Search

An elevation and azimuth direction-finding (DF) method is presented by introducing the pattern reconfigurable antenna (PRA) into a two-element array. An equivalent multi-dimensional array is built by the two-element PRA array with switchable beams of same or opposited directions. With the introduction of same-direction and opposite-direction modes of PRAs, the elevation and azimuth angles are estimated by the methods of time modulated array (TMA) and amplitude comparison, respectively. Meanwhile, a 2-D look-up table is built to correct the coning-error effect of the amplitude comparison. Compared with the conventional 2-D DF method with two orthogonal linear arrays, only a single linear array with not less than two elements is needed in the proposed method. Hence, it has the advantages of simple structure, compact size, and low cost. Simulated results are provided to verify the proposed 2-D DF method, and an S-band two-element PRA array is constructed to demonstrate its experimentally feasibility.

In this letter, we explore the feature of coprime linear array (CLA) motion for enhanced array aperture and higher degree of freedom (DOF) by implementing synthetic aperture processing. Since the traditional fixed CLA cannot achieve two-dimensional (2-D) DOA estimation, we propose a novel approach to construct the virtual coprime planar array (VCPA) just by the CLA motion. Specifically, the CLA moves along the vertical direction at a constant velocity and the two subarrays of CLA are controlled to snap at different time delays related to the coprime number of sensors, by which the received signals at different time delays are synthetically processed to construct a VCPA. Simulation results demonstrate that: a) our proposed approach outperforms the synthetic CLA moving along the direction of layout of the initial arrays on DOF and the dimension of DOA estimation; b) the proposed VCPA can achieve 2-D DOA estimation just by the motive CLA and achieve no worse performance than the practical coprime planar array but by using fewer sensors.

Airborne downward-looking sparse linear array 3-D synthetic aperture radar (DLSLA 3-D SAR) usually uses a sparse and nonuniform linear array that often does not satisfy the Nyquist sampling theorem. Therefore, the cross-track dimensional imaging will fail with the traditional 3-D frequency-domain imaging algorithms. Several grid-based sparse reconstruction (GB-SR) algorithms have been presented to solve this issue. However, they assume that the scatterers are located on the discretized grids; otherwise, the off-grid effect or basis mismatch problem will occur. To address this issue, we propose a novel hyperparameter-free gridless-based sparse reconstruction (GL-SR) algorithm (i.e., 2-D adaptive iterative reweighted atomic norm minimization algorithm called 2-D IRAN) by a combination of the optimal covariance fitting criterion and atomic norm. It is a generalized model, while the other GL-SR algorithms (e.g., GLS, RGLS, and RAM) can be interpreted as the variants of 2-D IRAN. Moreover, since the interior-point method employed in toolboxes has high computational efficiency only for the small-scale matrix optimization problem, a fast implementation of 2-D IRAN via alternating direction method of multipliers (ADMM) is presented for the large-scale matrix optimization problem. Finally, we carry out extensive numerical simulations to demonstrate the advantages and effectiveness of 2-D IRAN for DLSLA 3-D SAR imaging based on the complex 3-D ship model and 3-D distributed scenario.

Although X-Ray Computed Tomography (CT) is widely used for detecting pulmonary nodules inside the parenchyma, it cannot be used during video-assisted surgical procedures. Real-time, non-ionizing, ultrasound-based techniques are an attractive alternative for nodule localization to ensure safe resection margins during surgery. Conventional ultrasound B-mode imaging of the lung is challenging due to multiple scattering. However, the multiple scattering contribution can be exploited to detect regions inside the lung containing no scatterers. Pulmonary nodules are homogeneous regions in contrast to the highly scattering parenchyma containing millions of air-filled alveoli. We developed a method relying on mapping the multiple scattering contribution inside the highly scattering lung to detect and localize pulmonary nodules. Impulse response matrices were acquired in ex-vivo pig and dog lungs using a linear array transducer to semi-locally investigate the backscattered field. Extracting the multiple-scattering contribution using singular-value decomposition and combining it with a depression detection algorithm allowed us to detect and localize regions with less multiple scattering, associated with the nodules. The feasibility of this method was demonstrated in five ex-vivo lungs containing a total of 20 artificial nodules. Ninety-five percent of the nodules were detected. Nodule depth and diameter significantly correlated with their ex-vivo CT-estimated counterparts (R = 0.960, 0.563, respectively).

