Cross Array Research Articles

Parameter Estimation for Two-Dimensional Incoherently Distributed Source with Double Cross Arrays.

A direction of arrival (DOA) estimator for two-dimensional (2D) incoherently distributed (ID) sources is presented under proposed double cross arrays, satisfying both the small interval of parallel linear arrays and the aperture equalization in the elevation and azimuth dimensions. First, by virtue of a first-order Taylor expansion for array manifold vectors of parallel linear arrays, the received signal of arrays can be reconstructed by the products of generalized manifold matrices and extended signal vectors. Then, the rotating invariant relations concerning the nominal elevation and azimuth are derived. According to the rotating invariant relationships, the rotating operators are obtained through the subspace of the covariance matrix of the received vectors. Last, the angle matching approach and angular spreads are explored based on the Capon principle. The proposed method for estimating the DOA of 2D ID sources does not require a spectral search and prior knowledge of the angular power density function. The proposed DOA estimation has a significant advantage in terms of computational cost. Investigating the influence of experimental conditions and angular spreads on estimation, numerical simulations are carried out to validate the effectiveness of the proposed method. The experimental results show that the algorithm proposed in this paper has advantages in terms of estimation accuracy, with a similar number of sensors and the same experimental conditions when compared with existing methods, and that it shows a robustness in cases of model mismatch.

Optimal rotation of UAV for enhanced 2D direction of arrival estimation

Optimal rotation of an unmanned aerial vehicle (UAV) mounted with a cross array for enhanced two-dimensional (2D) direction estimation is discussed, and a novel method based on Cramer–Rao bound (CRB) minimisation is proposed. CRB serves as the lower bound for direction-of-arrival (DOA) estimation, which directly determines the localisation performance of jamming sources. Based on the fact that CRB differs while UAV's rotation angle changes, a theoretical closed-form solution for an optimal rotation in the 2D direction estimation is derived, and then the authors can acquire capability enhancement of DOA estimation after the optimal rotation. Rigorous analysis and multiple simulations demonstrate the feasibility and effectiveness of the proposed scheme.

Single Far-Field or Near-Field Source Localization With Sparse or Uniform Cross Array

Existing works for 3-D source localization are based on uniform cross arrays. In this correspondence, we propose a single far-field (FF) or near-field (NF) source localization method based on uniform cross arrays and then generalize it to the symmetric sparse cross arrays where each linear array is a symmetric sparse one. We utilize the cross-covariance matrix to exploit the full array aperture and employ the atomic norm minimization technique to retrieve the angle information without discretization. The range is estimated by MUSIC-like method. Our method is superior to traditional methods and exhibits enormous advantages in low signal-to-noise ratio (SNR) and small number of snapshots regions. Numerical simulations are carried out to verify the effectiveness of our method.

Calculation of Potential Green’s Functions for a Planar Metasurface Excited by an Electric Dipole Using Homogenization Method

One of the rapid and efficient methods to calculate the interaction between electromagnetic fields and periodic surfaces with periodicity much less than the wavelength in the surrounding medium is the homogenization method. In this paper, the Hertzian potential Green’s functions corresponding to electric dipoles which excite a homogenized metasurface are presented. The metasurface includes a periodic array of planar scatterers and is replaced by a thin sheet with equivalent electric and magnetic surface polarization density dyads. The magnetic vector potentials are calculated using the generalized sheet transition conditions on the plane of the metasurface. Also the scalar electric potential corresponding to the structure is calculated with the aid of the Lorentz gauge. These potentials together are necessary to use in the mixed potential integral equation formulation of the method of moment in an electromagnetic problem. Two metasurfaces are investigated to calculate the electric fields; a perfect electric conductor square patch array whose surface polarization densities are calculated analytically, and a Jerusalem cross array whose surface polarization dyads are retrieved from reflection and transmission coefficients.

