Millimeter-wave imaging has been regarded as key technique for next-generation personnel security inspection. Holographic imaging based on Fast Fourier Transform (FFT) is one of the most efficient algorithm for millimeter-wave imaging. However, during the process of holographic imaging, Stolt interpolation in the wavenumber-domain is employed to resample the 3-dimentional (3-D) data, which is time-consuming and also introduces additionally interpolation error. To overcome this weakness, an interpolation-free 3-D imaging algorithm is presented in this paper. The proposed algorithm reconstructs 3-D image exploiting 2-D FFT and inverse FFT (IFFT), and no interpolation is needed in the process. The algorithm is very suitable for parallel computation, and with prior knowledge of the position range of the target, the computation load of the 3-D image reconstruction could be further reduced. Numerical simulated data and real data from practical millimeter-wave imaging system have been used to verify the performance of the proposed algorithm. The results demonstrate that the proposed algorithm can achieve good image quality with high efficiency.
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.
Equivalent circuit model of the frequency select surface is given, and a feasible method of design of multi-pass frequency selective surface is discussed. Based on the method, a novel frequency selective surface with two pass bands is presented. The simulation results indicate that, the center frequencies of the bands are at 2.95GHz and 8.6GHz, and the 3dB bandwidth is 3.5% and 5%. Also the center frequencies and the transmittance of the pass bands are affected less by the polarization direction and incident angel of the wave, or the structure exhibits a great filter feature as a frequency selective surface.
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