full-field deformation measurement in experimental solid mechanics. Although DIC has been widely used in science and engineering, the resolution of strain measurement with DIC is limited by imaging resolution and is much lower than that obtained with a strain gauge. To achieve a breakthrough in strain measurement using DIC, a camera array-based DIC method is proposed herein for high-resolution strain measurement. Twenty-five industrial cameras were assembled into a plane array, with each camera capturing a part of the specimen. A novel calibration-based image stitching method is proposed and was applied to these images and their corresponding displacement fields. The strain field was then calculated based on the stitched displacement fields. The use of the camera array greatly improved the measurement spatial resolution of DIC and made high-resolution strain measurement possible. Both static error analysis and four point-bending experiments were performed to demonstrate the feasibility and effectiveness of the proposed method, and a full-field strain resolution of 10 was achieved.

Research on Accurate Ultrasonic Positioning Error under the Special Environment

This paper studies how to achieve the accurate position by an ultrasonic positioning system, which is for locating the autonomous vehicle in a special giant spherical container. A localization method using the least squares with a plane array which consists of four elements is proposed, the reason that causes the location error is analysed, and the relationship among the target distance and the array shape and the error of the ultrasonic positioning system is studied by Monte Carlo simulations. Finnally, in order to verify the positioning effect, the positioning experiment is done in an anechoic tank, the experimental results shown that when the ranging error is less than 20 mm, the positioning accuracy of x-y plane is less than about 30 mm.

Range-Angle Localization of Targets With Planar Frequency Diverse Subaperturing MIMO Radar

Target localization utilizing frequency diverse array (FDA) has received much attention in recent years. In this paper, we propose a tensor subspace-based multiple-target 3-D localization method with planar frequency diverse subaperturing multiple-input multiple-output (FDS-MIMO) radar. To fully exploit the inherent multidimensional FDS-MIMO radar matched filter output information, a tensor signal model is established first. Then, the FDS-MIMO radar range ambiguity problem is mitigated by applying co-prime frequency offsets along both the dimensions of the planer array. Next, a beamspace-based unitary tensor-multiple signal classification (UTMUSIC) algorithm is developed to utilize the inherent multidimensional structure through the higher order singular value decomposition (HOSVD)-based low-rank approximation. Moreover, two computationally efficient methods, namely, partial spectral search UTMUSIC and range-angle decoupling UTMUSIC algorithms, are also proposed accordingly. The superiority of the proposed approaches over conventional methods is verified with numerical results, in terms of both computational complexity and estimation accuracy.

用于声矢量阵列波达方向估计的四元数最小范数法

To reduce the calculation amount of quaternion Multiple Signal Classification(MUSIC)algorithm,a Minimum Norm(MN)quaternion method based on the quaternion form of an acoustic sensor vector was proposed for estimating Direction of Arrival(DOA).First,based on the MN principle,the(M-N)×Mdimension(Mis the number of array sensors,Nis the number of signal sources)orthogonal noise subspace vectors were converted to a 1×M dimension quaternion noise vector.Then,a simplified formula for peak search was proposed.The searching computation amount of Quaternion MN(Q-MN)was analyzed theoretically.Compared with the Q-MUSIC algorithm,the Q-MN algorithm can save at least 50% of the peak search volume.Experimental results show that the orthogonality of the steering vector with the low-dimensional noise vector derived by proposed methodis superior to that with high dimensional noise subspace.When the Signal to Noise Ratio(SNR)is 0dB,the Vandermonde norm and the spatial spectrum peak value of Q-MN algorithm are 1/3 times and 3 times as much as those of Q-MUSIC.The Q-MN algorithm can successfully identify the DOA of signal sources,and its resolution is equivalent to that of Q-MUSIC algorithm.Moreover,it can be applied to not only L-shaped arrays,but also plane arrays and parallel linear arrays.

Late Cenozoic Faults and Shallow Oil Accumulation in the Nanpu Sag

The Nanpu Sag, located in the north part of Huanghua Depression of Bohai Bay Basin, is a Cenozoic petroliferous extensional sag, the shallow oil reservoirs have great exploration potential. Former exploration suggested that there is complex relationship between Late cenozoic faults and hydrocarbon accumulation, but there is no detailed discussion. Based on the structural interpretation of 3D seismic data, the Late Cenozoic fault characters including typical fault configuration in profile and fault arrays in plane are analyzed, furthermore, the formation mechanism of the faults is discussed. It is concluded that late Cenozoic faults were formed by extension other than strike-slip movement, which was controlled by the mechanism of pure shear in the lower crust during the period. In addition, the relationship between Late Cenozoic faults and shallow hydrocarbon accumulation is discussed, it indicates that the faults controlled the formation of shallow closures and constituted the effective hydrocarbon pathways connecting deep source rock and shallow traps.

