This work aims to provide a physical interpretation of the ``Maxwell's displacement current'' and generalize the use of the derivative function of the electrical flux ``dΨ/dt'' in the magnetic field calculation. The innovative contribution of this study is a mathematical model to describe the origin of magnetic field as a variation of electric flux. By this approach, it follows that only the function ``dΨ/dt'' can generate a ``magnetic tension'': this leads to an interesting unification of electrical phenomena. Displacement current and conduction current are interpreted as complementary aspects of the same phenomena. It is shown how the use of the ``dΨ/dt'' allows the recovery of a formal symmetry in Maxwell's relations of electromagnetic induction law and circuit magnetic law. Included also is a generalized expression of the function ``dΨ/dt''.
In this paper, frequency reconfigurable slot-patch antenna with reflector at the back of an antenna is presented. The proposed antenna consists of a microstrip patch antenna and a microstrip slot antenna where the slot antenna is positioned at the ground plane underneath the patch. Three switches are placed in the slot. The antenna is capable to reconfigure up to six different frequency bands from 1.7 GHz to 3.5 GHz. The microstrip patch antenna produces three different frequency bands with directional radiation pattern while the microstrip slot antenna produces another three frequency bands with bidirectional radiation pattern. Due to the reflector placed at the back of the antenna, the radiation pattern is directional at all frequency bands. Simulated and measured results are used to demonstrate the performance of the antenna. The simulated and measured reflection coefficients and radiation patterns are presented and compared.
For the GSOLT calibration algorithm of n-port vector network analyzers (VNA), the sensitivity coefficients for the S-parameters of the n-port device under test (DUT) are developed as functions of the S-parameter deviations of SOLT standards. By introducing the generalized flow graph of the 3n-term error model, analytic formulas for the S-parameter deviations of the n-port DUT with respect to the error terms have been deduced. In addition, expressions for the deviations of the error terms in regard to the nonideal calibration elements are given by a series of matrix operations. Finally, the analytic expressions of the sensitivity coefficients are concluded, which can be used for establishing the type-B uncertainty budget for S-parameter measurements.
This paper proposes a fusion technique of feature vectors that improves the performance of radar target recognition. The proposed method utilizes more information than simple monostatic or bistatic (single receiver) algorithms by combining extracted feature vectors from multiple (two or three) receivers. In order to verify the performance of the proposed method, we use the calculated monostatic and bistatic RCS of three full-scale aircraft and the measured monotatic and bistatic RCS of four scale-model targets. The scattering centers are extracted using one-dimensional FFT-based CLEAN and then used as feature vectors for a neural network classifier. The results show that our method has better performance than algorithms that solely use monostatic or bistatic data.
A low-cost dual-wideband active global navigation satellite system (GNSS) antenna is proposed for vehicle applications. An inverted shorted annular ring (ISAR) and a shorted annular ring (SAR) are used as radiation patches for low-angle multipath mitigation and operated respectively at 1164-1279 MHz and 1559-1610 MHz. To reduce the effect of the mutual coupling between the ISAR and SAR, meanwhile broaden the impedance bandwidth of the ISAR, defected ground structures are etched under the microstrip feed lines of the ISAR. Two trans-directional couplers are adopted to form orthogonal dual-feed networks of the ISAR and SAR for wideband circularly polarized reception. A combiner is adopted to merge two way signals into one way amplified by a wideband low noise amplifier with the proposed DC and RF collinear transmission technology. The experimental results show that the proposed antenna is better than the NovAtel GPS-703-GGG pinwheel antenna in terms of signal reception.
This paper critically reviews the electromagnetic advantages of altering the dielectric substrate section of the antenna as opposed to the conducting elements. Changing the dielectric has been used to improve the bandwidth, efficiency and gain of antennas. Heterogeneous substrates have also been employed to lower the effective permittivity, suppress surface waves for high indexed substrate materials and reduce mutual coupling. In the second half of this paper, 3-D printing has been used to create substrates with reduced material consumption for a lightweight flexible wearable antenna.
