An ultrathin absorptive/transmissive radome with dual passbands is presented in this paper. The total thickness of radome is only 5 mm. The dual passbands are located at around 1.05 GHz and 2.2 GHz, respectively. The absorbing band ranges from 6.28 GHz to 15.04 GHz for TE wave incidence and from 6.3 GHz to 15.16 GHz for TM wave incidence. Due to the miniaturized elements, the grating lobes are shifted out of absorbing band to higher frequency. Both numerical and experimental results are also given out.
Transformation optics is a convenient method to control paths of electromagnetic waves and radiation characteristics of antennas. In this paper, we try to increase the gain of Balanced Antipodal Vivaldi Antenna (BAVA) over 8-16 GHz frequency band using an optical conformal transformation. The proposed antenna can be implemented by ordinary dielectric materials and graded photonic crystals (GPCs). In this designed BAVA, better side lobe level (SLL) and cross-polarization are achieved compared to a conventional BAVA. Simulation results validate the performance of the design approach.
The accuracy of wave propagation prediction is very important in telecommunication network planning. The parabolic equation model has an advantage in computation efficiency and accuracy for wave propagation prediction. The recursive convolution nonlocal boundary condition has an advantage in improving the computational efficiency. In this paper, the recursive convolution nonlocal boundary conditions are extended to deal with the issue of horizontal diffraction loss in multiple obstacles. The validation is performed with experiments and the results show a good agreement.
The scheme of energy and data wireless transmission with the same carrier based on M-ary Differentially-Encoded Amplitude and Phase Shift Keying (MDAPSK) technology is an effective method to implement energy supply and data communication for implantable medical devices. In this paper, based on a large number of finite-difference time-domain simulation analyses, combined with knowledge of the clinical demand for implantable medical devices, the 13.56-402 MHz band is selected as the biological channel frequency band, and attenuation characteristic analysis and mathematical modeling are carried out. Based on massive amounts of simulation data, the Levenberg-Marquardt and general global optimization methods are adopted to build a homogeneous and heterogeneous biological channel model in the aforementioned frequency band. In order to verify the reliability and versatility of the mathematical model, an adult male rabbit is employed for a living implantation experiment. Using a vector network analyzer, different frequency electromagnetic wave receiving efficiencies in different biological channels are measured. The measured data are highly consistent with the simulation data, which fully verifies the rationality of the proposed biological channel model. This work provides a theoretical basis and model reference for the clinical application of an implantable medical device wireless transmission system.
The currents flowing through a transmission line produce a rotating magnetic field of vertical and horizontal components which are orthogonal in space and vary with time. Buried and aerial metallic pipelines that run parallel to or are placed in the vicinity of overhead AC high voltage transmission lines are affected by this field resulting in an induced voltage on the pipelines. Several related studies and safety standards dealing with this problem have been published. Nevertheless on a multi-circuit line, the issue of current phase shift variation has not been fully covered yet. This paper provides a detailed analysis of the effect of current phase shifts on the magnetic field distribution and polarization pattern around power lines using analytical approach from electromagnetic field theory. In this study, not only the variation of the filed distribution with phase arrangements and phase shifts is further established, but also the characteristic nature of the variation of the field distributions for six phase arrangements is examined in more detail. The results show that the magnetic field distribution at the ground level and the spatial distribution of the magnetic field polarization ratio vary significantly with the phase sequence arrangement as well as the current phase shifts between the two circuits. The field polarization differs at different locations. The information from the results can be useful for consideration in designing an effective AC mitigation technique and in placing pipelines in the utility corridor with power lines. Pipelines should be placed in a region of minimum field intensity within the right-of-way of the line, in order to have minimal induction on the pipeline in normal operating conditions of the line.
Point target detection in space-based infrared (IR) imaging system is an important task in many applications such as IR searching and tracking and remote sensing. Although it has attracted great interest and tremendous efforts during last decades, it remains a challenging problem due to the uncertain heterogeneous background and the limited processing resources on the onboard platform. Aiming at this problem, a novel background suppression method based on multi-direction filtering fusion is proposed in this paper. The process of background prediction for each pixel by this method can be divided into two steps. Firstly, eight predicted values are obtained by using linear filtering methods along eight different directions respectively. Then, Gaussian weighted sum of the eight predicted values is computed to generate the final result. We conduct several groups of experiments on different categories scenes with simulated targets, and the final experimental results demonstrate that our methods can not only obtain state-of-the-art performance on background suppression (especially for heterogeneous backgrounds), but also detect targets accurately with low false alarm rate and high speed in IR point target detection tasks.
