This paper describes the ramifications in the capacity of Multiple Input Multiple Output (MIMO) wireless links when the antenna systems involved are mischaracterized and contain phase errors. Errors in simulated as well as measured radiation patterns are considered. Also, simple deterministic Line of Sight and stochastic propagation environments are examined. The analyses are carried out on a 2×2 MIMO system. Results show that the resultant error in capacity depends on the degree of the phase error between the antenna ports, the type of propagation environment, as well as the degree of the illumination Signal to Noise Ratio (i-SNR).
In this paper, a compact tri-band flexible MIMO antenna based on liquid crystal polymer (LCP) is designed to operate in WLAN and WiMAX bands. The antenna consists of two identical antenna elements. The isolation structure includes a ground slot, two I-shaped branches, and a parasitic strip. The measured results show that the impedance bandwidth (S11 < -10 dB) covers three frequency bands of 2.38-2.55 GHz, 3.37-3.60 GHz, and 4.92-5.37 GHz, and the S21 of working bands is basically better than -19 dB. Moreover, the flexibility of the MIMO antenna is analyzed at different bent cases. The specific absorption ratio (SAR) values are obtained by simulating the model of antenna approaching human body. The simulated results show that the SAR value of the antenna meets the European Union (EU) standard. The proposed antenna demonstrates the characteristics of satisfactory radiation, high isolation, sound gain in working bands and flexibility, which has good application prospects in the wearable field.
A fast solution for electromagnetic (EM) scattering problems over a wide incident angle based on compressed sensing (CS) has been proposed in recent years. Since current expansion coefficients are not known in advance, the parameters of this solution (e.g., the times of measurements, the selection of sparse transforms) for different scattering objects are difficult to determine. In order to solve this problem, this paper presents a prior parameter extraction method based on the principle of on-surface discretized boundary equation (OS-DBE), in which an approximate distribution of current expansion coefficients at any given point of the scatterer is first obtained with low-coverage and low-complexity, and then the prior parameters can be determined by CS tests for the approximate result. The implementation method is elaborated, and its effectiveness is verified by numerical results.
Despite the advancements in the field of glucose monitoring sensors, the development of noninvasive, wearable, continuous and comfortable systems is still a real challenge. New technologies are required for noninvasive, continuous and effective measurements remaining discreet, painless, comfortable to the patient and avoiding additional costs.This article presents a truly noninvasive microwavetomography prototype designed for glucose monitoring. The system is based on an array of dipole antennas placed in a circular configuration.The transmitted field data are collected using a switchmatrix connected to a vector network analyzer. A heterogeneous 3-D arm model and a 3-D electromagnetic solver have been used to model the human arm and to characterize the system. Blood electromagnetic properties are affected by the glucose concentration, a promising correlation between the dielectric properties of blood and glucose level should be investigated. By simulating the antenna array on the arm phantom, the characteristics of the S-Parameters were interesting at the frequencies of interest. The transmission coefficient amplitude decreases as the dielectric constant decreases from 63 to 40, and the conductivity increases from 1.5 S/m to 3.5 S/m. For each value of dielectric properties, a given transmission coefficient value can be clearly identified. Experimental measurements validated the arm phantom and confirmed the relationship between the response of the system and the dielectric properties of blood tissue. The armband sensor is designed as an inexpensive, noninvasive, and light weight device suitable for all patients with a high level of discretion. This work, under optimization for preclinical and clinical testing, demonstrates the proof of concept of an innovative microwave tomography system for noninvasive glucose monitoring. Compared to studies with a similar aim, this research may achieve distinct advances and offers promising hope in the field of noninvasive glucose sensors.
A high-gain wide-band planar antenna with H-Shaped Resonators (HSRs) for Self-Powered wireless systems is proposed in this paper. The proposed antenna consists of four major parts, namely, a grating Vivaldi electrical dipole, a half-ring magnetic dipole, HSRs, and a solar panel reflector. The dipoles are etched from both antenna substrate sides by each half on one side. The HSR structures are etched on a single side of the used substrate to avoid the capacitive coupling effects which cause the radiation efficiency reduction. HSR inclusions are designed and tested numerically to have the desired electromagnetic properties at frequency band of interest. After introducing the HSR inclusions to the antenna structure, the antenna performance is tested numerically and compared to that without HSR inclusions. The fabricated prototype based HSR structure shows an enhanced gain bandwidth product to cover the frequencies from 1.75 GHz up to 7.43 GHz with a gain varying from 9.52 dBi up to 16.71 dBi over the entire frequency range. Finally, an excellent agreement has been achieved between the gathered numerical results and those from the experimental measurements.
