Robert W. Scharstein

Bio: Robert W. Scharstein is an academic researcher from University of Alabama. The author has contributed to research in topics: Plane wave & Boundary value problem. The author has an hindex of 12, co-authored 41 publications receiving 359 citations. Previous affiliations of Robert W. Scharstein include Saab Sensis Corporation.

Electrostatics of graphene: Charge distribution and capacitance

Abstract: The distribution of net electric charge in graphene is investigated, using both a constitutive atomic charge–dipole interaction model and an approximate analytical solution to Laplace’s equation. These approximations, unlike first-principle calculations, are applicable to graphene sizes that are consistent with experiments. It is found that the analytical model gives a good description of the charge distribution, except for the very edge atoms because of the atomic edge state, which can instead be treated by the numerical model.

Computing elliptic membrane high frequencies by Mathieu and Galerkin methods

Abstract: Resonant modes of an elliptic membrane are computed for a wide range of frequencies using a Galerkin formulation. Results are confirmed using Mathieu functions and finite-element methods. Algorithms and their implementations are described to handle Dirichlet or Neumann boundary conditions and draw animations or contour plots of the modal surfaces. The methods agree to four or more digit accuracy for the first one hundred modes. The effects of high function order and high frequency parameter upon the convergence of the modified Mathieu function series are discussed and quantified. The Galerkin method is conceptually simple and requires only an eigenvalue solver without the need of special functions.

Electromagnetic Plane Wave Excitation of an Open-Ended, Finite-Length Conducting Cylinder

Abstract: A mixed boundary value problem is formulated for the surface currents that are induced by a time-harmonic plane wave incident upon an open-ended conducting tube of finite length. Scattered fields are represented by spatial Fourier transforms in the axial dimension for each of the uncoupled azimuthal Fourier modes of this body of revolution. Numerically efficient mathematical expressions having explicit physical significance are derived to solve the set of linear equations from a Galerkin expansion of the currents in terms of Chebyshev polynomials with edge-condition weighting. Resultant surface currents and axial fields are calculated for several combinations of scatterer geometry and frequency, and interpreted partially in terms of travelling waves external and internal to the conducting cylinder.

Mutual coupling in a slotted phased array, infinite in E-plane and finite in H-plane

Abstract: The mutual admittance matrix is computed for a planar phased array of thin slots with assumed single-mode cosinusoidal aperture electric field The array is of infinite extent in the E-plane and of finite extent in the H-plane The H-plane excitation is arbitrary and the array is phase scanned in the E-plane Resultant active row-port admittances and H-plane aperture distribution are in agreement with large strictly finite array calculations and with a Floquet mode infinite array model, for the example case of uniform H-plane excitation >

Capacitance of a tube

Abstract: The electrostatic problem of a hollow, conducting tube of finite length held at a fixed potential is solved using two methods. A two-term Galerkin solution is constructed for the surface distribution of induced charge. The sum of a uniform component and a simple edge-condition term provides a variational solution to the dual integral equations that are the equations-of-motion for the mixed boundary value problem. Comparisons are made with the numerical results of an independent boundary element or moment method. The numerical solution uses collocation or point matching and a piecewise constant basis for the charge density.

