Dirk Baumann

A generalized local time-step scheme for efficient FVTD simulations in strongly inhomogeneous meshes

A new generalized local time-step scheme is introduced to improve the computational efficiency of the finite-volume time-domain (FVTD) method. The flexibility of unstructured FVTD meshes is fully exploited by avoiding the disadvantage of a single short time step in the entire mesh. The great potential of this scheme is fully revealed in the FVTD simulation of electromagnetic (EM) problems with both large and fine structures in close proximity. The scheme is based on an automatic partition of the computational domain in subdomains where local time steps of the type 2/sup /spl lscr/-1//spl Delta/t(/spl lscr/=1,2,3,...) can be applied without violating the stability condition. Interfaces between subdomains are reduced to a generic two-level system which requires a very limited number of time interpolations during the FVTD iteration, therefore resulting in a very simple and robust technique. The application of local time stepping to three-dimensional EM problems demonstrates a significant speed-up of the computation without compromising the accuracy of the results.

Finite-volume time-domain analysis of a cavity-backed Archimedean spiral antenna

This paper presents a comprehensive analysis of a broadband (2-18 GHz) cavity-backed Archimedean spiral antenna. The simulation of the device is performed using the finite-volume time-domain method. The high geometrical flexibility of this method permits a detailed modeling of the antenna including the thin substrate, the feeding balun, and the cavity loaded with a honeycomb absorber. The simulated far-field radiation patterns and the return loss are compared to measurements, showing an excellent agreement over the whole frequency band. The radiation mechanism of the spiral is visualized by observing the current distribution on the spiral arms for both pulsed and harmonic excitation modes

A Human Body Model for Efficient Numerical Characterization of UWB Signal Propagation in Wireless Body Area Networks

Wireless body area network (WBAN) is a new enabling system with promising applications in areas such as remote health monitoring and interpersonal communication. Reliable and optimum design of a WBAN system relies on a good understanding and in-depth studies of the wave propagation around a human body. However, the human body is a very complex structure and is computationally demanding to model. This paper aims to investigate the effects of the numerical models structure complexity and feature details on the simulation results. Depending on the application, a simplified numerical model that meets desired simulation accuracy can be employed for efficient simulations. Measurements of ultra wideband (UWB) signal propagation along a human arm are performed and compared to the simulation results obtained with numerical arm models of different complexity levels. The influence of the arm shape and size, as well as tissue composition and complexity is investigated.

Field-based scattering-matrix extraction scheme for the FVTD method exploiting a flux-splitting algorithm

This paper introduces a novel field-based scheme for the extraction of a generalized-scattering matrix. A flux-splitting (FS) algorithm that separates the total electromagnetic field into an incident and a reflected part is used for a new definition of power waves. This flux-separation scheme, based on a plane-wave approach of the split waves, originates from finite-volume techniques. However, it can be applied locally in any numerical scheme that uses a volume discretization. To yield correct S-parameters, the FS matrix needs to be adapted through introduction of modified wave velocities to match the plane-wave condition. The introduced extraction scheme is applied to the finite-volume time-domain method and compared successfully to reference solutions for TEM and non-TEM structures, both with homogeneous and inhomogeneous cross sections.

A modular implementation of dispersive materials for time-domain simulations with application to gold nanospheres at optical frequencies

The development of photonic nano-structures can strongly benefit from full-field electromagnetic (EM) simulations. To this end, geometrical flexibility and accurate material modelling are crucial requirements set on the simulation method. This paper introduces a modular implementation of dispersive materials for time-domain EM simulations with focus on the Finite-Volume Time-Domain (FVTD) method. The proposed treatment can handle electric and magnetic dispersive materials exhibiting multi-pole Debye, Lorentz and Drude models, which can be mixed and combined without restrictions. The presented technique is verified in several illustrative examples, where the backscattering from dispersive spheres is calculated. The amount of flexibility and freedom gained from the proposed implementation will be demonstrated in the challenging simulation of the plasmonic resonance behavior of two gold nanospheres coupled in close proximity, where the dispersive characteristic of gold is approximated by realistic values in the optical frequency range.

