Author

# Natarajan Kalyanasundaram and Gnanamoorthi Babu

Bio: Natarajan Kalyanasundaram and Gnanamoorthi Babu is an academic researcher from Jaypee Institute of Information Technology. The author has contributed to research in topics: Electromagnetic radiation & Dispersion (optics). The author has an hindex of 1, co-authored 1 publications receiving 14 citations.

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TL;DR: The dispersion equation for electromagnetic waves guided by an open tape helix for the standard model of an inflitesimally thin and perfectly conducting tape is derived from an exact solution of a homogeneous boundary value problem for Maxwell's equations as mentioned in this paper.

Abstract: The dispersion equation for electromagnetic waves guided by an open tape helix for the standard model of an inflnitesimally thin and perfectly conducting tape is derived from an exact solution of a homogeneous boundary value problem for Maxwell's equations. A numerical analysis of the dispersion equation reveals that the tape current density component perpendicular to the winding direction does not afiect the dispersion characteristic to any signiflcant extent. In fact, there is a signiflcant deviation from the dominant-mode sheath- helix dispersion curve only in the third allowed region and towards the end of the second allowed region. It may be concluded that the anisotropically conducting model of the tape helix that neglects the above transverse-current contribution is a good approximation to the isotropically conducting model that takes into account this contribution except at high frequencies even for wide tapes.

16 citations

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22 May 2018TL;DR: In this article, the authors present a survey of the theory and design of commercially significant types of gridded, linear-beam, crossed-field and fast-wave tubes.

Abstract: Do you design and build vacuum electron devices, or work with the systems that use them? Quickly develop a solid understanding of how these devices work with this authoritative guide, written by an author with over fifty years of experience in the field. Rigorous in its approach, it focuses on the theory and design of commercially significant types of gridded, linear-beam, crossed-field and fast-wave tubes. Essential components such as waveguides, resonators, slow-wave structures, electron guns, beams, magnets and collectors are also covered, as well as the integration and reliable operation of devices in microwave and RF systems. Complex mathematical analysis is kept to a minimum, and Mathcad worksheets supporting the book online aid understanding of key concepts and connect the theory with practice. Including coverage of primary sources and current research trends, this is essential reading for researchers, practitioners and graduate students working on vacuum electron devices.

62 citations

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TL;DR: In this article, the homogeneous boundary value problem in the electromagnetic wave propagation in a dielectric-loaded perfectly conducting tape helix with infinitesimal tape thickness is investigated.

Abstract: The homogeneous boundary value problem existing in the electromagnetic wave propagation in a dielectric-loaded perfectly conducting tape helix with infinitesimal tape thickness is investigated in this study. The ill-posed boundary value problem is regularised using the mollification method. The homogeneous boundary value problem is solved for the dielectric loaded perfectly conducting tape helix taking into account the exact boundary conditions for the perfectly conducting dielectric loaded tape helix. The solved approximate dispersion equation takes the form of the solvability condition for an infinite system of linear homogeneous equations namely, the determinant of the infinite order coefficient matrix is zero. For the numerical computation of the dispersion equation, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The tape-current distribution is estimated from the null-space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation. The numerical results suggest that the propagation characteristic computed by the anisotropically conducting model (that neglects the component of the tape-current density perpendicular to the winding direction) is only an abstinent approximation to consider for moderately wide tapes.

15 citations

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TL;DR: In this paper, an analytical model for the design of the folded waveguide traveling wave tube (FWTWT) was developed for the physical view for rapid design optimization of the FWTWT.

Abstract: We are developing an analytical model for the design of the folded waveguide traveling wave tube (FWTWT). This analytical model provides the physical view for rapid design optimization of the FWTWT. The design and analysis of the FWTWT using the spatial harmonics method of the TE10 mode of the EM wave are presented. An X-band FWTWT is used to verify this method. The normalized dispersion and beam line equations are used to simplify the design process so that the FWTWT can be designed to operate at any desired frequency. The small signal gain of an FWTWT is calculated by using Madey's theorem. The results of this analysis are compared with the numerical single particle simulation carried out using MATLAB. The results are in excellent agreement. The Madey's theorem can be used to provide a potential indication of the gain magnitude of the FWTWT.