The imaging of targets embedded in a planar layered background media has been an important topic in subsurface and urban sensing. In this paper a fast and efficient tomographic algorithm for the imaging of targets embedded in a multilayered media is presented. The imaging algorithm is based on the first-order Born approximation and exploits the spectral multilayered media Green's function. The exploding reflection model is employed and then the Green's function is expanded in the spectral form to facilitate the easy implementation of the imaging algorithm with fast Fourier transform (FFT). The wave propagation effect due to the presence of the layered subsurface media is automatically taken into account in the imaging formulation through the multilayer media Green's function. The linearization of the inversion scheme and employment of FFT make the imaging algorithm suitable in several applications concerning the diagnostics of large probed domain and allow real-time processing. Representative examples are presented to show the effectiveness and efficiency of the proposed algorithm for radar imaging through multilayered media.
The present paper considers the connection between complex input impedance and the physical dimensions for planar ultra wideband (UWB) antennas. The first time the effect of both the actual radiator width and length for impedance behaviour is comprehensively presented. Also the effect of feed point dimensions on complex impedance is studied. The investigations involve both UWB single-resonant dipoles to cover bandwidth ≥ 500 MHz and a multi-resonant dipole for the entire Federal Communications Commission's (FCC) frequency band of 3.1-10.6 GHz. Lumped-element equivalent circuits are used identically with 3D antenna simulations in order to observe the corresponding impedance behaviour with the studied antennas. The used equivalent circuits consisting of series- and parallel-resonant stages are widely accepted in the open literature. The series-resonant circuit of equivalent is observed to have the analogue to the antenna feeding area. The physical dipole dimensions in terms of a length and width are connected to parallel-resonant part, which mainly determines the antenna input impedance. The resistance of a parallel-resonant stage behaves as the maximum value of real part of dipole impedance with an influence on bandwidth together with the ratio of parallel capacitance C and inductance L. The increase of the antenna physical width has an effect on bandwidth, because of the wider the antenna, the higher the capacitance in the antenna feed. Since the traditional dipoles are used for these studies, the results can be extended in several ways for other antenna types or, for instance, to verify the effect of body tissue, close to a wearable antenna.
The design of a novel low profile antenna is presented in this paper. By a cross-shaped structure shorted to the ground plane through shorting probes, the size reduction is achieved. A top-loading ring-disc is successfully employed to broaden the impedance bandwidth. Moreover, with the uniformly-arranged shorting pins and a circular sleeve structure placed on the ground, a good omnidirectional performance in the horizontal plane is obtained. An antenna prototype has been implemented and characterized. A measured impedance bandwidth for VSWR ≤ 2 of about 135% ranging from 1500 to 7800 MHz is achieved, and a monopole-like radiation pattern is also produced. The height of the proposed antenna is very low with 0.07λ tall. The proposed antenna is very suitable for indoor base station and the UWB applications.
This paper discusses the electromagnetic characteristics of a stratified metamaterial structure placed in fractional dimension space. Reflection and transmission coefficients for plane wave incident on multilayered structure in D-dimensional space are computed. Transfer matrix method is used to study the behaviour of different planer multilayered periodic metamaterial structures. The results are compared for integer and fractal dimensional spaces for both the cases of normal and oblique incidences. Classical results are recovered for integer dimensions. This work provides solution for examining the electromagnetic fields and waves in multilayered structures at fractal interfaces.
