We propose a technique for enhancing the angular resolution of a flat-base Luneburg lens antenna to enable it to detect multiple targets with arbitrary scattering cross-sections that are located in angular proximity. The technique involves measuring the electric field distribution on the flat plane of the Luneburg lens antenna, operating in the receive mode, at a specified number of positions, and correlating these distributions with the known distributions derived from the field distributions in the measurement plane generated by single target at different look angles. We show that the proposed approach can achieve enhanced resolution than the basis of the beam-width of the Luneburg lens antenna, and it is capable of distinguishing between two targets with different scattering cross-sections that have an angular separation as small as 1˚ for a Luneburg lens with 6.35λ aperture size, for Signal-to-Noise Ratio (SNR) better than 20 dB.
A tunable metasurface composed of multiple resonant units is proposed, with each unit containing a block of SrTiO3 ferroelectric and a periodical copper-wire structure. The local transmission coefficient of the metasurface is controlled by voltagetuning the permittivity of SrTiO3 in each resonant unit. The function of this tunable metasurface is demonstrated by simulating beam steering at the angles of 30˚ and 14.47˚, respectively; as well as beam focusing at the focal lengths of 2λ0 and 4λ0, respectively.
A typical magnetic resonance coupling based wireless Electric Vehicle (EV) charging system consists of a transmitting coil at the charging station and a receiving coil in the vehicle. In order to maintain good energy transfer efficiency of the wireless charging system, the effect of the proximal metallic object in the vicinity of the receiving coil has been investigated. Both from the theoretical simulation and experimental measurement, it has been observed that the resonance based wireless energy transfer system is very sensitive to the nearby metallic objects, leading to significant deterioration in energy transfer efficiency. This effect on the energy transfer efficiency is also seen to be different for different physical spacing between the transmitting and receiving coils. It is also found that the operating resonant frequency for optimum energy transfer efficiency changes with the metallic object in close proximity to the receiving coil. The theoretically simulated results well agree with the experimental results. The analysis will provide future guidelines for designing an efficient resonance coupling based wireless charging system for EVs even in the presence of metallic objects.
The rigorous evaluation of the NRCS (Normalized Radar Cross Section) of an object above a one-dimensional sea surface (2D case) needs to numerically solve a set of discretized integral equations involving a large number of unknowns. Thus, the direct solution of the impedance matrix equation via LU decomposition becomes the most expensive step in the MoM (Method of Moments) procedure. So, in order to minimize the computation cost, the iterative domain decomposition method called EPILE (Extended Propagation-Inside-Layer Expansion) was used and then was combined with the FBSA (Forward-Backward with Spectral Acceleration) to calculate the local interactions on the rough sea surface. The resulting fast method is called EPILE+FBSA. In this paper, we take advantage of the rank-deficient nature of the coupling matrices, corresponding to the object-surface interactions, to further reduce the complexity of the method by using the ACA (Adaptive Cross Approximation). Thus, the coupling matrices are strongly compressed without a loss of accuracy and the memory requirement is then strongly reduced. For a cylinder above a rough sea surface, the results show the efficiency of the accelerated EPILE+FBSA+ACA method.
Small ultra high frequency (UHF) radio frequency identification (RFID) tags of fragment-type structure can be designed for broadband operation and for versatile impedance matching to different chips. The fragment-type tag structure can be optimized by using genetic algorithm. In our design, multi-objective evolutionary algorithm based on decomposition combined with enhanced genetic operators (MOEA/D-GO) is used for optimization searching. The multiple objectives are defined in terms of power transmission coefficients for operation in multiple RFID bands and for impedance matching to several prevailing RFID chips. For demonstration, a fragmented tiny square UHF tag of dimensions of 5.5 mm * 5.5 mm is designed for multi-band operation over the 433 MHz, 869 MHz and 915 MHz RFID bands, and a fragmented round tiny RFID tag of radius of 4.5 mm is also designed for versatile connection to five prevailing RFID chips at 915 MHz. The tiny round versatile tag is tested by connecting two chips, the IMPIMJ Monza-4 chip (11-143j) and ALIEN Higgs-3 chip (27-195j), respectively. Effects of input impedance and adjunct fragments on versatility of the design are further discussed.
A pattern synthesis approach based on a modified alternating projection method for large planar arrays is presented in this paper. In the alternating projection method, pattern synthesis problem is considered as finding the intersection between two sets: the specification set and the feasible set. The former contains all the patterns that want to be obtained, while the latter contains all the patterns that can be realized. An element belongs to both sets is a solution to the problem. In this paper, a modified projection operator which varies with the iteration number is introduced because the conventional alternating projection method is known to suffer from low convergence rate and/or trapping on local optimum depending on the starting point. When the planar array has a nonuniform element layout, the unequally spaced elements are interpolated into virtual uniform elements with an interpolation of the least square sense. Then the synthesis problem is converted to the problem of a uniform array. Finally, several examples are presented to validate the advantages of the proposed method. Results show that the modified method is fast and obtains better results than the conventional one.
