Xujin Yuan

Graphene-Based Sandwich Structures for Frequency Selectable Electromagnetic Shielding

Due to substantial development of electronics and telecommunication techniques, materials with electromagnetic interference (EMI) shielding performance are significant in alleviating the interference impacts induced from a remarkable variety of devices. In the work, we propose novel sandwich structures for manipulating the EM wave transport, which holds unique EMI shielding features of frequency selectivity. By employing electrical and magnetic loss spacers, the resultant sandwich structures are endowed with tunable EMI shielding performance, showing substantial improvements in overall shielding effectiveness along with pronounced shielding peak shift. The mechanisms suggest that the multiple interfaces, electromagnetic loss media, and changes of representative EM wavelength could be critical roles in tailoring the EMI shielding performance. The results provide a versatile strategy that could be extended in other frequency ranges and various types of sandwich structures, promising great opportunities for designing and fabricating advanced electromagnetic attenuation materials and devices.

Integral Equation Analysis of EM Scattering from Multilayered Metallic Photonic Crystal Accelerated with Adaptive Cross Approximation

A space-domain integral equation method accelerated with adaptive cross approximation (ACA) is presented for the fast and accurate analysis of electromagnetic (EM) scattering from multilayered metallic photonic crystal (MPC). The method directly solves for the electric field in order to easily enable the periodic boundary condition (PBC) in the spatial domain. The ACA is a purely algebraic method allowing the compression of fully populated matrices; hence, its formulation and implementation are independent of integral equation kernel (Green’s function). Therefore, the ACA is very well suited for accelerating integral equation analysis of periodic structure with the integral kernel of the periodic Green’s function (PGF). The computation of the spatial-domain periodic Green’s function (PGF) is accelerated by the modified Ewald transformation, such that the multilayered periodic structure can be analyzed efficiently and accurately. An effective interpolation method is also proposed to fast compute the periodic Green’s function, which can greatly reduce the time of matrix filling. Numerical examples show that the proposed method can greatly save the frequency sweep time for multilayered periodic structure.

The Decorrelation Time Accumulation Restrain Method for Sea Clutter Spike

Modern wide-band radar system could resolve the refined sea surface structure, which results from the strong instantaneous clutter spike appearing in the background echo, and severely affects the target detection efficiency in searching process. It is important for radar design and efficiency-improving to investigate the high-resolution clutter restraint method. One of the typical restraint methods is decor relation time accumulation method, which can put down the clutter energy. This article studies its application on clutter-restraint and detection rate improvement of target detection in typical sea clutter scene. The detection effect under different-resolution in simulation spectacle is also studied, which shows that high resolution improved the right detection probability.

Ultrabroadband Three-Dimensional Printed Radial Perfectly Symmetric Gradient Honeycomb All-Dielectric Dual-Directional Lightweight Planar Luneburg Lens

An ultrabroadband all-dielectric planar Luneburg lens has been designed and fabricated in this study, which is in the form of a radial gradient lightweight honeycomb column. Because of the novel design of a radial symmetric honeycomb-like microstructure in the subwavelength dimension and the radial gradient configuration according to the refractive index distribution of Luneburg lens, the present lens can focus incident plane waves on the opposite side with high convergence, and its operating frequency range is rather broadband, spanning from 6 to 16 GHz. Besides, the all-dielectric honeycomb-like lens is lightweight with a mass density of 0.23 g/cm3, and its broadband transmittance is higher than the reported cases consisting of metallic metamaterial or gradient photonic crystal structures. A prototype of the lens is fabricated by using 3D printing techniques, on which the electric near-field distribution and far-field radiation pattern measurements have been carried out, and the aforementioned performances were demonstrated experimentally. It was also observed that for two point sources placed at the edge of the lens whose intersection angle with the center of the lens is 90°, the far-field radiation pattern was still kept highly directional, which means that the lens can generate two highly directional beams simultaneously, and is an efficient double input-double output device.

Sub-wavelength imaging and negative refraction measurement of triangle prism

Sub-wavelength imaging, which can transform evanescent wave into travelling wave and utilize wave component with small wave-vector, is receiving much study interest. Both negative refraction and beam forming can realize sub-wavelength imaging, and their mechanism are analyzed and compared. The refraction behavior under different incident angle is measured experimentally, and it is found that larger incident angle is better for near field energy transfer, while smaller incident angle is better for detection application.

The research of circuit analog absorber using square resistance arrays

Developing high-performance radar absorption material (RAM) is always important in the stealth projects. Circuit analog (CA) absorber studied in this thesis is better than traditional Jaumann absorber in many aspects, such as thickness and absorption band. The principle and design method of CA absorber is explored in this thesis. One sample of single-layer CA absorber is designed, and the simulation results agree well with the measurement results, so the validity of this design method is verified sufficiently. The contributions of this thesis provide the foundation for further designing CA absorber.

Study of a conformal elliptical tapered slot antenna for UWB applications

A conformal elliptical tapered slot antenna has been designed and developed for urtrawideband (UWB) wireless communications. It is studied mounted on a cylindrical surface and is proven to operate equally well compared to its planar rival. Return loss, gain and E and H plane radiation pattern simulations are presented covering the whole ultrawideband. The antenna has demonstrated good performance and the characteristics are not deterioration when the antenna is mounted on cylindrical surfaces of various radius when the direction of curvature is in the transverse direction. The presented study shows that the proposed antenna can be optimized and tested in planar shape and still be trusted to operate equally well under conditions like in wearable electronics, where their planar condition cannot be guaranteed.

New synthesis time accumulation sea spike restraint method

Sea clutter spike has more negative impact as maritime radar resolution improves, which could cause target detection error or tracking miss. Imaging mode has been gradually utilized in order to improve target detection ability in sea background. Decorrelation restraint method has been developed to suppress sea spike, but its effect has not been studied thoroughly. Our work proposed a new synthesis spike restraint method combined time decorrelation accumulation with improved self-adaptation multi-scale filtering algorithm in sea image target detection and tracking process. And its improvement to detection performance is evaluated, providing reference for spike restraint measurement and sea target stealth technology development.

A new correlation parameter extraction method for searching mode sea clutter restraint

Correlation characteristics are important for sea clutter restraint in radar image processing, which is universal in certain features for both radar and optical image. The spatial-temporal dispersion relation contained in sea clutter, which usually fits into the sum of wind friction linear item and gravity wave item, is proved effective for sea clutter restraint recently. A sea clutter restraint method for mobile searching mode observation point, which is prevalent in maritime air-borne platform, is developed from a former restraint method for shore-based stationary radar. A new extraction method for intrinsic dispersion linear item parameter of sea clutter aiming at range profile of searching mode radar system is proposed, which forms the core of the restraint method. The statistical model is founded on spatial-temporal dispersion relation and radar illumination geometry. Simulation results shows Doppler shift of measured wind linear item have a bias from the sum of sea wind and radar platform velocity. A systematic study suggests the bias could be attributed to interaction between wind friction and gravity wave item, and a rather good fitting result is obtained. CFAR detection processing for a set of experimental clutter data shows that this intrinsic dispersion extraction method formula is found to be effective in detection probability enhancement. The restraint method based on the proposed dispersion extraction method could be utilized in mobile maritime surveillance equipments.