Comparison of image reconstruction by using near‐field and far‐field data for an imperfect conductor

Image reconstruction by using near‐field and far‐field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near‐field data are better than those obtained by using far‐field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69–73, 2001.     

The multiple loop antenna for enhanced readability performances of near‐field UHF RFID applications

This research is concerned with a multiple loop antenna applicable to near field ultra‐high frequency (UHF) radio frequency identification (RFID). The proposed multi‐loop antenna is configured to induce the robust and even magnetic field distributions in the H_x, H_y, and H_z orientations so as to achieve the enhanced readability performances in all directions (i.e., x, y, and z). Simulations were carried out using CST Microwave Studio to determine the impedance bandwidth (|S₁₁|H_x‐, H_y‐, and H_z‐oriented magnetic field distributions. A prototype antenna of 14 cm × 16 cm × 0.6 mm (W × L × H) in overall dimension was subsequently fabricated on an FR4 substrate connected to a coaxial cable. In this research, the H_x‐, H_y‐, and H_z‐oriented magnetic field distributions of the prototype antenna were measured in the x‐axis, y‐axis, and x–y plane and are in good agreement with the simulation results. The measured readability performances in the x‐, y‐, and z‐directions in which seven near field UHF RFID tags were deployed unobstructed (i.e., in open air) are respectively 25.27%, 31.73%, and 85.43%. Furthermore, the performances on the antenna readability with the tags attached to the microcentrifuge tubes are 30.55%, 25.90%, and 69.09% for the x‐, y‐, and z‐directions. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:402–417, 2016.     

Phaseless near-field to far-field transformation based on source current reconstruction and signal subspace optimization

In this article, an algorithm for the phaseless near-field (NF) to far-field (FF) transformation based on the source current reconstruction method (SRM) is proposed. The algorithm starts with decomposing the equivalent currents of the antenna under test (AUT) into a deterministic and ambiguous current. The deterministic portion of the current is determined from the phaseless signal subspace-based optimization method (SOM), while several iterative forward-backward propagations add the ambiguous portion. It is shown that with the SOM initialization, no further prior information about the antenna under test is needed and the iterative scheme can converge to the desired result within a few iterations. A simulation and a measurement example validate the proposed algorithm. All results show an accurate, fast, and stable phaseless field transformation is obtained.     

Design of a low‐cost 1‐20 GHz magnetic near‐field probe with FR‐4 printed circuit board

An ultra‐wideband magnetic near‐field probe based on a conventional low‐cost four layers of FR‐4 printed circuit board is proposed in this article. It can be used to measure the magnetic near‐field strength from RF magnetic sources or electronic devices for EMI conformance test. The operating frequency of the probe is from 1 GHz up to 20 GHz. The probe is constructed based on a coplanar waveguide and stripline with a short‐end loop. The probe dimension is 10 mm × 25 mm × 0.6 mm. The prototype probe is electric field‐shield structure and has a very high unwanted electric field suppression ratio about 17.7 dB. The probe calibration factor from the simulation agrees well with the calibration factor computed from the measurement. The average probe factor is 38.8 dBS/m and probe sensitivity is 47.4 dB μ A/m.     

Wearable near‐field communication bracelet based on highly conductive graphene‐assembled films

Benefiting from the high conductivity and superb flexibility, graphene‐based materials are promising to replace metal for near‐field communication (NFC) applications. Herein, we report a flexible NFC tag antenna based on high‐conductivity graphene‐assembled films (HCGAFs) and investigate how the performance of the antenna is affected by antenna design and human body effect. The fabricated prototype via a one‐step laser‐direct mold engraving method shows a 10 dB bandwidth of 2.5 MHz centering at 13.70 MHz with a quality factor (Q) of 9.19. The maximum read range of the HCGAF NFC tag is measured to be around 7.5 cm, comparable to the commercially available metal NFC tags. Moreover, the flexible nature of HCGAFs guarantees excellent mechanical stability and deformation insensitivity, especially when compared to commercial metal‐based counterparts. We further demonstrate the practical applications of the HCGAF tag as key card and electronic business card in the vicinity of human body.     

Implementation and optimization of GPU‐based parallel one‐step leapfrog ADI‐FDTD for far‐field scattering problems

The one‐step leapfrog alternative‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD), free from the Courant‐Friedrichs‐Lewy (CFL) stability condition and sub‐step computations, is efficient when dealing with fine grid problems. However, solution of the numerous tridiagonal systems still imposes a great computational burden and makes the method hard to execute in parallel. In this paper, we proposed an efficient graphic processing unit (GPU)‐based parallel implementation of the one‐step leapfrog ADI‐FDTD for the far‐field EM scattering simulation of objects, in which we present and analyze the manners of calculation area division and thread allocation and a data layout transformation of z components is proposed to achieve better memory access mode, which is a key factor affecting GPU execution efficiency. The simulation experiment is carried out to verify the accuracy and efficiency of the GPU‐based implementation. The simulation results show that there is a good agreement between the proposed one‐step leapfrog ADI‐FDTD method and Yee's FDTD in solving the far‐field scattering problem and huge benefits in performance were encountered when the method was accelerated using GPU technology.     

