This paper proposes a robust Computer-Aided Design (CAD) tool for an Ultra-Wideband (UWB) antenna system which successfully integrates the design of the transmitting antenna, the receiving antenna and the shaping of the transmitted pulse. The distinctive features of this tool include: the efficient characterization of transfer function in terms of an analytical model, the effective evaluation from system point of view and the simultaneous optimization of multiple objectives. Using this tool, an automatic and efficient design can be realized to deliver the UWB antenna system upon the optimal performance.
Modulation methods such as homodyne and heterodyne detections are employed in A-SNOM in order to eliminate serious background effects from scattering fields. Usually, the frequency-modulated detection signal in apertureless scanning near-field optical microscopy (A-SNOM) is generally analyzed using a simple dipole-interaction model based only on the near-field interaction. However, the simulated A-SNOM spectra obtained using such models are in poor agreement with the experimental results since the effects of background signals are ignored. Accordingly, this study proposes a new phenomenological model for analyzing the A-SNOM detection signal in which the effects of both the dipole-interaction and the background fields are taken into account. It is shown that the simulated A-SNOM spectra for 6H-SiC crystal and polymethylmethacrylate (PMMA) samples are in good agreement with the experimental results. The validated phenomenological model is used to identify the experimental A-SNOM parameter settings which minimize the effects of background signals and ensure that the detection signal approaches the pure near-field interaction signal. Finally, the phenomenological model is used to evaluate the effects of the residual stress and strain in a SiC substrate on the corresponding A-SNOM spectrum.
The modified Watson transform is applied to the Mie series for the electromagnetic wave transmitted into the double negative cylinder due to high frequency plane wave incidence The Debye series expansion is adapted to the transmission coefficients to reveal the transmission mechanism at high frequency. The first term of the Debye series is examined. Two kinds of geometrical shadow regions and two kinds of geometrically lit regions are shown to exist. The field formation mechanisms in these regions are indicated. Several differences between a double positive cylinder and a double negative cylinder are determined. The field computations are performed in the geometrical shadow and the geometrically lit regions for the first term of the Debye series. The residue series and steepest descent computations are shown to be in good agreement with the Mie series computations.
In this paper a semi-analytical representation of the coupling impedance between coils composed of filamentary turns located between two layered media is provided on the basis of the spectral expansion of the fields involved in the system. Both media are composed of several layers of homogeneous materials characterized by their physical properties occupying, respectively, a half-space bounded by a plane. The domain in the middle, where the coils are placed, has vacuum properties. The development is focused on misaligned circular coils placed in parallel planes with respect to the media boundaries. Two different behavioral descriptions have been considered: first, the system is made up entirely of magnetic insulators and the coupling impedance is therefore purely inductive; second, at least one medium is an electrical conductor and, as a consequence, an additional resistive component emerges when the coupling impedance is evaluated. In the latter case, the coupling impedance exhibits a frequency dependence due to the dispersive effects associated with the induced currents generated in the conductive media. The model developed is verified by means of a comparison between numerical and experimental results.
Light scattering from small spherical particles has applications in a vast number of disciplines including astrophysics, meteorology optics and particle sizing. Mie theory provides an exact analytical characterization of plane wave scattering from spherical dielectric objects. There exist many variants of the Mie theory where fundamental assumptions of the theory has been relaxed to make generalizations. Notable such extensions are generalized Mie theory where plane waves are replaced by optical beams, scattering from lossy particles, scattering from layered particles or shells and scattering of partially coherent (non-classical) light. However, no work has yet been reported in the literature on modifications required to account for scattering when the particle or the source is in motion relative to each other. This is an important problem where many applications can be found in disciplines involving moving particle size characterization. In this paper we propose a novel approach, using special relativity, to address this problem by extending the standard Mie theory for scattering by a particle in motion with a constant speed, which may be very low, moderate or comparable to the speed of light. The proposed technique involves transforming the scattering problem to a reference frame co-moving with the particle, then applying the Mie theory in that frame and transforming the scattered field back to the reference frame of the observer.
