This paper presents a concept, by which radio frequency (RF) tags are employed as remotely read dielectric-property sensors to determine qualities of some construction material products (CMPs); e.g., light weight concrete (LWC), mortar specimens and concrete. Using the dependency of the read range of the passive RF identification (RFID) sensor system on the electromagnetic properties of CMPs near or in contact with RFID tags, the qualities of CMPs can be determined through their estimated dielectric properties. Theoretical formulation is provided, and numerical simulations are performed for optimal design of passive RFID tag antennas suitable for RFID sensors and for read-range calculations. In addition, a series of measurements is performed to measure read ranges of the passive RFID sensor system for an LWC as an example of CMPs, and these measured read ranges will be processed appropriately to inversely determine the dielectric constant of the LWC under test, which in turn provides information on its qualities. It is found that the novel RFID sensor can be employed to determine the dielectric properties of the LWC under test with reasonable accuracy.
The lightning return stroke current is an important parameter for considering the effect of lightning on power lines. In this study, a numerical method is proposed to evaluate the return stroke current based on measured electromagnetic fields at an observation point in the time domain. The proposed method considers all field components and the full wave shape of the current without the use of a special current model as a basic assumption compared to previous methods. Furthermore, the proposed algorithm is validated using measured fields obtained from a triggered lightning experiment. The results show a good agreement between the simulated field based on the evaluated currents from the proposed method and the corresponding measured field at a remote observation point. The proposed method can determine current wave shapes related to a greater number of lightning occurrences compared to the direct measurement of the current.
The problem of field focusing radiated onto a target location in an unknown scenario is considered. In particular, we devise an adaptive procedure in which first an image of the unknown region where the target point is located is formed via LSM. Then, the LSM result is used also to define the excitations coefficients for the array elements needed to focus the field. This novel approach to focusing is described and tested with numerical examples.
The adaptive linearly constrained minimum power (LCMP) beamformer can improve the robustness of the Capon beamformer. And quadratic constraints on the weighting vector of the LCMP beamformer can improve the robustness to pointing errors and to random perturbations in sensor parameters. But how to solve it and how to select the constraint parameters are its key problems. In this paper, the Lagrange multiplier method is proposed to solve the LCMP beamformer under quadratic inequality constraint (QIC). The problem of finding the optimal weight vector is solved, and the choice of the quadratic constraint parameter is analyzed and the selected bound is also given. Since the quadratic equality constraint (QEC) is stronger than the quadratic inequality constraint (QIC), the performance of the QECLCMP beamformer is more robust than that of the QICLCMP beamformer. Therefore, the QECLCMP beamformer is proposed and is solved effectively. Numerical examples attest the correctness and the efficiency of the proposed algorithms. And the results show that the QECLCMP beamformer has the advantage of overcoming the steering vector mismatch, namely the optimal negative loading has the preferable robustness.
For analyzing the electromagnetic problems with the fine structures in one or two directions, a novel weakly conditionally stable finite-difference time-domain (WCS-FDTD) algorithm is proposed. By dividing the 3-D Maxwell's equations into two parts, and applying the Crank-Nicolson (CN) scheme to each part, a four sub-step implicit procedures can be obtained. Then by adjusting the operational order of four sub-steps, a novel 3-D WCS-FDTD algorithm is derived. The proposed method only needs to solve four implicit equations, and the Courant-Friedrich-Levy (CFL) stability condition of the proposed algorithm is more relaxed and only determined by one space discretisation. In addition, numerical dispersion analysis demonstrates the numerical phase velocity error of the weakly conditionally stable scheme is less than that of the 3-D ADI-FDTD scheme.
In this work, we show how to manipulate the electromagnetic wave at will by using an indefinite medium with extremely strong anisotropy. The negative element in the indefinite permittivity tensor goes to the negative infinity while the positive element is equal to 1, which stretches the hyperbolic equifrequency contour into a straight line type. The direction of the Poynting vector and the wave vector is aligned by the straight line type equifrequency contour along the orientation of the extremely negative permittivity, thus control the wave propagation. The other permittivity of 1 makes the indefinite medium matched with the air. Moreover, because of the hyperbolic equifrequency contour, evanescent wave can also transmit in the indefinite medium under the propagation mode, implying the possibility of controlling an evanescent wave by this special indefinite medium. Simulations are performed to demonstrate the controlling performance and a potential design to realize such a medium by metamaterial with multilayered metal/dielectric structure. This work may supply a shortcut for those former devices based on the Transformation optics.