Partial Discharge detection techniques strive to ensure a safe and reliable power network by preventing power failure. In this work, electromagnetic sensing of partial discharge, in air-insulated medium voltage switchgear (Type D24-121114 of Driescher) is considered. The partial discharges are approximated by Gaussian sources. A versatile broadband sensor for detecting two major types of partial discharge was designed and optimized. The antenna has low return loss and high gain over the frequency band of corona discharge, 0.75-0.9 GHz and dry band arching, 1.25-1.4 GHz. The horn antenna is incorporated into the medium voltage switchgear for detecting partial discharges. The analysis of the electromagnetic field distributions generated by partial discharges in switchgear is coupled with the sensing efficiency of the horn antenna. The results indicate a good correlation between the intensity, location and frequency band of partial discharge and their sensing. This study provides the foundation for a dual band detection system of partial discharge in switchgear systems.
In this study a new analytical formulation for electromagnetic wave scattering from rough boundaries interfacing inhomogeneous media is presented based on the first-order approximation of the small perturbation method. First, we considered a scattering problem for a single rough boundary embedded in a piecewise continuously layered medium. As a key step, we introduced auxiliary wave propagation problems that are aimed to link reflection and transmission coefficients in the layered media with particular solutions of one-dimensional wave equations at the mean level of the rough interface. This approach enabled us to express the final solution in a closed form avoiding a prior discretization of the inhomogeneous medium. Second, we naturally extended the obtained solution to an arbitrary number of rough interfaces separating continuously layered media. As a validation step, we demonstrated that available solutions in the literature represent special cases of our general solution. Furthermore, we showed that our numerical results agree well with published data. Finally, as a particular special case, we presented a formulation for scattering from inhomogeneous snow-covered sea ice when the dominant scattering occurs at the snow-ice and air-snow interfaces.
This paper presents a novel miniaturized multi-evanescent-mode resonator. The resonator is achieved with a coaxial cavity. This coaxial cavity essentially has a direct short connection at one end and is connected with several lumped capacitances at the other end. The key technology of the resonator is the usage of multiple evanescent-modes of TM (transverse magnetic wave) modes. Due to the combined effects of the evanescent mode and multiple modes, the size of the resonator is greatly reduced. In this paper, the theory of resonator is discussed in detail. To verify the correctness of operation, the resonator is used in experimental measurements conducted to realize a third-order band-pass filter based on SIW (substrate-integrated waveguide) technology. The measured results are found to agree with the theoretical values.
A novel compact ultra-wideband (UWB) bandpass filter (BPF) with triple sharply notched bands and wide upper stopband is proposed. The basic UWB BPF is composed of two microstrip interdigital coupled lines and one multiple-mode resonator (MMR). Then, to achieve triple band-notched performance, the proposed triple-mode stepped impedance resonator (TMSIR) is studied and coupled to the interdigital coupled lines of the basic UWB BPF. To validate the design theory, a microstrip UWB BPF with three notched bands respectively centered at 5.2 GHz, 5.8 GHz, and 6.8 GHz is designed and fabricated. Both simulated and experimental results are provided with good agreement.
In this paper we proposed a novel classification system to distinguish among elderly subjects with Alzheimer's disease (AD), mild cognitive impairment (MCI), and normal controls (NC). The method employed the magnetic resonance imaging (MRI) data of 178 subjects consisting of 97 NCs, 57 MCIs, and 24 ADs. First, all these three dimensional (3D) MRI images were preprocessed with atlasregistered normalization. Then, gray matter images were extracted and the 3D images were undersampled. Afterwards, principle component analysis was applied for feature extraction. In total, 20 principal components (PC) were extracted from 3D MRI data using singular value decomposition (SVD) algorithm, and 2 PCs were extracted from additional information (consisting of demographics, clinical examination, and derived anatomic volumes) using alternating least squares (ALS). On the basic of the 22 features, we constructed a kernel support vector machine decision tree (kSVM-DT). The error penalty parameter C and kernel parameter σ were determined by Particle Swarm Optimization (PSO). The weights ω and biases b were still obtained by quadratic programming method. 5-fold cross validation was employed to obtain the out-of-sample estimate. The results show that the proposed kSVM-DT achieves 80% classification accuracy, better than 74% of the method without kernel. Besides, the PSO exceeds the random selection method in choosing the parameters of the classifier. The computation time to predict a new patient is only 0.022s.