A WiMedia compliant CMOS RF power amplifier (PA) for ultra-wideband (UWB) transmitter in the 3.1 to 4.8 GHz band is presented in this paper. The proposed two-stage PA employs a cascode topology on the first stage as driver while the second stage is a simple common source (CS) amplifier. In order to improve the efficiency and output power, the output impedance of the driver amplifier (first stage) is optimized so that it falls on the source-pull contours of the second stage amplifier. On-wafer measurement on the fabricated prototype showed a maximum power gain of +15.8 dB, 0.6 dB gain flatness, +11.3 dBm of output 1 dB gain compression and up to a maximum of 17.3% power added efficiency (PAE) at 4 GHz using a 50 Ω load termination, while consuming only 25.7 mW from a 1.8 V supply voltage. Measurement results obtained are used to create a non-linear powerdependent S-parameter (P2D) model for wideband input and output matching optimizations and co-simulations with the UWB modulated test signals. Using the created P2D model, the PA achieved a maximum output channel power of +3.48 dBm with an error vector magnitude (EVM) of −23.1 dB and complied with the WiMedia mask specifications.
For multi-channel SAR system, since the minimum antenna area constraint is eliminated, wide swath and high resolution SAR image can be achieved. However, compared to mono-channel SAR system, there exist many deleterious factors in multi-channel SAR system which significantly degrade the quality of SAR image. In this paper, all the deleterious factors in the system are analyzed and classified according to their impact on the SAR imaging processing, in addition an new array error estimation method is presented. The validity of the proposed method is verified by experimental results of measured Tri-channel SAR data.
A highly miniaturized 2.45/5.7 GHz dual-band bandpass filter is presented in this paper. It shows that the proposed filter which combines different sizes of open-loop resonators can excite two desired passbands. With the meandered technology and fractal geometry, the overall size is extremely compact compared with the published dual-band bandpass filters. Furthermore, the skirt selectivity of the proposed filter with two transmission zeros locating at both sides of the passbands is much improved. The rejection of the spurious response from 6.7 GHz to 14.5 GHz is successfully suppressed to the level lower than -15dB. The occupied area of the proposed filter is 9.8×8.7 mm2. The measurement is in good agreement with the simulation
Recent research on the array geometrical configuration shows that the two L-shaped array (TLSA) has a lower Cramer-Rao Low-Bound (CRLB) of two-dimensional (2-D) directions-of-arrival (DOAs) estimation than other array configurations. However, in this array configuration, there are some problems to note: i) three electric angles are independently obtained from three uniformly linear subarrays on three axes, so they must be matched before solving elevation and azimuth angles from them; ii) Similar to other array geometries, the effect of mutual coupling in the TLSA on the estimation performance cannot be ignored; and iii) the conventional elevation estimators may encounter estimation failure. In this paper, we develop a new TLSA-based 2-D DOAs estimation algorithm. The key points of this paper are: i) using some particularly selecting matrices, a trilinear model is constructed to compensate the effect of mutual coupling on three subarrays. In addition, the steering vector is restored using the trilinear alternating least square method; ii) 2-D DOAs are estimated from the properly chosen elements of the restored steering vector to avoid pairing parameters and the severe performance degradation resulted from the failure in pairing; and iii) a new elevation estimator is designed to avoid estimation failure. Simulation results are presented to validate the performance of the proposed method.
A theoretical study of optical properties of phase shift defects in one-dimensional asymmetrical photonic structures consisting of two rugate segments with different periodicities at both normal and oblique incidence is presented. Using the propagation matrix method we numerically calculated transmittance spectra, defect wavelengths, energy density distributions, and group velocities for TE and TM waves, respectively. Our study shows that by adjusting the periodicity of one rugate segment, the defect wavelengths can be shifted toward either a shorter wavelength or a longer wavelength. The differences of the energy density distributions of TE and TM waves at different angles of incidence are explained with the help of group velocity. Effects of the change of the period of one rugate segment on the peak energy densities of defect modes and minimum group velocities at different angles of incidence are also investigated.
