Freek Boeykens

An Efficient Technique Based on Polynomial Chaos to Model the Uncertainty in the Resonance Frequency of Textile Antennas Due to Bending

The generalized polynomial chaos theory is combined with a dedicated cavity model for curved textile antennas to statistically quantify variations in the antennas resonance frequency under randomly varying bending conditions. The nonintrusive stochastic method solves the dispersion relation for the resonance frequencies of a set of radius of curvature realizations corresponding to the Gauss quadrature points belonging to the orthogonal polynomials having the probability density function of the random variable as a weighting function. The formalism is applied to different distributions for the radius of curvature, either using a priori known or on-the-fly constructed sets of orthogonal polynomials. Numerical and experimental validation shows that the new approach is at least as accurate as Monte Carlo simulations while being at least 100 times faster. This makes the method especially suited as a design tool to account for performance variability when textile antennas are deployed on persons with varying body morphology.

Cylindrical Bending of Deformable Textile Rectangular Patch Antennas

Textile patch antennas are well known as basic components for wearable systems that allow communication between a human body and the external world. Due to their flexibility, textile antennas are subjected to bending when worn, causing a variation in resonance frequency and radiation pattern with respect to the flat state in which their nominal design is performed. Hence, it is important for textile antenna engineers to be able to predict these performance parameters as a function of the bending radius. Therefore, we propose a comprehensive analytical model that extends the cylindrical cavity model for conformal rigid patch antennas by incorporating the effects of patch stretching and substrate compression. It allows to predict the resonance frequency and the radiation pattern as a function of the bending radius. Its validity has been verified experimentally. Unlike previous contributions, which concerned only qualitative studies by means of measurements and numerical full-wave simulations, the proposed model offers advantages in terms of physical insight, accuracy, speed, and cost.

Rigorous Analysis of Internal Resonances in 3-D Hybrid FE-BIE Formulations by Means of the Poincaré–Steklov Operator

3-D hybrid finite-element (FE) boundary integral equation (BIE) formulations are widely used because of their ability to simulate large inhomogeneous structures in both open and bounded simulation domains by applying each method where it is the most efficient. However, some formulations suffer from breakdown frequencies at which the solution is not uniquely defined and errors are introduced due to internal resonances. In this paper, we investigate the occurrence of spurious solutions resulting from these resonances by using the concept of the Poincaré-Steklov or Dirichlet-to-Neumann operator, which provides a relation between the tangential electric field and the electric current on the boundary of a domain. By identifying this operator in both the FE and BIE method, several new properties of internal resonances in 3-D hybrid FE-BIE formulations are easily derived. Several conformal and nonconformal formulations are studied and the theory is then applied to a scattering problem.

Efficient calculation of coupling matrices for a decoupled FE/BIE formulation

This paper presents an efficient method for calculating coupling matrices that occur in a decoupled hybrid finite element / boundary integral equation (FE/BIE) system. These coupling matrices represent projections from basis functions of one domain to basis functions of an other domain. Based on a technique for evaluating singular integrals over polyhedral domains, it becomes possible to calculate the projection integrals analytically, instead of relying on quadrature integration rules. It is shown that this reduces the CPU-time, whereas the accuracy remains correct up to machine precision.

Advantages of PSWF-based models for UWB systems

The frequency dependency of signals plays a very important role in Ultra Wideband (UWB) systems. Being able to accurately model this frequency dependency can provide a multitude of benefits, especially for UWB systems in medical applications. The model, based on prolate spheroidal wave functions (PSWFs), presented in this contribution improves greatly upon the model relying on discrete prolate spheroidal sequences that was previously presented by the authors: it offers a much more compact representation, while retaining the same robustness to noise. Furthermore, with the improved model, a cascade of signals can be evaluated directly using the model coefficients. All of these properties can be of use when analysing UWB systems.

A stochastic framework to model bending of textile antennas

The polynomial chaos expansion is combined with a dedicated cylindrical cavity model to quantify the statistical variations in textile antenna performance under random bending conditions.

Optimal topology for an intra-vehicle antenna implemented on dashboard foams

This paper presents several antenna topologies for intra-vehicle communication in the unlicensed 2.45 GHz ISM band (2.4 GHz – 2.485 GHz). The antennas are implemented using flexible foam materials compatible with the production process of dashboards, as dashboards offer a large platform for easy and unobtrusive integration. In order to obtain the optimal intra-vehicle antenna, the different topologies are compared in terms of antenna gain, efficiency, AR bandwidth and AR robustness against small fabrication errors.