Theodoros T. Zygiridis

A comparative study of the biological effects of various mobile phone and wireless LAN antennas

This paper presents a comprehensive electromagnetic and thermal analysis of radiation and its impact on human beings, due to the use of various types of commonly used mobile phones and communication antennas. This is one of the first studies that deals with a wide-range comparative investigation of modern cell phones, unlike the majority of existing work, which do not extend beyond the obsolete generic phone case. The rather severe, although overlooked, case of wireless local area network antennas is also considered, due to their increasing use and the large times of exposure associated with them.

Vehicle-to-vehicle communication system EMI characterization on automotive electronics

The major issue of electromagnetic immunity of automotive electronics to the radiation of vehicle-to-vehicle systems is the subject of this paper. Inter-vehicle communication systems provide a wide range of new services and applications for vehicular environments, but they are still under development. Although very promising for the future of intelligent transportation systems, they may become hazardous for automotive electronics. A core numerical analysis of the electric field produced by such a system is performed by means of the full wave Finite Difference Time Domain method. The electric field intensity levels in a vehicle due to a vehicle-to-vehicle communication system is estimated for various cases according to the corresponding IEEE standard and compared to the maximum allowed levels for electronic devices.

High-Order Error-Optimized FDTD Algorithm With GPU Implementation

This paper presents the development of a two-dimensional (2-D) finite-difference time-domain (FDTD) solver that features reliable calculations and reduced simulation times. The accuracy of computations is guaranteed by specially-designed spatial operators with extended stencils, which are assisted by an optimized version of a high-order leapfrog integrator. Both discretization schemes rely on error-minimization concepts, and a proper least-squares treatment facilitates further control in a wideband sense. Given the parallelization capabilities of explicit FDTD algorithms, considerable speedup compared to serialized CPU calculations is accomplished by implementing the proposed algorithm on a modern graphics processing unit (GPU). As our study shows, the GPU version of our technique reduces computing times by several times, thus confirming its designation as a highly-efficient algorithm.

A Generalized Domain-Decomposition Stochastic FDTD Technique for Complex Nanomaterial and Graphene Structures

The systematic and accurate design process of realistic nanocomposite applications and finite-sized graphene setups with arbitrary media uncertainties is presented in this paper by a 3-D covariant/contravariant stochastic finite-difference time-domain method. The new technique uses extra nodes pertinent to a convex combination of all obtainable spatial increments and introduces a robust domain-decomposition formulation combined with Lagrange multipliers to considerably decrease the system overhead. In this way, the mean value and the standard deviation of field components are evaluated in a single run. The performance of the proposed algorithm is validated by various statistically varying nanoscale applications.

A curvilinear stochastic-FDTD algorithm for 3-D EMC problems with media uncertainties

Purpose – Stochastic uncertainties in material parameters have a significant impact on the analysis of real-world electromagnetic compatibility (EMC) problems. Conventional approaches via the Monte-Carlo scheme attempt to provide viable solutions, yet at the expense of prohibitively elongated simulations and system overhead, due to the large amount of statistical implementations. The purpose of this paper is to introduce a 3-D stochastic finite-difference time-domain (S-FDTD) technique for the accurate modelling of generalised EMC applications with highly random media properties, while concurrently offering fast and economical single-run realisations. Design/methodology/approach – The proposed method establishes the concept of covariant/contravariant metrics for robust tessellations of arbitrarily curved structures and derives the mean value and standard deviation of the generated fields in a single-run. Also, the critical case of geometrical and physical uncertainties is handled via an optimal parameteri...

Parallel LOD-FDTD Method With Error-Balancing Properties

We present an improved version of the locally-one-dimensional finite-difference time-domain method in 2-D formulation, featuring spatial expressions derived by an error-amending procedure. The latter targets at the balanced treatment of space-time flaws, and assures the efficient exploitation of four-point spatial operators that now depend on the time-step size. Simulations are also shortened by implementing the algorithm on graphics processing units, a process that necessitates the incorporation of a parallelizable implicit solver. This is accomplished by adapting parallel cyclic reduction to heptadiagonal systems. Therefore, a reliable computational framework free of time-step restrictions is developed.

Development of optimized operators based on spherical-harmonic expansions for 3D FDTD schemes

The subject of this paper pertains to the construction of finite-difference expressions with minimized, as well as controllable discretization errors, suitable for 3D FDTD simulations in large-scale setups. The proposed spatial approximations are designed to mimic the behavior of the exact operators, when applied to plane-wave trial functions. To eliminate undesirable directional dependencies, the expansion of proper error formulae in terms of spherical harmonic functions is performed, which facilitates accuracy improvement and produces optimized operator coefficients in closed-form expressions. The combination of the new operators with low- as well as high-order time integrators yields efficient space-time discrete models, whose reliability renders them desirable substitutes for other traditional solutions.

GPU-Accelerated Efficient Implementation of FDTD Methods With Optimum Time-Step Selection

The consistent combination of uneven space-time orders in finite-difference time-domain (FDTD) algorithms is the subject of this paper. When low-order time integration is used in conjunction with high-order spatial expressions, the operation of the numerical scheme close to the stability limit causes degraded performance and slow convergence. By exploiting accuracy considerations, we derive an estimate of the optimum-much smaller-time-step size that ameliorates errors in a mean-value sense and leads to improved precision. To deal with the augmentation of the required iterations, the parallel implementation of the FDTD techniques on graphics processing units is pursued, ensuring faster code executions and more efficient models.

Connectivity and coverage in machine-type communications

Machine-type communication (MTC) provides a potential playground for deploying machine-to-machine (M2M), IP-enabled ‘things’ and wireless sensor networks (WSNs) that support modern, added-value services and applications. 4G/5G technology can facilitate the connectivity and the coverage of the MTC entities and elements by providing M2M-enabled gateways and base stations for carrying traffic streams to/from the backbone network. For example, the latest releases of long-term evolution (LTE) such as LTE-Advanced (LTE-A) are being transformed to support the migration of M2M devices. MTC-oriented technical definitions and requirements are defined to support the emerging M2M proliferation. ETSI describes three types of MTC access methods, namely a) the direct access, b) the gateway access and c) the coordinator access. This work is focused on studying coverage aspects when a gateway access takes place. A deployment planar field is considered where a number of M2M devices are randomly deployed, e.g., a hospital where body sensor networks form a M2M infrastructure. An analytical framework is devised that computes the average number of connected M2M devices when a M2C gateway is randomly placed for supporting connectivity access to the M2M devices. The introduced analytical framework is verified by simulation and numerical results.

Improved Unconditionally Stable FDTD Method for 3-D Wave-Propagation Problems

The findings of this paper prove that the direct implementation of fourth-order operators in the alternating-direction-implicit finite-difference time-domain algorithm is not the most consistent way to improve its accuracy. Instead of applying the standard expressions, a methodology that exploits the scheme’s dispersion relation is introduced, so that space-time errors are balanced as equally as possible. After applying a matching-terms approach, new operator coefficients are extracted that depend on cell shape and time-step size. The resulting scheme offers an order of magnitude smaller error over practically all frequencies of interest, verifying the successful implementation of dispersion-reducing practices in this unconditionally stable technique.