The Split-Field Finite-Difference Time-Domain (SFFDTD) formulation is extended to periodic structures with Kerr-type nonlinearity. The optical Kerr effect is introduced by an iterative fixed-point procedure for solving the nonlinear system of equations. Using the method, formation of solitons inside homogenous nonlinear media is numerically observed. Furthermore, the performance of the approach with more complex photonic systems, such as high-reflectance coatings and binary phase gratings with high nonlinearity is investigated. The static and the dynamic behavior of the Kerr effect is studied and compared to previous works.
In this paper, electromagnetic scattering problems are analyzed using an electric field integral equation (EFIE) formulation that is based on loop-star basis functions so as to avoid low-frequency instability problems. Moreover, to improve the convergence rate of iterative methods, a block matrix preconditioner (BMP) is applied to the EFIE formulation which is based on loop star-basis functions. Because the matrix system resulting from the conventional method of moments is a dense matrix, a sparse matrix version of each block matrix is constructed, followed by the inversion of the resultant block sparse matrix using incomplete factorization. Numerical results show that the proposed BMP is efficient in terms of computation time and memory usage.
We numerically analyze a broadband plasmonic outline bowtie antenna over a large parameter space by means of finite element method with three-dimensional calculation. The antenna is composed of a pair of triangular gold with outline shape placed in close proximity to each another. We show how the structural parameters affect the antenna resonance conditions, such as peak resonances wavelengths, electric field intensities, propagation properties, component field and total field distributions, charge densities and electrical filed stream lines at spectral points of interest. In addition, the characteristics of transmittance spectral of a periodic antenna array corresponding to the bonding mode and anti-bonding mode are investigated as well. Simulation results show that it is possible to tune an antenna with a constant length over a wide spectral range (ranging in 0.3-5.0 μm or more range) while maintaining a constant antenna dimension, reduce the antenna footprint by a factor of 4.98, and increase the gap enhancement by 23%. This article has been removed from the website on January 3, 2013, because it has been found to violate plagiarism rule of our journal.
We report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Polyfluorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5-10 nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence efficiency increases by doping with MNPs into emissive layer. Different dopant concentrations varied from 0.4% to 2% were monitored. It was observed that the electroluminescence increases up to 1% v/v doping ratio. The luminance of OLEDs increased from 15.000 cd/m² to 24.000 cd/m² in comparison pristine device with 1% MNP doped device.
Diagonal loading has been regarded as an efficient manner to tackle the finite sample effect or the steering vector imprecision problem on adaptive array beamforming. However, the reason of the robustness improvement by the loading factor is still unknown and rarely discussed. In this paper, we consider the finite sample effect and derive the approximated output signal-to-interference-plus-noise ratio (SINR) of minimum variance distortionless response (MVDR) beamformers with diagonal loading. The obtained SINR expression is more explicit and compact than the existing formulas in the literature. Based on the theoretical results, we investigate the effects of a loading factor on the output SINR of MVDR beamformers. The theoretical analysis shows the effectiveness of diagonal loading on alleviating finite sample effect. Moreover, the price of using diagonal loading is also discussed. Simulation results are presented for confirming the validity of the research work.
In this paper, we present a method for detecting anti-tank or anti-personnel landmines buried in the ground. A set of data generated by a ground penetrating radar is processed to remove the surface reflection and clutter, yielding signals for possible landmines. In order to detect landmines in the signals, features are computed and compared against a database, which contains those of various landmines. Three features are proposed to use; principal components from principal component analysis, Fourier coefficients and singular values from singular value decomposition method, each of which is chosen to represent each landmine uniquely. Detection is performed using Mahalanobis distance-based method. Examples show that the proposed method can effectively detect landmines in various burial condition.