Finite antenna arrays and FSS

Abstract: Foreword. Preface. Acknowledgments. Symbols and Definitions. 1. Introduction. 1.1 Why Consider Finite Arrays? 1.2 Surface Waves Unique to Finite Periodic Structures. 1.3 Effects of Surface Waves. 1.4 How Do We Control the Surface Waves? 1.5 Common Misconceptions. 1.6 Conclusion. 1.7 Problems. 2. On the RCS of Arrays. 2.1 Introduction. 2.2 Fundamentals of Antenna RCS. 2.3 How to Obtain a Low sigmatot by Cancellation (Not Recommended). 2.4 How Do We Obtain Low sigmatot Over a Broad Band? 2.5 A Little History. 2.6 On the RCS of Arrays. 2.7 An Alternative Approach: The Equivalent Circuit. 2.8 On the Radiation from Infinite vs. Finite Arrays. 2.9 On Transmitting, Receiving and Scattering Radiation Pattern of Finite Arrays. 2.10 Minimum versus Non-Minimum Scattering Antennas. 2.11 Other Non-Minimum Scattering Antennas. 2.12. How to Prevent Coupling Between the Elements Through the Feed Network. 2.12 How to Eliminate Backscatter Due to Tapered Aperture Illumination. 2.13 Common Misconceptions. 2.15 Summary. 2.16 Problems. 3. Theory. 3.1 Introduction. 3.2 The Vector Potential and the H-Field for Column Arrays of Hertzian Elements. 3.3 Case I: Longitudinal Elements. 3.4 Case II: Transverse Elements. 3.5 Discussion. 3.6 Determination of the Element Currents. 3.7 The Double Infinite Arrays with Arbitrary Element Orientation. 3.8 Conclusions. 3.9 Problems. 4. Surface on Passive Surfaces of Finite Extent. 4.1 Introduction. 4.2 Model. 4.3 The Infinite Array Case. 4.4 The Finite Array Case Excited by Generators. 4.5 The Element Currents on a Finite Array Excited by an Incident Wave. 4.6 How the Surface Waves are Excited on a Finite Array. 4.7 How to Obtain the Actual Current Components. 4.8 The Bistatic Scattered Field from a Finite Array. 4.9 Parametric Study. 4.10 How to Control Surface Waves. 4.11 Finite Tuning the Load Resistors at a Single Frequency. 4.12 Variation with Angle of Incidence. 4.13 The Bistatic Scattered Field. 4.14 Previous Work. 4.15 On Scattering from Faceted Radomes. 4.16 Effects of Discontinuities in the Panels. 4.17 Scanning in the E-plane. 4.18 Effect of a Groundplane. 4.19 Common Misconceptions Concerning Element Currents on Finite Arrays. 4.20 Conclusion. 4.21 Problems. 5. Finite Active Arrays. 5.1 Introduction. 5.2 Modeling of a Finite x Infinite Groundplane. 5.3 Finite x Infinite Array with an FSS Groundplane. 5.4 Micro Management of the Backscattered Field. 5.5 The Model for Studying Surface Waves. 5.6 Controlling Surface Waves on Finite FSS Groundplanes. 5.7 Controlling Surface Waves on Finite Arrays of Active Elements with FSS Groundplane. 5.8 The Backscatterd Fields from the Triads in a Large Array. 5.9 On the Bistatic Scattered Field from a Large Array. 5.10 Further Reduction: Broadband Matching. 5.11 Common Misconceptions. 5.12 Conclusion. 5.13 Problems. 6. Broadband Wire Arrays. 6.1 Introduction. 6.2 The Equivalent Circuit. 6.3 An Array with Groundplane and No Dielectric. 6.4 Practical Layouts of Closely Spaced Dipole Arrays. 6.5 Combination of the Impedance Components. 6.6 How to Obtain Grater Braodwidth. 6.7 Array with a Groundplane and a Single Dielectric Slab. 6.8 Actual Calculated Case: Array with Groundplane and Single Dielectric Slab. 6.9 Array with Groundplane and Two Dielectric Slab. 6.10 Comparison Between the Single and Double Slab Array. 6.11 Calculated Scan Impedance for Array with Groundplane and Two Dielectric Slabs. 6.12 Common Misconceptions. 6.13 Conclusions. 7. An Omnidirectional Antenna with Low RCS. 7.1 Introduction. 7.2 The Concept. 7.3 How Do We Feed the Elements? 7.4 Calculated Scattering Pattern for Omnidirectional Antenna with Low RCS. 7.5 Measured Backscatter from a Low RCS Omnidirectional Antenna. 7.6 Common Misconceptions. 7.7 Conclusions and Recommendations. 8. The RCS of Two-Dimensional Parabolic Antennas. 8.1 The Major Scattering Components. 8.2 Total Scattering from a Parabolic Reflector with a Typical Feed. 8.3 Practical Execution of the Low RCS Feed. 8.4 Out of Band Reduction. 8.5 Common Misconceptions on Edge Currents. 8.6 Conclusion. 9. Aperiodicity: Is it a Good Idea? 9.1 Introduction. 9.2 General Analysis of Periodic Structures with Perturbation of Element Loads and/or Inter-element Spacings. 9.3 Perturbation of Arrays of Tripoles. 9.4 Making Use of Our Observations. 9.5 Anomalies due to Insufficient Number of Models. 9.6 Aperiodicity on Finite Arrays. 9.7 Conclusions. 10. Summary and Final Remarks. 10.1 Summary. 10.2 Are We Going in the Right Direction? 10.3 Let Use Make Up! Appendix A. Determination of Transformation and Position Circles. Appendix B. Broadband Matching. Appendix C. Meander-Line Polarizers for Oblique Incidence. Appendix D. On the Scan versus the Embedded Impedance. References. Index.

Transparent Flexible Graphene Triboelectric Nanogenerators

Abstract: S. Kim, Dr. M. K. Gupta, K. Y. Lee, K.-S. Shin, S. K. Kim, K. H. Lee, Prof. S.-W. Kim School of Advanced Materials Science and Engineering Sungkyunkwan University (SKKU) Suwon 440–746 , Republic of Korea E-mail: kimsw1@skku.edu A. Sohn, Prof. D.-W. Kim School of Department of Physics Ewha Womens University Seoul 120–750 , Republic of Korea T. Y. Kim, D. Kim, Prof. S.-W. Kim SKKU Advanced Institute of Nanotechnology (SAINT) Center for Human Interface Nanotechnology (HINT) SKKU-Samsung Graphene Center Sungkyunkwan University (SKKU) Suwon 440–746 , Republic of Korea Dr. H.-J. Shin Samsung Advanced Institute of Technology Yongin 446–712 , Republic of Korea

Spatial Filtering for Wall-Clutter Mitigation in Through-the-Wall Radar Imaging

Abstract: Radio-frequency imaging of targets behind walls is of value in several civilian and defense applications. Wall reflections are often stronger than target reflections, and they tend to persist over a long duration of time. Therefore, weak and close by targets behind walls become obscured and invisible in the image. In this paper, we apply spatial filters across the antenna array to remove, or at least significantly mitigate, the spatial zero-frequency and low-frequency components which correspond to wall reflections. Unmasking the behind-the-wall targets via the application of spatial filters recognizes the fact that the wall electromagnetic (EM) responses do not significantly differ when viewed by the different antennas along the axis of a real or synthesized array aperture which is parallel to the wall. The proposed approach is tested with experimental data using solid wall, multilayered wall, and cinder block wall. It is shown that the wall reflections can be effectively reduced by spatial preprocessing prior to beamforming, producing similar imaging results to those achieved when a background scene without the target is available.