The characteristics of guided modes in the four-layer slab waveguide containing chiral nihility core have been investigated theoretically. The characteristic equation of guided modes is derived. The dispersion curves, energy flux and normalized power of guided modes for three cases of chiral metamaterial parameters are presented. Some abnormal features are found, such as the existence of fundamental mode and surface wave mode, unusual dispersion curves, positive energy flux in the chiral nihility core, and zero power at some normalized frequencies.
In this paper a new method based on the complex images technique has been presented to efficiently compute the Green's functions required in a Mixed Potential Integral Equation (MPIE) analysis of a periodic structure located in a layered medium. This method leads to a closed-form representation for these slowly convergent series valid for sub-wavelength as well as super-wavelength cell sizes for all source point to field point distances. Comparison between the results obtained by the proposed method with ones obtained from other numerical approaches verifies its accuracy. Fast convergence, simple final form and versatility of the proposed method are its main advantages which make it suitable for the analysis of the periodic structures using the integral equation techniques.
We report on free space transmission experiments carried out on stacked split ring resonator (SRRs) arrays operating at microwave frequencies. We start from the case of a single frequency selective surface which exhibits a rejection at the SRR resonance frequency. By stacking SRR arrays in the propagation direction, we then show experimentally the possibility to induce a transmission band just below this resonance frequency. Full wave analysis shows the role played by the longitudinal and transverse coupling effects in the electromagnetic properties of such bulk metamaterials, with the appearance of a transmission band resulting from an artificial magnetic activity.
Compared with MPI, OpenMP provides us an easy way to parallelize the multilevel fast multipole algorithm (MLFMA) on shared-memory systems. However, the implementation of OpenMP parallelization has many pitfalls because different parts of the MLFMA have distinct numerical characteristics due to its complicated algorithm structure. These pitfalls often cause very low efficiency, especially when many threads are employed. Through an in-depth investigation on these pitfalls with analysis and numerical experiments, we propose an efficient OpenMP parallel MLFMA. Three strategies are proposed in the parallelization, including: 1) the choice of OpenMP schedule manners; 2) loop reorganization for far-field interaction in the MLFMA; 3) determination of a transition level. Numerical experiments on large scale targets show the proposed OpenMP parallel scheme can perform as efficiently as the MPI counterpart, and much more efficiently than the straightforward OpenMP parallel one.
This paper is devoted on the characterization method of RF/digital PCB interconnections for the prediction of the high-speed signal transient responses. The introduced method is based on the use of the interconnection line RLCG-model. Theoretical formulae enabling the extraction of the electrical per-unit length parameters R, L, C and G in function of the interconnection line physical characteristics (width, length, metal conductivity, dielectric permittivity ...) are established. Then, by considering the second order approximation of the interconnection RLCG-model transfer matrix, the calculation process of the transient responses from the interconnection system transfer function is originally established. To demonstrate the relevance of the proposed model, microwave-digital interconnection structure comprised of millimetre microstrip line driven and loaded by logic gates which are respectively modelled by their input and output impedances was considered. Then, comparisons between the SPICE-computation results and those obtained from the proposed analytical model implemented in Matlab were made. As results, by considering a periodical square microwave-digital excitation signal with 2 Gbits/s rate, transient responses which are very well-correlated to the SPICE-results and showing the degradation of the tested signal fidelity are observed. The numerical computations confirm that the proposed modelling method enables also to evaluate accurately the transient signal parameters as the rise-/fall-times and the 50% propagation delay in very less computation time. For this reason, this analytical-numerical modelling method is potentially interesting for the analysis of the signal integrity which propagates in the high-speed complex interconnection systems as the clock tree distribution networks. In the continuation of this work, we would like to apply the proposed modelling process for the enhancement of signal quality degraded by the RF/digital circuit board interconnection where the signal delays and losses became considerably critical.