In this paper a robust technique for the design of high performance directional couplers is proposed. It combines the advantages of wiggly coupled lines and slot-coupled lines but overcomes their main limitations. The key to this novel technique is a new corrugated slot that allows perfect compensation of the even and odd mode phase velocities and can be easily designed using Bloch-Floquet theory, yielding outstanding performance. To demonstrate the validity of the proposed technique, the design of two different wideband directional couplers is presented. The first design consists of a 10 dB asymmetric directional coupler with a one decade bandwidth (1.2-12 GHz) that exhibits a coupling accuracy of 10±0.6 dB, a return loss better than 23 dB and an isolation better than 28 dB across the complete frequency band. The second design consists of a symmetric quadature hybrid that operates over the complete UWB band (3.1 to 10.6 GHz) showing an amplitude and phase imbalance between the output ports lower than ±0.5 dB and ±0.7°, respectively.
Conventional equivalent source reconstruction methods (SRM) require both phase and amplitude information of the acquired field data. However, there are situations where the phase information is not available or impractical to obtain. Hence, the development of SRM using phaseless fields is important. In this paper, a novel iterative SRM based on phaseless electric fields is presented. The reconstructed equivalent current source can be electric, magnetic current, or both. They can fit the physical geometry of the radiator. Electric field integral equation (EFIE) is employed to build the relationship between the reconstructed current source and measured fields. It can precisely reproduce the original 3D radiation pattern with very good accuracy. To investigate the robustness and accuracy of the proposed approach, both strong and weakly-directional radiators are benchmarked.
A novel miniaturized dual-band bandstop filter (DBBSF) is proposed by using the T-shaped defected microstrip structures (DMSs) and the U-shaped defected ground structures (DGSs) in this paper. The layout of the dual-band bandstop resonator (DBBSR) is presented at first. The dual stopbands of the DBBSR can be separately controlled since the mutual coupling of the defected structures is negligible. The working principles of the T-shaped DMS and U-shaped DGS are then provided and their design process is summarized. On the basis of the DBBSR, the design methodology of the compact DBBSF is proposed before its design procedures are presented. Following the design procedures, a second-order and third-order DBBSFs with Butterworth frequency response are designed, simulated and fabricated. The equivalent circuit models of the designed filters are also developed. Full-wave simulation results of the fabricated DBBSFs are in good agreement with the circuit simulation and measurement results, validating our proposed design methodology.
In this paper the numerical and experimental investigations of four-port circulator utilizing longitudinally magnetized cylindrical ferrite coupled lines (CFCL) section are presented for the first time. In comparison to earlier models the proposed structure of circulator utilizes multilayer magic-T junction cascaded with cylindrical ferrite section of π/4 Faraday angle. The advantage of utilization of cylindrical section over the planar one is the possibility to design shorter ferrite junctions ensuring lower insertion losses. Moreover, the multilayer magic T-junction allows to improve performance of the proposed circulator by omitting the bandwidth limitation which exists in commonly used hybrid couplers with air-bridges. In the analysis of CFCL junction the full wave hybrid approach combining finite difference frequency domain method with method of moments and mode matching technique is applied. The planar feeding structures of circulator are designed with the use of commercial software. The simulated results of the entire circulator are compared with the measurement results of the fabricated prototype and a good agreement is achieved.
There are serious electromagnetic compatibility (EMC) problems in electric vehicles. In order to explain and solve them, a systematic method to analyze conducted interferences of the electric drive system is shown in this paper. This method represents the effects of the power battery which is the most different part between electric drive systems used in electric vehicles and other cases. Also, Equivalent models are established from power electronics devices to the entire system by considering both the working mechanism and stray parameters. Firstly, insulated gate bipolar transistor (IGBT) and inverter are studied as the main interference source. A new expression is put forward to estimate the frequency domain features of the inverter disturbances. Then, power battery and electric motor are discussed as the main propagation paths. Their high frequency circuit models are given with parameters obtained from tests and measurements. Finally, the system model is established. The system interferences are analyzed to get their generation causes, influence factors and frequency domain characteristics. Comparisons between simulations and experiments verify the correctness of the models and the method.