In this letter, we consider a distributed satellite MIMO scenario that includes two GEO satellites and a uniform linear array (ULA). The effect of geometrical arrangement of ULA on channel capacity is investigated, and it is proved that the optimal capacity can always be obtained as long as its antenna spacing is larger than a threshold. The closed-form expressions of this threshold and its asymptotic form are derived. Considering the threshold may be too large to satisfy when a low frequency is used or two satellites are close, the exact capacity reduction when the threshold cannot be satisfied is also analyzed, which can help to reach a compromise between capacity and antenna spacing.

In this paper, we propose a new amplitude-only method for pattern synthesis of uniform linear array (ULA) based on genetic algorithm (GA) and artificial neural network (ANN), which can produce a low sidelobe pattern with deep nulls. Unlike existing schemes for pattern synthesis, our method can avoid falling into local optimum and exhibits a faster convergence speed, and is also easy to implement due to its low computational complexity. In complicated and changing environments, the proposed method can quickly and accurately synthesize the desired pattern of the ULA. Numerical results demonstrate the effectiveness of the devised algorithm.

Unmanned aerial vehicle (UAV) swarms have shown great potential for Internet of Things (IoT). Meantime, its malicious use may cause huge threat to the national security. UAV swarms show the characteristic of high density which poses formidable challenges to radar resolution in the defense of critical areas. In this article, we consider a radar equipped with the coprime array, and then, use the coherent long-time integration (LTI) technique and gridless sparse technique to detect and localize UAVs in a swarm. This strategy takes full account of advantages of the coprime array, coherent LTI technique, and gridless sparse technique, i.e.: 1) the coprime array can provide a larger array aperture than the uniform linear array with the same number of array elements to relieve the stress of the gridless sparse technique and 2) the combination of coherent LTI technique and gridless sparse technique can maximize their advantages and make up for their shortcomings. By mathematical analyses and extensive numerical examples, we show the superiority of the proposed strategy in terms of accurate detection and localization of UAV swarms.

Beamforming is widely used in structural health monitoring (SHM) systems for impact or damage localization. Beamforming directionality is achieved by the constructive interference of sensor wavefronts, which results in a significant amplification of the measured signal in a particular direction. For beamforming applications, the cost per sensor is typically significant, because of the sensor itself, and the associated electronics. Therefore, in order to minimize the cost of SHM in practice, it is highly desirable to reduce the number of sensors. Beamforming with an array of sensors requires an advanced signal processing technique to detect the direction-of-arrival (DOA). In addition, by deploying more sensors, better detection accuracy can be achieved. In this paper, the non-equidistant linear sensor array is proposed, to obtain lower costs while guaranteeing reasonable detection accuracy. In addition, the proposed sensor deployment scheme is able to reduce the effects of “spatial aliasing,” which phenomenon is typically encountered in the equidistant linear sensor array layout. To validate the performance of the proposed non-equidistant linear array technique in SHM applications, several finite element models (FEM) simulation and experimental investigations are carried out. Different sensor array layouts are also compared to optimize the performance of the non-equidistant linear array.

This prospective study aimed to assess the usefulness of an intracavitary convex array probe (ICAP) in visualizing the lateral meniscus (LM) and improving the diagnostic utility of ultrasound (US) when diagnosing or screening for discoid lateral meniscus (DLM) in children. We included 105 knees (66 patients) that had symptomatic or asymptomatic DLM. We extracted and retrospectively reviewed data regarding patient demographics, medical records, magnetic resonance imaging (MRI), ultrasonographic features and arthroscopic findings. The inner edge of the LM visualized using an ICAP was significantly clearer than that visualized using a linear array probe, and the difference was significant (p0.01). The edges were better visualized in patients aged8 y than in those aged8 y, and the difference was significant (p0.001). The average widths of the LM body using an ICAP and MRI were 19.85 ± 3.63 and 24.46 ± 4.94 mm, respectively, and the wider the meniscal width, the greater was the deviation between the US and MRI measurements, which were positively correlated (r = 0.612, p0.001). With the use of MRI measurements and an ICAP, meniscal widths in poorly visualized LMs were greater than those in clearly visualized LMs, but this difference was not significant (p = 0.161). US scans using an ICAP and MRI were highly consistent in assessing the shape of the menisci (κ = 0.849, p0.001). US scan using an ICAP is a non-invasive, convenient and low-cost modality for diagnosing or screening for DLM in the pediatric population, especially in children aged8 y.