The paper describes the modelling of the average rainfall rate distribution measured at different locations in South Africa. There are three major aspects this paper addresses: to develop a rainfall rate model based on the maximum likelihood method (ML); to develop contour maps based on rainfall rate at 0.01% percentage of exceedence; and re-classification of the ITU-R and Crane rain zones for the Southern Africa region. The work presented is based on five-minute rainfall data converted to one-minute equivalent using a newly proposed hybrid method. The results are mapped and compared with conventional models such as the ITU-R model, Rice-Holmberg, Moupfouma and Crane models. The proposed rainfall rate models are compared and evaluated using root mean square and chi-square (χ2) statistics. Then re-classification of the rain zone using ITU-R and Crane designations is suggested for easy integration with existing radio planning tools. The rainfall rate contour maps at 0.01% percentage of exceedence are then developed for South Africa and its surrounding islands.
To investigate the effects of pulsed electromagnetic field (PEMF) with high electric field intensity on bone formation in murine osteoblast-like MC3T3-E1 cells, proliferation, alkaline phosphotase (ALP) activity, mineralized nodule formation, Collagen Type I (COL-I) and core-binding factor (Cbf)a1 mRNA expression, and bone morphogenetic protein (BMP)2/4 and mothers against decapentaplegic (Smad)1/5/8 protein expression were examined in cultured MC3T3-E1 cells after exposure to PEMF at the field intensities of 0kV/m, 50kV/m or 400kV/m for 400 consecutive pulses daily for 7 consecutive days. After 50 kV/m of PEMF exposure, none of the above parameters of MC3T3-E1 cells changed significantly when compared to the control groups. However, the proliferation, ALP activity and mineralized nodule formation of MC3T3-E1 cells in 400 kV/m PEMF exposure groups decreased significantly although COL-I and Cbfa1 mRNA expression and BMP2/4 and Smad1/5/8 protein expression did not change. The PEMF we used at high electric field intensity suppressed proliferation, differentiation and mineralization of MC3T3-E1 cells in culture and appeared to be harmful for bone formation.
This paper focuses on the noise and vibrations of induction motors. It proposes an analytical method to distinguish the phenomenon responsible on the magnetic noise, especially the toothing and the saturation. A 3-speed 3-phase induction motor, which works sporadically at low speed for hoisting, serve as a support for experiments. Its acoustic noise during this operating mode is really important. A complete diagnosis is proposed with a 2D analytical model. The approach is progressive and it shows analytically that magnetic saturation is mainly responsible on these noise level. Then, the presented developments makes it possible to identify, in simple way, the noise components due to the both magnetic saturation and toothing effects.
A simple approach is proposed for retrieving the forward and backward wave impedances of lossless and lossy bianisotropic metamaterials. Compared with other methods in the literature, its main advantage is that forward and backward wave impedances can be uniquely and noniteratively extracted. It has been validated for both lossless and lossy bianisotropic metamaterials by performing a numerical analysis. The proposed approach can be applied for checking whether the metamaterial structure shows the bianisotropic property by monitoring forward and backward wave impedances, since the forward and backward wave impedances of a metamaterial structure depend on different polarizations of the incident wave.
In this paper, the design method of a quadruple-band rejection ultra-wideband (UWB) antenna with three co-directional complementary split ring resonators (CSRRs) is proposed. Within the design step, individual antennas corresponding to each rejection band is first designed, and then a finalized structure is determined by assembling these individual antennas altogether. The shape of the final antenna achieves both the impedance matching of ultra-wideband and the respective resonances at four rejection bands. Here, the mutual coupling among the band rejection elements is minimized, and the placement of the resonators is optimized. The fabricated antenna is compact enough to be integrated into the UWB system, and also the measured results show the validity of the proposed design strategy.
