The Transportation Security Administration is tasked with the job of performing safety screening of millions of air travel passengers annually in a safe and efficient manner. One of the most widely deployed detection systems is the L3 Technologies “Provision” body scanner, which utilizes millimeter wave radio frequencies (RF). Have you ever wondered what type and levels of RF energy are used to execute this routine security screening test? Recently, the Department of Homeland Security, Transportation Security Administration, tasked the National Academies of Science (NAS) to execute an updated safety analysis of the L3 manufactured TSA ProVision Body Scanner units deployed in airports world-wide. In the process of executing their tasking, the NAS realized there was very little peer-reviewed published data on calibrated field incident power within the ProVision scanner itself. While L3 has their own factory acceptance program, the NAS wanted independent measurements executed on operational L3 machines at four randomly selected airports. The NAS contracted with the team of BerrieHill Research and Applied Research Associates to design a specialized field probe system that measures the RF field strength of the Provision Units. This very challenging measurement environment required design ingenuity to fulfill the contract needs, since this system was not allowed to physically connect to any part of the ProVision machine. We had to place a field measurement device inside the unit where the passenger stands, and record all data “over the air” only. This paper will completely describe the BRC/ARA Provision Scanner field probe measurement system, and present calibrated RF field measurements.

Applicability of the Adaptive Cross Approximation and hierarchical matrix approach to the problems of computational electromagnetics is examined both theoretically and numerically. Reduction of the required storage and computational speed-up during each step of a numerical solution are analyzed. Numerical examples are produced using a Northrop Grumman's proprietary code SWITCH, which is based on the hybrid FEM-BIE method.

In this paper, we propose a novel scheme to accelerate integral equation solvers when applied to multiscale problems. These class of problems exhibit multiple length/frequency scales and arise when analyzing scattering/radiation from realistic structures where dense discretization is necessary to accurately capture geometric features. Solutions to the discretized integral equations due to these structures is challenging, due to their high computational cost and ill-conditioning of the resulting matrix system. The focus of this paper is on ameliorating the computational cost. Our approach will rely on exploiting the recently developed accelerated Cartesian expansion (ACE) algorithm to arrive at a method that is stable and efficient at low frequencies. These will then be integrated with the well known fast multipole method, thus forming a scheme that is wideband. Rigorous convergence estimates of this method are derived, and convergence and efficiency of the overall fast method is demonstrated. These are then integrated into an existing integral equation solver, whose efficiency is demonstrated for some practical problems.

Commercial windmill-driven power turbines ("wind turbines") are expanding in popularity and use in the commercial power industry, since they can generate significant electricity without using fuel or emitting carbon-dioxide ldquogreenhouse gasrdquo. In-country and near-off-shore wind turbines are becoming more common on the European continent. The United States has recently set long-term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind-turbine towers and rotors are very large, with blades exceeding 67 m in diameter, and tower heights exceeding 55 m. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving, metallic devices is the potential interference such structures present to an array of civilian air-traffic-control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when located within line of site of air-traffic-control or air-route radars [Report to the Congressional Defense Committees on The Effect of Windmill Farms On Military Readiness, 2006]. In the spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so that the interference issues could be credibly studied. This paper, the first of two parts, will discuss the calibrated RCS measurement of the turbines, and compare this data (with its uncertainty) to modeled data.

In this paper, we propose a fast solver based on recently developed accelerated Cartesian expansion (ACE) algorithm. ACE is a tree code based algorithm like FMM but based on Cartesian harmonics instead of spherical harmonics. It can be shown that expansion in Cartesian harmonics is stable for low-frequencies unlike conventional FMM. Here, a method to combine ACE and FMM algorithm for efficient analysis of mixed-scale geometries is presented. Results demonstrating the viability of the fast kernel is presented here and their integration with MoM solvers will be presented at the conference.

For future Shuttle missions, a radar system consisting of a new wideband C-band radar and two Weibel continuous pulse Doppler X-band radars has been implemented for adequate detection of debris during launch and ascent. Three radars will digitally record tracking data of the Shuttle from launch until signal is lost with the primary timeframe of interest being launch to launch plus 150 seconds. In this paper, radar cross sections and range profiles of the Shuttle are computed by Xpatch for these three radars.

In this paper, Newmark time-stepping scheme and edge elements are used to numerically solve the time-dependent scattering problem in a three-dimensional cavity. Finite element methods based on the variational formulation derived in [23] are considered. Due to the lack of regularity of ε r , the existence and uniqueness of the discrete solutions and their convergence are proved by using the concept of collectively compact operators. An optimal convergence rate in the energy norm is also established.

We present a finite element method for the electromagnetic scattering from a 2-D cavity embedded in the infinite ground plane.The problem is first discretized in time by the β, γ Newmark time-marching scheme.The resulting semi-discrete problem is well-posed.Error analysis of the fully discrete finite element formulation is performed.Stability criteria of the time-stepping scheme are also established.Numerical experiments demonstrate the accuracy and stability of the method.

In this paper, we study the plane wave scattering from perfectly electric conducting (PEC) bodies of revolution (BOR) with tip singularities. It is known that solutions to surface integral equations such as magnetic, electric, and combined field integral equations (MFIE, EFIE, and CFIE, respectively) are singular near the tips. Consequently, the convergence of method of moments (MoM) based on those surface integral equations is not optimal or guaranteed. By using appropriate graded meshes, one can retain the optimal convergence rate in MoM.