Objectives To investigate the prevalence of high-risk human papillomavirus (HPV)–negative cervical intraepithelial neoplasia (CIN) and invasive cervical carcinoma (ICC) and to analyze the distribution of other genotypes in this subset. Methods In total, 431 women who underwent excisional surgical treatment for CIN or ICC at the European Institute of Oncology, Milan, Italy, from January 2016 to December 2017 were retrospectively analyzed. The Linear Array HPV genotyping test (Roche Diagnostics) was performed on a postaliquot from high-risk-HPV–negative liquid-based cervical specimens, when available. Patient characteristics and the prevalence of high-risk-HPV–negative CIN grade 2 or worse (CIN2+) were tabulated. We used t tests to compare age between high-risk-HPV–positive and high-risk-HPV–negative patients. Results Overall, 8.9% of CIN2+ and 7.5% of ICC cases were high-risk HPV negative. There was no age difference between high-risk-HPV–negative CIN2+ women (mean [SD], 41.3 [8.7] years) and high-risk-HPV–positive women (mean [SD], 39.5 [9.0] years) (P = .28). The Linear Array result was available in 22 cases. Most high-risk-HPV–negative patients were positive for a single other genotype infection (32.6%). HPV 73 was the most prevalent genotype, followed by HPV 53 and HPV 84. HPV 26 was detected in 1 case of ICC. Conclusions Our results showed a not-negligible proportion of high-risk-HPV–negative CIN2+, suggesting that cotesting would not miss these cases.

A sparse array synthesis method based on improved wind-driven optimization algorithm (IWDO) and fast Fourier transform (FFT) for the purpose of sidelobe suppression was introduced. First, the unifo...

In the linear array synthetic aperture radar (LASAR) three-dimensional (3D) imaging, the spacing between adjacent elements in the uniform linear array (ULA) must satisfy the Nyquist sampling theore...

An efficient analysis of time-modulated array (TMA) toward realizing less-attenuating radiation patterns with simultaneously suppressed sidelobe and sidebands is presented in this paper. In this framework, an optimal outer element-controlled time sequence is derived. The proposed time scheme, along with optimized array excitations, is profitably applied for the desired solution. TMAs are considered unconventional alternatives to the phased arrays. The desired array radiation features can be attained by periodically enabling and disabling the array elements through high-speed switches. Despite the advantages of architectural simplicity and real-time reconfigurability of periodic time sequences, time-domain antenna arrays inherently generate unavoidable sideband radiations (SRs). The undesired SRs obtained at multiple harmonics around the carrier frequency of the array resembles power loss in unintended directions. This paper aims to minimize the SRs as well as the sidelobe level (SLL) for an efficient analysis of time-modulated linear array (TMLA) with high-directive radiation patterns. The starting instants and the period of on-times are optimized to generate a unique shifted time scheme for the edge elements of the TMLA to reduce the sideband levels (SBLs). The array excitations and the uniform spacing between the elements are also optimized together with the shifted time scheme for the coveted solution. Other methods of suppressing SLLs and SBLs with shifted pulse schemes and sub-sectioned pulse schemes are also presented for a fair comparison. Modified versions of the particle swarm optimization algorithm (PSO) are applied for the desired solutions. The optimal results attained by wavelet mutation-based novel PSO is compared with the conventional PSO and the modified novel PSO-based results. The representative results are reported, and the superior performance abilities of the proposed method compared to other published studies are assessed.