3-D Mixed Far-Field and Near-Field Sources Localization With Cross Array

This correspondence proposes a localization method for mixed far-field (FF) and near-field (NF) sources based on cross arrays where two-dimensional (2-D) direction-of-arrival (DOA) and range estimation are considered. For 2-D DOA estimation, we first construct a range-free cumulant-based vector and employ the covariance matching criterion and Vandermonde decomposition theorem to retrieve DOA information. We then build a sparse model with respect to range parameter and solve an l 1 -norm minimization problem to obtain range estimates. Our method enjoys the following advantages: 1) our method can locate mixed FF and NF sources; 2) the azimuth, elevation and range can be automatically paired; 3) array aperture loss can be avoided. Simulation results show the effectiveness of our method.

A Lightweight Planar Ultrawideband UHF Monopole Mills Cross Array for Ice Sounding

An electrically large ultrawideband ultrahigh frequency (UHF) monopole antenna array has been designed to sound up to 3 km of ice and meet the logistical requirements of transportation to arctic regions. The monopole array is comprised of 16 planar subarray modules, which in combination form a 16 m by 17 m Mills cross array configuration to maximize sensitivity and spatial selectivity in both cross-track and along-track directions. Each planar subarray module is 1 m by 2 m in size with a 6.35 cm thick rigid insulation foam panel separating the individual monopole elements from metal foil ground plane on the top such that the maximum radiation is directed to nadir. Each subarray panel consists of 4 by 8 circular monopole antenna elements with a spacing of 0.25 m. Each monopole element is printed on a 130 mm by 80 mm 62 mil FR4 board. The total weight of each subarray panel is 9 kg, making for very lightweight and low-profile antenna construction. The antenna array together with the radar system was deployed to the East Greenland Ice-coring Project site in August 2018 for demonstrating surface-based ice sounding at the UHF band.

Triple-Band Perfect Light Absorber Based on Hybrid Metasurface for Sensing Application

A simple design of triple-band perfect light absorber (PLA) based on hybrid metasurface in visible region has been presented in this work, which turns out to be applicable for refractive index (RI) sensing. Distinct from previous designs, the proposed hybrid metasurface for visible PLA is only consisted of periodic silicon cross nanostructure arrays and gold substrate. The periodic silicon cross arrays deposited on the gold substrate contribute to excite the guided modes under the normal incident light illumination. According to the simulation results, it can be found that three perfect absorption peaks of 98.1%, 98.7%, and 99.6% which are located at 402.5 THz, 429.5 THz, and 471.5 THz, respectively, have been clearly observed in PLA. This triple-band perfect absorption effect could be attributed to the intrinsic loss of silicon material originated from the guided mode excitations caused by the standing waves of different orders. It has been confirmed that the perfect absorption properties of the PLA can be easily regulated by changing the geometric parameters of the unit-cell nanostructure. Furthermore, the designed PLA served as a RI sensor can achieve sensitivity of about 25.3, 41.3, and 31.9 THz /refractive index unit (RIU). It can be believed that the proposed design of PLA for RI sensing would provide great potential applications in sensing, detecting, the enhanced visible spectroscopy, etc.

An ADS-Based Sparse Optimization Method for Sonar Imaging Sensor Arrays

The Mills Cross sonar sensor array, achieved by the virtual element technology, is one way to build a low-complexity and low-cost imaging system while not decreasing the imaging quality. This type of sensor array is widely investigated and applied in sensor imaging. However, the Mills Cross array still holds some redundancy in sensor spatial sampling, and it means that this sensor array may be further thinned. For this reason, the Almost Different Sets (ADS) method is proposed to further thin the Mills Cross array. First, the original Mills Cross array is divided into several transversal linear arrays and one longitudinal linear array. Secondly, the Peak Side Lobe Level (PSLL) of each virtual linear array is estimated in advance. After the ADS parameters are matched according to the thinned ratio of the expectant array, all linear arrays are thinned in order. In the end, the element locations in the thinned linear array are used to determine which elements are kept or discarded from the original Mills array. Simulations demonstrate that the ADS method can be used to thin the Mills array and to further decrease the complexity of the imaging system while retaining beam performance.