The Bateman-Whittaker theory, which was developed a century ago, is shown to be a comprehensive basis for deriving a large class of null spatiotemporally localized electromagneticwaves characterized by intriguing vortical structures. In addition, it provides the modeling for studying topological structures dealing with linked and knotted electromagnetic waves.
A novel and compact triple-band two-element Multiple Input Multiple Output (MIMO) antenna array is designed to provide simultaneous communications for uplink and downlink which covers GSM, LTE, and sub-6 base station applications. The proposed MIMO system is a configuration of four triple-band two-element arrays in which two are used for uplink and the other two for downlink. This compact structure with separate antennas for uplink and downlink provides simultaneous communication. For this proposed structure, the parameters like impedance bandwidth, efficiency, gain and cross polarization aspects are presented for all the three specified bands. To achieve good isolation uplink and downlink arrays are placed orthogonal to each other. Further, to enhance the isolation a defected ground is incorporated for the antenna array structure, and isolation strips are provided between uplink and downlink arrays. In addition, for the proposed structure diversity performance with Envelope Correlation Coefficient (ECC) and diversity gains are also calculated. The simulated and measured results are in acceptable correlation.
In this paper we present a simple approach to compute quickly and accurately the global inductance of multilayer circular air coils with a wire of rectangular cross section. The case of the uniform current density distribution in the wire cross section is considered. The approach, implemented under GNU Octave, computes the inductance of the multilayer coil in three steps. First, the self-inductance of each coil turn is computed using the Maxwell's formula. Secondly, each wire section is subdivided into several negligible square or rectangular subsections to form a filiform turn, and then the mutual inductances between the turns are computed using Rosa's formula. The last step sums all obtained self-inductances and mutual inductances to deduce the global inductance of the multilayer coil. To verify the efficiency and accuracy of the proposed approach, the obtained equivalent inductance of each turn is compared to the computed one using finite element method implemented in FEMM open source. Furthermore, the global coil inductance is compared to the measured one. The proposed approach shows a good accuracy with a relative error less than 1% for all considered coils.
A new local method for magnetic resonance electrical properties tomography (EPT), dubbed transverse-EPT (T-EPT), is introduced. This approach iteratively optimizes the dielectric properties (conductivity and permittivity) and the z-component of the electric field strength, exploiting the locally E-polarized field structure typically present in the midplane of a birdcage radiofrequency (RF) coil. In contrast to conventional Helmholtz-based EPT, T-EPT does not impose homogeneity assumptions on the object, and requires only first order differences, which makes the method more accurate near tissue boundaries and more noise robust. Additionally, in contrast to integral equation-based approaches, estimation of the incident fields is not required. The EPT approach is derived from Maxwell's equations and evaluated on simulated data of a realistic tuned RF coil model to demonstrate its potential.
In this paper, a triple-band reflective polarization converter with high efficiency for both linear-to-linear and linear-to-circular polarizations based on a metasurface is proposed, which can rotate a linearly polarized (LP) incident wave into its orthogonal direction with over 90% polarization conversion ratio (PCR) in the bands of 5.5-5.9 GHz (relative bandwidth of 7%) and 12-17.7 GHz (relative bandwidth of 38.4%). Besides, the proposed converter can also transform a linearly polarized incident wave to circularly polarized (CP) wave in the band of 6-12 GHz (relative bandwidth of 66.7%). Additionally, the performance of proposed polarization converter stays in considerable stability with the incident angle increasing 60˚ in circular polarization and 30˚ in linear polarization. Moreover, the physical mechanism of multiple resonances is discussed based on surface current distributions and equivalent circuit model. A prototype of the proposed converter is fabricated and measured, and the experiments and simulations are in great agreement. This polarization converter can be employed to manipulate the polarization of the signal in microwave communication.