In this paper, the dispersive properties and switching state of three-dimensional (3D) photonic crystals (PCs) with diamond lattices, which are composed of the core isotropic dielectric spheres with surrounded by the epsilon-negative (ENG) materials shells inserted in the isotropic dielectric background (air), are theoretically investigated in detail based on a modified plane wave expansion method. The wavelength division multiplexer can be realized easily by tuning the switching state of such PCs. The equations for computing band structures for such 3D PCs are presented. Our analysis shows that the proposed double-shell structures can obtain the complete photonic band gaps (PBGs) which can be realized optical switching with on or off states by manipulating the radius of core dielectric sphere, the relative dielectric constant of background, the dielectric constant of ENG materials and the electronic plasma frequency, respectively. However, the thickness of the ENG materials shell cannot change the switching state as the radius of core dielectric sphere is certain. Numerical simulations also show that a flatbands region, and the stop band gaps (SBGs) in (1 0 0) and (1 1 1) directions which are above the flatbands region can be achieved. The SBGs in (1 0 0) and (1 1 1) directions can also be tuned by the parameters as mentioned above. There also exists a threshold value for the thickness of ENG material shell, which can make the band structures for the 3D PCs with double-shell structures similar to those obtained from the same structure containing the pure ENG materials spheres. In this case, the dielectric function of inserted core sphere will not affect the band structures. It means that we can achieve the PBGs by replacing the pure ENG materials spheres with such double-shell structures to make fabricate easily and save the material in the realization. It is also noticed that the flatband region is determined by the existence of surface plasmon modes, and the upper edge of flatband region does not depend on the topology of lattice. Such presented 3D PCs with double-shell structures offer a novel way to realize the wavelength division multiplexers.
The focusing of a magnetic field, at low frequencies, in the very near field is difficult as flux lines naturally tend to disperse. It is not possible to use antenna array techniques due to large wavelengths at low frequencies. A method for synthesizing a concentrated magnetic field in a large air gap between two magnetic poles is presented. The focusing effect is brought about by the inclusion of side poles, adjacent to each of the main poles. Through the correct dimensioning of the side poles' reluctances and relative magneto-motive forces it is possible to focus the field in the center of the gap. General design curves for normalized parameters, determined via finite element modelling, are presented. A scale model is experimentally verified.
We present a robust multiple-channel vector-matching localization approach (MCVM) based on signal strength difference (SSD) fingerprinting of ZigBee Network. Compared with some existing algorithms, our presented approach has threefold advantages: firstly, far fewer numbers of received signal strength(RSS) measurements and reference nodes are needed; secondly, it shows more robustness to the fluctuation of RSS; thirdly, it requires low time-consuming signal strength collection surveys in the location space. We demonstrate the performances of our algorithm experimentally using different numbers of channels, reference nodes and training points. The Cramer-Rao Low Bound(CRLB) of SSD is derived in order to compare the performance of the different localization methods addressed. The experiment results show the efficacy of our proposed approach.
Polarization and incident angle independent metamaterial-based absorber (MA) which acts as a strong dual-band resonator is designed and constructed. Besides, a method to design single/dual-band MA is presented in detail. The proposed model is based on isotropic ring resonator with gaps and octa-star strip (OSS) which allows maximization in the absorption because of the characteristic features of the structure. Reflection and absorption responses are obtained both numerically and experimentally and compared to each other. Two maxima in the absorption are experimentally obtained around 90% at 4.42 GHz for the first band and 99.7% at 5.62 GHz for the second band which are in good agreement with the numerical simulations (95.6% and 99.9%, respectively). The numerical studies verify that the dual-band MA can provide perfect absorption at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. The proposed model can easily be used in many potential application areas such as security systems, sensors, medical imaging technology.