The near‐field processing and narrowband imaging algorithm for MIMO array

PurposeImaging is a really difficult problem when systems are implemented in the near‐field region and real‐time needs. The purpose of this paper is to consider a novel system model and present a narrowband 2‐D imaging algorithm in the near‐field region and under the real time constraint.Design/methodology/approachThe first part of this paper proposes a novel approximation for the round‐trip distance of the near‐field echoed data based on a 2‐D synthetic aperture planar array. The second part of this work proposes a near‐field narrow imaging algorithm based on the above system model. Narrowband waveforms are employed in the array system, so that the range alignment and decoupling in range‐azimuth are not necessary.FindingsThe errors of the proposed approximation are much smaller as compared with those of the Fresnel approximation. For example, the errors of the proposed approximation are negligible when the antenna is fixed at (0, 0). In other cases, the errors are decreased by almost 50 percent. Compared with 2‐D plane array, the synthetic aperture plane of the paper reduces the number of antennas. Finally, numerical simulation results verify the validity of the imaging algorithm.Originality/valueThe near‐field difficulty is solved by the adoption of the proposed approximation. The theoretical analysis and simulation results verify the validity of the imaging algorithm in the near‐field region and under the real time constraint.

Non-Linear Synthesis Problems for Plane Radiating Systems According to the Prescribed Power Directivity Pattern

A variational formulation of the synthesis problem for plane radiating systems according to the prescribed power directivity pattern (DP) is considered. The function representing the mean-square deviation of the prescribed and synthesized power DPs and containing the additional term with squared norm of the current or field in the antenna aperture is considered as the criterion of optimization. Freedom to choose the phase DP is used to improve the proximity of the prescribed and synthesized DPs. In such formulation, the classes of non-linear problems, for which the non-uniqueness of solutions, their branching and bifurcation are characteristic, arise. The properties of solutions depend on the electric size of radiating system and prescribed power DP. From a practical point of view, the existence of different solutions creating the same or similar DPs, gives the opportunity to choose the solution that has a simpler implementation. The synthesis problems for plane radiating systems and plane arrays are considered.

Coupling to External Structures: Boundary Conditions for the Bi2212-based Superconducting THz Emitter

It is known that a mesa fabricated from intrinsic Josephson junctions of Bi2Sr2CaCu2O8+δ emits intense terahertz radiation at a certain frequency in accordance with the ac-Josephson relation and the general resonance conditions determined by the geometrical shape and dimensions. When more than two mesas are placed on the crystal surface, synchronization phenomenon of two mesas and the cavity resonance due to the coupling to the external structures outside the biased mesa are observed. These phenomena are interpreted by the current propagation effect through the superconducting substrate over the range of a few hundreds of μm even with the phase coherency. This opens up the possibilities of improving the individual device by external antenna and cavity, and of constructing the large-scale planer array of mesas for the purpose of power enhancement.

Adaptive sonar beamformer based on inverse QR decomposition and recursive least squares filter for underwater target detection

To enhance underwater target detection performance, a standard hexagonal array (HA) (plane array) is designed for active sonar implementation in shallow water environments. For the hexagonal receiving array, the numerically robust inverse QR (Q, orthogonal matrix; R, upper triangular matrix) decomposition and recursive least-squares (RLS) are used to derive the minimum variance distortionless response (MVDR) beamformer (BF) under a hexagonal fast Fourier transform (HFFT) framework. The HFFT inverse QR (IQR)-RLS algorithm offers computational saving and can be mapped onto coordinate rotation digital computer processor-based systolic arrays, which makes it suitable for array real-time application. An analysis of the numerical robustness and computational complexity of the adaptive beamforming is presented. Using the proposed scheme to build HA adaptive BF reduces the computational burden and offers a better convergence rate than conventional BF. The experimental data analysis demonstrates the effectiveness of the algorithm against reverberation interference, and its improvement of target localization accuracy in a reverberation-limited area during the underwater target detection process.

