The Radio Frequency Identification (RFID) applications are growing rapidly, especially in the UHF frequency band that is being used in inventory management. Passive UHF tags are preferred for these applications. In this paper, RFID reader-to-reader interference is analyzed. A model to estimate the minimum distance between readers to achieve a desired probability of detection in real multipath environments is derived and compared to the ideal case (AWGN channel). Diversity techniques to combat multipath and interference effects are proposed and studied.
Flat left-handed metamaterial (LHM) lens can generate appropriate focusing spot in biological tissue as required in microwave tumor hyperthermia treatment. By using single flat LHM lens to concentrate microwave in a mass of tissue covered by water bolus, microwave hyperthermia scheme is proposed for superficial tumor hyperthermia. The power distribution in tissue is simulated by finite-difference time-domain method, and the thermal pattern is calculated by solving the bio-heat transfer equation. It is demonstrated that, by using a flat LHM lens of thickness of 4 cm to concentrate microwave of 2.45 GHz, a temperature above 42oC can be achieved and maintained in one hour in a tissue region of about 1.0 cm in width and 1.2 cm in depth in tissue with the source amplitude of 43.40 V/cm, which is suitable for superficial tumor hyperthermia. By adjusting the position of microwave source, the heating zone in tissue can be adjusted in both the lateral and depth direction in tissue. The effects of fat layer and water bolus on the performance of hyperthermia are investigated as well.
This paper deals with the experimental validation of an effective near-field-far-field transformation technique with helicoidal scanning particularly suitable for electrically long antennas, whose validity has been numerically assessed in a previous authors' paper. Such a technique relies on the results relevant to the nonredundant sampling representations of the electromagnetic fields and makes use of an optimal sampling interpolation algorithm, which allows the reconstruction of the near-field data needed by the near-field-far-field transformation with cylindrical scan. The use of a prolate ellipsoid instead of a sphere to model an elongated antenna allows one to consider measurement cylinders with a diameter smaller than the antenna height, thus reducing the error related to the truncation of the scanning zone. Moreover, a significant reduction of the needed near-field data is also obtained. The comparison of the far-field patterns reconstructed from the acquired helicoidal measurements with those obtained from the data directly measured on the classical cylindrical grid assesses the effectiveness of the near-field-far-field transformation using this innovative scanning technique. At last, its validity is further confirmed by the very good agreement with the direct far-field measurements.
A numerical method is developed to calculate/simulate the separation of non-metallic inclusions from an aluminum melt by using a strong magnetic field (e.g., 10 Tesla) with high gradient generated via a superconducting magnet. The cases with and without imposed DC current on liquid aluminum in a cylindrical channel are discussed and compared. The migrating velocities of the non-metallic inclusions in an aluminum melt are calculated through force analysis and Navier-Stokes equations. In addition, the trajectories and removal efficiencies of the inclusions are evaluated. It is found that particle trajectories are influenced by the imposed flow rate and inclusion particle size. In addition, the removal efficiency is improved significantly, especially for small inclusions, e.g., <10 μm, by an imposed DC current on liquid aluminum in the high gradient area of a magnetic field.
Although classical imaging is limited by the Rayleigh criterion, it has been demonstrated that subwavelength imaging of two point-like scatterers can be achieved with probing sensors arrays, even if the scatterers are located in the far field of the sensors. However, the role of noise is crucial to determine the resolution limit. This paper proposes a quantitative study of the influence of noise on the subwavelength resolution obtained with the DORT-MUSIC method. The DORT method, French acronym for decomposition of the time reversal operator, consists in studying the invariants of the time reversal operator. The method is combined here with the estimator MUSIC (MUltiple SIgnal Classification) to detect and image two close metallic wires. The microwaves measurements are performed between 2.6 GHz and 4 GHz. Two wires of λ/100 diameters separated by λ/6 are imaged and separated experimentally. To interpret this result in terms of noise level, the analytical expression of the eigenvectors of the time reversal operator perturbed by the noise is established. We then deduce the noise level above which the subwavelength resolution fails. Numerical simulations and experimental results validate the theoretical developments.