The space-variant motion errors are specic to different targets and proportional to the beamwidth of a synthetic aperture radar (SAR) system, which makes them very difficult to be compensated for a SAR system with wide beamwidth. In this paper, a motion compensation (MoCo) algorithm that exploits the features of the geometry of near-range SAR applications is proposed. By dividing the whole range swath into several octave sub-swaths, the effects of space variant motion errors can be greatly reduced, especially for targets at nearer range, with low computational load.
The aim of this paper is to present a frequency domain method for synthetic aperture radar (SAR) imaging. By using two consecutive linear mappings along Doppler and frequency domains, an azimuth-dependent SAR transfer function has been discovered. Based on this new transfer function, the SAR image can be reconstructed by the proposed azimuth stacking algorithm. The new algorithm can form SAR image at each azimuth position without DFT wrap around errors. If Chirp z-transform (CZT) is applied to carry out the two consecutive mappings (since they are linear mappings), the proposed algorithm will not require interpolations and thus its reconstructed image would be free of truncation errors. The new algorithm has been validated using both simulated and experimental ultrawideband/widebeam (UWB/WB) SAR data.
We design, characterize, and analyze a new kind of metamaterial (MTM) absorber (MA) in different frequency regions for the solar cell applications. This MTM based structure is particularly presented in a range of the solar spectrum in order to utilize the solar energy effectively. The proposed MTM based solar cell provides perfect absorption for both infrared and visible frequency ranges and can be used for the realization of more efficient new solar cells. The structure is also tested in terms of the polarization angle independency. The suggested MA has a simple configuration which introduces flexibility to adjust its MTM properties to be used in solar cells and can easily be re-scaled for other frequency ranges. Our experimental results in microwave frequencies confirm the perfect absorption for the resonance frequency and agree with the simulation results. This means that the developed MA for solar cells will offer perfect absorption in infrared and even in visible frequencies.
Various interference sources either intentional or unintentional can mask the synthetic aperture radar (SAR) signals and cause image degradation. With a novel data acquisition mode, a new method based on dual-channel SAR is applied to suppress the interference. Using the received dual-channel data, the two-dimensional location of the interference source can be estimated and then the interference can be removed via a Two-Channel Cancelation method. By establishing a linear model of the interference-removed signal, the SAR image is reconstructed based on compressed sensing (CS) theory. Our method requires only a minor change to the traditional SAR system hardware while obtains a higher resolution. Simulation results are shown to demonstrate the validity of the proposed method.
This paper presents a new efficient algorithm of filtering and unwrapping phase images for interferometric synthetic aperture radar (InSAR) based on nonlinear phase model. First, we analyzed the statistical and signal properties of interferometric phase, and proposed the concept of nonlinear phase model. The model of reflecting topographic contour is used to approximate the interferometric phase variation occured over the local window. And the lower amplitude bound of the principal vector is decided and the value solution method is given, which can solve effectively and adaptively the nonlinear factor of the phase. Second, we studied the application of nonlinear phase model in interferometric phase filtering. When compared with other advanced filters, the nonlinear phase compensation filter, with a higher computation efficiency and a better phase estimation accuracy in low coherence areas, has a stronger ability to reduce interferometric phase noise in rugged terrain Finally, we introduced the nonlinear phase model to phase unwrapping, which increased the reliability of integration path and the accuracy of the phase gradient, and improved effectively the performance of phase unwrapping. And the real data processing results demonstrated the validity of the proposed nonlinear phase model and of the corresponding solutions.
A compact and low-correlation multiple input multiple output antenna system covering 1710-2690 MHz band for wireless communication standards is proposed. It comprises two identical elements with coupled feeding plate and radiating strip, and each element has a volume of 24.5×15×1.2mm3. Simulated and measured results show that it has good potentials for high-band-only mobile phone. 45% bandwidth (based on S11 < -6 dB), -20 dB isolation, over 70% efficiency and less than 0.15 correlation coefficient are achieved in the frequency ranging from 1710 MHz to 2690 MHz. Several key parameters are also discussed in this study to better understand the antenna principles.