The goal of vector control of interior permanent magnet synchronous motor (IPMSM) is to make IPMSM have excellent dynamic and steady-state performance, but there is coupling between the d-q axis in the synchronous rotating coordinate system, which affects the torque response performance. In view of the fact that the traditional voltage compensation strategy is sensitive to the change of motor parameters, genetic algorithm is introduced to identify the parameters, and a feedforward voltage compensation control based on genetic algorithm parameter identification is proposed. The compensation voltage is calculated by the inductance and flux value of the motor identified by genetic algorithm. Compensation voltage is used to counteract the change of feedback voltage caused by the change of motor parameters in feedforward decoupling control. Simulated and experimental results show that the proposed strategy can effectively achieve d-q axis current decoupling, improve the dynamic performance of the system, and have excellent robustness.
In order to solve the problem of the low direct control accuracy of permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM), which caused by transmission delay, the predictive control is applied to direct control of PMa-BSynRM. Meanwhile, in view of the disadvantages of large ripple (torque ripple, flux linkage ripple) and poor robustness in traditional predictive direct control (PDC), a fractional super twisting sliding mode controller (FSTMC) is proposed. Firstly, the mathematical models of torque and radial suspension force of PMa-BSynRM are derived. Secondly, the torque and flux controller based on FSTMC are designed, and the stability is verified. Thirdly, the torque predictive controller and levitation force predictive controller are designed, and the algorithm of PDC is described. Finally, the FSTMC-PDC system of PMa-BSynRM is built and simulated by Matlab/Simulink module. The simulated and experimental results confirm the validity and superiority of the proposed method.
In this article, a hybrid inversion algorithm based on an innovative stochastic algorithm, namely, the bat algorithm (BA) is proposed. Electromagnetic inverse scattering problems are ill-posed and are often transformed into optimization problems by defining a suitable cost function. As typical methods to solve optimization problems, stochastic optimization algorithms are more flexible and have better global searching ability than deterministic algorithms. However, they share a common disadvantage: heavy computing load. This directly restricts the application of the algorithms in high-dimensional problems and real-time imaging environments. To solve this issue, diffraction tomography (DT) is introduced to provide a reference for the initialization of the BA. Furthermore, the hybrid method makes full use of the complementary advantages of linear reconstruction algorithms and stochastic optimization algorithms to improve accuracy and efficiency at the same time. Moreover, in order to avoid the algorithm falling into local extrema, a linear attenuation strategy of the pulse emission rate is proposed to enable more bats to perform global search in the early stage of the algorithm. In the numerical experiments for different types of dielectric objects, the reconstruction results of this hybrid BA-based algorithm are compared with those of the DT and the particle swarm optimization (PSO).
A numeric-analytical solution of a problem concerning an impedance vibrator with local asymmetric excitation is derived in the thin-wire approximation. Solution correctness is confirmed by satisfactory agreement of numerical and experimental results from well-known literary sources. Based on the optimization modeling, the design of the impedance antenna characterized by three resonant frequencies intended for mobile communications operating in GSM 900, GSM 1800, and WiMAX ranges is developed. The analysis of basic electrodynamic characteristics of the vibrator antenna has proved the possibility of practical applications of this antenna for phones, portable radio stations, electronic gadgets, and base stations.
Radar data collected on two sides of a horizontally dissipative layered medium are required to invert for the medium parameters. The two-sided reflection and transmission responses are reduced to two single-sided reflection responses. One is the measured dissipative medium response, and the other is the reflection response of the corresponding effectual medium, which has negative dissipation. Marchenko-type equations are solved using these two reflection responses. The obtained focusing functions in the dissipative and effectual media are used to invert for the permittivity and the permeability under the assumption of weak dissipation in reflection. Once these parameters are known, the travel times are used to estimate the layer thicknesses. Finally, the focusing functions are used to estimate the conductivity in each layer. The method does not require any model information and runs as a fully automated process. A numerical example shows that the method works well for a horizontally dissipative layered medium. Statistical analysis for several noise models shows that the method is robust at least up to 40 dB additive and multiplicative white noise.
