Array Design Techniques Research Articles

A self-decoupled 32-channel receive array for human-brain MRI at 10.5 T.

Receive array layout, noise mitigation, and B0 field strength are crucial contributors to SNR and parallel-imaging performance. Here, we investigate SNR and parallel-imaging gains at 10.5 T compared with 7 T using 32-channel receive arrays at both fields. A self-decoupled 32-channel receive array for human brain imaging at 10.5 T (10.5T-32Rx), consisting of 31 loops and one cloverleaf element, was co-designed and built in tandem with a 16-channel dual-row loop transmitter. Novel receive array design and self-decoupling techniques were implemented. Parallel imaging performance, in terms of SNR and noise amplification (g-factor), of the 10.5T-32Rx was compared with the performance of an industry-standard 32-channel receiver at 7 T (7T-32Rx) through experimental phantom measurements. Compared with the 7T-32Rx, the 10.5T-32Rx provided 1.46 times the central SNR and 2.08 times the peripheral SNR. Minimum inverse g-factor value of the 10.5T-32Rx (min[1/g] = 0.56) was 51% higher than that of the 7T-32Rx (min[1/g] = 0.37) with R = 4 × 4 2D acceleration, resulting in significantly enhanced parallel-imaging performance at 10.5 T compared with 7 T. The g-factor values of 10.5 T-32 Rx were on par with those of a 64-channel receiver at 7 T (eg, 1.8 vs 1.9, respectively, with R = 4 × 4 axial acceleration). Experimental measurements demonstrated effective self-decoupling of the receive array as well as substantial gains in SNR and parallel-imaging performance at 10.5 T compared with 7 T.

Mutual Coupling Effect in Unequally - Spaced Linear Antenna Array Performance

Unequally-spaced arrays can offer some advantages over equally-spaced arrays as follows: reducing the side-lobed level for the broadband array with an identical excitation coefficient. However, array design techniques do not take into account the mutual coupling effect among elements. In this article, the effect of mutual coupling on the array radiation pattern is investigated and discussed through studying the input impedance of the elements. Next, a technique for reducingmutual coupling based on radiation patterns of elements is presented. In this technique, the log-periodic dipole antenna with a frequency ranging from 900 MHz to 2500 MHz is selected as an array element. The results based on the FEKO magnetic field calculation program have shown that at 900 MHz, the proposed antenna array reaches a side-lobed level of -17.4 dB. At frequencies of 1500 MHz, 2000 MHz, 2500 MHz, the grating lobe levels of this antenna array are lower than 6.7 dB, 9.5 dBand 8.3 dB compared to those of the equally - spaced antenna array.

The effect of fundamental curves on geometric orifice and coaptation areas of polymeric heart valves

Valvular diseases, such as aortic stenosis, are considered a common condition in the US. In severe cases, either mechanical or prosthetic heart valves are employed to replace the diseased native valve. The prosthetic heart valve has been a focal point for researchers to gain a better understanding of the mechanics, which will lead to improved longevity. In this study, our objective was to evaluate the effect of fundamental curves on the geometric orifice area and the coaptation area by implementing a two-level Taguchi Orthogonal Array (OA) design (Analysis of Variance (ANOVA) technique) and the interaction plots to investigate the individual contributions. The leaflet geometry was represented with the attachment curve, the free edge, and the belly curve. A total of three varying control coordinates were used to form different leaflet surfaces. With two different biocompatible polymers, 16 finite element models were prepared. Each model was subjected to time-varying transvalvular pressure. The results showed that the control coordinate for the belly curve has the highest impact on the coaptation area of the valve models with higher average 100% modulus. The geometric orifice area was affected by both control points of the attachment curve and the belly curve. A similar effect was also observed for the valve models with lower average 100% modulus.

Influence of Shot Peening on Surface Characteristics of Case Hardened SAE9310 Gear Material

The shot peening is the cold working process by which the compressive residual stresses are induced in the component, and that increases surface hardness, which can be helpful to avoid the fatigue failure of the component. Shot peening process is using to improve the fatigue life of the automobile and aerospace components. Effectiveness of the shot peening in surface characteristics can be measured by the Almen Intensity, Surface hardness and Surface roughness. The impact of shot peening on case-hardened differential bevel gear is defined in this study. In the shot peening process, the surface of the gear rammed by the small hardened cut wire shots with high velocity and overlapping indentations are created on the gear surface. Hence, thecharacteristics of surface of the gear can be greatly improved by shot peening. For bevel gears, bending fatigue crack is the major failure mode. This study is discussed to enhance the mechanical and surface properties of SAE9310 bevel gear by using the shot peening process. The optimization of shot peening process is done by including multi-performance characteristics i.e. Intensity, Surface hardness and surface roughness of the bevel gear. The analysis includes air pressure, nozzle distance, shot flow rate, exposure time as process parameters. The main objective of this study to decide the optimized shot peening process parameters for required performance characteristics and most influencing factors on surface layer characteristics. The experiments have been conducted using Taguchi’s L9 orthogonal array design techniques.