Simulation and fabrication of a single-band tunable absorber in 20–50 THz range based on cross array metamaterials

In this paper, a tunable metamaterial is designed and measured in the 20–50 THz band. An absorption peak (80%) is obtained at resonance frequency point 40THz based on the LSP mode resonance on the surface of metal array and the dielectric loss mode in two dielectric layers. In experiments, the amplitude is increased and the resonance frequency is reduced through decreasing the lattice constant P or increasing the side length W1. In the third and fourth sets of experiments, this absorption peak can be controlled through increasing or reducing the temperature. This is due to the insulator-metal or metal-insulator phase transitions are achieved. Moreover, under the room temperature 300 K and normal pressure, the absorption amplitudes are enhanced and the resonance frequency is shifted with different liquid layers. This sample shows the feasibility of application to temperature or liquid sensing.

A fusion algorithm of passive sound source localization based on the two-plane four-element cross array

In this work, a fusion algorithm is proposed for improving the accuracy and stability of passive sound source localization. Different from the traditional algorithm that contains a single-plane cross array, here, the fusion algorithm is used to overcome the position blur in the process of localization. First, the two-plane four-element cross array model is established. Based on this model, the method is defined to judge the position where the sound source is located. According to the localization principle, we derive the calculation formula of the sound source position, based on a single four-element planar array. Then, the elevation angle sine value is introduced into the coordinate formula as the weighted coefficient by analyzing the indirect measurement error, and the fusion algorithm is employed to conduct the sound source localization, based on the two-plane four-element cross array. Finally, the relationships are obtained, between the time delay estimation error, the elevation angle, the horizontal angle, and the localization performance. Besides, the validity of this algorithm is validated by measuring the ranging and direction-finding accuracy. The results show that the distance error rate is within 2%, and the angle error rate is within 3%, which means a good localization effect. The proposed algorithm is expected to be widely used in thunderstorm cloud detection for its quick measurement and high precision.

Quantum Chemical Exploration of Intermolecular Reactions of Acetylene.

Quantum chemical explorations of potential energy surfaces showed that acetylene produces various products starting from molecular arrays in short distances of 1.3-2.5 Å. Arrays of (C2 H2 )2 gave cyclobutadiene, tetrahedrane, and acetylene dimers. Arrays of (C2 H2 )3 gave benzene, prismane, benzvalene, Dewar benzene, and acetylene trimers. Arrays of (C2 H2 )4 gave cubane, cyclooctatetranene, and acetylene tetramers. Different forms of initial arrays yielded different sets of products; a parallel array of two monomers gave cyclobutadiene, whereas a cross array gave tetrahedrane. Initial molecular arrays with unusually close contacts were estimated to require local forces of 1-9 × 10-8 N. © 2019 Wiley Periodicals, Inc.

Effect of graphene intercalation on nonlinearity of Ag/quartz/Pt selector: first-principle calculations

In this work, Ag/graphene(GR)/quartz/Pt and Ag/quartz/Pt selectors were investigated using first-principle calculations. Comparison of the electrostatic potential distribution, plane-averaged electron density difference, and density of states (DOS) of the Ag(111)/quartz(001) and Ag(111)/GR/quartz(001) interfaces shows that the insertion of GR increases the interfacial Schottky barrier height (SBH), decreases the interfacial charge transfer, and improves the conductivity and reliability of quartz. Ag/GR/quartz/Pt and Ag/quartz/Pt selectors are then designed using the above interfaces. Results show that the OFF-state current of the Ag/GR/quartz/Pt selector is reduced by about one order of magnitude, Idrive is improved (especially the positive drive current), and its nonlinearity (NL) is significantly increased. Thus, the Ag/GR/quartz/Pt selectors can better suppress leakage current in one-Selector one-RRAM (1S1R) cross array than the Ag/quartz/Pt selectors. This work may be instructive and valuable for the design and optimization of Ag/quartz/Pt selectors.

