Serkan Aksoy

EVOLUTION EQUATIONS FOR ANALYTICAL STUDY OF DIGITAL SIGNALS IN WAVEGUIDES

excitation and propagation problem of the digital signals in a hollow waveguide is considered by an analytical timedomain method. The waveguide is geometrically regular along Oz axis, and its cross section is a closed singly connected domain. The waveguide surface is a perfect electric conductor. A complete set of TE and TM waveguide modes is obtained in Time Domain (TD) directly. Every modal field is deduced as the sum of its longitudinal and transverse vector components, where each component is the product of two factors. One factor is an element of the waveguide modal basis, which is a vector function of the transverse waveguide coordinates. The other one is a modal amplitude of appropriate field component, which is a scalar function of time t and the axial coordinate z. All the elements of the modal basis are specified via two scalar potentials. They are eigensolutions (normalized in a proper way) of Dirichlet and Neumann boundary eigenvalue problems for the Laplacian. Every element of the modal basis satisfies appropriate boundary conditions over the waveguide surface. The modal amplitudes are solutions of a system of evolution partial differential equations. The problem of Walsh function signals in the waveguide is solved explicitly in compliance with the causality principle and the special theory of relativity.

Study of a Time Variant Cavity System

A cavity with a time signal applied taken jointly is treated as a time variant physical system. Standard formulation of the boundary-value problem for system of Maxwells equations (with ∂t) is supplemented with the initial conditions and the causality principle. It is proved that electromagnetic field can be presented as the classical decompositions in terms of the solenoidal and irrotational modes but with time dependent modal amplitudes. For the latters, evolutionary (i.e., with time derivative) ordinary differential equations are derived and solved analytically, in quadratures. Simple explicit solutions (in elementary functions) for the modal amplitudes as functions of time are obtained in a particular case. Numerical examples are exhibited, time-domain resonances are studied.

Time-domain cavity oscillations supported by a temporally dispersive dielectric

Forced time-domain oscillations in a cavity filled with a temporally dispersive polar dielectric are studied. The cavity is bounded by a singly connected closed perfect electric conductor surface S of rather arbitrary shape. A given source pumps a signal of finite duration to the cavity. Hence, the principle of causality is involved in the formulation of the problem. The temporal cavity oscillations are obtained as a self-consistent solution to the system of Maxwells equations and Debye equation supplemented with appropriate initial conditions . Analytical solutions are obtained by using the evolutionary approach to electromagnetics proposed and implemented recently. Temporal oscillations of the cavity modes are studied. Obtained results are compared with the finite-difference time-domain solutions.

The evolution equations in study of the cavity oscillations excited by a digital signal

The problem of electromagnetic oscillations in a cavity excited by a signal of finite duration is considered. The singly connected cavity surface has arbitrary geometrical form and it is perfectly conducting physically; its volume is filled with a homogeneous lossy medium. The formulation of the problem involves the principle of causality. The problem is solved within the frames of the evolutionary approach to electromagnetics. The electromagnetic field is presented as an eigenmodal expansion with time dependent modal amplitudes. The amplitudes satisfy a system of evolution (i.e., with time derivative) ordinary differential equations, which are derived and studied. Explicit solutions are obtained satisfying the principle of causality automatically. Numerical examples for the cavity oscillations excited by the Walsh function signals are exhibited, some resonances of the digital signals are revealed.

An Alternative Algorithm for Both Narrowband and Wideband Lorentzian Dispersive Materials Modeling in the Finite-Difference Time-Domain Method

In this study, an alternative algorithm is proposed for modeling narrowband and wideband Lorentzian dispersive materials using the finite-difference time-domain (FDTD) method. Previous algorithms for modeling narrowband and wideband Lorentzian dispersive materials using the FDTD method have been based on a recursive convolution technique. They present two different and independent algorithms for the modeling of the narrowband and wideband Lorentzian dispersive materials, known as the narrowband and wideband Lorentzian recursive convolution algorithms, respectively. The proposed alternative algorithm may be used as a general algorithm for both narrowband and wideband Lorentzian dispersive materials modeling with the FDTD method. The second-order motion equation for the Lorentzian materials is employed as an auxilary differential equation. The proposed auxiliary differential-equation-based algorithm can also be applied to solve the borderline case dispersive electromagnetic problems in the FDTD method. In contrast, the narrowband and wideband Lorentzian recursive convolution algorithms cannot be used for the borderline case. A rectangular cavity, which is partially filled with narrowband and wideband Lorentzian dispersive materials, is presented as a numerical example. The time response of the electric field z component is used to validate and compare the results

Numerical Investigation of the Effect of a Longitudinally Layered Armature on Coilgun Performance

The effect of a longitudinally layered armature on coilgun performance is investigated by using a 2-D axially symmetric cylindrical quasi-static finite-difference time domain method. The singularity extraction and Mur-type absorbing boundary condition are adopted with the numerical solution. The results obtained show that the best coilgun performance in the sense of the induced propulsive armature force is observed when the conductivity of the outer layer of the armature is smaller than that of the inner layer. This phenomenon can be explained in terms of impedance matching based on skin depth evaluation.

A new look at the stability analysis of the finite-difference time-domain method [open problems in cem]

The stability analysis of a numerical time-domain method plays a crucial role in well understanding the numerical behavior of the algorithm. The stability analysis should therefore be investigated in all senses. In this work, a new look at the stability analysis of the Finite-Difference Time-Domain Method is given. A novel link is constructed between the numerical-dispersion analysis and the stability analysis by using the sampled values of the unit space and time steps. Unification of these two analyses therefore becomes possible. The stability criterion is extracted in a simple way, and the amplification factor is formulated. The theoretical findings are tested via a numerical experiment. Some open problems in this area are also discussed.

Diffraction Tomography Method Applications in Wide Frequency Range

Development of millimeter wave and microwave tomography for nondestructive testing and subsurface investigations is suggested. It may be manufactured as well in waveguide modification as in quasioptical one. Description of the main principles of creation of the tomographic system both for millimeter waves band and for microwaves is given below. The system combines possibilities as well of tomograph operating “on passage” as tomograph operating in regime of undersurface measurements. Using both of these approaches will allow us to create microwave or millimeter wave tomograph providing the image reconstruction of the object under investigation. The suggesting version of tomography is orientated towards applications in industry, medicine, detection and identification of abandoned objects and other fields.

Security network interface for alarm systems

Authors suggested the development of a specialized network interface for network of detectors that are part of alarm system. Providing a high level of network security against intruder is achieved using a large number of security elements and their dynamic change in on-line mode network operation. The proposed system uses traditional detectors; each is connected to the network through node based on a microcontroller. This allows connection of traditional detectors into two-wired network with common bus type and to reduce the number of wired lines without loss of system informative channels. An additional advantage is in powering sensors by a server via informational network channel.

ANALYTICAL TIME DOMAIN NORMAL MODE SOLUTION OF AN ACOUSTIC WAVEGUIDE WITH PERFECTLY REFLECTING WALLS

Solution of wide-band underwater acoustic problems with the classical Normal Mode method in the frequency domain needs to solve the problem repeating for every frequency component of the wide-band source signal. In this paper, a direct and causal analytical Time Domain Normal Mode Method is presented for arbitrary time-dependent acoustic sources for a single layered isovelocity waveguide. An incomplete separation of variables technique is used to solve the inhomogeneous wave equation, directly in the time domain. Therefore, it becomes possible to calculate the time domain acoustic pressure in a single run.