The temperature performances of GaInNAs-based semiconductor devices, for next generation communication networks and photonic integrated circuits, are investigated. In particular, GaInNAs-GaInAs Multi Quantum Well active ridge waveguides, patterned with a periodic one-dimensional grating and an active defective region placed in the central layer, have been designed for efficient active optical switches and modulators. The switching mechanism was obtained around the Bragg wavelength λ≌1.2896 μm at room temperature T=298 K by properly designing the periodic grating and changing the injected current density from JOFF=0 mA/μm2 to JON=0.496 mA/μm2. The proposed device exhibits high performances in terms of crosstalk, contrast ratio, and modulation depth. The temperature performance of the proposed device is analyzed in the range T=298 K - 400 K, showing a good stability of the figures of merit: crosstalk CT, contrast ratio CR, and bandwidth Δλ. In particular, the CT varies at about 1.2 dB in the whole temperature range, whereas CR and Δλ experience, respectively, a maximum variation of 25% and 30% of their maximum values.
The compressed sensing (CS) based imaging methods for tomography SAR perform well in the case of large number of baselines. Unfortunately, for the current tomography SAR, the baselines are obtained from many multi-pass acquisitions on the same scene, which is expensive and can be severely affected by temporal decorrelation. In order to reduce the number of baselines, a novel strategy for tomography SAR imaging by introducing the block-sparsity theory into the imaging processing is proposed in this paper. Using neighboring pixels information in reconstruction, the proposed method can overcome the imaging quality limitation imposed by the low number of baselines. The results with simulation data under the additive gaussian noise case are presented to verify the effectiveness of the proposed method.
In this paper, the uniaxial anisotropic perfectly matched layer (UPML) absorbing boundary condition in unconditionally stable five-step locally one-dimensional finite-difference time-domain (LOD5-FDTD) method is deduced. The UPML absorbing boundary condition (ABC) is validated based on comparison with a simulation in larger domain (and thus without reflection) in the first test. Then using a sinusoidal source, target field phase distribution surrounded by the UPML-ABC is analyzed. The results further illustrate the stability and efficiency of the UPML absorbing boundary condition.
This paper presents the theoretical framework for a new technique in the field of linear antenna arrays with amplitude control called error coefficient matrix. First of all, the array factor is expressed as a summation of contribution from the elements of the array. It will be shown that for small errors in excitation amplitude, the error in the overall radiation pattern at a given angle is a summation of errors contributed by the individual elements of the array at that angle. An error coefficient matrix is proposed, and its properties are discussed in great detail. The accuracy of the proposed method is investigated for varying levels of errors in weights and for varying number of error elements, using Monte-Carlo simulation. Finally, the applications of this new technique in the field of antenna arrays are presented.
This paper reports the design and performance of a compact planar arrangement of concentric rings designed with defected ground plane. The radiating circular patch and ground plane of antenna are modified in several steps to achieve a broadband circularly polarized antenna. In each stage of modification, antenna is simulated by applying CST Microwave Studio simulator, and finally, a prototype is developed and tested in free space. The developed prototype efficiently operates at frequencies 2.34 GHz and 4.41 GHz, and provides an overall impedance bandwidth close to 2.31 GHz or 67.45% with respect to central frequency 3.425 GHz. This antenna provides nearly flat gain in the desired frequency band with maximum measured gain close to 2.94 dBi at frequency 3.02 GHz. It also provides circularly polarized radiations in the frequency bands extended from 2.67 to 3.05 GHz and 3.44 to 3.57 GHz. The co-polar and cross-polar radiation patterns of the antenna in azimuth and elevation planes are obtained at frequencies 2.316 GHz and 4.41 GHz. The proposed antenna can be used for mobile and lower bands of Wi-Max and UWB communication systems.
A compact microstrip antenna loaded with periodic patterns etched in the ground plane is proposed. The etched patterns are Jerusalem crosses which look the same as one of the common electromagnetic band gap structures, uni-planar electromagnetic band gap. In this paper, the dielectric backed with etched ground plane is analysed in terms of metamaterial. The permittivity and permeability are derived from the simulated reflection and transmission coefficients. Then a patch is stacked on the metasubstrate, and the antenna is designed to operate at 2.4 GHz. The proposed antenna has a small dimension in comparison to two other published compact antennas. Compared to the conventional patch antenna, the proposed antenna achieves a 68.38% miniaturization of the patch, and a 2.84 times impedance bandwidth broadening. Furthermore, the operating frequency of the proposed antenna can be tuned over a large range of frequencies by physically adjusting the length of the surrounding slots or by voltage adjusting of the voltage controlled tunable inductive elements. The proposed antenna is fabricated and measured. The measurement results are found to agree well with the simulation ones.