During the Columbia Shuttle investigation, AFRL tried to identify a piece of on-orbit debris that originated from the Orbiter during its second day in space. This "Flight Day Two (FD2)" object was detected by UHF radar and tracked for three days before falling out of orbit. Extensive RCS measurements performed by AFRL and corresponding ballistic analysis by USAF Space Command narrowed the potential candidates down to just two possible classes of objects; (1)a section of Reinforced Carbon-Carbon (RCC) leading edge panel acreage, and (2) a section of RCC "Tee-seals". During the investigation, AFRL was asked to estimate the UHF RCS of various whole and fragmentary Tee-seals originating between panel segment #6 and #11 on the Shuttle Orbiter left wing, in order to compare with the on-orbit UHF RCS observations. Since actual Orbiter Tee-seal hardware, either whole or fractured, from the left wing area were not available, we predicted UHF RCS on various virtual Tee-seal fragment geometries to confirm or eliminate the Tee-seal as a candidate for the FD2 object. In this paper, we summarize our RCS predictions which conclusively show that a whole or partial RCC Tee-seal could not be the FD2 object. This left the RCC panel acreage as the only known object that satisfies both the on-orbit observed ballistic and UHF RCS data, a confirming piece of evidence in the Columbia investigation.

In this paper, Newmark time-stepping scheme and edge elements are used to numerically solve the time-dependent scattering problem in a three-dimensional polyhedral cavity. Finite element methods based on the variational formulation derived in Van and Wood (Adv. Comput. Math., to appear) are considered. Existence and uniqueness of the discrete problem is proved by using Babuska-Brezzi theory. Finite element error estimate and stability of the Newmark scheme are also established. Copyright (C) 2003 John Wiley Sons, Ltd.

In this paper, we consider the time-domain scattering problem of a two-dimensional overfilled cavity embedded in the infinite ground plane. The problem is first discretized in time by the $\beta,\ \gamma$ Newmark time-marching scheme. At each time step, the variational formulation of the semidiscrete problem is derived via a nonlocal boundary condition to truncate the infinite problem domain. Existence and uniqueness of the variational solutions are established. Error analysis of the fully discrete problem is performed. Stability criteria of the time-stepping scheme are also obtained.

In this paper, a finite element method (FEM) is implemented to compute the radar cross section of a two-dimensional (2-D) cavity embedded in an infinite ground plane. The method is based on the variational formulation. which uses the Fourier transform to couple the fields outside the cavity and those inside the cavity; hence, the scattering problem can be reduced to a bounded domain. The convergence of the discrete finite element problem is analyzed. Numerical results are presented and compared with those obtained by the standard finite element-Green function method and by the 2-D integral equation method.

Abstract : In this final report, we have summarized the progress made during the period of September 1. 2002-September 30, 2003. We derive the integral equations for (electric fields propagating in a fiber of arbitrary cross section and arbitrary refractive index. Mathematical analysis of conventional optical fibers is rich and widely available in literature, for example 3, 9, 11 and references therein. It helps the advancement of optical fiber industry in understanding and designing fibers for data transport and telecommunications. In knowledge, there is little of rigorous mathematical study of Bragg fibers due to the fabrication difficulty. Recently, the publications of A dielectric omnidirectional reflector 4, An all-dielectric coaxial wave guide 8, and External reflection from omnidirectional dielectric mirror fibers 7 in Science report successful fabrications of omnidirectional reflectors and multi-layered fibers for optical wavelengths. These articles create a new interest in studying low-loss Bragg fibers at microwave and millimeter wavelengths for radar applications. From previous examples in Section 4, multi-layered fibers of radii between 7 mm and 19 mm concentrate wave propagation within their air core for wavelengths in the microwave range.

Presented here is a time-domain finite element method for approximating Maxwell's equations. The problem is to approximate the electromagnetic fields scattered by a bounded, inhomogeneous cavity embedded in an infinite ground plane. The time-dependent scattering problem is first discretized in time by Newmark's time-stepping scheme. The resulting semidiscrete problem is proved to be well posed. A nonlocal boundary condition on the cavity aperture is constructed to reduce the computational domain to the cavity itself. Stability analysis and error estimates of the fully discrete problem are provided.

Time–domain Maxwell's equations are studied for the electromagnetic scattering of plane waves from an arbitrarily shaped cavity filled with nonhomogeneous medium. A transparent boundary condition is introduced to reduce the problem to the bounded cavity. Existence and uniqueness of the model problem are established by a variational approach and the Hodge decomposition. The analysis forms a basis for numerical solution of the model problem.

Consider a time-harmonic electromagnetic plane wave incident on a cavity in a ground plane. Inside the cavity, the medium may be inhomogeneous. Variational formulations are studied in this note. Existence and uniqueness of the solutions for the model problems are established. The variational approach also forms a basis for a class of finite element methods.

Optical fibers have found important applications in chemical imaging and single-particle detection. The applications make use of the propagating evanescent energy existing outside the core of a fiber. In this paper, a variational method is described to solve two-dimensional Helmholtz eigenvalue problems for a core of arbitrary shape. The method enables the problem in the infinite domain to be reduced to a bounded one by using a transparent boundary condition. It is shown that the variational formulation does not produce spurious solutions. An optimal error estimate is obtained for the associated finite element method. Finally, numerical experiments indicate that square fibers yield sufficient evanescent energy for imaging application.

A finite element method is presented to find the propagation characteristics of an optical fiber with arbitrary cross section. This method uses a non-local boundary operator to reduce the infinite problem (open waveguide) to a bounded one. Evanescent energy in circular and square fibers of the same core area are computed and compared to show that square fibers can be effectively used in single molecule detection.