This paper describes a U-net based Deep Learning (DL) approach in combination with Subspace-Based Variational Born Iterative Method (SVBIM) to provide a solution for quantitative reconstruction of scatterer from the measured scattered field. The proposed technique can be used as an alternative to conventional time consuming and computationally complex iterative methods. This technique comprises of a numerical solver (SVBIM) for generating the initial contrast function and a DL network to reconstruct the scatterer profile from the initial contrast function. Further, the proposed technique is validated against theoretical and experimental results available from the literature. Root Mean Square Error (RMSE) value is used as the metric to measure the accuracy of the reconstructed image. The RMSE values of the proposed method show a significant reduction in the reconstruction error when compared with the recent Back Propagation-Direct Sampling Method (BP-DSM). The proposed method produces an RMSE value of 0.0813 against 0.1070 in the case of simulation (Austria Profile). The error value obtained by validating against the FoamDielExt experimental database in the case of the proposed method is 0.1037 against 0.1631 reported for BP-DSM method.
This paper investigates the effect of an external plane wave on a Multi-conductor transmission line (MTL) located above a multilayer soil directly in the time domain. An improved finite-difference time-domain (FDTD) method is used, in conjunction with the Vector Fitting (VF), to obtain the recursion relations of voltages and currents along the line by discretizing the equations in time and one-dimensional space. The source terms of the coupling equations are efficiently obtained in the time domain based on the Gaver-Stehfest algorithm. An equivalent model is also established in this work, where the geometry with three conductors is reduced to two conductors. Finally, some examples are presented to illustrate the effect of the soil and the plane wave on the transient.
A coplanar waveguide (CPW) fed multiple-input multiple-output (MIMO) ultra-wideband (UWB) antenna with high isolation and dual band-notched characteristic is proposed. The antenna consists of two orthogonal circle patches. An annular SRR slot and a rectangular SRR slot are added on the patches to produce two notched bands. High isolation is successfully acquired by adopting a double Y-shaped branch between the two radiation elements. By cutting the fractional substrate, the antenna size has been reduced by 31.4 percent. The measured results show that the working bandwidth of the antenna covers 2.36-12 GHz, and at the same time, the notched bands cover 3.37 GHz-3.98 GHz and 4.71 GHz-5.51 GHz. The isolation is better than 21 dB. The paper also studies the radiation pattern, peak gain, and envelope correlation coefficient (ECC) of the UWB MIMO antenna.
Owing to its all-day and all-weather imaging capabilities, high-resolution spaceborne synthetic aperture radar has shown great potential for the effective monitoring of wide-area, ultra-high-voltage (UHV) transmission lines. Scattering characteristics of UHV power lines in 3-m-resolution TerraSAR-X images is analyzed in this paper. First the study area and structure of the UHV transmission line are introduced. Then, the data processing method is described, which includes the preprocessing of TerraSAR-X images and target feature extraction. Finally, the scattering characteristics of the UHV power line are analyzed, and the analysis results demonstrate that the UHV power line can be visible in a TerraSAR-X image only when the angle between its extension direction and the azimuth of the sub-satellite ground track is within ±15°. Furthermore, besides the span length, the spatial location of the UHV power line in a TerraSAR-X image is also influenced by the angle between its extension direction and the azimuth of the sub-satellite ground track, as well as by the height difference between adjacent pylons.
Modern combat teams face an increasingly complex battlefield, where threats may arise from a number of different sources. Examples include not only conventional attacks through rocket propelled grenades but also improvised explosive devices and weaponised unmanned aerial vehicles. Combat teams can now be equipped with sophisticated surveillance and reconnaissance capability, as well as automatically activated defences. The focus of this paper is to consider the utility of collaborative active protection systems, which are designed to provide an active defence against threats to a combat team. Specifically, a general statistical framework for the analysis of such systems is introduced, with a particular focus on high power radio frequency directed energy weapon countermeasures. The mathematical model allows for a subset of the combat team to be responsible for target detection and tracking, and a time-varying subset of team members with suitable countermeasures to be specified separately. The overall probability of threat defeat and team survivability is then derived. Some examples are provided to investigate the utility of such systems.