14 citations

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01 Jan 2015

TL;DR: In this paper, an accurate and efficient model based on the free space Green's function under the eigenmode approximation is developed for the study of chiral metamaterials, in particular the optomechanical properties and nonlinear effects that arise from the coupling between electromagnetic and elastic degrees of freedom.

Abstract: The advent and rapid development of metamaterials introduced many revolutionary concepts for manipulating electromagnetic waves. As an important class of metamaterials, chiral metamaterials allow us to control the polarization of electromagnetic waves at the subwavelength scale. While much work has been done on using chiral metamaterials to control electromagnetic waves, the accompanying effects, such as the electromagnetic force and torque acting on the structures, as well as nonlinear optomechanical effects, are still largely unexplored. The exploration of these areas could provide useful insight from both fundamental and practical points of view. In this thesis, we study new properties of chiral metamaterials, in particular the optomechanical properties and nonlinear effects that arise from the coupling between electromagnetic and elastic degrees of freedom. An accurate and efficient model based on the free-space Green's function under the eigenmode approximation is developed for the study. In Chapter 1, we provide a comprehensive introduction to the basic concepts and history of metamaterials, followed by more focused reviews on chiral metamaterials, different paradigms of tunable metamaterials, the nontrivial electromagnetic force and torque, as well as the nonlinear optomechanical effect in different platforms. Finally, the motivation and the scope of the thesis are summarized. To understand the optical activity in coupled structures, in Chapter 2, we employ the model developed to study the rvear-field coupling, far-field scattering and optical activity of chiral meta-molecules based on twisted coupled cut-wire pairs. The numerical results from our model agree well quantitatively with full-wave calculation. We also discuss the optimum twist angle of the structure. After exploring the optical activity, in Chapter 3, we study the optomechanical properties of chiral meta-molecules based on a pair of twisted split-ring resonators. This structure can provide a strong and tunable torque, and can support different optomechanical dynamics, making it a good candidate for subwavelength light-driven actuators. To achieve strong coupling between electromagnetic resonance and elastic deformation in metamaterials, in Chapter 4, we introduce chiral torsional meta-molecules based on twisted split-ring pairs. We predict a rich range of nonlinear stationary effects including self-tuning and bistability. Importantly, these nonlinear effects including bistability are successfully observed in experiment. After understanding the nonlinear stationary responses of torsional meta-molecules, in Chapter 5, we study their nontrivial nonlinear dynamic effects. We introduce a simple structure based on three connected split-rings and find that this structure can support novel nonlinear dynamics such as chaos, damping-immune self-oscillations and dynamic nonlinear optical activity. To understand how intermolecular interaction can change system dynamics, in Chapter 6, we study the nonlinear effects of ensembles of enantiomeric torsional meta-molecules. We find that spontaneous chiral symmetry breaking can exist due to intermolecular interaction. For the first time in metamaterials, both spontaneous chiral symmetry breaking and self-oscillations are successfully demonstrated exper-

12 citations

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TL;DR: In this article, the homogeneous boundary value problem arising in the propagation of electromagnetic waves guided by an open tape helix modelled to be of infinitesimal tape thickness and infinite tape-material conductivity is shown to be inherently ill posed.

Abstract: The homogeneous boundary value problem arising in the propagation of electromagnetic waves guided by an open tape helix modelled to be of infinitesimal tape thickness and infinite tape-material conductivity is shown to be inherently ill posed. It is demonstrated how the ill posed problem may be regularised using the mollification method. The regularised boundary value problem is then solved to yield the approximate dispersion equation which takes the form of the solvability condition for an infinite system of linear homogeneous algebraic equations viz., the determinant of the infinite-order coefficient matrix is zero. For the numerical computation of the dispersion characteristic, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging (after regularisation) series for them. The tape-current distribution is estimated from the null-space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation. A comparison of the numerical results with those for the anisotropically conducting model (that neglects the component of the tape-current density perpendicular to the winding direction) of the tape helix reveals that the propagation characteristic computed on the basis of the anisotropically conducting model could be substantially in error even for moderately wide tapes.

12 citations