A novel method of the aerosolized gene delivery is proposed, and its feasibility is computationally analyzed. Aerosolized DNA or siRNA attached to magnetic particles can be accelerated using ponderomotive force to high velocities in a pulsed magnetic field of a solenoid and efficiently delivered to cell culture or to the lung epithelium. The proposed noninvasive method of intra-cellular gene delivery can be considered as a combination of principles of classical high-pressure air jet gene delivery with magnetophoresis.
In optical region, the scattering center model is very useful in scattering analysis, target recognition and data compression. The method based on Hough transformation performs well in most cases. However, the algorithm extracts the scattering centers one by one via a clean method, which is time consuming. To solve this problem, a novel method is proposed in this paper to extract the scattering centers. By searching the estimated 1D scattering centers, the candidate positions for 3D scattering centers are extracted. Then the candidates are discriminated by a clustering based procedure. By employing the new algorithm, the 3D scattering centers can be extracted simply and the clean step is unnecessary, which makes the procedure efficient. The experiment results of the high-frequency-electro-magnetic data demonstrate the performance of the proposed method.
A generalization propagator method (GPM) is presented. It is the extension of traditional propagator method (PM). In order to make full use of the received data, many propagators are structured according to different block structures of array manifold. By these propagators, a high order matrix is obtained in a symmetric mode, and it is orthogonal with array manifold. Based on this matrix, a generalization spectral function is obtained to solve the problem of direction-of-arrival (DOA) estimation by spectral peak searching. Moreover, in order to avoid spectral peak searching, a generalization root-propagator method (GRPM) is also proposed, and shows excellent estimation precision. Numerical simulations demonstrate the performance of the proposed method.
It is well known that MUltiple SIgnal Classification (MUSIC)-type algorithm produces a good result for the imaging of thin dielectric inhomogeneity in full-view inverse scattering problems. In contrast, it yields a poor result in limited-view inverse scattering problems. In this paper, we verify the reason for the above by establishing a relationship between a MUSIC-type imaging function and the Bessel functions of the integer order of the first kind. This verification is based on the asymptotic expansion formula for thin dielectric inhomogeneity. Various numerical examples are shown for confirming our verification.
In this paper the scanning properties of dual reflector antenna systems constituted by two confocal paraboloidal reflectors fed by a planar array are investigated. This antenna architecture combines the interesting features of reflectors and array antennas. Because of the offset configuration the radiation pattern exhibits an anomalous deviation in the beam pointing when the beam is scanned out of the boresight direction. Heuristic equations, representing an extension of the linear equations available in the literature, are derived, which permit predicting the pointing direction of the overall system as a function of the pointing direction of the feeding array in a significant field of view.
Micro-Doppler (MD) caused by the motion of the ballistic missile can contribute to successful recognition of the ballistic missile. Considering the real observation scenario. This paper proposes a method to derive the MD image of the ballistic missile by applying the range-Doppler algorithm (RDA) based on the real flight scenario and analyzes the factor for the real-time MD imaging. Simulation results using the flight trajectory constructed using the real target parameter demonstrate that we need a new cost function for phase adjustment and a new method for range alignment. In addition, matched-filtering needs to be performed in the baseband, and a sufficient PRF is required to prevent discontinuity of the MD image. Dechirping of MD and filtering of the random movement are also needed for a clear MD image.
In this paper, we propose a modified version of the Random Sample Consensus (RANSAC) method for Interferometric Synthetic Aperture Radar (InSAR) image registration based on the Scale-Invariant Feature Transform (SIFT). Because of speckle, the ``maximization of inliers'' criterion in the original RANSAC cannot obtain the optimal results. Since in InSAR image registration, the registration accuracy is in inverse proportion to number of residues. Therefore, we modify the old criterion with a new one --- minimization of residues --- to obtain the optimal results. We tested our method on a variety of real data from different sensors, and the experimental results demonstrated the validity and robustness of the proposed method.
Due to the traditional recognition researches prevalently fastening on HRRP's amplitudes while almost completely neglecting the phases, this paper attempts to directly prove the discriminant availability of HRRP's phases via two proposed fusion recognition strategies. The first strategy includes three sub-processes, respectively, based on phase cosine, phase sine and their fusion. The second strategy also includes three sub-processes, respectively, based on phases, amplitudes and their fusion. Additionally, a trigonometric function couple (TFC) method is used to reduce the phase sensitivity. Several measured experimental results indicate as follows. Firstly, employing TFC can perform much better. Secondly, the two fusion recognition sub-processes apparently outperform the corresponding subprocesses constructing them. Finally, phase information usually has a better noise immunity compared with amplitude information, and fusing phase information into amplitudes may improve the traditional recognition performance. Therefore, the availabilities of HRRP's phases and the two fusion strategies have been experimentally proven.