Finite-volume time-domain (FVTD) method and its application to the analysis of hemispherical dielectric-resonator antennas

In this paper, the finite-volume time-domain (FVTD) method is refined and applied to analyze a probe-fed hemispherical dielectric resonator antenna (DRA). To improve the applicability of the FVTD method to microwave problems, a new scheme is introduced taking advantage of the methods inherent flux separation into incoming and outgoing waves. A 3D simulation is performed using an unstructured tetrahedral mesh permitting precise modeling of curved surfaces and fine structures. The obtained results are compared to those from other methods.

Sensitivity and specificity analysis of fringing-field dielectric spectroscopy applied to a multi-layer system modelling the human skin

The sensitivity and specificity of dielectric spectroscopy for the detection of dielectric changes inside a multi-layered structure is investigated. We focus on providing a base for sensing physiological changes in the human skin, i.e. in the epidermal and dermal layers. The correlation between changes of the human skins effective permittivity and changes of dielectric parameters and layer thickness of the epidermal and dermal layers is assessed using numerical simulations. Numerical models include fringing-field probes placed directly on a multi-layer model of the skin. The resulting dielectric spectra in the range from 100 kHz up to 100 MHz for different layer parameters and sensor geometries are used for a sensitivity and specificity analysis of this multi-layer system. First, employing a coaxial probe, a sensitivity analysis is performed for specific variations of the parameters of the epidermal and dermal layers. Second, the specificity of this system is analysed based on the roots and corresponding sign changes of the computed dielectric spectra and their first and second derivatives. The transferability of the derived results is shown by a comparison of the dielectric spectra of a coplanar probe and a scaled coaxial probe. Additionally, a comparison of the sensitivity of a coaxial probe and an interdigitated probe as a function of electrode distance is performed. It is found that the sensitivity for detecting changes of dielectric properties in the epidermal and dermal layers strongly depends on frequency. Based on an analysis of the dielectric spectra, changes in the effective dielectric parameters can theoretically be uniquely assigned to specific changes in permittivity and conductivity. However, in practice, measurement uncertainties may degrade the performance of the system.

Time-domain simulations of a 31-antenna array for breast cancer imaging

In this paper we discuss challenges related with time-domain simulations of a complete microwave radar imaging system for breast cancer detection. Two different numerical methods are considered to address this demanding electromagnetic problem featuring 31 ultra-wideband antennas. The first method is the Finite Integration Technique (FIT) applied in a regular grid and implemented in a commercial solver, whereas the second method is an in-house developed Finite-Volume Time-Domain (FVTD) code applied in a tetrahedral mesh. Our work focuses on the fundamental differences between the two approaches for the comprehensive full-wave modeling of the considered problem. The emphasis of the comparison is placed on the computational cost, which reveals the strengths and limitations of both methods for the problem considered.

Antennae Polarization for Effective Transmission of UWB Signal around Human Body

Ultra wideband (UWB) is an emerging technology with promising applications in wireless body area networks (WBANs). Detailed understanding of the propagation mechanism of UWB signal around human body is essential for the development of wearable sensors. However there are currently limited studies describing UWB signal propagation around human body. In this paper, the favorable antennae polarization for effective transmission of signal to receiver is investigated through numerical simulations. The results showed that antennae oriented in perpendicular polarization with respect to body surface provide a lower path loss as compared to horizontal polarization.

Model Order Reduction for a Field Averaging Finite-Volume Scheme

In this work the applicability of model order reduction schemes to models that are obtained through finite-volume space discretizations is examined. While some state-space formulations of this method fail to allow the efficient generation of reduced order models, the application to a 2-dimensional field-averaging version that has recently been developed yields excellent results in terms of both accuracy and computational efficiency. This permits the first reported simulation of a microwave filter with the help of the finite-volume technique