Octree based technique for fast analyzing shadowing relationship of complex target

In this study, physical optics (PO) method have been applied to electromagnetic scattering problem related to high order inhomogeneous impedance cylinder of arbitrary shape. In the solution, induced electric and magnetic currents on the illuminated region of surface are expressed by means of incident field and high order inhomogeneous impedance boundary condition then scattered field is calculated using Huygens type Green's formula. Obtained scattering width results are compared with those obtained by other analytical and numeric methods and good agreements are observed especially monostatic case. Because of the fact that PO method does not need matrix inversion, which requires high CPU time, PO method also significantly reduces computer calculation time according the other methods. In this study, TM case is considered, but similar procedure can be easily applied to TE case and even also three‐dimensional inhomogeneous impedance objects using dyadic Green's functions as well. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1031–1036, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22339

In this work, a hemispheric radome with conformal frequency selective surface is designed and analyzed by using the physical optics method. The conformal frequency selective surface consists of two layers of substrate and three layers of periodic patches and grids. The radome is manufactured and measured. The comparison between the analysis result of the physical optics method and the experimental result show that they are agree very well, which verify that the physical optics method is an effective method for calculating the electrical large structures.

As the classic analytical methods cannot calculate the electromagnetic scattering characteristics at Low Grazing Angle (LGA), a novel numerical method is presented by utilizing the Radar Cross Section (RCS) of the low grazing two-dimensional PM sea spectrum based on the triangles-based Physical Optics (PO) method in this paper. The calculated RCS is compared with the numerical calculation method of different targets and frequencies of incident wave. The results show that PO method is more accurate, especially under LGA condition, and it has a better agreement with the results calculated by commercial software FEKO.

In this paper, physical optical (PO) method is introduced and applied to calculate the echo data from a missile illuminated by plane waves with arbitrary aspects and different frequencies for inverse synthetic aperture radar (ISAR) imaging. The missile is approximated by component disassembly method (CMD) and concept of scattering matrix is introduced in order to simplify complexity of the numerical calculation. Generated images of several incidence angles are analyzed by signal processing theory and can precisely represent the mirror scattering region and the rotation of the target. The results of the simulation indicate that PO method is simple and effective to calculate the radar echo of a missile for ISAR imaging.

In order to control its attitude, there usually have wings or other structures on the midcourse target. It is the foundation to simulate the radar echo of this kind of rotationally asymmetric target to get it recognized correctly. Firstly, the position variation of each scattering center on both the body and the wing is analyzed. After that, according to the high frequency method and local field theory, the RCS calculation formulas of body and wings of the target are derived with the Geometrical Theory of Diffraction(GTD) and Physical Optics(PO) method respectively. Then, a simple method is put forward to judge whether the wing is shielded with the target's movement according to the PO method. Finally, the wideband radar echo is simulated and the impacts of non-idealization of the scattering centers and rotationally asymmetry of the target on the echo are also analyzed.

The Physical Optics (PO) method is used to derive simplified expressions to compute the radiation electric fields of planar graded-index and geodesic lenses based on a parallel-plate waveguide (PPW) implementation. If the PO method is combined with ray-tracing (RT) techniques, the resulting RT-PO procedure is capable of computing radiation patterns and gain of the PPW-based lens antennas when their apertures have a general shape and the electric field is vertically polarized. The RT-PO method is validated by comparing it with the full-wave simulation results of the commercial software ANSYS HFSS for three application cases. The results show that the RT-PO approach is not only very efficient from a computational point of view but also accurate, thus being a very convenient analysis/design tool for this kind of antenna.

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from L-band to X-band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the S-band and the band range of 7-11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets.

The application of radar absorbing materials on the surface of metal aircraft can effectively reduce the radar cross section (RCS). In this paper, the physical optics (PO) method is used to calculate the RCS of electrically large coated targets. First, we calculate the RCS of the original X29 aircraft and the X29 aircraft coated with a broadband two-layer radar absorbing coating. In addition, the backscattered electric field data of coated and uncoated X29 aircraft are obtained by using the PO method, respectively. Finally, the two-dimensional Inverse Fourier Transform (IFT) of the collected data is taken to form the Inverse Synthetic Aperture Radar (ISAR) image.