Moxon Antenna Array Design and Pattern Synthesis Technique

A four-element moxon antenna array is proposed in this paper. Its directive properties are shown with simulations and compared with the classical dipole array. In order to synthesize the pattern of moxon array, a hybrid method that consists of differential evolution (DE) and numerical electromagnetics code version 2 (NEC2) is also introduced. Basically, the cost function used by DE is designed with the help of NEC2 simulations to achieve more realistic optimum antenna array designs. Patterns having one and double sidelobe suppression at predetermined angles are successfully synthesized by using this method whereas the gain value is maintained properly. Robustness of the proposed method is also examined. For this aim, multiple executions of the method implementation are performed under same conditions. The results show that the method introduced in this paper is very stable in terms of the radiation pattern and convergence curves.

Optimization of WEDM process during machining of Al-Al2O3 composite using Taguchi based Grey Relational Analysis

Aluminium ceramic (Al-Al2O3) is used comprehensively all over the world. In this paper, input parameters on Al-Al2O3 workpiece are applied to investigate the MRR and surface roughness by the process of wire electrical machining (WEDM).Four varying input parameters (Ton, Toff, Wf and Cs%) were tabulated for nine samples using L9 orthogonal array design technique whereas keeping wire tension as constant. Tool wear is calculated as the change in initial thickness and final thickness after cutting operation using screw gauge. The surface roughness is found using surface roughness tester.Minitab is used to plot the graph between input parameters against various output parameters. To find the impact of process parameters, ANOVA (Analysis of Variance) is used .

Reducing Multi-sensor Monthly Mean Aerosol Optical Depth Uncertainty Part II: Optimal Locations for Potential Ground Observation Deployments.

Surface remote sensing of aerosol properties provides "ground truth" for satellite and model validation, and is an important component of aerosol observation system. Due to the different characteristics of background aerosol variability, information obtained at different locations usually have different spatial representativeness, implying that the location should be carefully chosen so that its measurement could be extended to a greater area. In this study, we present an objective observation array design technique that automatically determines the optimal locations with the highest spatial representativeness based on the Ensemble Kalman Filter (EnKF) theory. The ensemble is constructed using aerosol optical depth (AOD) products from five satellite sensors. The optimal locations are solved sequentially by minimizing the total analysis error variance, which means that observations at these locations will reduce the background error variance to the largest extent. The location determined by the algorithm is further verified to have larger spatial representativeness than some other arbitrary location. In addition to the existing active AERONET sites, the 40 selected optimal locations are mostly concentrated on regions with both high AOD inhomogeneity and its spatial representativeness, namely the Sahel, South Africa, East Asia and North Pacific Islands. These places should be the focuses of establishing future AERONET sites in order to further reduce the uncertainty in the monthly mean AOD. Observations at these locations contribute to approximately 50% of the total background uncertainty reduction.

Concentric Circular Arrays for Stratospheric High-Altitude Platforms Wireless Sensor Networks

In this paper, a concentric circular array (CCA) is designed to provide feasible link between High-Altitude Platform (HAP)--which acts as a sink station--to sensor nodes placed on ground to form a Wireless Sensor Network. The proposed array design technique provides two types of coverage cells namely; wider coverage cell of 30 km radius and another smaller cell of 8 km radius. The link feasibility is examined for practical sensor models at two different frequencies (2.4 GHz and 868 MHz) and two corresponding bit rates (250 and 38.4 kbps) and shows the possibility of communications between the HAP and sensors at all scenarios. The CCA is optimized to improve the power gain inside the cell and reduce the out-of-cell sidelobe radiation using a modified Dolph-Chebyshev CCA. The comparison with conventional antenna models that give the same coverage radii shows that the link performance in terms of bit energy to noise power spectral density ratio can be improved by 11.37 dB for cells of 8 km radius and by 16.8 dB in the case of 30 km radius cells which make the link at 2.4 GHz to be feasible and realizable compared to using conventional antenna techniques.