At the edge of a continental shelf, where the depth of the ocean column can vary rapidly by a factor of $$\sim $$ 20, tsunamis are expected to be severely refracted in application of Snell’s Law. We use beaming techniques applied to numerical simulations under the shallow-water approximation, in the geometry of two real-life provinces of the Pacific Basin featuring sharp bathymetric discontinuities and extended shelves (Southeastern Alaska and Nicaragua). We conclude that tsunamis do indeed undergo refraction under Snell’s Law with equivalent refraction indices as high as 5. We apply the same technique to actual records of the 2011 Tohoku tsunami by an array of seafloor pressure sensors off the coast of Southern California, and similarly observe Snell refraction despite a smaller velocity contrast and the presence of a shelf with extremely irregular bathymetry. Finally, we show numerically that for a source and a linear array of receivers both deployed on a well developed continental shelf bordering a deep basin, the tsunami will develop a head wave in all ways similar to the familiar case of refraction seismology.

This study proposes a new sensor cluster configuration for localizing an acoustic source in a plate using uniform linear array beamforming and T-shaped sensor clusters. This technique requires neither the properties of the plate material nor a dense array of sensors to find the direction of arrival of the acoustic source. It functions by placing four sensors in a cluster in the shape of the letter “‘T” over a small region of the plate. Uniform linear array beamforming-based source localization is carried out by the constructive interference of different sensor signals. However, this approach has the disadvantage of a very low resolution when the direction of arrival approaches certain values. The L-shaped sensor clusters use the information from the time difference of arrival between the sensors to estimate the direction of arrival, which has a high resolution in all directions except for the direction that is very close to vertical to the cluster. In this study, we numerically and experimentally demonstrate that the proposed T-shaped sensor cluster can accurately localize the acoustic source with no blind area. We also detail its superior performance compared to both uniform linear array beamforming and L-shaped clusters. In the experimental investigation, the maximum deviation of impact source localization was reduced significantly, from 54° to 4° for an aluminum plate, and from 42° to 3° for a composite plate. Furthermore, this novel combined sensor array layout requires only a few sensors, which can significantly reduce the cost of structural health monitoring practice.

We image the shallow structure across the East Bench segment of the Wasatch fault system in Salt Lake City using ambient noise recorded by a month-long temporary linear seismic array of 32 stations. We first extract Rayleigh-wave signals between 0.4 and 1.1 s period using noise cross correlation. We then apply double beamforming to enhance coherent cross-correlation signals and at the same time measure frequency-dependent phase velocities across the array. For each location, based on available dispersion measurements, we perform an uncertainty-weighted least-squares inversion to obtain a 1D VS model from the surface to 400 m depth. We put all piece-wise continuous 1D models together to construct the final 2D VS model. The model reveals high velocities to the east of the Pleistocene Lake Bonneville shoreline reflecting thinner sediments and low velocities particularly in the top 200 m to the west corresponding to the Salt Lake basin sediments. In addition, there is an ∼400-m-wide low-velocity zone that narrows with depth adjacent to the surface trace of the East Bench fault, which we interpret as a fault-related damage zone. The damage zone is asymmetric, wider on the hanging wall (western) side and with greater velocity reduction. These results provide important constraints on normal-fault earthquake mechanics, Wasatch fault earthquake behavior, and urban seismic hazard in Salt Lake City.

Room temperature linear arrays (up to 160 detectors in array) from silicon metal- oxide-semiconductor field-effect transistors (Si-MOSFETs) have been designed for sub- THz (radiation frequency 140 GHz) close to real-time direct detection operation scanner to be used for detection and recognition of hidden objects. For this scanner, the optical system with aspherical lenses has been designed and manufactured. To estimate the quality of optical system and its resolution, the system modulation transfer function was applied. The scanner can perform real-time imaging with the spatial resolution better than 5 mm at the radiation frequency 140 GHz and contrast 0.5 for the moving object speed up to 200 mm/s and the depth of field 20 mm. The average dynamic range of real time imaging system with 160-detector linear array is close to 35 dB, when the sources with the output radiation power of 23 mW (IMPATT diodes) are used (scan speed 200 mm/s). For the system with 32-detector array, the dynamic range was about 48 dB and for the single-detector system with raster scanning 80 dB with lock-in amplifier. However, in the latter case for obtaining the image with the sizes 20×40 mm and step of 1 mm, the average scanning time close to 15 min is needed. Convolutional neural network was exploited for automatic detection and recognition of hidden items.