Design Smart Antenna by Microstrip Patch Antenna Array

Smart have been studied extensively this decade because of its low profile structure and formidable rate, thereby creating new and improved services at lower costs. They are extremely compatible for embedded in handheld wireless devices such as cellular phones, pagers etc. Because of its versatility, Smart antenna which is designed by planer array can be used to synthesize a required pattern that cannot be achieved with a single patch element. Index Terms—Radiation patterns, Mobile communication, planar array, PCCAD 5.0 software etc. I. I NTRODUCTION In high-performance aircraft, spacecraft, satellite and missile application, where size, weight, cost, performance, ease of installation, and aerodynamic profile are constraints, so low profile may be required. Presently there are many other government and commercial applications, such as mobile, radio and wireless communications that have similar specifications .To meet these requirements antennas have been researched extensively. This has resulted in an increase in airtime usage and in the number of subscribers. Spatial processing is the central idea of smart- antenna systems. Although it might seem that smart have been recently discovered, they date back to World War II with the conventional Bartlett beamformer (1). It is only of today's advancement in powerful low-cost digital signal processors, general purpose processors (and ASICs—Application-Specific Integrated Circuits), as well as innovative software-based signal-processing techniques (algorithms), that smart antenna systems have received enormous interest worldwide. To approach the feature, design smart antenna by microstrip patch antenna array (2). Quality factor (Q) of microstrip is a very high. Quality factor can be reduced by increasing the dielectric substrate. But due to increasing thickness, unwanted power loss occurs by the surface wave. However, this surface waves can be minimized by the use of photonic bandgap structures (3). Recent studies on microstrip have primarily concentrated on the improvement of bandwidth and on the design of multifunction operations (4)-(7). As a result, almost 100% bandwidth in terms of VSWR and dual-band

Focal plane resolution and overlapped array time delay and integrate imaging

In this paper we model sub-pixel image registration for a generic earth-observing satellite system with a focal plane using two offset time delay and integrate (TDI) arrays in the focal plane to improve the achievable ground resolution over the resolution achievable with a single array. The modeling process starts with a high-resolution image as ground truth. The Parameterized Image Chain Analysis & Simulation Software (PICASSO) modeling tool is used to degrade the images to match the optical transfer function, sampling, and noise characteristics of the target system. The model outputs a pair of images with a separation close to the nominal half-pixel separation between the overlapped arrays. A registration estimation algorithm is used to measure the offset for image reconstruction. The two images are aligned and summed on a grid with twice the capture resolution. We compare the resolution in images between the inputs before overlap, the reconstructed image, and a simulation for the image which would have been captured on a focal plane with twice the resolution. We find the performance to always be better than the lower resolution baseline, and to approach the performance of the high-resolution array in the ideal case. We show that the overlapped array imager significantly outperforms both the conventional high- and low-resolution imagers in conditions with high image smear.

Narrow-Wall-Slotted Hollow-Waveguide Array Antenna Using Partially Parallel Feeding System in Millimeter-Wave Band

We developed a slotted waveguide planer array antenna with partially parallel feeding in millimeter-wave band. Travelling-wave excitation is more effective for low loss feeding of array antennas than parallel feeding systems. However, array antenna with travelling-wave excitation essentially possesses a significant problem of long line effect which degrades gain due to beam shift by frequency change when the array antenna is fed from the edge of the radiating waveguide. We propose the way to reduce the gain degradation due to frequency change, thus, partially parallel feeding system is developed. Measured performance of the developed antenna is evaluated in this paper.

Polarization Control in Three-Dimensional Resonant Coherent Excitation

We present an experimental demonstration of an ingenious technique to control the alignment of the atomic internal state in the x-ray region using a periodic crystal field. The alignment directions of Ar16+ and Fe24+ ions were readily controlled by selecting the array of atomic planes using three-dimensional resonant coherent excitation, and were probed via the anisotropy of the deexcitation x-ray emission. We applied this method to a double resonance experiment, and succeeded in controlling the population of the specific magnetic substate in a Lambda-type three-level configuration.

Curved arrays for pipe wall inspection – Fundamentals of electronic focusing for curved and plane arrays

The paper studies important aspects of focusing with curved and plane arrays: (i) The differences between the focus position calculated geometrically with simple rays and that one determined by sound-field simulation based on GREEN’s functions are shown and discussed in detail. (ii) Appearing side lobes significantly spoil resolution. Therefore, the reasons for side lobes require further research. Side lobes can either be caused by grating lobes or by insufficiently steered sound-field beams of the peripheral array elements. Adequate remedies are suggested: the classification of side lobes provides the best opportunity to improve the control mode. The study is done by calculating the time harmonic sound field in water. As an example of use, an application with pipe wall inspection is given. Inside the pipe wall, the intended location of the focus is achieved with small off-axis secondary structures. Thereby, double readings are avoided, and resolution is improved. To verify the results, the harmonic and transient sound fields are simulated and compared with each other.

Modeling of Field Emission from Nano Carbons

We report here a comparative study by computer modeling of cold cathodes made from carbon nanotubes and plate‐like graphite nanocrystallites. To simulate the infinite arrays of emitters the 3D Laplace problem with periodic boundary conditions has been solved. The obtained values of electric field strength were used for calculation of the emission current density in accordance with Fowler‐Nordheim equation. We considered the nano‐carbon film as a flat array of cylinders (nanotubes) and planes (nanoflakes) with perpendicular orientation to the substrate. We have found the dependences of field enhancement factor β and current densities on distance between emitters. As a result we have obtained the optimum distances between emitters where the emission is strongest for both types of cathodes. These results have been verified experimentally.