Anyong Qing

Design of wideband multilayer planar absorber using a new differential evolution algorithm

Design of wideband planar absorber using real electromagnetic composite materials is considered in this paper. A new differential evolution, dynamic differential evolution with best of random differential mutation, is applied to solve this problem. To simplify the problem, a suitable objective function and regulation scheme have been designed to transform the constrained multi-objective problem into unconstrained single-objective one. The effects of total thickness and investigated frequency band have been studied. Four-layer planar absorbers for different cases have been successfully designed.

Dual-band Circular Polarizer Based on Simultaneous Anisotropy and Chirality in Planar Metamaterial

Metamaterial of dual-square array is proposed to design a dual-band circular polarizer. The novel design of asymmetric unit cell and layout of duplicate arrays significantly enhances the coupling between electric and magnetic fields. Simulation and measurement results show that the polarizer presents wide angle circular dichroism and circular birefringence. Moreover, the polarization conversion of the proposed metamaterial changes with frequency, incident angle, and polarization of incident waves. The fundamental mechanism behind is concluded to be the angle-dependent chirality and dispersion of our novel design.

Algebraic reconstruction technique with adaptive relaxation parameter based on hyperplane distance and data noise level

An Algebraic reconstruction technique (ART) with adaptive relaxation parameter based on hyperplane distance and data noise level is proposed in this paper. At each iteration of the proposed algorithm, the relaxation parameter for each hyperplane is adaptively adjusted based on the distance from the current vector to the hyperplane and the noise level in the measurement data. Numerical results show that both fast convergence and high quality of reconstructed image could be obtained.

Passive Millimeter Wave Imaging System Based on Helical Scanning.

A simple and fast single channel passive millimeter wave (PMMW) imaging system for public security check is presented in this paper. It distinguishes itself with traditional ones by an innovative scanning mechanism. Indoor experiments against human body with or without concealed items in clothes show that imaging could be completed in 3 s with angular resolution of about 0.7°. In addition, its field of view (FOV) is adjustable according to the size of actual target.

Suppression of sidelobe level and sideband of time-modulated linear antenna arrays by using NSDE

Nondominated sorting differential evolution (NSDE) is applied to simultaneously suppress sidelobe level (SLL) and sideband level (SBL) in time-modulated linear antenna arrays. The SLL and SBL of a time-modulated linear array can be reduced by optimizing excitation amplitudes and the switch-on time intervals of each element. Numerical results confirm the effectiveness and flexibility of this method.

Sidelobe level and sideband suppression in time-modulated linear arrays by NSGA-II

A novel approach based on nondominated sorting genetic algorithm II (NSGA-II) is proposed to suppress sidelobe level (SLL) and sideband level (SBL) in time-modulated linear antenna arrays. The SLL and SBL of a time-modulated linear array can be reduced by optimizing the excitation amplitudes as well as the switch-on time intervals of each element. A 32-element linear array has been synthesized to show the effectiveness of the approach.

A new design of 3D electromagnetic inverse scattering imaging system

Summary form only given. In a 3D electromagnetic inverse scattering imaging system, the illuminating zones of different array elements may not necessarily overlap, as shown in Fig. 1. On the other hand, the imaging domain covers the superposed area illuminated by each and every element. Therefore, the active dimension of the imaging domain corresponding to each array element is much smaller than that of the imaging domain. Significant ill-posedness is therefore present in the governing equations. In view of the above problems, a new 3D electromagnetic imaging system as shown in Fig. 1 is proposed, which can be used in some special situations, such as fault inspection and clinical medical imaging. In this system, these are two identical arrays excited by coherent sources. One of arrays is called reference array, which illuminates the standard sample, while the other one is probe array, which illuminates the object to be imaged. The difference between signals received by the two arrays must come from the difference between the sample and the object. Difference image between the sample and the object will then be reconstructed if the difference signals are used as measurement data. As a matter of fact, it is exactly the information of our interest.

Reconfigurable antenna based on liquid crystal (LC) technology

Summary form only given. A reconfigurable antenna based on liquid crystal technology is presented in this paper. It comprises of a 1×4 microstrip patch antenna array, LC-based inverted microstrip line (IMSL) phase shifters, and RF-feeding and biasing networks. Nematic LC (N-LC) cell is used as tunable substrates for both the microstrip patch antenna array and the phase shifters. The dielectric tensor of N-LC is controlled a DC or low-frequency AC bias voltage. The microstrip patches are used as waveguide radiating elements while the LC-based IMSL phase shifters are used to steer the main beam. The RF signal coupled between the phase shifters and microstrip patch antennas are guided and then radiated from the top face of the microstrip patch antennas. As a proof of concept, the beam steering capability of the reconfigurable antenna is demonstrated by steering the main beam to -27°, 0 and 27° at 14.5 GHz and the frequency tuning capability is demonstrated by changing the frequency from 15.9 GHz at 0V to 14.3 GHz at 10 V, a tuning range of 10%. Comparisons with measurements are provided in order to validate the proposed numerical approach and illustrate the potential use of LCs as tunable materials in microwave and millimeter-wave frequencies.

A generalized Kaczmarz algorithm with projection adjustment

Kaczmarz algorithm (KA), also known as algebraic reconstruction technique (ART) in medical imaging area, is a commonly used iterative method for solving large-scale linear system of equations. It has found wide applications in many fields such as medical imaging, electromagnetic inverse scattering and geophysics. Various improved KAs have been developed to promote the efficiency of the algorithm, e.g., Block KA, Simultaneous Algebraic Reconstruction Technique (SART), and so on. The author has also presented an accelerated Kaczmarc algorithm with projection adjustment (KAPA), which remarkably promotes the convergence speed of KA. However, KAPA has to additionally store the previous vector for each hyperplane defined by an equation. For some very large-scale practical problems, e.g., 3D CT imaging problem, the additional storage load of KAPA may become unaffordable. To alleviate this problem, a generalized KAPA (denoted as GKAPA1) is proposed in this paper. In the generalized KAPA (GKAPA1), additional acceleration adjustment is only implemented for a subset of hyperplanes, instead of all hyperplanes in KAPA. By using a very small subset, the additional storage are remarkably reduced, and a good balance of speed acceleration and additional storage could be achieved. A randomized version of GKAPA1 (GRKAPA1) has also been proposed in this paper to further speed up the convergence. Numerical simulations of solving linear equations have been conducted to verify the efficiency of the proposed algorithms. GRKAPA1 is also applied to the computed tomography (CT) image reconstruction problem and compared with other algorithms. The simulation results show that the performance of generalized KAPA is much better than KA and close to KAPA. Considering its much less additional storage and smaller computation load, it seems that generalized KAPA is more attractive for practical applications.

Homogenization of non-uniform data grid in millimeter scanning imaging system by time shifting

In our millimeter wave scanning imaging system, two-dimensional non-uniform data grid as shown in Fig. 1 is generated. Consequently, fast Fourier transform (FFT) for uniform data grid as shown in Fig. 2 cannot be immediately applied. In general, there are two ways to compute discrete Fourier transform (DFT) for non-uniform data grid, non-uniform FFT (NUFFT) and interpolation. However, computational efficiency for both of them is not satisfactory.