An efficient systolic array grid-based structure of the robust Bayesian regularization technique for real-time enhanced imaging in uncertain remote sensing environment

In this paper, we address a hardware implementation of the efficient robust Bayesian regularization architecture for the real-time enhancement of large-scale remote sensing (RS) imaging. The efficient sense of the proposed architecture is related to the high-performance embedded implementation that is achieved with the aggregation of parallel computing and systolic array design techniques in a novel grid connected-based accelerator. Then, the developed high-speed accelerator is integrated with an embedded processor via the HW/SW co-design paradigm. The presented approach is used for solving RS image enhancement/reconstruction of the ill-conditioned inverse spatial spectrum pattern estimation problems via an interesting low-cost high-performance embedded computing solution. Finally, we show the achieved results and how we drastically reduced the computational load for real-world large-scale geospatial images.

Exploiting Rotational Symmetry for the Design of Ultra-Wideband Planar Phased Array Layouts

Two new phased array design techniques are introduced that utilize rotational symmetry to avoid grating lobes during scanning and over ultra-wide bandwidths. The first is an optimization method, which employs the covariance matrix adaptation evolutionary strategy to determine the best locations of elements inside a sector of a circle. The second technique uses standard periodic lattices inside the same circular sector. Although the segments themselves are internally periodic, the rotational symmetry of the full array eliminates the occurrence of grating lobes and is capable of generating antenna element layouts with useful ultra-wideband properties. These design techniques yield arrays with not only ultra-wideband characteristics, but properties that lend themselves to relatively straightforward modular construction, especially the semi-periodic variety.

Multi-Channel Microstrip Transceiver Arrays Using Harmonics for High Field MR Imaging in Humans

Radio-frequency (RF) transceiver array design using primary and higher order harmonics for in vivo parallel magnetic resonance imaging imaging (MRI) and spectroscopic imaging is proposed. The improved electromagnetic decoupling performance, unique magnetic field distributions and high-frequency operation capabilities of higher-order harmonics of resonators would benefit transceiver arrays for parallel MRI, especially for ultrahigh field parallel MRI. To demonstrate this technique, microstrip transceiver arrays using first and second harmonic resonators were developed for human head parallel imaging at 7T. Phantom and human head images were acquired and evaluated using the GRAPPA reconstruction algorithm. The higher-order harmonic transceiver array design technique was also assessed numerically using FDTD simulation. Compared with regular primary-resonance transceiver designs, the proposed higher-order harmonic technique provided an improved g-factor and increased decoupling among resonant elements without using dedicated decoupling circuits, which would potentially lead to a better parallel imaging performance and ultimately faster and higher quality imaging. The proposed technique is particularly suitable for densely spaced transceiver array design where the increased mutual inductance among the elements becomes problematic. In addition, it also provides a simple approach to readily upgrade the channels of a conventional primary resonator microstrip array to a larger number for faster imaging.

Two‐dimensional array design techniques of millimeter‐wave microstrip comb‐line antenna array

Two‐dimensional array design techniques are developed for microstrip comb‐line antenna array. Low sidelobe design is proposed in the plane parallel to the feeding line. Element radiation is controlled by both widths of the radiating element and the feeding line simultaneously. Beam‐tilting design is proposed in the perpendicular plane to the feeding line even though only two feeding lines are arranged. Microstrip slit structure is located around each radiating element in order to cancel reflections from element and slit and to achieve high design accuracy. By using these items, three antennas with different beams are developed for three‐beam switching system. Performance of these antennas is evaluated by experiments in the millimeter‐wave band.

LINEAR ANTENNA ARRAY DESIGN WITH USE OF GENETIC, MEMETIC AND TABU SEARCH OPTIMIZATION ALGORITHMS

Antenna array design techniques are focused on two main classes: uniformly spaced antenna arrays and the non-uniform spacing case. These include techniques based on mathematical programming, such as constrained programming and non-linear programming. More recently, meta-heuristics approaches have been successful at designing antenna arrays (5). In this work, this paper presents efficient methods of genetic algorithm (GA), memetic algorithm (MA) and tabu search algorithm (TSA) for the synthesis of linear antenna design. We present three examples of antenna array design to compare the efficiency of the algorithms through simple design to complex design. The GA, TSA and MA has been used to optimize the spacings between the elements of the linear array to produce a radiation pattern with minimum SLL and null placement control.