The effects of anisotropic turbulence on the wander and spreading of Gaussian-Schell model beams propagating in non-Kolmogorov marine-atmospheric channel are investigated. Expressions for beam wander and long-term beam spreading are derived in all conditions of marine-atmospheric turbulence. Our results indicate that the beam wander and spreading of Gaussian-Schell model beams are lower in the anisotropic turbulence than the beam in isotropic turbulence. This model can be evaluated ship-to-ship/shore optical laser communication system performance.
As an emerging wireless localization technique, the electromagnetic passive localization without the need of carrying any device, named device-free passive localization (DFPL) technique has drawn considerable research attentions. The DFPL technique detects the shadowed links in the monitored area and realizes localization with the received signal strength (RSS) measurements of these links. However, the current RSS-based DFPL techniques have two major challenges: one is that the RSS signal is particularly sensitive to noise and another one is that it needs the large number of nodes to provide enough RSS measurements of wireless links to guarantee good performance. To overcome these problems, in this paper we take advantage of compressive sensing (CS) theory to handle the spatial sparsity of the DFPL problem for reducing the number of nodes required by DFPL systems and exploit the frequency diversity technique to deal with the problem of the RSS sensitivity. Meanwhile, inspired by the fact that the target's movement is continuous and the target's current location must be around the last location, we add prior information on the support region into the sparse reconstruction process for enhancing sparse reconstruction performance. The effectiveness and robustness of the proposed scheme are demonstrated by experimental results where the proposed algorithm yields substantial improvement for localization performance.
The ever-growing usage of new information and communication technology devices by different age groups is followed with public concerns of exposure induced biological effects. The aim of this paper is to assess and compare personal exposure levels to electromagnetic fields of wireless communications for different age-groups, including children, under the same exposure conditions.Assessment of personal exposure of the following age groups: 08-15, 16-20, 21-35 and 36-60 years old is conducted with sophisticated tri-axial E-field frequency selective personal exposure meters, enabling measurements of electric field strength in 14 pre-defined frequency bands in the range of 80 MHz-6 GHz. Participants are selected to be with similar social conditions and occupation, including children, students and administrative employees. The measurements were conducted in typical residential environments collecting 161 280 measurement samples. The mean value of power density of different wireless technologies is presented for each age-group, including the contribute of specific wireless technology to the total personal exposure. The highest personal exposure values per frequency band for all age groups are in GSM and Wi-Fi 2G. The results show a difference in mean power density levels between different age groups for the same exposure environment. Ultimately, all measured values were far below international safety guidelines and exposure limits.
The image produced by metamaterial slabs is discussed in a number of papers in terms of the electromagnetic field distribution. In this paper a procedure is proposed to efficiently calculate the image of an extended object placed behind a metamaterial slab as it will be seen by an observer - which can greatly differ from the image formed by the intensity maxima. The first step of the procedure retrieves the dispersion relation of a periodic metamaterial slab from the S parameters calculated with full wave electromagnetic simulation of the unit cell. The second step of the procedure utilizes the retrieved dispersion relation in the transfer matrix method to calculate the image of a point source placed behind the metamaterial slab as a function of the observation angle. Knowing the image distance of the point source for all observation angles, the image of an extended object can be efficiently calculated. The procedure is demonstrated with a Fishnet type metamaterial.
Antenna arrays for direction finding (DF) are usually designed and tested in controlled environments such as anechoic chambers. However, antenna pattern may change significantly when antennas are placed in their operational environment. In such perturbing close context, the antennas calibration validity becomes a major issue which can lead to DF performance degradation and costly recalibration process. This paper presents an innovative design and implementation of a non-disturbing solution for quasi-real time antenna monitoring. The proposed system is based on optically modulated scattering (OMS) technique. Its capacity to detect the presence of various types of obstacles, which perturb significantly the antenna radiation pattern, is evaluated. A relation between monitoring mode and DF mode measurement signals is established. Finally, a design and sizing of the overall system is proposed.