In this paper a novel approach is proposed to solve the issue of the absolute accuracy required by the most of passive chip-less RFID sensors. To this purpose the sensor information is encoded as the phase difference between two signals, one of the two acting as the reference signal for the other one. First the tag receives a carrier at frequency f0, then two equal signals at frequency 2 f0 are generated by means of a diode-based frequency doubler and a power divider. At this point one of the two signals is phase-shifted using a passive sensing element. Finally the 2 f0 signals are re-irradiated by exploiting two orthogonally polarized antennas. With this approach the sensor information can be extracted by a suitable reader equipped with two complex (I/Q) receivers. The idea will be first developed from a theoretical basis and then verified with several particular cases. The novel tag concept is compatible with paper substrate and ink-jet printing technology since antennas diodes and passive sensing elements, i.e. all the main tag components, are going to be developed on paper materials.
Microwave induced thermo-acoustic tomography (MITAT) has become a keen research topic in recent years due to its great potential in early breast cancer detection. A secure and accurate MITAT system has been established. Some experiments have been made to demonstrate the performance of the MITAT system. Based on an experiment using phantom, some quantitative features of the system have been obtained. Some imaging experiments with real human breast cancer tissues are performed to demonstrate its effectiveness and the potential in clinical diagnosis. Images with both high contrast and fine spatial resolution are achieved by using time reversal mirror (TRM) technique in the imaging processing. Moreover, comparisons between the MITAT system result and an ultrasound imaging system result are made. From the comparison, the MITAT system shows its advantages of better contrast over the ultrasound imaging system. The system and the experiments in this paper verify the mechanism of MITAT for breast cancer detection and provide a prototype basis for clinical practice.
Synthetic Aperture Radar is well known for producing a radar image of the ground, so it can be used for detecting on-the-ground object which is interesting for some applications. A possible application can be Foreign Object Detection (FOD), which is an important issue in aviation safety. A ground-based Circular Bistatic Synthetic Aperture Radar (Circular-BiSAR) is introduced in this paper. The circular movement makes it more practical while the bistatic configuration offers some advantages. Wideband Linear Frequency Modulated (LFM) chirp pulses are employed here, for transmission and reception of reflection pulses to and from the under test object. A simulated model is developed for the system which analyzes the transmitting, receiving, Doppler and LFM signals by considering the distances and movement of antennas. A prototype system is launched, and some experiments are done to detect and localize various objects based on their reflection properties of microwaves. A processing algorithm is proposed in this paper to confirm the detection. The results show that the proposed system can detect and localize on-the ground objects with as small a dimension as 2 cm height and 2 cm diameter located several metres away.
We present the design, fabrication and measurment of a dual-resonant broadband terahertz (THz) matamterial based on a modified split-ring resonator (MSRR) structure. The proposed MSRR is constructed by connecting the inner split ring with the outer split ring of adjacent cell. Transmission and reflection characteristics of the proposed structure are simulated using Ansoft HFSS, and the permittivities show negative values in 0.492-0.693 THz and 0.727-0.811 THz bands. The designed sample is fabricated on a gallium arsenide layer, and experiments are performed in Terahertz Time-Domain Spectroscopy. Measured transmission characteristics agree well with the simulations.
Two fusion strategies for target recognition using multi-aspect synthetic aperture radar (SAR) images are presented for recognizing ground vehicles in MSTAR database. Due to radar cross-section variability, the ability to discriminate between targets varies greatly with target aspect. Multi-aspect images of a given target are used to support recognition. In this paper, two fusion strategies for target recognition using multi-aspect SAR images are proposed, which are data fusion strategy and decision fusion strategy. The recognition performance sensitivity to the number of images and the aspect separations is analyzed for those two target recognition strategies. The two strategies are also compared with each other in probability of correct classification and operating efficiency. The experimental results indicate that if we have a small number of multi-aspect images of a target and the aspect separations between those images are proper, the probability of correct classification obtained by the two proposed strategies can be advanced significantly compared with that obtained by the method using single image.