Impact of amplitude weights on power focusing for near‐field‐focused planar arrays

Near‐field‐focused (NFF) arrays have gained great interest owing to its ability to focus the electromagnetic power at a point near to the antenna. The power focusing can basically be reflected by the sidelobe level and the area of the ?3‐dB focal spot at the focal plane. For an ordinary NFF array with the given phase tapering, it would be an effective way to realize the changing of focused power by controlling the feeding‐current amplitude of the array element. In this article, the effects of the amplitude weights of array element rings on the power focusing with reference to an original NFF array are investigated to address this issue. The focus is on the power focusing changing introduced by amplitude weights changing of element rings, in which different cases of amplitude weights changing are considered. The results from amplitude weights changing are compared with that from an original amplitude weights combination, and compared among those from different cases of amplitude weights changing.     

Closed‐form method for the reconstruction of 2‐D objects: Preliminary experimental results

An analytical approach to inverse electromagnetic scattering is tested on 2‐D experimental data. The closed‐form singular value decomposition of the scattering integral operator is the basis for determining the radiating components of the equivalent source density. This equivalent source is used to reconstruct the features of a scatterer. Reconstructions performed on different scattering data show the capabilities of the method and, thanks to the closed‐form solution, results are available after a very short time of computation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Task‐driven latent active correction for physics‐inspired input method in near‐field mixed reality applications

Calibration accuracy is one of the most important factors to affect the user experience in mixed reality applications. For a typical mixed reality system built with the optical see‐through head‐mounted display, a key problem is how to guarantee the accuracy of hand–eye coordination by decreasing the instability of the eye and the head‐mounted display in long‐term use. In this paper, we propose a real‐time latent active correction algorithm to decrease hand–eye calibration errors accumulated over time. Experimental results show that we can guarantee an effective calibration result and improve the user experience with the proposed latent active correction algorithm. Based on the proposed system, experiments about virtual buttons are also designed, and the interactive performance regarding different scales of virtual buttons is presented. Finally, a direct physics‐inspired input method is constructed, which shares a similar performance with the gesture‐based input method but provides a lower learning cost due to its naturalness.     

A non‐deterministic reconstruction approach for isotropic reflectances and transmittances

Physically and biologically based reflectance and transmittance models add realism to image synthesis applications at the expense of a significant increase in rendering time. Current research efforts in this area focus on developing practical solutions to quickly access a BDF (which represents a combination of BRDF and BTDF) while preserving its original characteristics. In this paper an approach to reconstruct relatively complex isotropic BDFs is presented. The spectral curves obtained using the proposed approach are compared with measured spectral curves, and some issues regarding its performance and storage requirements are examined. Copyright © 1999 John Wiley & Sons, Ltd.     

Asymmetric source/drain offset structure for reduced leakage current in polycrystalline‐silicon thin‐film transistors

Abstract— An asymmetric source/drain offset structured (AOS) polycrystalline‐silicon (poly‐Si) thin‐film transistor (TFT) has ben developed by employing alternating magnetic‐field‐enhanced rapid thermal annealing (AMFERTA). The realized AOS poly‐Si TFT, with long drain‐side offset length L_Off1 and short source‐side offset length L_Off2, considerably suppresses leakage current without sacrificing ON‐current. The offset regions of the AOS TFT are naturally lightly doped due to the diffusion of n⁺ ions by AMFERTA crystallization. The fabrication process of the AOS TFT does not require any additional offset mask step or doping process. Experimental results show that the leakage current is considerably suppressed when the drain‐side offset length L_Off1 is larger than 1.25 μm.     

A computational model of bounded developable surfaces with application to image‐based three‐dimensional reconstruction

Developable surfaces have been extensively studied in computer graphics because they are involved in a large body of applications. This type of surfaces has also been used in computer vision and document processing in the context of three‐dimensional (3D) reconstruction for book digitization and augmented reality. Indeed, the shape of a smoothly deformed piece of paper can be very well modeled by a developable surface. Most of the existing developable surface parameterizations do not handle boundaries or are driven by overly large parameter sets. These two characteristics become issues in the context of developable surface reconstruction from real observations. Our main contribution is a generative model of bounded developable surfaces that solves these two issues. Our model is governed by intuitive parameters whose number depends on the actual deformation and including the “flat shape boundary”. A vast majority of the existing image‐based paper 3D reconstruction methods either require a tightly controlled environment or restricts the set of possible deformations. We propose an algorithm for reconstructing our model's parameters from a general smooth 3D surface interpolating a sparse cloud of 3D points. The latter is assumed to be reconstructed from images of a static piece of paper or any other developable surface. Our 3D reconstruction method is well adapted to the use of keypoint matches over multiple images. In this context, the initial 3D point cloud is reconstructed by structure‐from‐motion for which mature and reliable algorithms now exist and the thin‐plate spline is used as a general smooth surface model. After initialization, our model's parameters are refined with model‐based bundle adjustment. We experimentally validated our model and 3D reconstruction algorithm for shape capture and augmented reality on seven real datasets. The first six datasets consist of multiple images or videos and a sparse set of 3D points obtained by structure‐from‐motion. The last dataset is a dense 3D point cloud acquired by structured light. Our implementation has been made publicly available on the authors' web home pages. Copyright © 2012 John Wiley & Sons, Ltd.     

