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1 – 10 of over 10000Yuanhao Wang, Michael Berens, Alexander Nietsch, Werner John and Wolfgang Mathis
– The purpose of this paper is to present an optimization process for the design of a 2×2 patch antenna phased array with application for an UHF RFID system.
Abstract
Purpose
The purpose of this paper is to present an optimization process for the design of a 2×2 patch antenna phased array with application for an UHF RFID system.
Design/methodology/approach
The optimization process is based on a method of moment (MoM)-solver, which was individually made to create such patch antenna phased arrays and simulate the radiated field pattern. In combination with this MoM-solver, a GUI, which gives the opportunity to change every physical antenna factor and create the antenna structure within a few minutes is presented. Furthermore the golden section search method is used to produce an even better solution in a more efficient way compared to the first attempt. After the simulation, different types of presentation of results can be chosen for a fast and easy optimization.
Findings
The design process is discussed while the authors try to optimize the distance between the elements and the difference of input phase for each patch element. The final goal is to create an antenna with maximum directivity and coverage of field pattern.
Practical implications
A physical implementation of an optimized patch antenna phased array and the results of measurement are presented in the end.
Originality/value
An optimization process for the design of a 2×2 patch antenna phased array with application for an UHF RFID system is presented. Furthermore the golden section search method is combined with the design process to increase the accuracy of the solution and decrease the time effort.
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Keywords
The Hurst exponent has been very important in telling the difference between fractal signals and explaining their significance. For estimators of the Hurst exponent, accuracy and…
Abstract
Purpose
The Hurst exponent has been very important in telling the difference between fractal signals and explaining their significance. For estimators of the Hurst exponent, accuracy and efficiency are two inevitable considerations. The main purpose of this study is to raise the execution efficiency of the existing estimators, especially the fast maximum likelihood estimator (MLE), which has optimal accuracy.
Design/methodology/approach
A two-stage procedure combining a quicker method and a more accurate one to estimate the Hurst exponent from a large to small range will be developed. For the best possible accuracy, the data-induction method is currently ideal for the first-stage estimator and the fast MLE is the best candidate for the second-stage estimator.
Findings
For signals modeled as discrete-time fractional Gaussian noise, the proposed two-stage estimator can save up to 41.18 per cent the computational time of the fast MLE while remaining almost as accurate as the fast MLE, and even for signals modeled as discrete-time fractional Brownian motion, it can also save about 35.29 per cent except for smaller data sizes.
Originality/value
The proposed two-stage estimation procedure is a novel idea. It can be expected that other fields of parameter estimation can apply the concept of the two-stage estimation procedure to raise computational performance while remaining almost as accurate as the more accurate of two estimators.
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Roberto Spallino, Giuseppe Giambanco and Santi Rizzo
This paper is devoted to the optimal design of laminated composite structures. The goal of the study is to assess the quality and the performance of an algorithm based on the…
Abstract
This paper is devoted to the optimal design of laminated composite structures. The goal of the study is to assess the quality and the performance of an algorithm based on the directional derivative method. Particular attention is paid to the one‐dimensional search, a critical step of the process, performed by cubic splines approximation. The optimization problem is formulated as weight minimization, under constraints on the mechanical behavior of the structure. The assumed design variables are the ply thicknesses, treated as continuous design variables, constrained by technological requirements. The structural analysis is performed making use of quadrilateral four‐node composite elements, based on the first order shear deformation theory. The algorithm is applied to the optimization of a rectangular laminated plate. The results obtained are compared with those obtained by other similar studies and show the effectiveness and accuracy of the proposed approach.
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Tao Bo, Yin Zhouping, Ding Han and Wu Yiping
The purpose of this paper is to present a novel reflow profile optimization method using mechanical reliability estimation of micro‐ball grid array (μBGA) solder joints, based on…
Abstract
Purpose
The purpose of this paper is to present a novel reflow profile optimization method using mechanical reliability estimation of micro‐ball grid array (μBGA) solder joints, based on the heating factor, Qη is introduced, where the coupling effect of reflow temperature and time on the mechanical reliability of μBGA joints is considered.
Design/methodology/approach
The method presented is actualized through vibration fatigue tests. First, a two‐parameter Weibull distribution is used to model the collected data of vibration fatigue lifetime for different Qη. After that, two explicit functions are deduced in a unified mathematic expression form, which give an intuitionistic description of the mean time to failure and reliability of solder joints against induced variable Qη, thus revealing definitely the effect of Qη on the mechanical fatigue lifetime of solder joints suffering from cyclic vibration loading. Finally, for a specified reliability goal, how to choose proper Qη values, based an improved Golden Section Search arithmetic, is discussed.
Findings
Numerical analysis and calculation are performed. The results show that the solder joints made at Qη near 510 have higher mechanical reliability, and those reflowed farther away this optimal value have less reliability.
Originality/value
This paper presents a useful and applicable solution to achieve reflow profile optimization and process control for a quantitative mechanical reliability estimation of μBGA solder joints.
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Lin Li, Jiadong Xiao, Yanbiao Zou and Tie Zhang
The purpose of this paper is to propose a precise time-optimal path tracking approach for robots under kinematic and dynamic constraints to improve the work efficiency of robots…
Abstract
Purpose
The purpose of this paper is to propose a precise time-optimal path tracking approach for robots under kinematic and dynamic constraints to improve the work efficiency of robots and guarantee tracking accuracy.
Design/methodology/approach
In the proposed approach, the robot path is expressed by a scalar path coordinate and discretized into N points. The motion between two neighbouring points is assumed to be uniformly accelerated motion, so the time-optimal trajectory that satisfies constraints is obtained by using equations of uniformly accelerated motion instead of numerical integration. To improve dynamic model accuracy, the Coulomb and viscous friction are taken into account (while most publications neglect these effects). Furthermore, an iterative learning algorithm is designed to correct model-plant mismatch by adding an iterative compensation item into the dynamic model at each discrete point before trajectory planning.