Optimized Design for Sparse Cross Arrays in Both Near-Field and Far-Field

Two-dimensional arrays are required to generate 3-D acoustic images in both near-field and far-field regions. However, almost all of the sparse methods, which decrease the number of elements, only synthesize the 2-D sparse arrays in far-field conditions. In this paper, a novel method is proposed for optimizing sparse array in both near-field and far-field conditions that improving the sparseness of the optimized array. First, a new energy function is proposed and successfully synthesizes sparse arrays in both near-field and far-field conditions. The simplified form of the new energy function is then presented for cutting down computational load during optimization process. Second, the nongrid sparse array technology, which connotes irregular element positioning, is introduced into the simulated annealing algorithm to extensively reduce the number of active elements. Finally, the optimized method is demonstrated through designing a cross array with 100 + 100 elements. The results show notable improvements on the array characteristics in random working distances over those reported in the literature.

Development of Evaluation Model in Three-dimensional Hole Shape made by Rotary Ultrasonic Machining and Elucidation of the Machining Mechanism Based on Designed Experiment

This paper describes the evaluation of the inner shape of three-dimensional small glass holes and elucidation of the machining mechanism using statistical analysis based on designed experiment. The glass hole made by rotary ultrasonic machining had a 1mm diameter, and 4 characteristics to evaluate which were expansion of hole size, inner surface roughness, distortion, and direction of distortion. We assumed an elliptical cross-sectional hole shape and distortion, stipulating that an elliptical shape was a more accurate index than a true circle shape to evaluate hole shape and research machining mechanism. Furthermore the replica method used was both accurate and cost efficient enough to evaluate those characteristics. First we did a “Cross Array” experiment to construct models of each characteristic. In this designed experiment, tool factor and mode factor were set in outer array to identify any high order interaction with the machining factors set in inner array. Next we analyzed the correlation of those characteristics and executed analysis of variance. Finally we evaluated hole shape, discussed the machining mechanism and recognized the importance of main effect of the tool and its interactions with feed speed and feed mode. In conclusion, our approach to evaluating three-dimensional hole shape are useful.

Acoustic Localization for a Moving Source Based on Cross Array Azimuth

Acoustic localization for a moving source plays a key role in engineering applications, such as wildlife conservation and health protection. Acoustic detection methods provide an alternative to traditional radar and infrared detection methods. Here, an acoustic locating method of array signal processing based on intersecting azimuth lines of two arrays is introduced. The locating algorithm and the precision simulation of a single array shows that such a single array has good azimuth precision and bad range estimation. Once another array of the same type is added, the moving acoustic source can be located precisely by intersecting azimuth lines. A low-speed vehicle is used as the simulated moving source for the locating experiments. The length selection of short correlation and moving path compensation are studied in the experiments. All results show that the proposed novel method locates the moving sound source with high precision (<5%), while requiring fewer instruments than current methods.

Design and fabrication of plasmonic cavities for magneto-optical sensing

The design and fabrication of a novel plasmonic cavity, intended to allow far-field recovery of signals arising from near field magneto-optical interactions, is presented. Finite element modeling is used to describe the interaction between a gold film, containing cross-shaped cavities, with a nearby magnetic under-layer. The modeling revealed strong electric field confinement near the center of the cross structure for certain optical wavelengths, which may be tuned by varying the length of the cross through a range that is compatible with available fabrication techniques. Furthermore, the magneto optical Kerr effect (MOKE) response of the composite structure can be enhanced with respect to that of the bare magnetic film. To confirm these findings, cavities were milled within gold films deposited upon a soluble film, allowing relocation to a ferromagnetic film using a float transfer technique. Cross cavity arrays were fabricated and characterized by optical transmission spectroscopy prior to floating, revealing resonances at optical wavelengths in good agreement with the finite element modeling. Following transfer to the magnetic film, circular test apertures within the gold film yielded clear magneto-optical signals even for diameters within the sub-wavelength regime. However, no magneto-optical signal was observed for the cross cavity arrays, since the FIB milling process was found to produce nanotube structures within the soluble under-layer that adhered to the gold. Further optimization of the fabrication process should allow recovery of magneto-optical signal from cross cavity structures.