The analysis of the scattering by a tilted perfectly conducting strip buried in a lossy half-space at oblique incidence is formulated as an electric field integral equation (EFIE) in the spectral domain and discretized by means of Galerkin's method with Chebyshev polynomials basis functions weighted with the edge behaviour of the surface current density on the strip. In this way, a convergence of exponential type is achieved. Moreover, a new analytical technique is introduced to rapidly evaluate the slowly converging integrals of the scattering matrix coefficients consisting of algebraic manipulations and a suitable integration procedure in the complex plane.
In this paper, an improved robust minimum variance beamformer against direction of arrival (DOA) mismatch and finite sample effect is proposed. Multiple inequality magnitude constraints are imposed to broaden the main lobe of beampattern. The conjugate symmetric structure of the optimal weight is utilized to transform the non-convex inequality magnitude constraints into convex ones. A quadratic constraint on the norm of weight is introducing to make further improvement on robustness against DOA mismatch and finite sample effect. The proposed beamforming problem can be reformulated in the form of the second order cone programming and solved efficiently by interior point method. Simulation results show that the proposed beamformer outperforms several other adaptive beamformers.
In this paper, a combination of Lumped-Parameters Model, Quasi-Poisson's equations and Conformal Mapping methods is used for predicting radial and tangential air gap flux density of Interior Permanent Magnet Synchronous Machine for calculation of cogging torque. In the proposed method, Lumped Parameters Model is used for calculation of saturation and flux leakage. Quasi-Poisson's equation is used for forming radial and tangential flux density in slotless stator, and finally Conformal Mapping is used to account for slot effects. Using the results of this method, cogging torque waveform can be calculated using Maxwell stress tensor and virtual work methods. To validate the method, results are compared with Finite Element Method results for a candidate Interior Permanent Magnet Synchronous Machine.
As a very powerful optimization algorithm, invasive weed optimization has been widely applied to continuous optimization problems in electromagnetic (EM) field. However, the optimization of a thinned array can be formulated as a discrete-variable optimization problem with solutions encoded as binary strings. Therefore, in this paper, an improved binary invasive weed optimization (IBIWO) is proposed to design a thinned array with minimum sidelobe levels. To evaluate the performance of the proposed algorithm, two examples have been presented and solved. Simulation results of the proposed thinned arrays obtained by IBIWO are compared with published results to verify the effectiveness of the proposed method.
Environment monitoring and automatic control of a building is a vital application of wireless sensor network, however, to maximize the network lifetime is a key challenge. The investigation of designing an efficient sensor network that minimizes energy dissipation in a battery of the sensor node, with limited battery power, is a vital consideration for the sensor network lifetime. Battery lifetime greatly affects the overall network communication performance, hence, the careful management of communication distance is very important. In this paper we propose a model to estimate the mean square distance from the sensor to the cluster head in sensor fields, such as the ones used for monitoring humidity, temperature, light intensity and air quality (CO and CO2 level), considering three dimensional building structures. We use experimental datasets of the link quality distribution in an indoor building environment (single storey as well as multi-storey buildings) to investigate the possible building length of the different clusters and the data success rates. We then statistically analysed the data success rate of the experimental datasets using the Wilcoxon Rank Sum test and found that there was no statistically significant difference (p > 0.05). Our results show that the clustering is important for the single storey and multi-storey building sensor networks, however, after a certain size of the building it is unimportant. Our results also demonstrate that we can save sensor battery energy, significantly, by optimizing the distance from the sensor to the cluster head, while obtaining a high data success rate. The results over different clusters of sensor networks suggest its applicability for different building sizes. Based on this paper the designers can optimize energy e±ciency subject to the required specifications.
Forward-looking imaging has extensive potential applications, such as self-navigation and self-landing. By choosing proper geometry, bistatic synthetic aperture radar (BiSAR) can break through the limitations of monostatic SAR on forward-looking imaging and provide possibility of the forward-looking imaging. In this special bistatic configuration, two problems involving large range cell migration (RCM) and large range-azimuth coupling are introduced by the forward-looking beam, which make it difficult to use traditional data focusing algorithms. To address these problems, a novel Omega-K algorithm based on two-dimensional non-uniform FFT (2-D NUFFT) for translational variant (TV) bistatic forward-looking SAR (BFSAR) imaging is proposed in this paper. In this study, we derive an accurate spectrum expression based on two-dimensional principle of stationary phase (2-D POSP). 2-D NUFFT is utilized to eliminate the range-variant term, which can make full use of the data and improve the computational efficiency as well. The experimental results, presented herein, demonstrate the effectiveness and advantages of the proposed algorithm.
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