A dual-band dual-element multiple-input-multiple-output (MIMO) antenna system with enhanced isolation is proposed. The MIMO antenna system is based on printed 4-shaped antenna elements. Dual band isolation is achieved by using an array of printed capacitively loaded loops (CLLs) on the top side of the board for high band isolation improvement and a complementary CLL structure on the GND plane of the antenna for lower band isolation improvement. The lower band of operation covers 827-853 MHz and the higher band covers 2.3-2.98 GHz. Two prototypes were investigated to access the effect of the isolation mechanism. Measured isolation improvement of 10 dBs was observed in the lower operating band while the improvement in the higher band was approximately 2.5 dBs. The isolation improvement was at the expense of 5% reduction in efficiency. The measured gain patterns as well MIMO figures of merits such as the correlation factor, TARC and MEG were investigated as well.
Asymptotic limits of Negative Group Delay (NGD) in linear causal media satisfying Kramers-Kronig relations are investigated. Even though there is no limit on the NGD-bandwidth product of a linear medium, it is shown that the out-of-band to center frequency amplitude ratio, or out-of-band gain, increases with the NGD-bandwidth product, and is proportional to the amplitude of undesired transients when waveforms with defined "turn on/off" times propagate in the media. The optimal causal dispersion characteristic exhibiting NGD is obtained through Kramers-Kronig relations, which maximizes the NGD-bandwidth product as a function of the out-of-band gain. It is shown that the NGD-bandwidth product has an upper asymptotic limit proportional to the square root of the logarithm of the maximum out-of-band gain. The derived NGD-bandwidth upper asymptotic limit of the optimally engineered causal dispersion characteristic is validated with two examples of physical media, a Lorentzian dielectric medium, and an artificially fabricated loaded transmission line medium.
A despeckling technique based on multiple image reconstruction and selective 3-dimensional filtering is proposed. Multiple SAR images are reconstructed from a single SAR image by employing compressive sensing (CS) theory. In order to obtain multiple images from single SAR image, multiple subsets of pixels are selected from input SAR image by imposing restriction that each subset has at least 20% different pixels than any other subset. These subsets are taken as measurement vectors in CS framework to obtain multiple SAR images. A despeckled image is obtained by employing selective 3-dimensional filtering to multiple reconstructed SAR image. The proposed technique is tested on single look complex TerraSAT-X data set, and experimental results exhibit that the proposed technique outperformed benchmark despekling methods in terms of visual quality and despeckling quality metrics.
In this paper, we propose a new approach to generate quadrupling-frequency optical millimeter-wave (mm-wave) signal with carrier suppression by using two parallel Mach-Zehnder modulators (MZMs) in Radio-over-fiber (RoF) system. Among the numerous properties of this approach, the most important is that a filterless optical mm-wave at 60 GHz with an optical sideband suppression ratio (OSSR) as high as 40 dB can be obtained when the extinction ratio of the MZM is 25 dB. Simplicity and cost-effectiveness have made this approach a compelling candidate for future wave-division-multiplexing RoF systems. Theoretical analysis is conducted to suppress the undesired optical sidebands for the high-quality generation of frequency quadrupling mm-wave signal. The simulation results show that a 60 GHz mm-wave is generated from a 15 GHz radio frequency (RF) oscillator with an OSSR as high as 40 dB and an radio frequency spurious suppression ratio (RFSSR) exceeding 35 dB without any optical or electrical filter when the extinction ratio of the MZM is 25 dB. Furthermore, the effect of the non-ideal RF-driven voltage as well as the phase difference of RF-driven signals applied to the two MZMs on OSSR and RFSSR is discussed and analyzed. Finally, we establish a RoF system through simulation to verify the transmission performance of the proposed scheme. The Q-factor performance and eye patterns are given.