This paper analyzes rectangular and circular patch antennas fabricated from meshed conductors and backed with solid ground planes. Because of the meshing, the antennas are rendered optically transparent, where the transparency is determined by the mesh geometry. It is found that although there is a compromise between the antenna's efficiency and the optical transparency of the meshed patch, it is possible to optimize the antenna by refining mesh lines to certain extent. The limiting factors for refining mesh lines include material handling and fabrication process as well as the increased line impedance when being refined, which accordingly causes loss in antenna's efficiency. A refined mesh with thin linewidth increases both antenna performance and transparency. Additionally, it is found that the reduction of certain mesh lines increases the optical transparency with minimal hindrance to the antenna's efficiency, leading to further enhancement to the see-through percentage. Although it is possible to refine mesh lines to improve the antenna's efficiency or gain, it is seen that there is a limit for such an optimization method. This limit is closer to the efficiency of a solid patch for a lower transparency, whereas it is lower for increased transparency. Cross polarization level was also examined, and there was no signifficant efft on such a parameter due to meshing.
This paper aims at designing a wideband planar inverted F antenna (PIFA). The design of a PIFA begins with an elementary step such as the etching of antenna element pattern in a metal trace. After the etching adherence is developed by incorporating bonding between it and a printed circuit board which is primarily an insulating dielectric substrate. A ground plane is developed by a prolonging metallic layer which is adhered to the opposite side of the substrate. The simulation is done using ANSYS HFSS full wave 3D simulation software. The proposed PIFA is very compact and also provides a gain of 2.86 dB. As a consequence of the exemplary feature like an omnidirectional radiation pattern, there is an exceptional improvement in coverage. Moreover, the frequency bands covered by the PIFA are for applications including USPCS, UMTS, ISM/Bluetooth and WLAN at (1.85 to 1.99) GHz, (1.90 to 2.20) GHz, (2.4 to 2.485) GHz and (5.1 to 5.90) GHz, respectively.
In this correspondence, the two-dimensional (2-D) direction-of-arrival (DOA) estimation problem for partially polarized (PP) signals is considered. In particular, we focus on an array geometry containing three identical uniform linear arrays (ULAs). Compared with existing methods, the proposed one has three main advantages. Firstly, the estimation accuracy is higher since it exploits the polarization information. Secondly, it can work effectively under the coexistence of both noncircular and circular signals. Finally, pair matching for 2-D DOA is not required which reduces the computational complexity. Simulation results are presented verifying the efficacy of the algorithm.
Wearable wireless technology has developed as an exciting topic over the last couple of years. With the extensive use of Wearable Wireless Devices (WWD) in greater proximity to the body for various wireless applications, the concern about biological effects due to the interaction of human tissues with the radiations is growing. In this research, we investigate the application of Infrared Thermography (IRT) to obtain temperature dynamics and reconstruct Specific Absorption Rate (SAR) to evaluate the exposure amenability of WWDs. A microstrip monopole antenna on a wearable substrate is used to determine the biological effects of the interaction of electromagnetic (EM) waves on the body. SAR is obtained using EM field simulations and by reconstruction from thermal measurements with the use of Bio-heat equationsfor a continuous exposure of 300 s. Validation of IRT to reconstruct SAR is demonstrated by comparison with EM computations. The maximum SAR was 32 mW/kg, for simulations and 35 mW/kg, from reconstruction after IRT experiments. The maximum temperature change in both cases was always less than 1˚C. The difference between the SAR obtained through IRT and simulation tools accounted for an average of 8.7%. Information acquired using IR temperature dynamics can yield SAR values which can assess radio frequency exposure compliance for WWD at frequencies used for modern wireless technologies, with reliability.
A semi-analytical method to analyze post-wall waveguides and circuits based on the model of two-dimensional photonic crystals formed by layered periodic arrays of circular cylinders is presented. The propagation constant of the fundamental TE mode, the attenuation constant due to the leakage loss and the effective width of an equivalent rectangular waveguide are calculated. Using the concept of the effective width, the original structure is replaced by an equivalent rectangular structure. When additional metallic posts are loaded in the rectangular waveguide, functional post-wall waveguide-based passive circuits are formed. The S-parameters of the post-wall circuits, which act as bandpass filters, are calculated using the image theory combined with the lattice sums technique.
This paper extends the parabolic integral equation method, which is very effective for forward scattering from one-dimensional rough surfaces, to include backscatter. This is done by applying left-right splitting to a modied two-way governing integral operator, to express the solution as a series of Volterra operators; this series describes successively higher-order surface interactions between forward and backward going components, and allows highly efficient numerical evaluation. This and equivalent methods such as ordered multiple interactions have been developed for the full Helmholtz integral equations, but not previously applied to the parabolic Green's function. Equations are derived for both Dirichlet and Neumann boundary conditions (TE and TM).
A composite wideband absorbing material (WAM) covering dual bands is designed, to reduce the in-band radar cross section (RCS) for broadband antenna in this paper. The upper layer is a traditional absorber while the lower one is a dual-band frequency selective surface (FSS), which is formed by a square ring and an improved Jerusalem cross structure. The absorbing band has been broadened to 112% compared with the magnetic sheet without FSS. Over C and X bands, the absorption rate is over 90%. By using the FSS-based WAM as the ground plane of a Vivaldi antenna, substantial RCS reduction is obtained from 2-18 GHz. Moreover, the RCS is reduced remarkably over -80°-80° incident angles except for minority angles, with the radiation performance preserved at the same time. The experimental results are in good agreement with the simulated ones.