A method for diagnosis of current faults in antenna arrays using neural networks

A method for detection of faulty elements in antenna arrays from far‐field radiation pattern is presented. The proposed technique finds variation of current from correct values in the faulty elements. A step wise approach is proposed to determine magnitude and phase of current excitation and location of faulty element using neural networks. The results with radial basis function neural network and probabilistic neural network are compared. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A pair of parallel differential magnetic‐field probes with high measurement accuracy and high electric‐field suppression ratio

Magnetic‐field probes can be used for electromagnetic interference measurement of high‐speed circuits. The main magnetic probe performance includes sensitivity, spatial resolution, electric‐field suppression ratio (EFSR), and measurement accuracy. In this article, a pair of differential magnetic‐field probes is proposed to improve measurement accuracy without reducing sensitivity. The proposed differential probes consist of two asymmetric loop probes, which are designed in the same plane and separated by a row of periodic vias. The proposed differential probes are fabricated under PCB process. High accuracy can be achieved by measuring difference between outputs of the two probes. In addition, EFSR can be improved by size optimization of the differential magnetic‐field probes. Simulation and measurement results show the operating bandwidth is from 100 MHz to 12 GHz, the measurement error is 3.4% and the EFSR is about 40 dB. The proposed probes have higher measurement accuracy and higher EFSR than the conventional single probe, and larger operation bandwidth than the stacked differential probes.     

Necessary and Sufficient Near‐Optimal Conditions for Mean‐Field Singular Stochastic Controls

We consider the near‐optimal control problems for mean‐field singular stochastic systems, where the control domain is non‐convex. By virtue of Ekeland's principle and some estimates on the state and adjoint processes, necessary and sufficient conditions for near‐optimality are established in the mean‐field framework. As an application, an example is presented to demonstrate the results.     

A plastic holographic waveguide combiner for light‐weight and highly‐transparent augmented reality glasses

There is a high demand for light‐weight, stylishly designed augmented reality (AR) glasses with natural see‐through capabilities for the wide‐spread distribution of novel wearable device to general consumers. We have successfully developed a unique production process of a holographic waveguide combiner that enables us to laminate holographic optical elements (HOEs) onto a plastic substrate with optical grade quality. The plastic substrate waveguide combiner has a number of advantages over conventional glass substrate combiners; the plastic substrate makes AR glasses lighter in weight and unbreakable. With the lamination process of HOEs, we can apply them to a various designs to satisfy general customers' wide range of preferences for the style. We also potentially made it possible for the holographic waveguide combiner to be produced in larger volumes at lower costs by using our novel roll‐to‐roll hologram recording and laminating process. In this paper, we present our approach of the plastic substrate HOE production process for AR glasses.     

A novel driving method for field sequential color using an OCB TFT‐LCD

We report a new technique for the design of field‐sequential‐color liquid‐crystal displays (FS‐LCDs), which maximizes the liquid‐crystal response,t_LC, by dividing the display area into as few sub‐areas,N, as possible. We obtained the following results: (1) ^tLC increased as N increased, although saturation tended to occur. Increasing N from 1 to 2 gave the largest increase in ^tLC. (2) ^tLC was maximized by dividing the display area unequally.     

A specified‐time control framework for control‐affine systems and rigid bodies: A time‐rescaling approach

This paper addresses the specified‐time control problem for control‐affine systems and rigid bodies, wherein the specified‐time duration can be designed in advance according to the task requirements. By using the time‐rescaling approach, a novel framework to solve the specified‐time control problem is proposed, and the original systems are converted to the transformation systems based on which the specified‐time control laws for both control‐affine systems and rigid bodies are studied. Compared with the existing approaches, our proposed specified‐time control laws can be derived from the known stabilization control laws. To our best knowledge, it is the first time that transformation system–based specified‐time control framework for control‐affine system and rigid body dynamics is proposed. To further improve the convergence performance of specified‐time control, a finite‐time attitude synchronization control law for rigid bodies on rotation matrices is proposed, and thereby, the finite‐time–based specified‐time control law is designed eventually. In the end, numerical simulations and SimMechanics experiments are provided to illustrate effectiveness of the theoretical results.     

Fault reconstruction for delay systems via least squares and time‐shifted sliding mode observers

In this article, we address the problem of fault reconstruction in delayed systems by introducing a time‐shifted sliding mode observer (SMO). While time‐varying delays of arbitrary duration are considered in the measured output signal, the actuator fault is parametrized as a weighted sum of known regressor functions with unknown coefficients. The prediction scheme utilizes the variation of constants formula to obtain the present time estimate of the unmeasured state. The fault is also identified at present time by means of the continuous‐time Least Squares approaches. Ideal sliding mode can be guaranteed in theory, even in the presence of such adverse delays, since there is no chattering in the output estimation error of the SMO. An application to petroleum engineering with numerical simulations is presented to show the effectiveness of the proposed method.