Calculation of a double reflector Cassegrain antenna by physical optics method with taking into account multiple reflections between the reflector and the subreflector was performed. It was shown that the convergence of antenna characteristics (gain, antenna efficiency, side-lobe level) with the increase of accounting reflections is observed. To check the method of multiple reflections the same Cassegrain antenna was calculated by the method of electric field integral equation with the unknown surface electric currents on the reflector and the sub-reflector. The comparison showed the coincidence of the result obtained by two different methods. The calculation of gain and efficiency of a Cassegrain antenna in frequency range from 1 to 10 GHz was performed by physical optics method with multiple reflections.

Modelling, simulation, and visualization of porous media have practical applications in the petroleum and chemical industries. Advances in modelling and simulation of porous media can help in the understanding of processes in petroleum rocks. The paper presents new algorithms for modelling and visualizing fluid interfaces within porous media. These algorithms allow the creation and nondestructive testing of porous samples in a virtual laboratory of porous media. The visualization process is one of the main elements in such a laboratory. Results of these simulated processes can be visualized as 3D or 2D images, where colour and shading emphasize fluid saturations and interfaces between two interacting fluids as a function of varying pressure. These algorithms are based on the octree data structure. The idea is to create a porous media sample with a realistic structure and at a level of complexity commensurate with actual samples. Simulations are then run on this model. This method contrasts with traditional porous media modelling where a mathematical model (lattice) is simulated using sets of equations.

Multi-agent systems and stereo vision navigation is a challenging area in Robotic research. The task can be widely scalable and optimized for a specific application. An efficient centralized heterogeneous swarm robotic system is proposed and implemented for digital elevation mapping of an unknown terrain using stereo vision. The utility of vision sensors compared to other sensor systems is shown in mapping and navigation application on planetary terrain. The cloud computing paradigm is implemented in the communication module via a private cloud over OLSR. The system utilizes real-time odometry, disparity mapping, cloud computing, and network hazard recovery algorithms for efficient terrain mapping. The map is stored in an octree data structure. The system is designed keeping in perspective planetary exploration mission, however it is widely scalable and can be modified for various civilian and military purposes.

Food color is an important attribute of food quality. This paper discusses issues in using machine vision for the objective assessment of food color, such as color image segmentation, calibration and statistical parameter design, and their application to pea color assessment. The algorithm first established a 3D histogram on RGB color space based on an octree data structure. From the color space, a statistical index was calculated to measure the major color of an object simulating the characteristics of human color perception. This method was applied to assess the major color of peas. Accuracy and efficiency were achieved in measuring pea seed and its variations.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents a study on physically based modeling and simulation of soft tissue deformation, with the goal of producing realistic, real-time effects during the simulation. We consider soft tissue deformation as a solid mechanics problem with a linear elastic constitutive law. A point collocation based meshfree method is employed to solve the governing equations. To achieve real-time performance, an octree data structure is used to organize the support sets and the nodes to expedite the computation in the meshfree method. The developed system brings together the surface representation for visualization and meshfree modeling for physically based animation to set up a virtual reality environment for soft tissue surgery simulation.

The Dynamic Brain Project will create an interactive database on the human brain, available via the Internet. In addition to medical images and textual information, the completed project will give users access to all types of data, including video and sound. One of the primary tasks is to create a point-and-click navigation interface for the user, giving access to the data through a 3-dimensional, volumetric image generated from medical scans. The project uses Postgres, an object-oriented database management system. Data relations (tables) are spatially linked to the interface image by the x,y,z-coordinates to which they belong. These coordinates are determined by building the volume with an octree data structure and outputting the spatially registered data to a Postgres table. This paper summarizes the database schema and the octree algorithm for the project.

In the paper, high resolution range profile (HRRP) of a target above rough ground is analyzed based on the scattered echo data. The electromagnetic scattering of composite model is solved by the hybrid method of physical optics (PO)- shooting and bouncing ray (SBR). And an octree data structure is used to accelerate the ray tracing progress. The bistatic electromagnetic scattering of a reduced-scale vehicle target above rough ground is calculated by our method and compared with the simulation result with MLFMM in FEKO. Then by inverse Fourier transform of backscattering echo data, the range profile of composite model is obtained.