Stepped frequency ground penetrating radar (SFGPR) has received increasing attention in the field of ground penetrating radar technology due to its superiority in the detection performance. Compressed sensing (CS) SFGPR imaging reconstruction method can not merely reduce the measured imaging data volume, but also reconstruct target image with less sidelobe. However, the imaging algorithm using CS approach will lose efficacy in strong clutter environment. To solve this problem, a CS SFGPR imaging reconstruction method combined with subspace projection clutter suppression approach is proposed in this paper. First, all frequency domain data at each measurement position are reconstructed from reduced frequency measurements via sparse reconstruction technique. Then subspace projection ground clutter suppression technique is used to suppress the strong ground clutter. Finally, orthogonal matching pursuit (OMP) algorithm is utilized to reconstruct the underground target image. Synthetic and experimental data processing results have verified the effectiveness and accuracy of the proposed imaging method.
We systematically study the Cherenkov optical emission by a nonrelativistic charge uniformly moving in parallel to surface of a photonic crystal by the FDTD simulations. It is found that a near-static structure of field oscillations produced by a discontinuity of dielectric permittivity in the surface of photonic lattice is generated. Such oscillations have large amplitude in the Cherenkov group cone and generate a number of well defined spectral resonances corresponding to eigenmodes of the photonic grid. The dynamics and field properties in photonic lattice with random vacancies are investigated too. It is found that even at medium level of a random perturbation the field shape shows the structural stability of the Cherenkov emission field in a photonic crystal.
An analytical formulation has been developed to evaluate the shielding effectiveness (SE) of two coplanar rectangular metallic enclosures with acircular aperture excitedby an internal electric dipole source. The formulation consists of three parts: First, the near-field electromagnetic interference (EMI) of the electromagnetic leakage from the aperture is represented by the electric dipole in one enclosure. Then, the aperture equivalent magnetic and electric dipole moments are calculated according to the Bethe's small aperture coupling theory. Finally, the electric field of the other enclosure is derived by using the equivalent magnetic dipole field, equivalent electric dipole field and the corresponding enclosure's Green's functions in the two fields. In this formulation, the electric field of the enclosure can be expressed as a function of the observation point, the aperture's center point, source point, shape of the aperture and the enclosure's conductivity. The formulation then is employed to analyze the effect of the above factors on the SE. The analytical results have been successfully compared with the full-wave simulation software Computer Simulation Technology (CST) from 0.3~2.4 GHz.
In this paper, a novel numerical temporal convolution method is presented to calculate the convolutions between the retarded-time potentials and temporal basis functions (or its integration, derivation) in marching-on-in-time (MOT) solver. This approach can smooth and eliminate the singularity of integrated functions by variable substitution. It can also effectively control the precision of numerical quadratures over the surface of the source distribution. Thus it is suitable for more types of temporal basis functions including non-piecewise polynomial functions. Numerical results demonstrates that this improved method can ensure the accuracy and late time stability of the MOT solver with different types of temporal basis functions.
Target-supporting metal pylon predominantly contributes to background scattering in radar cross section measurement. The separation of scattering from the target and background demands stable background scattering. However, target translation creates variations in metal pylon deformation and changes its scattering, which yields errors in background separation. Analyzing the relationship between the structural parameters of metal pylon and the error caused by its deformation is necessary to reduce errors. A simplified mapping of the relationship is deduced according to the mechanical and electromagnetic theories involved. The approach combines geometrical theory of diffraction for pylon scattering and numerical integration in calculating the deflection of metal pylon to determine the variation of metal pylon scattering, and calculates error in the circle fitting caused by the variation. Simulations with commercial software are employed to verify the efficiency of the numerical model. Although it is slightly contaminated by target-pylon interaction, the approach is 800 times faster than the software simulation. An example of optimization and analysis is provided to demonstrate the trends of optimum structural parameters and fitting error within different pylon weight limits. Such an example proves that the approach can overcome the deficiency of traditional analysis which separately assesses the mechanical and RCS performances of metal pylon.