PurposeThe purpose of this paper is to improve energy efficiency and further reduction of side lobe level the algorithm proposed is firework algorithm. In this paper, roused by the eminent swarm conduct of firecrackers, a novel multitude insight calculation called fireworks algorithm (FA) is proposed for work enhancement. The FA is introduced and actualized by mimicking the blast procedure of firecrackers. In the FA, two blast (search) forms are utilized and systems for keeping decent variety of sparkles are likewise all around planned. To approve the presentation of the proposed FA, correlation tests were led on nine benchmark test capacities among the FA, the standard PSO (SPSO) and the clonal PSO (CPSO).Design/methodology/approachThe antenna arrays are used to improve the capacity and spectral efficiency of wireless communication system. The latest communication systems use the antenna array technology to improve the spectral efficiency, fill rate and the energy efficiency of the communication system can be enhanced. One of the most important properties of antenna array is beam pattern. A directional main lobe with low side lobe level (SLL) of the beam pattern will reduce the interference and enhance the quality of communication. The classical methods for reducing the side lobe level are differential evolution algorithm and PSO algorithm. In this paper, roused by the eminent swarm conduct of firecrackers, a novel multitude insight calculation called fireworks algorithm (FA) is proposed for work enhancement. The FA is introduced and actualized by mimicking the blast procedure of firecrackers. In the FA, two blast (search) forms are utilized and systems for keeping decent variety of sparkles are likewise all around planned. To approve the presentation of the proposed FA, correlation tests were led on nine benchmark test capacities among the FA, the standard PSO (SPSO) and the clonal PSO (CPSO). It is demonstrated that the FA plainly beats the SPSO and the CPSO in both enhancement exactness and combination speed. The results convey that the side lobe level is reduced to −34.78dB and fill rate is increased to 78.53.FindingsSamples including 16-element LAAs are conducted to verify the optimization performances of the SLL reductions. Simulation results show that the SLLs can be effectively reduced by FA. Moreover, compared with other benchmark algorithms, fireworks has a better performance in terms of the accuracy, the convergence rate and the stability.Research limitations/implicationsWith the use of algorithms radiation is prone to noise one way or other. Even with any optimizations we cannot expect radiation to be ideal. Power dissipation or electro magnetic interference is bound to happen, but the use of optimization algorithms tries to reduce them to the extent that is possible.Practical implications16-element linear antenna array is available with latest versions of Matlab.Social implicationsThe latest technologies and emerging developments in the field of communication and with exponential growth in users the capacity of communication system has bottlenecks. The antenna arrays are used to improve the capacity and spectral efficiency of wireless communication system. The latest communication systems use the antenna array technology which is to improve the spectral efficiency, fill rate and the energy efficiency of the communication system can be enhanced.Originality/valueBy using FA, the fill rate is increased to 78.53 and the side lobe level is reduced to 35dB, when compared with the bench mark algorithms.

In this paper, we propose a novel kind of time delay integration (TDI) image sensor based on single photon avalanche diode (SPAD), i.e. TDI-SPAD. Compared with existing TDI imaging devices, the proposed TDI-SPAD sensor is characterized by low noise, high sensitivity, high modulation transfer function (MTF) and transfer efficiency. The proposed architecture design of multi-stages TDI-SPAD sensor and the digital transfer circuits are discussed in detail, and the full function of TDI-imaging is demonstrated with experiments based upon two SPAD sensors. First, the imaging function of TDI-SPAD is verified through imaging of scanning scene with a $128\times128$ SPAD array. Then, we fabricate a $256\times2$ TDI-SPAD sensor, build a TDI-imaging camera system, and demonstrate the feasibility and SNR improvement of the proposed TDI-imaging sensor.

Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.

A method for accurate and quantitative nondestructive testing of small defects inside metal components has been developed by experimentally investigating the grayscale distribution in computerized tomography (CT) images for a typical 304 stainless-steel material that is extensively used in industrial products. CT scans were performed as a function of the defect pore size. The grayscale level and the noise deviation distribution were measured in each CT image. The localized grayscale features where the defects are located in the CT image were studied using wavelet decomposition. A quantitative correlation between the defect size and the grayscale distribution in the CT images was established based on the coefficient of variation. The experimental findings, when combined with the advantages of an industrial CT detection method, allow for small defects to be characterized, imaged, and presented. The results show that the quantitative accuracy of this method is higher when compared with the traditional full-width at half-maximum method. The measurement process developed herein is simple and highly practicable and, furthermore, represents an effective way to characterize the size of small defects.