A Selective Survey of the Waveguide-Fed Slot Radiators

Waveguide-fed slot radiators are widely used in several strategic applications. The published literature in this area is vast, spanning a period of nearly 50 years. There is a need for consolidating the information and present it at a glance, to aid future research. The purpose of this article is to present a survey of the published literature in the area of waveguide-fed slot radiators. Specifically, the topics covered include longitudinal / transverse broadwall radiating slots, dielectric filled/ covered slots, compound/centred-inclined radiating slots, narrow wall slots, ridged waveguide slots, etc. This survey does not include the literature on the array design, as it would have resulted in limiting the information on the slot radiators. Besides, it is felt that the slot array analysis and design techniques would merit a survey of their own.

Gate Array Versus Standard Cell Realization of an Analog/Digital /spl mu/C Interface Circuit

An interface circuit containing analog and digital functions was realized in gate array and standard cell design techniques. Realization on gate arrays became possible by using circuit tricks which can also be applied to the standard cell version. Based on this example various aspects of the two design styles are compared. For such designs it is most important to have CAD tools which give sufficient support to the designer, and which do not restrict him into a fixed set of macro cells.

New Concepts in Traveling-Wave Amplifiers (Short Paper)

Two new networks with the potential for good port VSWR over very broad bandwidths are proposed for use in both low-power balanced amplifiers, and high-power combining systems. These new structures which are called Low-Sidelobe and Squintless Traveling-Wave Amplifiers (LSTWA and SQTWA, respectively) have been derived from conventional Traveling-Wave Amplifiers (TWA) by utilizing Phased Array Antenna concepts and design techniques. Using Monte-Carlo simulations the relative performance of the three structures is compared. Finite loss and mismatch effects are also considered.

Approximate models in multivariable process control. An inverse Nyquist array and robust tuning regulator interpretation

Using the widely accepted philosophy that simple control design procedures are of great value in producing acceptable controllers for plant with a degree of dynamic and/or structural simplicity, particularly in the situation where closed-loop performance requirements are modest, recent work on the use of approximate models and plant step data in multivariable design is applied to produce simple, robust design algorithms for process plant which, in the presence of suitable precompensation, has ‘small’ interaction effects and/or simple loop dynamics that can be approximated by delay-lag models. In one form, the results have a structure and generate a procedure identical to the inverse Nyquist array design technique, with Gershgorin circles replaced by ‘confidence circles’ deduced from simple graphical operations on plant step data. Other interpretations of the work lead to estimates of the maximum gain required to retain stability in Davison's robust feedback regulator. An optimisation procedure for choice of precompensator using step data is also outlined with strong connections with the method of pseudodiagonalisation.

Active and passive imaging of features on a rough seafloor

We are exploring array design and signal processing techniques for imaging features on the seafloor. In our numerical studies, rough features are modeled as diffracting wedges. Active imaging uses known sources. Passive imaging uses natural sources such as storms, earthquakes, etc. Natural sources are modeled as occurring at random times and random locations. We use delay and sum array processing to focus the array on diffraction sources. The results are displayed as two‐dimensional vertical and horizontal pictures of diffraction sources. We also compare two methods of processing, squaring the array output and split array cross correlation. The diffractograms show that a wedge can be identified for active and passive sources. [Work supported by Weeks Bequest, Wisconsin Alumni Research Foundation, National Science Foundation, and NORDA.]

Extension of the direct Nyquist array design technique to uncertain multivariable systems subject to external disturbances

Abstract The properties of a linear matrix feedback system with two degrees of freedom which allows Rosenbrock's direct Nyquist array design method to be extended to the case of uncertain multivariable systems are examined. Criteria for assessing the global and loop disturbance rejection properties of a multivariable control system are developed, and a design methodology for uncertain multivariable plants, subject to external disturbance inputs is given. The proposed design method is illustrated by means of an example.

Synthesis of Feedback Systems for Specified Time Domain Insensitivity to Interaction Induced Plant Ignorance

By regarding the fuzzy transfer functions arising in the Nyquist array design techniques, as interaction induced bounded ignorance transfer functions, the synthesis/design method of Horowitz and Sidi immediately becomes available and applicable, In this way, the ad-hoc aspects of the Nyquist Array based design methods are eliminated.