Radar imaging experiment of ground moving target --- a light rail-way train by Ku-band radar with two receiving channel is introduced. Both coherent and incoherent imaging as well as co-pol and cross-pol interferometric imaging were conducted with SAR amplitude images as well as interferometric --- phase images obtained. In the obtained SAR images, there are 24 stronger scattering centers which correspond to 24 bigger doors of the train. Along-track interferometric --- phase images indicate that the train travels at an increasing speed in one direction and at a decreasing speed in the opposite direction. Short Time Fourier Transform (STFT) is applied to the azimuthal signals to get the instant Doppler frequencies (IDFs), from which one can judge acceleration or deceleration status of the moving train. Electromagnetic scattering characteristics of the train are analyzed according to the SAR images. The estimated speed and length of the train are very well agreed with real situation.
In this paper, an inverse procedure algorithm is proposed in the time domain to evaluate lightning return stroke currents along a lightning channel using measured magnetic flux density at an observation point while the current velocity along a lightning channel is assumed to be a height dependent variable. The proposed method considers all field components and it can evaluate the full shape of currents and the current velocity at different heights along a lightning channel. Moreover, a sample of measured magnetic flux density from a triggered lightning experiment is applied to the proposed algorithm and the evaluated currents and current velocities are validated using a measured channel base current and magnetic flux density at another observation point.
In the field of automatic target recognition and tracking, traditional image metrics focus on single images, ignoring the sequence information of multiple images. We show that measures extracted from image sequences are highly relevant concerning the performances of automatic target tracking algorithms. To compensate the current lack of image sequence characterization systems from the perspective of the target tracking difficulties, this paper proposes three new metrics for measuring image sequences: inter-frame change degree of texture, inter-frame change degree of target size and inter-frame change degree of target location. All are based on the fact that inter-frame change is the main cause interfering with target tracking in an image sequence. As image sequences are an important type of data in the field of automatic target recognition and tracking, it can be concluded that the work in this paper is a necessary supplement for the existing image measurement systems. Experimental results reported show that the proposed metrics are valid and useful.
Localized surface plasmon resonance (LSPR) biosensors are employed to detect target biomolecules which have particular resonance wavelengths. Accordingly, tunability of the LSPR wavelength is essential in designing LSPR devices. LSPR devices employing silver nano-particles present better efficiencies than those using other noble metals such as gold; however, silver nano-particles are easily oxidized when they come in contact with liquids, which is inevitable in biosensing applications. To attain both durability and tunabilty in a LSPR biosensor, this paper proposes alumina (AL2O3) capped silver nano-disks. It is shown that through controlling the thickness of the cap, the LSPR resonance frequency can be finely tuned over a wide range; and moreover, the cap protects silver nano-particles from oxidation and high temperature.
From the point of view of mixed-mode scattering parameters, Smm, a two-port device can be excited using different driving conditions. Each condition leads to a particular set of input reflection and input impedance coefficient definitions that should be carefully applied depending on the type of excitation and symmetry of the two-port device. Therefore, the aim of this paper is to explain the general analytic procedure for the evaluation of such reflection and impedance coefficients in terms of mixed-mode scattering parameters. Moreover, the driving of a two-port device as a one-port device is explained as a particular case of a two-port mixed-mode excitation using a given set of mixed-mode loads. The theory is applied to the evaluation of the quality factor, Q, of symmetrical and non-symmetrical inductors.