In this paper, one of the subspace signal processing methods, namely time reversal multiple signal classification (TR-MUSIC), is firstly employed for electromagnetic subsurface detection where the multilayered dyadic Green's function is used. Therewith, one obtains the improved location and superresolution imaging for underground detecting application. The imaging pseudo-spectrum is accordingly defined for both the echo-mode and transmit-mode TR-MUSIC methods, by analyzing the obtained multistatic response matrix. Based on the theoretical formula, we carry out the numerical simulation using the half-space dyadic Green's function in noisy scenario. The results show that the MUSIC imaging algorithm achieves the enhanced resolution and the transmit-mode method gives more robust output when performance comparison of the four methods is made, therefore indicate the TR-MUSIC could be a good candidate for subsurface detection.
Using ultra-wide band (UWB) microwave pulse for breast cancer detection has been greatly investigated recently since it does not impose the patient to any harmful radiation and the implementation is relatively cheaper than other methods such as MRI or X-ray. An issue in UWB imaging of breast cancer is the strong backscatter from the breast skin which is in orders of magnitude larger than the pulse backscattered from the tumor and should be eliminated before processing the signal for the tumor detection and imaging. At present no existing method can effectively remove this artifact without introducing corruption to the tumor signature. In this paper, a novel method to eliminate this artifact is proposed which employs a frequency domain model to isolate and remove skin related information from the signal. This method is compared with the existing methods of the skin artifact removal in different scenarios. The results show that the new method can overcome the shortcomings of the previous methods and improve the detection of the tumor in the sense of the tumor to clutter response ratio.
In this work, a far field imaging model based on the array structure of positive- and negative-refractive-index media and modulation subwavelength-gratings is firstly presented and is named as the multilayer far field superlens (MLFSL). This new lens is capable of producing optical images by enhancing evanescent waves to the far field. The principle of MLFSL is discussed in detail, and the necessary and sufficient condition for designing MLFSL is obtained. Simultaneously, off-axis illumination technology is introduced to MLFSL system to further improve super-resolution, and the transfer matrix which contains the incidence angles is obtained. The results demonstrate that, compared with other far field superlens, the subwavelength resolution of MLFSL has been enhanced. Such remarkable imaging capability of MLFSL promises new potential for nanoscale imaging and lithography.
Electromagnetic field will scatter when incident on boundaries separating media with different constitutive parameters. This paper demonstrates the use of a differential operator on recorded scattered waves to reveal the shape of the boundary. The method is noninvasive and is composed of three phases. First, the area of interest is illuminated and the resulting scattered electromagnetic fields are recorded. In the 2nd phase, the captured data is numerically reverse simulated in time to reconstruct the field distribution in the region of interest. Finally, the differential imaging operator is applied on the reconstructed wave field, creating an image delineating the boundary where scattered fields originated. This technique does not require the knowledge of location of the boundaries nor the nature of the discontinuity in the constitutive parameters. The proposed imaging system is scalable, whereby modification of the source signal, recorder sampling, and numerical model allows imaging objects of smaller dimensions and creation of sharper and more accurate images.
On the basis of analyzing the principle of multicarrier DS-CDMA, we propose a novel multiband complex wavelet based multicarrier DS-CDMA system in this paper by using the optimized multiband complex wavelet as multicarrier basis function. The system bit error rate (BER) performance is investigated over Nakagami-m Rayleigh fading channel. Without any cyclic prefix (CP), the proposed system can avoid the decrease of spectrum efficiency and data rate of conventional multicarrier DS-CDMA with CP. Meanwhile, the space diversity combining (SDC) technique based on multi-antenna receiver is employed to improve the system performance further. By the mathematical derivation, the BER analysis of the system with or without SDC is given in detail. Theoretical analysis and simulation results show that the proposed multicarrier system outperforms the conventional multicarrier DS-CDMA system and real wavelet packet based multicarrier DS-CDMA system due to the superior properties of the optimized multiband complex wavelet. Especially, the application of SDC technique can effectively improve the system ability against spatial fading and interferences, and thus the superior performance is obtained.
Gaussian process (GP) regression is proposed as a structured supervised learning alternative to neural networks for the modeling of CPW-fed slot antenna input characteristics. A Gaussian process is a stochastic process and entails the generalization of the Gaussian probability distribution to functions. Standard GP regression is applied to modeling S11 against frequency of a CPW-fed secondresonant slot dipole, while an approximate method for large datasets is applied to an ultrawideband (UWB) slot with U-shaped tuning stub --- a challenging problem given the highly non-linear underlying function that maps tunable geometry variables and frequency to S11/input impedance. Predictions using large test data sets yielded results of an accuracy comparable to the target moment-method-based full-wave simulations, with normalized root mean squared errors of 0.50% for the slot dipole, and below 1.8% for the UWB antenna. The GP methodology has various inherent benefits, including the need to learn only a handful of (hyper) parameters, and training errors that are effectively zero for noise-free observations. GP regression would be eminently suitable for integration in antenna design algorithms as a fast substitute for computationally intensive full-wave analyses.
