Transformation optics opens an exciting gateway to design electromagnetic "invisibility" cloaks with anisotropic and inhomogeneous medium. In this paper, we establish a generalized transformation procedure to highly improve the flexibilities for the design of two-dimensional (2D) cloaks. The general expressions for the complex medium parameters are developed, which can be readily applied to design 2D cloaks with arbitrary geometries. An example of 2D cloak with irregular cross section is designed and studied by full-wave simulations. The Huygens' Principle is applied to quantitatively evaluate its unusual electromagnetic behaviors. All the theoretical and numerical results verify the effectiveness of the proposed approach. The generalization in this Paper makes a great step forward for the flexible design of electromagnetic cloaks with arbitrary shapes.

The automatic extraction of the targets which we are interested from a given image is the fundamental of the automatic detection and identification for security screening systems based on imaging technologies. Suffering from the comparatively low signal to noise ratio (SNR), the automatic detection of targets in a passive Terahertz (THz) imaging system facing great challenges, but in urgent necessary. In this paper, a comprehensive method for automatic detection of concealed targets in passive THz image by making the best use of the ‘block statistics uniformity’ properties of the passive images is firstly studied. A theoretical model for the ‘featured regions’ decomposition based on the minimization of a ‘fit energy’ functional with respect to a ‘surface function’ is established, to overcome the drawbacks of conventional methods with gradient-based edge operators for their unsuccessful application in low SNR passive images with blurred boundaries. Based on above theoretical basis and taking advantages of the distinguished contrasts of the convergent ‘surface function’ in different ‘featured regions’, an automatic detection algorithm with three steps was further developed to automatically extract the number, the locations and the shapes of all the concealed targets, with the shape of each target derived as the contour point series arranged in clockwise direction. With plenty of experimental results in 0.2THz band, it's found that, the proposed method has high detection accuracy about 95% with quite good real-time performance, even for the single channel proof-of-state system with low SNR. The theorem, algorithm and results in this paper may have important applications in unmanned and intelligent security screening systems without any artificial interventions.

Transformation optics is extended to the design of two-dimensional (2D) cloaks with non-conformal inner and outer boundaries. General and explicit expressions of the transformed medium parameters are derived, which are of the utmost importance in a cloak design procedure. A 2D cloak with irregular and non-conformal boundaries is designed as an example. Full-wave simulations combined with Huygens’ Principle are applied to verify the invisibility of the cloak to external incident waves. All the theoretical and numerical results verify the effectiveness of the proposed method. The generalization in this Paper highly improves the flexibilities for cloak design.

In this paper, the extended phase shift migration (PSM) for three-dimensional (3-D) multi-input-multi-output synthetic aperture radar (MIMO-SAR) imaging in terahertz (THz) band was studied. Based on one-dimensional MIMO arrays combined with synthetic aperture scan along another dimension, MIMO-SAR imaging scheme allows the number of array elements to be greatly reduced compared with the two-dimensional (2-D) MIMO arrays. By analyzing the derived analytical expression of the scattered waves in the frequency-wavenumber domain, the MIMO-SAR data in a certain frequency is mapped to another frequency of the `explode fields' of the monostatic form in accordance with a newly defined 3-D dispersion relations. By multiplying the modified phase shift terms in each frequency of `explode fields', the `explode fields' at different range planes can be reconstructed. Finally, the `explode fields' at time t = 0 can be successfully derived to realize fast imaging reconstruction for MIMO-SAR, with great reduction on the time consuming as compared with the BP algorithm and better accuracy compared with the Stolt migration. Additionally, due to its iterative nature in the range direction, the proposed algorithm is more flexible in treating more complicated scenarios, such as the image reconstruction in the multi-layer medium. A bistatic prototype imager was designed for the proof-of-principle experiments in THz band. The 3-D imaging results of different targets and computational complexity were also given to demonstrate the good performance of the proposed algorithm for THz MIMO-SAR imaging.

Multiple-input-multiple-output synthetic aperture radar (MIMO-SAR) technology is an effective scheme to achieve there-dimensional (3-D) imaging in millimeter wave and terahertz band. Compared with the 2-D array, the system complexity and the number of array elements are greatly reduced. In this paper, an efficient image reconstruction algorithm in wavenumber domain based on phase shift migration (PSM) was proposed for MIMO-SAR 3-D real-time imaging application. By decomposing the range-wavenumber based on binomial approximation theory, the PSM operation can be achieved only by matrix multiplication and Fourier transform (FT) algorithm without time-consuming wavenumber accumulation. Proof-of-principle experiments were also carried out in 0.1THz band based on a MIMO-SAR prototype system. Both simulation and experimental results of different targets show that the image quality of the proposed algorithm is comparable to that of back-projection algorithm (BPA). The partial enlarged images of the imaging results validate that compared with the range migration algorithm (RMA) the proposed algorithm can achieve higher reconstruction accuracy with comparable efficiency.

In this article, a novel 3-D imaging method based on the chirp scaling algorithm (CSA) is proposed for millimeter-wave near-field imaging. We deduce the theoretical formula of CSA applied to multiple-input–multiple-output (MIMO)/single-input–single-output (SISO) array imaging and then analyze the computational complexity and phase error. Compared to the classical Fourier-based algorithm, such as range migration algorithm (RMA), they can replace the redundant interpolation with the phase multiplication. Meanwhile, it can handle the large relative bandwidth system compared with frequency scaling algorithm (FSA). It greatly improves imaging speed and broadens the application scenarios. The rearrangement operation of the MIMO wavenumber spectrum is also accelerated by the sparse matrix multiplication. To further reduce the computation time, we perform the direct rearrangement of the MIMO wavenumber spectrum before phase compensation. It works well but also sacrifices part of the signal-to-noise ratio (SNR), so it may not be suitable for the weakly scattering targets. The simulation data of a 2-D uniform array with the large number of antennas and a published dataset are used to verify the effect of the proposed algorithm. The simulation and experiment results show that the proposed method can effectively improve the computational efficiency.