A novel design of an electromagnetic bandgap (EBG) structure based on the uniplanar compact EBG (UCEBG) concept is proposed in this paper. The structure is realized by inserting split-ring slots inside two reversely connected rectangular patches, which is known as a split-ring slotted electromagnetic bandgap (SRS-EBG) structure. The bandgap properties of the EBG structure are examined by the suspended microstrip line and finite element methods (FEM). The achieved bandgaps have widths of 4.3 (59.31%) and 5.16 GHz (38.88%), which are centered at 7 and 13 GHz, respectively. The SRS-EBG is applied to enhance the performance of a single-element microstrip patch antenna (at 7 GHz) and a two-element array (at 13 GHz) configuration. A wider bandwidth is obtained with a better reflection coefficient level for the single element antenna; a reduction in mutual coupling of more than 20.57 dB is obtained for the array design. In both cases, the gain and radiation characteristics are improved. The results are verified by measuring the fabricated lab prototype, and a comparison with the computed results showed good agreement.
Automated and accurate classification of MR brain images is extremely important for medical analysis and interpretation. Over the last decade numerous methods have already been proposed. In this paper, we presented a novel method to classify a given MR brain image as normal or abnormal. The proposed method first employed wavelet transform to extract features from images, followed by applying principle component analysis (PCA) to reduce the dimensions of features. The reduced features were submitted to a kernel support vector machine (KSVM). The strategy of K-fold stratified cross validation was used to enhance generalization of KSVM. We chose seven common brain diseases (glioma, meningioma, Alzheimer's disease, Alzheimer's disease plus visual agnosia, Pick's disease, sarcoma, and Huntington's disease) as abnormal brains, and collected 160 MR brain images (20 normal and 140 abnormal) from Harvard Medical School website. We performed our proposed methods with four different kernels, and found that the GRB kernel achieves the highest classification accuracy as 99.38%. The LIN, HPOL, and IPOL kernel achieves 95%, 96.88%, and 98.12%, respectively. We also compared our method to those from literatures in the last decade, and the results showed our DWT+PCA+KSVM with GRB kernel still achieved the best accurate classification results. The averaged processing time for a 256x256 size image on a laptop of P4 IBM with 3 GHz processor and 2 GB RAM is 0.0448 s. From the experimental data, our method was effective and rapid. It could be applied to the field of MR brain image classification and can assist the doctors to diagnose a patient normal or abnormal in some degree.
This paper deals with a feasibility study for a System-on-Chip (SoC) mmwave radiometer devoted to space-based observation of solar flares and operating in the Ka-band. The radiometer has been designed in 250 nm SiGe BiCMOS process. The circuit integrates a three stages differential LNA with 37.2 dB gain and 4.8 dB noise figure at 36.8 GHz and a differential square-law detector based on HBTs, featuring a 96 mV/μW responsivity. The full radiometer achieves, potentially, a NETD of 0.1 K for 1 s integration time in Dicke mode. This work represents the first study of such an integrated instrument for Ka-band space-based observation of solar flares.
In this work, the propagation loss of three short range directive channels at 5.5 GHz is measured using different directive antennas and a Vector Network Analyzer (VNA). Results are given for a channel bandwidth of 300 MHz which will be the future channel bandwidth of IEEE 802.11 ac system. It has been noted that the multipath induced fading tends to have Normal Distribution at low distance between the transmitting and the reception antennas. At higher distances, it tends to have Normal distribution plus Rayleigh one. Channel Impulse response (CIR) is also measured indicating that the main contribution is due to the direct ray and the one reflected from the floor. The human being obstruction causes an extra propagation loss of 2 to 10 dB depending on its distance from the transmitting antenna.
A linearly constrained minimum variance (LCMV) antenna array beamformer using finite data samples suffers from slow convergence when the received array data contain the desired signal. It has been reported that signal blocking techniques speed up the convergence rate and increase the robustness of LCMV antenna array beamformers. However, the reason of this improvement has not been explored in the literature. Moreover, the existing formulas for the output signal-to-interference-plus-noise ratio (SINR) are too rough to realize the influence of signal blocking techniques on the performance. In this paper, we show that the correlation due to finite samples causes the redundant component (termed as the cross weight) embedded in the weight vector of a LCMV beamformer even if the signal sources and noise are independent. The cross power results from the cross weight degrades the performance when the sample size is small. In contrast, the cross weight and cross power can be fully eliminated when a signal blocking technique is used. The theoretical results presented in this paper provide a comprehensive description on the effectiveness and the price of using signal blocking for antenna array beamforming. Simulation results are also given for confirming the validity of the theoretical results.