A real time linear array ultrasound machine was assessed for bias accuracy and precision. A total of 51 heifers, and steers were scanned for fat thickness over the longissimus muscle, the shoulder and rump; for M. longissimus area between the 12th and 13th ribs; and marbling was subjectively evaluated from M. longissimus scans. Ultrasound data were compared with a live judging committee estimates and with carcass values obtained during USDA grading. Data adjusted for live weight were analysed by correlation and regression techniques. Ultrasound estimates of fat thickness were lower (P.05) influenced by fat thickness and sex. Ultrasound estimates of M. longissimus area were not different (P>.05) from carcass values and were high in precision (RSD: 2.6 to 6.5cm2). The precision and accuracy of data collected by real time linear array ultrasound system indicate a potential for the application of the ultrasound technique to grading of livestock and carcasses.

This paper reports on an experimental investigation of a falling fluid coverage over plain and longitudinally enhanced horizontal copper tubes. Four different fluid distributors made out of O15 mm copper pipe were prepared by drilling a linear array of 11 holes along the tube length. Distributor (a) had an array of 4.5 mm holes, distributor (b) had 3.5 mm, distributor (c) had 2.5 mm, and distributor (d) had 1.5 mm. Holes of all distributors were drilled at the same center-to-center pitch of 8 mm. A horizontal tube bundle of four O15 mm copper tubes was also prepared. The study aimed to investigate the fluid coverage on the horizontal tubes using varied distributors at 25 mm and 45 mm height between the distributor and tube bundle. It was established that not only radial enhancement on tubes can improve the falling fluid film but also the longitudinally arranged enhancement can improve the fluid flowing around the horizontal tubes.

This paper presents an antenna that utilizes two beam steering techniques in concert in order to improve the antenna gain and steering resolution. Phased array steering is employed to achieve coarse resolution beam steering while parasitic steering is employed to achieve fine resolution beam steering within each coarse angle step provided by the phased array. A proof-of-concept antenna operating at 11.5 GHz was designed, fabricated and measured. The antenna incorporated 3-bit phase shifters and achieved a steering resolution of 1° over a steering range of ±40°. In order to achieve the same steering resolution, using a conventional array, it would be necessary to use 6-bit phase shifters. When compared to a conventional array the realised gain of the novel antenna was 4 dB higher. The antenna shows an improvement in scan loss when steering off boresight. The key advantage of the proposed Hybrid Parasitic Array Antenna is its low profile and high steering speed when compared with the alternative steering techniques.

In array processing, the fourth-order difference co-array of sparse arrays with $N$ sensors admits to resolve $\mathcal {O}(N^4)$ source directions with proper assumptions. This $\mathcal {O}(N^4)$ property is relevant to the size of the central uniform linear array (ULA) segment of the fourth-order difference co-array. However, among the existing sparse arrays, the fundamental limits for the sizes of the fourth-order difference co-array remain a topic for further study. This paper characterizes the lower and upper bounds of the size of the fourth-order difference co-array. It is proved that the ULA and the exponential array achieve the lower and upper bounds, respectively. We also propose the fourth-order redundancy to quantify the efficiency of the ULA segment in the fourth-order difference co-array. The fourth-order redundancy owns a provable lower bound depending only on $N$ , providing further insights into the size of the central ULA segment of the fourth-order difference co-array. These bounds are validated through numerical examples.

A design of sub-Nyquist uniform linear array receiver with different sampling rates is proposed, investigated, and reported in this paper. The proposed architecture increases functionality of conventional linear array receiver with modest modifications. Simulation results show that the proposed receiver is capable of determining angle of arrival (AOA) and signal frequencies of multiple continuous-wave/chirp signals over several Nyquist zones.