A low profile double-layer polarizer structure is presented for planar patch antennas to obtain circular polarization in 3.5 GHz WiMAX band (3.4-3.6 GHz≈5.7% bandwidth). Each polarizer layer is composed of 45º tilted metallic strips on a printed circuit. A bandwidth widening is obtained due to a significant reduction of the distance between polarizer and patches. The associated effects from the interaction of the two structures have been studied. A 2x2 array prototype has been implemented and measured, with a 8% average bandwidth in reflection and dual linear/circular polarization.
This paper deals with the modeling of parallelepipedic magnets of various polarization directions. For this purpose, we use the coulombian model of a magnet for calculating the magnetic potential in all points in space. Then, we determine the three components of the magnetic field created by a parallepiped magnet of various polarization direction. These three components and the scalar magnetic potential are also expressed in terms of fully analytical terms. It is to be noted that the formulas determined in this paper are more general that the ones established in the literature and can be used for optimization purposes. Moreover, our study is carried out without using any simplifying assumptions. Consequently, these expressions are accurate whatever the magnet dimensions. This analytical formulation is suitable for the design of unconventional magnetic couplings, electric machines and wigglers.
In this paper, reducing Specific Absorption Rate (SAR) with ferrite sheet attachment is investigated. The finite-difference time-domain method with Lossy-Drude model is adopted in this study. The methodology of SAR reduction is addressed and then the effects of attaching location, distance, size and material properties of ferrite sheet on the SAR reduction are investigated. Computational results show that the SAR averaging over 10 gm was better than that for 1 gm and SAR reduction of 57.75% is achieved for SAR 10 gm. These results show the way to choose a ferrite sheet with the maximum SAR reducing effect for phone model.
Time modulated linear antenna arrays consisting of printed dipoles above a ground plane are simulated using the finite-difference time-domain (FDTD) method. The FDTD method brings great convenience to the investigation of the time domain responses of the time modulated arrays. In conjunction with the near-to-far field transformation in time domain, the far-field transient response can be computed to explain the physical essence of different time sequences. By employing the discrete Fourier Transform (DFT) and the frequency domain near-to-far field transformation, the radiation patterns at the frequencies of interest are obtained and are compared with the measured results. Simulation results show that the FDTD method is an effective and accurate approach for the full-wave simulation of time modulated antenna arrays.
A broadband inverted E-H shaped microstrip patch antenna is proposed and experimentally investigated. The antenna employs novel E-H shaped patch with L-probe feed technique. Prototype of the proposed antenna has been fabricated and measured for electromagnetic analysis including the impedance bandwidth, radiation pattern, and antenna gain. The designed antenna has a dimension of 80 mm by 50 mm, leading to broad bandwidths covering 1.76 GHz to 2.38 GHz. Stable radiation patterns across the operating bandwidth are observed. In addition, a parametric study is conducted to facilitate the design and optimization process.
We are developing an analytical model for the design of the folded waveguide traveling wave tube (FWTWT). This analytical model provides the physical view for rapid design optimization of the FWTWT. The design and analysis of the FWTWT using the spatial harmonics method of the TE10 mode of the EM wave are presented. An X-band FWTWT is used to verify this method. The normalized dispersion and beam line equations are used to simplify the design process so that the FWTWT can be designed to operate at any desired frequency. The small signal gain of an FWTWT is calculated by using Madey's theorem. The results of this analysis are compared with the numerical single particle simulation carried out using MATLAB. The results are in excellent agreement. The Madey's theorem can be used to provide a potential indication of the gain magnitude of the FWTWT.
In this paper we propose a sparse antenna array with nine elements for the integrated system of communication and direction finding. The main idea is that the sparse antenna array, whose element spacing is relatively larger than half wavelength, are divided into six two-element subarrays to transmit multi-beam. According to the spatial correlation characteristics of multi-beam, a packet exciting method employing multi-carrier Orthogonal Frequency Division Multiplexing (OFDM) signal is designed to modulate the directional information into the signal space of subcarriers. In this way, a receiver with a single antenna can accomplish communication and direction-finding function by demodulation received signal. For the direction finding algorithm of the sparse antenna array, an approximate algorithm is designed to resolve the ambiguity problem based on the Chinese remainder theorem. Simulation results show that the proposed sparse antenna array can be applied to the integrated application of communication and direction finding.