Findings
An experiment shows that compared with the sequential convex log barrier method, the proposed numerical integration-like (NI-like) approach has less computation time and a smoother planning trajectory. Compared with the experimental results before iteration, the torque deviation, tracking error and trajectory execution time are reduced after 10 iterations.
Originality/value
As the proposed approach not only yields a time-optimal solution but also improves tracking performance, this approach can be used for any repetitive robot tasks that require more rapidity and less tracking error, such as assembly.
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Shabbir Talukder and Gerald M. Knapp
This paper covers the development of a heuristic method for grouping equipment into blocks for application of preventive maintenance overhauls within a series system, so as to…
Abstract
This paper covers the development of a heuristic method for grouping equipment into blocks for application of preventive maintenance overhauls within a series system, so as to minimize total maintenance‐related costs for the system. Previously, group technology (GT) concepts have not been applied to this problem, and this research investigated the applicability of such concepts to the block overhaul problem (specifically, the SLCA method was applied). Performance of the heuristic is analyzed with respect to runtime and solution quality.
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Keywords
The purpose of this paper is to integrate the decisions regarding optimal process mean and the parameters of a sampling plan.
Abstract
Purpose
The purpose of this paper is to integrate the decisions regarding optimal process mean and the parameters of a sampling plan.
Design/methodology/approach
A model is developed to determine these parameters. The model maximizes producer expected profit, while protecting the consumer through a constraint on the probability of accepting lots with low incoming quality. The model is presented for two cases. The first one is for non‐destructive testing and the other for destructive testing. An example is presented to demonstrate that the utility of the model and sensitivity analysis on key parameters of the model has been conducted.
Findings
The findings indicated that the optimal parameters for the process and the sampling plan are significantly different from when determined separately. The sensitivity analysis showed that the process parameters are very sensitive to changes in the process variance, moderately sensitive to the limit on incoming quality, and insensitive to the consumer risk and inspection cost.
Practical implications
The models developed offer an alternative approach for quality managers to address setting process targets, taking into consideration a sampling plan.
Originality/value
The originality of the paper is in the integration of two elements of quality that are usually treated separately in the literature.
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Yangyang Lai and Seungbae Park
This paper aims to propose a method to quickly set the heating zone temperatures and conveyor speed of the reflow oven. This novel approach intensely eases the trial and error in…
Abstract
Purpose
This paper aims to propose a method to quickly set the heating zone temperatures and conveyor speed of the reflow oven. This novel approach intensely eases the trial and error in reflow profiling and is especially helpful when reflowing thick printed circuit boards (PCBs) with bulky components. Machine learning (ML) models can reduce the time required for profiling from at least half a day of trial and error to just 1 h.
Design/methodology/approach
A highly compact computational fluid dynamics (CFD) model was used to simulate the reflow process, exhibiting an error rate of less than 1.5%. Validated models were used to generate data for training regression models. By leveraging a set of experiment results, the unknown input factors (i.e. the heat capacities of the bulkiest component and PCB) can be determined inversely. The trained Gaussian process regression models are then used to perform virtual reflow optimization while allowing a 4°C tolerance for peak temperatures. Upon ensuring that the profiles are inside the safe zone, the corresponding reflow recipes can be implemented to set up the reflow oven.
Findings
ML algorithms can be used to interpolate sparse data and provide speedy responses to simulate the reflow profile. This proposed approach can effectively address optimization problems involving multiple factors.
Practical implications
The methodology used in this study can considerably reduce labor costs and time consumption associated with reflow profiling, which presently relies heavily on individual experience and skill. With the user interface and regression models used in this approach, reflow profiles can be swiftly simulated, facilitating iterative experiments and numerical modeling with great effectiveness. Smart reflow profiling has the potential to enhance quality control and increase throughput.
Originality/value
In this study, the employment of the ultimate compact CFD model eliminates the constraint of components’ configuration, as effective heat capacities are able to determine the temperature profiles of the component and PCB. The temperature profiles generated by the regression models are time-sequenced and in the same format as the CFD results. This approach considerably reduces the cost associated with training data, which is often a major challenge in the development of ML models.
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Eiichi Taniguchi, Russell G Thompson, Tadashi Yamada and Ron van Duin
Akil Jassim Harfash and Ahmed K. Alshara
The purpose of this paper is to explore a model for thermal convection in a plane layer when the density-temperature relation in the buoyancy term is quadratic. A heat source/sink…
Abstract
Purpose
The purpose of this paper is to explore a model for thermal convection in a plane layer when the density-temperature relation in the buoyancy term is quadratic. A heat source/sink varying in a linear fashion with a vertical height expressed as z was allowed, functioning as a heat sink in an area of the layer and as a heat source in the remainder.
Design/methodology/approach
First, the authors present the governing equations of motion and derive the associated perturbation equations. Second, the authors introduce the linear and nonlinear analysis of the system. Third, the authors transform the system to velocity-vorticity-potential formulation and introduce a numerical study of the problem in three dimensions.
Findings
First, the linear instability and nonlinear stability thresholds are derived. Second, the linear instability thresholds accurately predict the onset of instability. Third, the required time to arrive at the steady state increases as Ra tends to RaL . Fourth, the authors find that the convection has three different interesting patterns.
Originality/value
With the modernday need for heat transfer or insulation devices in industry, particularly those connected with nanotechnology, the usefulness of a mathematical analysis of such resonance became apparent. Thus, this study is believed to be of value.
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