This paper comprehensively deals with the parametric effects of the joint clearance and friction coefficient on the dynamics of planar deployable structures consisting of scissor-like elements (SLEs). The dynamic model for scissor deployable structure is based on a comprehensive consideration of the symmetry and array characteristics of this mechanism and on a Lagrange method, which represents the motion equations. A modified nonlinear contact-force model is employed to evaluate the intrajoint contact force, and the incorporation of the friction effect between the inter-connecting bodies is included in this study. The total impact forces produced in the real mechanical joint are embedded into the dynamics and the differential equations of motion are solved numerically based on a set of initial conditions. The clearance size, angle velocity, and friction coefficient are analyzed and discussed separately. Using Poincaré map, the regular and irregular responses of the deployable mulitibody systems are observed. Next, a control scheme is evaluated to maintain a more stable behavior and continuous contact between the clearance joints. The controlled results are compared with those without control, concluding that some undesired effects caused by the clearance joints can be prevented or reduced, resulting in continuous contact at the clearance joint.

Popularly used to collect data for the direction-of-arrival estimation of an incident source. Since the dipole elements of the uniform linear array are electromagnetically and mutually coupled, the presence of mutual coupling may degrade the performance of any direction finding algorithms. In order to mitigate mutual coupling, several references introduced modifications of the well-known ESPRIT algorithm. These modifications involve discarding the data collected by linear array at the two ends. However, the assumption of several literature that the mutual coupling matrix to be both Toeplitz and banded are invalid. This is pointed out by the “method of moments” based computer simulation tool used in this paper. The Toeplitz-and-banded coupling-matrix assumption leads to the mutual coupling being mis-modeled. Furthermore, previous studies failed to consider how varying the dipoles’ electrical length affect the performance of the direction-of-arrival estimation under mutual coupling.

A modified differential evolution (MDE) algorithm based on a novel mutation strategy and adaptive adjustment strategy of parameter crossover rate (CR) is proposed to improve the population diversity and to avoid frapping in local optima. Also the simplified quadratic interpolation is employed to accelerate the convergence rate. Benchmark functions have been provided to verify the MDE algorithm. Compared with other improved evolutionary algorithms, experiment results reveal that the MDE has a promising performance in the convergence rate and the exploration ability. Finally, the proposed algorithm is proved to realize accelerating the optimization of time-modulated arrays (TMA).

In this paper, we consider the problem of robust adaptive beamforming (RAB) for a linear array in the presence of gain-phase errors. By setting a few calibrated auxiliary elements on one side of a linear array, we propose a novel gain error and phase error estimation algorithm to calibrate gain-phase errors. According to the proposed estimation algorithm, the unknown gain error and phase error are jointly estimated by calculating the eigenvector corresponding to the minimum eigenvalue of the available transitional matrices. Furthermore, we calibrate the received data and compensate for the nonwhite noise caused by the calibration process. Then, the interference-plus-noise covariance matrix (INCM) is reconstructed based on the calibrated steering vector. By incorporating the reconstructed INCM with the minimum variance distortionless response principle, a novel robust adaptive beamformer for a linear array with gain-phase errors is designed. The proposed beamformer can obviously improve RAB performance in a linear array with gain-phase errors. The robustness and superiority of the designed beamformer are demonstrated in simulations.

Beamforming algorithms are designed for generating main beams in the direction of interest and place nulls in the direction of interferences. Adaptive beamforming can be achieved by various optimization criteria. The criteria for an efficient design of algorithm is the speed of convergence, deeper null placement, better signal to noise ratio, and robustness. Motivated by the reduction in the computational complexity a new adaptive beamforming algorithm based on variable step size is proposed in this paper called sign variable step size LMS algorithm. The proposed algorithm is applied to the uniform linear array antenna. Simulation results show that it gives a better null placement in the direction of interference and the signal to noise ratio is improved upon the existing algorithms with less computational complexity.

This study explores the application of algorithms with linear array ultrasonic testing for the characterization of hidden regions of impact damage in composites. An idealized ray tracing model was ...

In this paper, we exploit the idea of virtual ESPRIT (VESPA) to develop a multi-baseline VESPA (MB-VESPA) approach for direction finding. Specially, we define several cumulant matrices to provide ambiguous direction estimates under different baselines. Fine and unambiguous estimation is then obtained by a simple refinement step. Two refine approaches, termed as successive baseline approach and coprime baseline approach, are subsequently introduced. MB-VESPA shares all the advantages of the VESPA. It is simple, closed-form, search-free, and is applicable to irregularly linear array. In addition, it is free of the impact on the sensor gain uncertainties.