In this work we examine, for the first time, the use of classification algorithms for early-stage tumor detection with an experimental time-domain microwave breast screening system. The experimental system contains a 16-element antenna array, and testing is done on breast phantoms that mimic breast tissue dielectric properties. We obtain experimental data from multiple breast phantoms with two possible tumor locations. In this work, we investigate a method for detecting the tumors within the breast but without the usual complexity inherent to image-generation methods, and confirm its feasibility on experimental data. The proposed method uses machine learning techniques, namely Support Vector Machines (SVM) and Linear Discriminant Analysis (LDA), to determine whether the current breast being scanned is tumor-free. Our results show that both SVM and LDA methods have promise as algorithms supporting early breast cancer microwave screening.
In this paper, a computational model is established for the finite-difference time-domain analyses of induced voltage on the overhead line at oil exploiting port under lightning strike. The MTLL approximate formulation is used to simulate the lightning strike, and convolutional perfectly matched layers are used to truncate the computational domain. A two-step method is established to calculate the coupling to the overhead lines to reduce the huge computational domain of the conventional 3-D FDTD simulation. Parallel implementation is introduced for the second-step calculation to overcome the memory storage limit of a single computer. With this model, the electromagnetic field at the adjacent areas and the induced voltage on the overhead line are studied when lightning strikes an oil derrick. It is demonstrated that the electromagnetic field decreases as the distance from the oil derrick increases, but the vertical field decrease much slower than the horizontal field. It is also shown that the transversely located overhead line will introduce lower voltage than the radially located line. As the length of the overhead line increases, the induced voltage increases and the low-frequency induction is strengthened. The overhead line should be set as low as possible to reduce the induced voltage.
The range profile (RP) and the inverse synthetic aperture radar (ISAR) image are the useful radar signature for classifying unknown targets because they can be used regardless of day-night and weather conditions. Since classification that uses RP and ISAR is heavily dependent on flight conditions, however, much more study is required on this topic. This paper proposes an efficient method of classifying targets by using a classifier-level fusion of RP and ISAR as well as a scenario-based construction method of the training database. Simulation results using the five targets composed of point scatterers prove that the proposed method yields high classification results when the targets are flying in a variety of directions at both short and long ranges.
In this paper, the range-spread target detection in compound Gaussian clutter with reciprocal of the square root of gamma (RSRG) texture is investigated. The RSRG distribution has been proved to be a good model for texture component of extremely heterogeneous radar clutter. Taking this compound Gaussian model as a spherically invariant random process (SIRP), the Neyman-Pearson optimal detector for the range-spread target detection with known target amplitude is derived firstly. By replacing the ideal target amplitude with its maximum likelihood estimate (MLE), the generalized likelihood ratio test (GLRT) is then obtained. The statistical property of the texture component is taken into account in both of these two detectors, which makes the detectors computationally complicated. A suboptimal generalized likelihood ratio test based on order statistics (OS-GLRT) is finally proposed by substituting the texture component with its MLE. The OS-GLRT makes use of some largest observations from the range cells occupied by the most likely target scatters. The performance assessment conducted by Monte Carlo simulation validates the effectiveness of the proposed detectors.
A wideband circularly polarized patch antenna is proposed. The wide impedance and axial ratio bandwidths are achieved by the proposed feeding mechanism, which entails the use of a circular microstrip line coupling through four Γ-shaped slots to generate four sequentially phased sources to excite the single layer patch antenna. The proposed antenna can provide an SWR bandwidth of over 16.5% (for SWR<1.5) and an axial-ratio bandwidth of 13.3% (for AR<3 dB). The performance of the antenna has been confirmed by both measurement and simulation. The antenna gain is enhanced and backlobe radiation is reduced by placing a reflector at an optimized location.