This paper deals with passive microwave imaging for fire detection by means of a single-channel ground-based radiometer. The simulation of images sensed in the presence of fire spots under different environmental and operative conditions will be presented. We will refer to a low-cost ground-based radiometer operating at 12.65 GHz. Scenarios with fires where visible and IR sensors are not useful with respect to a microwave imager will be investigated in deep, such as in the presence of vegetation canopy optically masking fire sources and smoke plumes in the early stage. These simulations will assess limits and capabilities of microwave imaging for the identification of little fires masked by forest areas.
The mutual correlation function of the phase fluctuations of scattered ordinary and extraordinary waves by the magnetized plasma slab with electron density fluctuations and the variance of the Faraday angle is calculated by the perturbation method. Analytical expression of broadening of the spatial spectrum of scattered radiation is obtained for arbitrary fluctuation spectrum. Numerical calculations are carried out for the anisotropic Gaussian fluctuation spectrum at different anisotropy factor and the angle of inclination of prolate irregularities with respect to the external magnetic field. Isolines of the normalized root mean square deviation of the Faraday angle nonlinearly depends on the angle of inclination of prolate irregularities and increases in proportion to the anisotropy factor; two receiving antennas are located in orthogonal planes. It is shown that the broadening of the spatial spectrum of scattered electromagnetic waves by turbulent magnetized plasma slab in the principle plane (location of an external magnetic field) is less than in the perpendicular one.
In this paper, a new method is proposed to calculate the simultaneous switching noise (SSN) in order to reduce the complexity of SSN circuit models and computational burden based on the rational function (RF) in time domain. The time-domain impedance function of a power delivery network (PDN) is calculated by approximating the impedance frequency response of a PDN with a rational function, and the SSN is calculated based on switching current characteristics. It is also found that the SSN can be suppressed through adjusting the period of time-domain impedance function and switching current. Compared with the results of lumped and distributed PDNs, the performance of the new method for calculating and suppressing the SSN is verified, and the simulation time of SSN is reduced effectively.
This paper proposes a new mobile handset antenna structure to reduce the value of the specific absorption rate (SAR). The antenna is based on the PIFA structure and operates at dual-bands of 0.9 GHz and 1.8 GHz. The chassis current is reduced using a metallic shim-layer inserted between the patch and chassis. This shim-layer is connected to the handset chassis through posts whose number and positions are determined using optimization techniques. Sidewalls are attached to increase the gain of the antenna and reduce the radiation towards human head. Simulations in the cheek mode show that the SAR reduction factor (SRF) of the proposed structure averaged over 10-g is more than 75% at 0.9 GHz and 46% at 1.8 GHz. The SRF values obtained using simulations and measurements are found to be better than 51% and 76% at 0.9 GHz and 1.8 GHz, respectively.
A non-canonical inhomogeneous background medium is one whose Green's function cannot be obtained by an analytical method. Electromagnetic scattering from objects embedded in a non-canonical inhomogeneous background medium is very challenging because of the computational complexity with the calculation of its Green's function and the multiple scattering between objects and the background. This work applies the Diagonal Tensor Approximation (DTA) to calculate the scattering from arbitrary objects in a noncanonical inhomogeneous background. Previously, the DTA has only been applied to a canonical background such as a homogeneous or layered background media. This approach employs a numerical method to obtain all Green's functions required in the calculation; an accurate DTA is used to calculate the scattering properties. In order to reduce the large number of simulations, we employ the symmetry and reciprocity in the Green's function calculation. Furthermore, considering that most realistic imaging measurements are made through a voltage probe usually represented by a wave port, we develop a method to convert the scattered field on the probe (the antenna) to the measured wave port voltage. Numerical results show that this method can obtain accurate scattering characteristics from arbitrary objects in a non-canonical inhomogeneous background medium in a microwave imaging system.