The influence of atmospheric gases and tropospheric phenomena becomes more relevant at frequencies within the THz band (100 GHz to 10 THz), severely affecting the propagation conditions. The use of radiosoundings in propagation studies is a well established measurement technique in order to collect information about the vertical structure of the atmosphere, from which gaseous and cloud attenuation can be estimated with the use of propagation models. However, some of these prediction models are not suitable to be used under rainy conditions. In the present study, a method to identify the presence of rainy conditions during radiosoundings is introduced, with the aim of filtering out these events from yearly statistics of predicted atmospheric attenuation. The detection procedure is based on the analysis of a set of parameters, some of them extracted from synoptical observations of weather (SYNOP reports) and other derived from radiosonde observations (RAOBs). The performance of the method has been evaluated under different climatic conditions, corresponding to three locations in Spain, where colocated rain gauge data were available. Rain events detected by the method have been compared with those precipitations identified by the rain gauge. The pertinence of the method is discussed on the basis of an analysis of cumulative distributions of total attenuation at 100 and 300 GHz. This study demonstrates that the proposed method can be useful to identify events probably associated to rainy conditions. Hence, it can be considered as a suitable algorithm in order to filter out this kind of events from annual attenuation statistics.
A parametric analysis is performed for a wideband Archimedean spiral antenna in recognition of an emerging concept to integrate RFID along with several applications by using a single antenna. The antenna is fabricated using state-of-the-art inkjet printing technology on various commercially available paper substrates to provide the low-cost, flexible RF modules for the next generation of "green" electronics. The effects on electromagnetic characteristics of the planar Archimedean spiral antenna, due to the use of paper are investigated besides other parameters. The proposed antenna is evaluated and optimized for operational range from 0.8-3.0 GHz. It exhibits exceptional coverage throughout numerous RFID ISM bands so do for other wireless applications.
Aiming to efficiently overcome the acoustic refraction and accurately reconstruct the microwave absorption properties in heterogeneous tissue, an iterative reconstruction method is proposed for microwave-induced thermo-acoustic tomography (MITAT) system. Most current imaging methods in MITAT assume that the heterogeneous sound velocity (SV) distribution obeys a simple Gaussian distribution. In real problem, the biological tissue may have several different inclusions with different SV distribution. In this case, the acoustic refraction must be taken into account. The proposed iterative method is consisted of an iterative engine with time reversal mirror (TRM), fast marching method (FMM) and simultaneous algebraic reconstruction technique (SART). This method utilizes TRM, FMM and SART to estimate the SV distribution of tissue to solve the phase distortion problem caused by the acoustic refraction effect and needs little prior knowledge of the tissue. The proposed method has great advantages in both spatial resolution and contrast for imaging tumors in acoustically heterogeneous medium. Some numerical simulation results are given to demonstrate the excellent performance of the proposed method.
Koch-like fractal curve and Sierpinski Gasket are syncretized into a novel Sierpinskized Koch-like sided bow-tie (SKLB) multifractal in superior-inferior way. A K4S4 SKLB multifractal dipole fed by a linearly tapered microstrip Balun is designed, simulated, fabricated and measured. The well consistent results from measurement and experiment corroborate validity of design and the multifractal antenna's superiority and advantages over its monofractal counterparts in impedance, bandwidth, directivity, efficiency, and dimension. Six good matched bands(S11 ≤ -10 dB) with moderate gain (2.12 dBi-9.55 dBi) and high efficiency (87%-97%) are obtained within band 1.5 GHz-14.5 GHz, of which f1 = 1.92 GHz, f2 = 3.94 GHz, and f3 = 5.09 GHz are generally useful. The multibands are all almost omnidirectional or quasi-omnidirectional in H-plane (Phi=0°, XOZ) and doughnut-shaped or dented doughnut-shaped in E-plane (Phi = 90°, YOZ). So it is an attractive candidate for applications like PCS, IMT2000, UMTS, WLAN, WiFi, WiMAX and other fixed or mobile wireless multiband communication systems.