In this article, we study the far-field trapping behavior of dielectric nanospheres with diameter of 200 nm by utilizing a plasmon enhanced far-field nanofocusing lens. Based on our high effectnanofocusing circular plasmonic lens, such a far-field plasmonictrap is constituted by illuminating with a laser to form a sharper focus (subwavelength) due to a constructive interference of cylindrical surface plasmon wave. The nanoparticles can be steadily trapped in the far-field focal region (4.4λ) with an optical force to nanonewton (-4.76 nN) order, and the required optical power is less than 0.5 W. Compared with other surface plasmon tweezers, the proposed far-filed plasmonic tweezers can not only avoid physical contact with the trapped particles to prevent contamination and reduce thermal damage effects due to metal absorption, but also enable the easy trapping and manipulation of nanosizedielectric particles owing to nanonewton scale forces.
This work proposes a modified Volterra-based series suitable for the low-pass equivalent behavioral modeling of radio frequency power amplifiers (RFPAs) for wireless communication systems. In a Volterra-based series, the instantaneous sample of the complex-valued output envelope is calculated by the sum of products that depend on the instantaneous and past (up to the memory length M) samples of the complex-valued input envelope. To comply with the constraints imposed by the bandpass behavior of RFPAs, the derivation of the proposed model starts from a general Volterra-based series given by the sum of contributions that include exactly one complex-valued information multiplied by a varying number (ranging from zero up to one less than the polynomial order truncation P) of real-valued amplitude components. A first reduction in the number of parameters is then performed by retaining only the one and two dimensional contributions. A second reduction in the number of parameters is finally achieved by introducing a third truncation factor S. In fact, if this additional truncation factor S is set equal to P-1, the proposed model contains all the two dimensional contributions. Moreover, when S is set equal to 0, the proposed model reduces to the largely adopted generalized memory polynomial (GMP) model. The proposed Volterra-based series retains the important property of being linear in its parameters and, in comparison with previous Volterra-based approaches, can provide a better compromise between number of parameters and modeling error. The proposed model is then compared with the GMP model in a scenario of same number of parameters. When applied to the modeling of input-output data obtained from a circuit-level description of a GaN HEMT Doherty PA excited by a LTE OFDMA signal, the proposed model reduces the normalized mean square error (NMSE) by up to 3.4 dB. Additionally, when applied to the modeling of input-output data measured on a GaN HEMT class AB PA excited by a WCDMA signal, the proposed model reduces the NMSE by up to 1.3 dB.
The radial suspension force with a new structure of a bearingless induction motor based on single winding is researched. Compared to the conventional double-winding structure of bearingless induction motor, torque and suspension forces are produced with a single-winding system. Bearingless induction motor is a nonlinear, multi-variable and strong coupling system. It is difficult to obtain an accurate mathematical model on the radial suspension force. So the research method about radial suspension force of a single-winding bearingless induction motor is proposed, based on two fundamentals. Firstly, a new structure and operation principle of a single-winding bearingless induction motor is introduced. Then the air-gap flux density distribution of the single-winding bearingless induction motor is analyzed in detail. The accurate mathematical model of radial suspension force is deduced by using two-fundamental wave method and Maxwell's stress tensor method. Secondly, according to the transient analysis of the single-winding bearingless induction motor which its speed is 6000 r/min, by finite element method (FEM), the component of radial suspension force in x-axis and y-axis is obtained by FEM simulation analysis. The calculation results used by FEM and the theoretical calculation results of mathematical model used by two fundamental wave method have been compared. Thirdly, an experimental prototype is produced, and suspension experiment of prototype is carried out. Then measured result of radial suspension force is analyzed. The analysis results show that the prototype has excellent suspension characteristics, and the mathematical model of radial suspension force based on two-fundamental wave method has low error and high precision.
To visualize eddy current distribution (ECD) of an arbitrarily shaped coil arranged parallel to a moving conductor slab, an exact theoretical solution is derived using an analytical method based on the double Fourier transform method. The arbitrarily shaped coil is regarded as a plane coil of a single turn, and both DC and AC excitation currents can be applied. Furthermore, ECD charts are obtained when the conductor slab is moving. We calculate some examples with respect to a circular coil, rectangular coil, and triangular coil and show the effect of coil excitation frequency and speed of the conductor on ECDs. Results show that the eddy current generated in the moving conductor slab is composed of current induced by the excitation frequency and conductor speed.