In this study, the effective magnetic response of magnetic metamaterial is considered in the microwave frequency range. The metamaterial is an infinite isotropic dielectric host medium with periodically embedded ferric cylindrical inclusions. It is assumed that the inclusions are partially magnetized by a dc bias magnetic field. The electromagnetic wave propagation is considered in the direction of bias magnetic field and transverse to it. It is shown that the real part of effective relative permeability can have Re(μeff)<0 or 0< Re(μeff)<1 or Re(μeff)>1 subject to the value of bias field.
Conventional radar imaging methods use coherent analysis which highlights the necessity of signal phase measurement setups and complex inverse algorithms. To mitigate these drawbacks, this paper proposes a novel phase-less imaging algorithm. A nonlinear over-determined system of equations based on signal Doppler shift is developed, and a new error function originated from least square method is introduced. To obtain the exact position of targets, hybrid optimization is applied to the achieved error function. Simulation results demonstrate that the proposed method is well capable of detecting the targets containing strong point scatterers, even with the distance of 1cm. Also, the resolution of imaging algorithm for point scatterer circumstances is obtained in the order of millimeter. Concurrent with the priory imaging algorithms with the same imaging setups using proposed method reduces complexity and increases imaging swiftness.
Direction of arrival estimation has a noteworthy significance in numerous applications, such as radar systems, smart antennas, sonar, mobile communications, and space communications. The algorithms used to estimate the direction of arrival are to some degree complex and time consuming. Also, the number of antenna elements is a discriminating parameter for assessing the performance of the DoA technique. For real time systems, quick and savvy techniques are required. Along these lines, decreasing the estimation time and also reducing the system cost while keeping a generally high precision are crucial issues. In this paper, a new technique for linear antenna arrays synthesis using optimized number of antenna elements and its application to direction of arrival estimation is introduced. The synthesized arrays exhibit approximately the same radiation pattern as the original arrays. The optimized antenna arrays are synthesized using reduced number of antenna elements. In this case, the number of antenna elements reduction will minimize the system cost and decrease the number of picked samples from the different signal sources. As the number of samples decreases, the dimensions of the steering matrix and data correlation matrix are reduced. In this context, the computational burden, estimation time, and system cost are optimized. The proposed technique can be applied to single or multi-snapshot DoA estimation techniques.
This paper examines the electromagnetic shielding characteristics of milano, cardigan and lacoste with respect to weft and rib type composite knitted fabrics. All of these fabrics, made of hybrid yarns containing 50µm diameter metal fibres such as copper, silver and stainless steel, were produced for electromagnetic shielding purposes. The shielding eeffectiveness (SE) of the fabrics was measured by reading S parameters from the signal when the sample was placed in the path of signal at the frequency range 1.7 to 2.6 GHz inside the WR430 waveguide system. After which S parameters was converted to SE values. The variation in electromagnetic shielding effeffectiveness (EMSE) with the factors, such as radiant frequency, metal type, course density and geometry, were discussed. Experimental results show that all factors, especially the geometry of the fabric, have significant effect on SE. The best EMSE values were obtained by milano type knitted fabrics which was above 20dB. It was found that milano, cardigan and lacoste composite fabrics, uncommon in EMSE experiments found in literature, give better shielding performances than rib and weft composite fabrics, under the same conditions.
This paper investigates an angle of arrival (AOA) and polarization joint estimation algorithm for an L-shaped electromagnetic vector sensor array based on rank-(L, L, 1) block component decomposition (BCD) tensor modeling. The proposed algorithm can take full advantage of the multidimensional information of electromagnetic signal to obtain the parameter estimation more accurately than the matrix-based method and the existing tensor decomposition method. In addition, the algorithm can accomplish pair-matching of estimated parameters automatically. The numerical experiments demonstrate that even under the conditions of low SNR and limited snapshots, the proposed algorithm can still steadily achieve high detection probability with low estimation error, which is important for practical applications.
A generalized multiphysics model using COMSOL Multiphysics software for optimizing the sintering process of iron powders having various green densities is developed. The modeling is facilitated by designing a 30 GHz multimode applicator, where the test sample is placed for the microwave processing. The effective dielectric and magnetic properties of the resultant metal powder compact is estimated using the effective electromagnetic model considering the idea of core - shell particle approach followed by the Lichtenecker's mixture formula. A theoretical approach relating the penetration depth, proper impedance matching and volume fraction of different density powder compacts is also discussed here. From the study, it is clear that the effective dielectric, magnetic, and thermal properties all contribute to the microwave sintering process of metal powders.
A procedure is reported to determine accurate, invertible, block-diagonal factorizations for matrices obtained by discretizing integral equation formulations of electromagnetic interaction problems. The algorithm is based on the combination of localizing source/receiver transformations with orthogonally matched receiver/source transformations. The resulting factorization provides a single, sparse data structure for the system matrix and its inverse, and no approximation is required to convert between the two. Numerical examples illustrate the performance of the factorization for electromagnetic scattering from perfectly conducting elliptical cylinders of different electrical size.