A novel generalized design procedure of broadband planar baluns based on wire-bonded multiconductor transmission lines (MTL) is presented hereby based on analytical equations. The proposed balun consists of two parts. The first one is an in-phase power divider, which equally splits the input power through its two outputs. The later are two MTLs with wire bonding between alternate conductors configured to introduce +90 and -90 degrees phase shift respectively, so that the balanced output signal has a 180 degree phase difference. In that sense, new closed-form design equations in order to calculate the design parameters of both multiconductor elements are obtained. These equations allow the proper dimensions of both MTLs to be computed irrespective of both the number of conductors and the coupling factor, and therefore, to determine the performance of the balun. The design procedure for wire-bonded MTL baluns has been assessed by means of full-wave electromagnetic simulations and by experimental work. In addition, the very good agreement between the theoretical results and measurements makes possible to define a time-saving design methodology.
A scalar potential formulation for a uniaxial anisotropic medium is succinctly derived through the exclusive use of Helmholtz's theorem and subsequent identification of operator orthogonality. The resulting formulation is shown to be identical to prior published research, with the notable exception that certain scalar potential fields not considered in previous work are rigorously demonstrated to be unimportant in the field recovery process, thus ensuring uniqueness. In addition, it is revealed that both a physically expected and unexpected depolarizing dyad contribution appears in the development. Using a Green's function spectral domain analysis and subsequent careful application of Leibnitz's rule it is shown that, for an unbounded homogeneous uniaxial medium, the unexpected depolarizing dyad term is canceled, leading to a mathematically and physically consistent and correct theory.
We report on the design, simulation and characterization of a solid-state W-band in-phase power-combined frequency tripler. In order to increase the output power of the frequency tripler without sacrificing efficiency and bandwidth, two mirror-image tripler circuits with four UMS® Schottky varistor diode chips are designed and mounted in a waveguide block, which includes a compact double-probe power divider at the input waveguide and a Y-junction power combiner at the output waveguide, respectively. Each circuit chip features four anodes on a 50 mil thick Rogers RT/duroid 5880 substrate. The tripler has 1.2~3.8 % conversion efficiency measured across the 75~110 GHz band when driven with 24 dBm of input power at room temperature. With the input power of 27 dBm, 5.5~11 dBm of saturated output power is produced over 75~110 GHz. Suppression of undesired harmonics is greater than 17 dB.
Magnetic antennas are suitable in short range medical in-body applications because they are less perturbed in the presence of the human tissues comparing to electrical antennas. After a preliminary study on magnetic antennas designed separately at 40 MHz with a matching system, a link budget between a spiral coil ingestible capsule transmitter antenna and a square coil onbody receiver antenna has been established in the presence of the human body. The efficiency (ratio of received power to transmitted power) of the magnetic induction link through a homogeneous human body (muscle) is equal to 0.6 % when the TX (transmitter) capsule is in front of the RX (receiver) antenna. If the transmission channel is a three-layered human body (muscle / fat / skin) the performances of the inductive link can be enhanced and the efficiency reaches 0.8 %. These performances can be improved (up to 1 %) when the dimensions of the receiver antenna increase. Consequently, the power consumption can be reduced and hence the battery life of the wireless capsule increases. Additionally, when the TX antenna is located randomly at an arbitrary orientation and position, the efficiency of the magnetic induction link can be improved by orienting the RX antenna parallel and perpendicularly to the human body surface.
We show that a metal can be turned into a broadband and omnidirectional absorber by coating a purely-dielectric thin layer of grating. An optimal design for such an absorber is proposed by putting a dielectric slot waveguide grating (SWG) on the metallic substrate. The SWG consists of two germanium nanowires (Ge NWs) separated by a sub-100 nm slot in each period. Average absorption reaches 90% when the incident angle varies between 0° and 80° over a broad wavelength range from 300 nm to 1400 nm. Multiple optical mechanisms/effects, namely, diffraction, waveguiding in the high-index Ge NWs and low-index air slot, Fabry-Perot resonances as well as surface plasmon polaritons (SPPs), are identified to govern the absorption characteristics of the present absorber. The designed absorber with such a dielectric grating is easier to fabricate as compared with other absorbers with metallic structures, and has potential applications in e.g. solar cells and photodetectors.