The di®raction of a plane electromagnetic wave by an ideal metallic sphere (Mie's theory) is investigated by a new method. The method represents the charge disturbances (polarization) by a displacement field in the positions of the mobile charges (electrons) and uses the equation of motion for the polarization together with the electromagnetic potentials. We employ a special set of orthogonal functions, which are combinations of spherical Bessel functions and vector spherical harmonics. This way, we obtain coupled integral equations for the displacement field, which we solve. In the non-retarded limit (Coulomb interaction) we get the branch of "spherical" (surface) plasmons at frequencies ω = ωpsqrt(l/(2(l/ + 1)), where ωp is the (bulk) plasma frequency and l = 1, 2,.... When retardation is included, for an incident plane wave, we compute the field inside and outside the sphere (the scattered field), the corresponding energy stored by these fields, Poynting vector and scattering cross-section. The results agree with the so-called theory of "effective medium permittivity", although we do not start the calculations with the dielectric function. In turn, we recover in our results the well-known dielectric function of metals. We have checked the continuity of the tangential components of the electric field and continuity of the normal component of the electric displacement at the sphere surface, as well as the conservation of the energy flow and re-derived the "optical theorem". In the limit of small radii (in comparison with the electromagnetic wavelength) the sphere exhibits a series of resonant absorptions at frequencies close to the plasmon frequencies given above. For large radii these resonances disappear.
This paper deals with the potential of ultra-wideband (UWB) microwave imaging for the detection and localization of breast cancer in its early stages. A method is proposed for locating tumors which is based on the signal time-of-flight backscattered by the tumor. Time-of-flight is detected using a wavelet transform algorithm. The feasibility of the method has been investigated by means of simulated results using Finite-Difference Time-Domain (FDTD) and experimental results with a UWB radar and a phantom.
A series of curved microstrip antennae with defected ground structure for multiband are proposed，which are more smaller, conveniently conformal, wider radiation beam and suitable for WLAN terminal for different environment. The relation between the main geometry parameters and the antennas' characters are studied with the cavity model method and EM simulation, and the optimum size antenna is achieved later. If keeping the other parameters but increasing the curving angle α, the return loss is almost good at f=2.45 GHz, but poor at f=5.25 GHz and 5.8 GHz. After slight tuning the key parameters, these curved antennae all can work at f=2.45 GHz, 5.25 GHz and 5.8 GHz, and their patterns in the plane that is vertical to the curve axes become more wider or even omni-directional with the curving angle α increasing, which are verified by experiment, their measured gain are 2 dB--6.3 dB.
The Linear Frequency Modulation (LFM) waveform is the most commonly and extensively used signal in practical radar system. However a compressed LFM signal at the receiver will produce the first sidelobe at a level of -13 dB to the peak of the main lobe. A weighting function is needed to apply in order to reduce the sidelobes. However, the penalty of mismatch loss is clearly evident. It may reduce output SNR, typically by 1 to 2 dB. Every single dB of additional SNR can have great effects in reducing false alarm rates in target detection applications. In an effort to achieve low autocorrelation sidelobe level without applying weighting function, Non-Linear Frequency Modulation (NLFM) signal has been investigated. This paper describes the sidelobe reduction techniques using simple two-stage FM waveform, modified two-stage FM waveform and tri-stage FM waveform. Simulation results of the proposed NLFM signal are presented. Sidelobe reduction of more than -19 dB can be achieved by this design without any weighting technique applied.
The edge-based finite element method is used for the solution of scattering problems. The factorized sparse inverse preconditioner is considered for the conjugate gradient iterative solution of the large sparse linear systems generated from the finite element method. The efficiency of the proposed preconditioner is illustrated on a set of model problems in the final of the paper. The results suggest that the sparse inverse preconditioner is very efficient for the solution of large-scale electromagnetic scattering problems.
A simple half oval patch antenna is proposed for the active breast cancer imaging over a wide bandwidth. The antenna consists of a half oval and a trapezium, with a total length 15.1 mm and is fed by a coaxial cable. The antenna performance is simulated and measured as immersed in a dielectric matching medium. Measurement and simulation results show that it can obtain a return loss less than -10 dB from 2.7 to 5 GHz. The scattered field detection capability is also studied by simulations of two opposite placed antennas and a full antenna array on a cubic chamber.