A novel low-cost, millimetre-wave antenna has been presented in this communication. The proposed antenna is a proximity-coupled linear array with coupled feedlines to achieve wideband characteristics. Good agreement between simulated and measured results is achieved and proves that the proposed antenna structure is capable of attaining over twice the bandwidth with the coupled lines than that attained with a single microstrip feedline while achieving lower sidelobe levels. The antenna has a gain of about 15.0 dBi with an half-power beam width of 12° ± 2° over a frequency range of 27.25–29.25 GHz. It also exhibits an impedance bandwidth of 19.6% from 24.48 to 29.8 GHz.

In this study, a novel method is proposed to obtain the minimum elements and a specific sidelobe in time-modulated sparse linear arrays. A genetic algorithm is used to optimise each generation of arrays to reach the required level and range of the sidelobe. Furthermore, the number, arrangement, and switching sequences of the array that satisfy the requirements are obtained. This method provides a scheme to reduce the number of elements using the optimised sparse structure and switching time. However, besides the control of the fundamental component, this method can also be applied to multi-beam forming with the fundamental component and ±first harmonic. Finally, the effectiveness of the proposed method is verified by the simulation and numerical results.

The focusing principle and acoustic field characteristics of curved array probe are studied. Delay laws are first computed in the same way as linear array probe, and its effects on the axial acoustic pressure distributions are quantitatively examined. It is shown that the maximum points of axial acoustic pressure occur at positions deviating from the predefined focal depths. To further analyze the focusing principle of curved array probe, simulations of acoustic field are conducted under different settings of focal depth and active aperture size. It reveals that the circular array profile and the inconsistent electronic delay laws make the pulsed ultrasonic waves unable to constructively interfere at target positions. Subsidiary beams arise and further interfere with the axial acoustic pressure distributions of the main beam. To control the transmitted acoustic field, and thus customize the inspection strategy, an optimized delay law calculation scheme is proposed. The good behavior is well validated both by theoretical calculation and experimental examination.

In this work, we tackle the difficulty of direction-of-arrival estimation (DOA) for a uniform linear array (ULA). Furthermore, a spectrum estimation method using a new two-dimensional (2D) ULA is d...

To solve the beamforming performance degradation problem of the towed linear array caused by the shape distortion, we propose a robust beamforming way for distorted towed linear array. The proposed method basically uses the segmented processing, which can be divided into 3 steps. Firstly, towed linear array is divided into sub-arrays. Then, the weights of sub-arrays are obtained and outputs of beamforming of sub-arrays are obtained. In the end, according to the principle of the product theorem, the correlation calculations are performed on the output of the sub-array. Due to the adoption of sub-array correlation calculations, the proposed method can upgrade beamforming performance. Compared with the traditional distortion array processing method, the proposed method can improve the local signal-to-interference plus noise ratio (SINR) by about 2–3 dB. Simulation and sea trial data verify the effectiveness of the proposed method.

We explore the RIPless theory for the analysis of single snapshot DOA estimation with uniform linear array using the compressed sensing technique. Starting with a sparse signal recovery model constructed for single snapshot DOA estimation, we prove the isotropy property and incoherence property are fulfilled for the estimation problem. A vital proposition is obtained using the RIPless theory, which establishes the fundamental relationship of the probability of recovery with the number of targets and sensors.

The traditional 3-D localization methods based on angle of arrival (AOA) using 2-D arrays has been well studied over the past few decades. However, in some situations, the sensors are only allowed to equip linear arrays for the space limitation. In those cases, the traditional methods could not locate the unknown source precisely in the 3-D space. This letter proposes a novel 3-D localization technique using 1-D AOAs of the source. This technique gives the measurement model between the 3-D location of the source where the 1-D AOAs measured by the linear array at each sensor. The localization problem is formulated as a constrained weighted least-squares optimization problem. The semidefinite programming method is applied to solve this problem after relaxing the nonconvex constraints by semidefinite relaxing technology. To improve the performance further, a Gaussian–Newton iteration is implemented for the maximum likelihood estimator. The Cramer–Rao lower bound (CRLB) is analyzed for evaluating the performance. Simulation results show that the performance of the proposed method reaches the CRLB.