In this paper, a planar metallic nanostructure design, which supports two distinct Fano resonances in its extinction crosssection spectrum under normally incident and linearly polarized electromagnetic field, is proposed. The proposed design involves a circular disk embedding an elongated cavity; shifting and rotating the cavity break the symmetry of the structure with respect to the incident field and induce higher order plasmon modes. As a result, Fano resonances are generated in the visible spectrum due to the destructive interference between the sub-radiant higher order modes and super-radiant the dipolar mode. The Fano resonances can be tuned by varying the cavity's width and the rotation angle. An RLC circuit, which is mathematically equivalent to a mass-spring oscillator, is proposed to model the optical response of the nanostructure design.
The Doppler spectral characteristics of electromagnetic backscattered echoes from dynamic nonlinear surfaces of finite-depth sea is investigated with the second-order small-slope approximation (SSA-II). The revised nonlinear hydrodynamic choppy wave model (CWM) combining with an experiment-verified shoaling coefficient is utilized to model the finite-depth sea wave profiles, and the simulated surfaces of finite-depth sea show steeper crests and more flat troughs as depth decreases. First, Comparison of the Doppler spectra for linear sea surfaces and nonlinear choppy sea surfaces shows that nonlinear hydrodynamic effect greatly enhances the Doppler shift and the Doppler spectrum bandwidth, and the predicted results agree well with the rigorous numerical model data. The Doppler spectra of backscattered echoes from finite-depth sea with different depths are further evaluated. At small incident angles, the Doppler shifts and the spectra bandwidths are much lower for shallower sea, and the opposite situation can be gradually observed for increased incident angles. This indicates that the nonlinear wave-wave interactions among waves occur more frequently in finite-depth sea and the long waves will be suppressed while shorter wind waves will be boosted in shallower water. Moreover, the dependence of the Doppler spectral characteristics on polarization is also discussed.
A new technique for designing the substrate integrated waveguide (SIW) frequency-agile slot antenna is presented in this paper. Similar to the metallic waveguide counterpart, the SIW is a uniconductor guided-wave structure and inherently difficult in the electronically tunable applications. To solve this problem, a single slot etched on the top conductor layer of a conventional antenna is instead of two slots to construct an isolated area, which is convenient for the DC bias. The electric length of slots can then be adjusted through two shunt varactors welded near the center of slot. As such, a SIW frequency-agile slot antenna is realized and fabricated to cover the frequency of 2.30~2.74 GHz with different bias voltages. Experiments verify our theory analysis and design process. Then, a frequency-agile multibeam antenna is developed to cover several frequency bands while switching between four different radiation patterns pointing at different spatial locations for each frequency. It presents an excellent candidate for software and cognitive radio system applications.
The idea behind the coupling matrix identification is to find the coupling matrix corresponding to the measured or designed scattering characteristics of the microwave filter. The typical attitude towards coupling matrix parameter extraction is to use some optimization methods to minimize the appropriate cost function. In this paper we concentrate on the analytic solutions - how they may be found and their application in further optimization processes. In general case the suggested method generates complex-valued coupling matrix. For a special case of the filter without cross-couplings we give fast and simple recursive method of finding such complex-valued coupling matrix. The method is based on Laplace's formula for expanding the determinant. The complex-valued coupling matrix is used as a good starting point for the optimization methods to find the regular coupling matrix. The examples are presented showing that the optimization arrives to global minimum starting from real parts of complex-valued entries considerably more often than when the starting point is selected randomly.
The growing interest of Radar community in retrieving the 3D reflectivity map makes both polarimetric SAR interferometry and SAR tomography hot topics in recent years. It is expected that combining these two techniques would provide much better discriminating ability for scatterers lying in the same pixel. Generally, this is about reconstruction of scattering profiles from limited and irregular polarimetric measurements. As an emerging technique, Compressive Sensing (CS) provides a powerful tool to achieve the purpose. In this paper, we propose a l2,1 mixed norm sparse reconstruction method for jointly processing multibaseline PolInSAR data based on multiple measurement vector compressive sensing (MMV-CS) model, and also address the signal leakage problem with MMV-CS inversion by presenting a window based iterative algorithm. The results obtained by processing simulated data show that the proposed method possesses superior performance advantage over existing methods.