A hierarchical interpolative decomposition multilevel fast multipole algorithm (ID-MLFMA) is proposed to handle multiscale, dynamic electromagnetic problems. The hierarchical scheme to conduct the ID skeletonization and to implement the matrix vector multiplication is discussed. A strategy to improve the efficiency of ID skeletonization is developed. The hierarchical ID-MLFMA are investigated by numerical experiments on complex targets, demonstrating the capability of the hierarchical ID-MLFMA.
The conventional integrated lens antennas (ILAs) for beam steering suffer from internal reflections that deteriorate the scanning properties. The internal reflections are known to affect side lobes, cross-polarisation level, input impedance of the feed, and mutual coupling. In this paper, ILAs are designed to exhibit very low reflection loss, i.e., to minimize the internal reflections. Wide ranges of realistic relative permittivities of the lens and of the feed element directivities are considered. It is shown that with any permittivity and with any feed directivity it is possible to design the lens shape in such a way that the reflection loss is low, for moderate beam-steering angles, without resorting to a complicated matching layer. The gain, directivity, beam-width, and the resulting distance between the feed elements are compared for all the designed lenses.
In order to perfectly match arbitrary frequency-dependent complex load impedances at two uncorrelated frequencies, a novel coupled-line impedance transformer without transmission-line stubs is proposed in this paper. This transformer mainly features small size, wide bandwidth, simple analytical design method, and easy planar implementation. The transformer simply consists of a coupled-line section and an additional transmission-line section. Due to the usage of a coupled-line section, the theoretical synthesis of the proposed transformer becomes very simple when compared with previous transformers and the total size of the planar circuit without deterioration of operating bandwidth becomes small. Furthermore, several numerical examples are presented to demonstrate the flexible dual-frequency matching performance. Finally, the profile of matching frequency-dependent complex load impedance at two arbitrary frequencies has been examined by simulation and measurement of two microstrip generalized T-junction power dividers. Good agreement between the calculated results and measured ones justifies this proposed transformer and the design theory.
Statistical modeling of Synthetic Aperture Radar (SAR) images is of great importance for speckle noise filtering, target detection and classification, etc. Moreover, it can provide a comprehensive understanding of terrain electromagnetics scattering mechanism. Over the past three decades, many sophisticated models have been developed for SAR images, such as Rayleigh, Gamma, K and G, etc. The G° distribution is a special form of the G model, which can model the speckle fluctuations of many classes of objects like homogeneous, heterogeneous and extremely heterogeneous ones, and is widely used in SAR images interpretation. However, as many improvements have been performed on SAR sensors, the traditional parameter estimation methods of the G° distribution may be not sufficient, notably in high resolution SAR images. They cannot arrive at a solution frequently when modeling regions in high resolution SAR images, especially the extremely homogeneous regions. In order to deal with this problem, this paper proposes an improved parameter estimation scheme of the G° distribution, which combines the classical moment estimation with the mellin transform. To quantitatively assess the fitting precision of the proposed method, we adopt the Kullback-Leibler (KL) distance, Kolmogorov-Smirnov (KS) test and Mean Square Error (MSE) as similarity measurements. The advantage of this proposed parameter estimation method becomes evident through the analysis of a variety of areas (ground, vegetation, trees and buildings) in two high resolution SAR images.
We combine experimental electrorotation data and the numerical analysis of the electrorotation chamber and cell to electrically characterize the Saccharomyces cerevisiae yeast budding cell cycle and to obtain the electrical parameters of the cell. To model the yeast cell we use spherical and doublet-shaped geometries with a four layered structure: cytoplasm, membrane, inner and outer walls. To derive the geometrical and electrical parameters of the yeast model we use the finite element method to calculate the yeast rotational velocity spectrum and apply the least-square method to fit the calculated values to experimental data. We show that the calculated yeast electrorotation spectra undergo significant changes throughout its budding cycle and that the calculated spectra fit experimental data obtained for 0% (start) and 50% representative budding stages very well. The analysis also shows the small variation of the rotation crossover frequency within a full span of the yeast growth cycle. As an application of this work, we apply the Maxwell-Wagner formalism to obtain the dielectric spectra of truly synchronized yeast suspensions.