A Dual-Band Tunable Metamaterial Near-Unity Absorber Composed of Periodic Cross and Disk Graphene Arrays

A three-dimensional dual-band perfect absorber in the THz range (3–10 THz) is theoretically investigated. The absorber is composed of periodically placed cross- and disk-shaped graphene arrays on the top of a gold layer separated by a thick SiO $_{2}$ dielectric spacer. The simulated results show two absorption peaks with near-unity absorbance ( $99.923\%$ and $99.601\%$ ) at wavelengths 43.747 $\mu$ m and 69.94 $\mu$ m, respectively. Also, the absorber is insensitive to the polarization of the incident light and has a good tolerance to the incident angle whether it is TE or TM waves. Moreover, the peak wavelengths of the absorber can be flexibly modulated by varying the Fermi level $\mu _{C}$ of graphene while no need to refabricate the structure. This paper provides a new perspective for the design of graphene-based tunable multiband perfect THz absorbers, but not limited to THz absorbers, and may also be used in other THz graphene-based photonic devices.

Robust optimization of the billet for isothermal local loading transitional region of a Ti-alloy rib-web component based on dual-response surface method

Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming (ILLF) of large-scale Ti-alloy rib-web components. However, the final quality of the transitional region may be deteriorated by uncontrollable factors, such as the manufacturing tolerance of the preforming billet, fluctuation of the stroke length, and friction factor. Thus, a dual-response surface method (RSM)-based robust optimization of the billet was proposed to address the uncontrollable factors in transitional region of the ILLF. Given that the die underfilling and folding defect are two key factors that influence the forming quality of the transitional region, minimizing the mean and standard deviation of the die underfilling rate and avoiding folding defect were defined as the objective function and constraint condition in robust optimization. Then, the cross array design was constructed, a dual-RSM model was established for the mean and standard deviation of the die underfilling rate by considering the size parameters of the billet and uncontrollable factors. Subsequently, an optimum solution was derived to achieve the robust optimization of the billet. A case study on robust optimization was conducted. Good results were attained for improving the die filling and avoiding folding defect, suggesting that the robust optimization of the billet in the transitional region of the ILLF was efficient and reliable.

Low frequency and broadband metamaterial absorber with cross arrays and a flaked iron powder magnetic composite

In this paper, we present a design, simulation and experimental measurement of a cross array metamaterial absorber (MMA) based on the flaked Carbonyl iron powder (CIP) filled rubber plate in the microwave regime. The metamaterial absorber is a layered structure consisting of multilayer periodic cross electric resonators, magnetic rubber plate and the ground metal plate. The MMA exhibits dual band absorbing property and the absorption can be tuned from 1∼8GHz in the same thickness depending on the dimension and position of the cross arrays. The obviously broadened absorbing band of the designed structure is a result of the synergistic effects of the electrical resonance of the cross arrays and intrinsic absorption of the magnetic layer. The polarization and oblique incident angle in TE and TM model are also investigated in detail to explore the absorbing mechanisms. The resonance current of the cross array can excite the enhanced local magnetic field and dielectric field which can promote the absorption. The measurement results are basically consistent with the simulations but the absorbing peaks move a little bit to higher frequency for the reason that the surface oxidation of the flaked CIP in the preparation process.

Tunable polarization-independent coherent perfect absorber based on a metal-graphene nanostructure

A tunable polarization-independent coherent perfect absorber (CPA) is proposed based on the metal-graphene hollowed-out cross array nanostructure at the mid-infrared region. By adjusting the phase difference between the incident beams, the coherent absorption at 9969nm is all-optically modulated from 99.97% to nearly 0 with the modulation depth over 80dB. The absorption resonance of the CPA is tuned by the gate-controlled Fermi energy with the coherent absorption remaining nearly 100%. The CPA is also found to be angular insensitive to incident beams within the range of −12° to 12°. The central-symmetry nanostructure leads to the polarization independence and the introduced graphene layer results in the electrical tunability of the CPA at the absorption resonance, which have prospects in applications such as for tunable mid-infrared detectors, transducers, modulators, and optical switches.