The higher order method of moments (HMOM) has been proposed to calculate the bistatic scattering from two-dimensional (2D) perfectly electric conducting (PEC) rough surface in this paper. The electric field integral equation (EFIE) is solved through the HMOM with the hierarchical higher order basis functions which are the modified Legendre polynomials. The non-uniform rational B-spline (NURBS) surface is applied to model the plane surface related to the rough surface. Validity of this approach is shown by comparing the bistatic scattering coefficient (BSC) to that of lower order MOM (LMOM) with the Rao-Wilton-Glisson (RWG) or rooftop basis function. This approach has fewer segments in the parametric directions than the LMOM with rooftop basis, and is more efficient for the fewer unknowns and requires less memory than the LMOM with RWG basis. Properties of EM scattering from a 2D Gaussian rough surface are also exhibited and analyzed.
In this manuscript, a novel multiport matching method is devised to directly maximize the mean capacity with rigorous consideration of the mutual coupling effects of the matching network. In the RF front end of the real communication circuits, the mutual couplings always exist. In this paper, 1) a theoretical capacity upper bound of the 2-by-2 MIMO system with a matching network using the water-filling as the power allocation rule is analytically derived for the first time, 2) the Genetic Algorithm is employed to optimize the parameters of the matching network for the maximization of the mean capacity, 3) a coupled microstrip lines structure is devised to implement the matching network of the real MIMO receiving circuits by this matching method. The numerical results in the last section demonstrate that an optimized matching network obtained using our novel MPM method is capable to enhance the performance of the MIMO systems in a range of different indoor environments. This verifies that our method is not only effective but also practical.
This study introduces an extended optimal filtering technique for adaptive-on-transmit radar based on the transmission of pseudorandom noise waveforms as a method to simultaneously achieve low sidelobe level and spectral purity without degrading the main peak of the cross-correlation function. The proposed method is an extended version of the classical optimal filtering technique, resulting in longer codes with three simultaneously improved features that usually work in trade-off: 1) the cross-correlation function (CCF) sidelobe level is reduced in direct proportion to the filter length, K; 2) the out-of-band spectral suppression is at least 40 dB for pseudorandom binary sequences (PRBS); and 3) the frequency spectrum tail presents a decay given by K-4, offering larger out-of-band frequency suppression. The proposed technique provides skewsymmetry to the input signal and is tested on PRBS, Barker, and Golay pair of complementary codes. The proposed codes are also demonstrated to be Doppler resistant and offer better multipath capability.
Air is not the only medium that can spread and can be used to detect speech. In our previous paper, another valuable medium - millimeter wave (MMW) was introduced to develop a new kind of speech acquisition technique [Li et al., Progress In Electromagnetics Research B, 9, 199-214, 2008]. Because of the special features of the MMW radar, this speech acquisition method may provide some exciting possibilities for a wide range of applications. In the proposed study, we have designed a new kind of speech acquisition radar system. The super-heterodyne receiver was used in the new system so that to mitigate the severe DC offset problem and the associated 1/f noise at baseband. Furthermore, in order to decrease the harmonic noise, electro-circuit noise, and ambient noise which were combined in the MMW detected speech, an adaptive wavelet packet entropy algorithm is also proposed in this study, which incorporates the wavelet packet entropy based voice/unvoiced radar speech adaptive detection method and the human ear perception properties in a wavelet packet time-scale adaptation speech enhancement process. The performance of the proposed method is evaluated objectively by signal-to-noise ratio and subjectively by mean-opinion-score. The results confirm that the proposed method offers improved effects over other traditional speech enhancement methods for MMW radar speech.
In this paper, novel Bowtie antennas which cover complete UHF RFID band (860-960MHz), fabricated on various ultra-low-cost substrates using state-of-the-art printing technologies are investigated as an approach that aims to accommodate the antenna during the package printing process whilst faster production on commercially available paper. The proposed antenna structures are evaluated in reference to circuit and field concepts, to exhibit extreme degree of functional versatility. These antennas are developed to cater the variations which appear in electromagnetic properties and thickness of paper substrate due to various environmental effects. Computed (simulated) and well-agreed measurement results confirm a superior performance of the tag modules while stepping towards next generation of ``green'' tags.
Submit
