Juan V. Balbastre

Analysis of general lossy inhomogeneous and anisotropic waveguides by the finite-element method (FEM) using edge elements

Several finite element formulations based on edge elements have been developed in recent years, avoiding the appearance of spurious modes in waveguides. However, no formulation of this kind dealing with general lossy inhomogeneous and anisotropic waveguides has been found in the literature. In this paper, a new finite element scheme for the most general linear waveguides has been derived from vector wave equations via a Galerkin procedure. In this formulation, triangular and quadrilateral edge elements have been used in order to avoid the spurious solutions. Furthermore, the final eigensystem involves only very sparse matrices, thus allowing important savings in time and memory.

New recovery error indicator for adaptive finite-element analysis on waveguiding structures

The adaptive finite-element method (FEM) is an iterative variant of the FEM where, in a first step, an initial mesh with few and low-order elements is generated, the corresponding algebraic problem is solved and the error in the solution is estimated in order to add degrees of freedom in those regions of the domain with the biggest error estimation. This process is repeated until an ending condition is reached. The two basic stages in this method are the error indication and the mesh enrichment. In this paper, within the analysis of waveguiding structures, a new error indicator based on the curl recovery is described. In addition, an overview on refinement techniques is presented, and the h-refinement employed in this study is briefly described. Results obtained with the curl-recovery indicator are discussed and compared with the classical nonadaptive FEM and two previously developed error indicators: the residual and flux continuity indicators.

Microwave Disinfestation of Bulk Timber

In this paper a complete microwave system for bulk timber disinfestation is developed and tested. A commercial FEM simulator has been used to design the applicator, looking for structures providing uniform field distributions, which is a factor of capital relevance for a successful treatment. Special attention has also been given to the reduction of electromagnetic energy leakage. A dual polarized cylindrical applicator with a corrugated flange has been designed. The applicator has also been numerically tested emulating some real-life operating conditions. A prototype has been built using two low-cost magnetrons of900 W and high power coaxial cables and it has been tested inside a shielded semianechoic chamber. The tests have been carried out in three stages: validation of the applicator design, determination of the lethal dosage as a function of the insect position and the maximum wood temperature allowed and statement of safe operation procedures.

Study of NiZn ferrite absorption: Effect of relative density and microstructure

A study to optimize the reflectivity of ferrite absorbers is presented. The study considers the variation of the magnetic loss factor with the evolution of fired relative density and microstructure of ferrites made from a Zn-Ni-Cu ferrite powder, and from mixture of Zn-Ni and a Cu ferrite powder. From the results, an equation which relates the magnetic loss factor to fired relative density, average grain size, and grain size distribution width, is proposed. This equation is valid for the ferrites studied, which had an average grain size below 10smm and a grain size distribution width below 30smm.

MONITORING THE DESALTING PROCESS OF COD USING DIELECTRIC SPECTROSCOPY

The desalted cod industry needs a suitable and reliable control system to check the desalting point of cod in order to provide a safe and high-quality product. The growth of the industries that are interested in a non-contacting, real-time control, encourages the development of new methods based on low-power radiation, such as dielectric spectroscopy. These techniques use the modification of wave parameters at some specific frequencies to provide information of the compositional characteristics of foods. In this work, cod parallelepipeds were desalted at 5 °C by immersing them in distilled water for different desalting times (15 and 30 minutes and 1, 2, 4, 6, 8, 12, 24 and 48 hours). Dielectric Spectroscopy studies have been performed on cod samples in the frequency range 200 MHz-20 GHz. The dielectric properties were measured using a coaxial probe (Agilent 85070E) connected to a Network Analyzer (Agilent E8362B) immediately after removing the cod samples from their desalting solutions. After desalting, the cod samples were separated from their desalting solutions and kept in repose for 24 h at 5 °C after which some of their physical properties were measured. This experimental procedure ensures that those properties have already reached their final values. Good correlations were found between the quality properties of the cod samples (aw, xw, zNaCi and xNaC) after 24 h and their loss factor (e’) measured at 10 GHz just before leaving them in repose, showing the feasibility of an in-line control system for cod desalting process at that frequency.

Design Guidelines for Applicators Used in the Microwave Heating of High Losses Materials

Multiple port travelling wave applicators and distribution networks are tested for improved microwave heating of materials with high dielectric loss factors, based on simulation using a commercial code, ANSYS 5.6. Single point feed applicators, phase shifted by a distribution network appear to be superior over multiple feeding point applicators.

Susceptibility Analysis of Arbitrarily Shaped 2-D Dielectric Screens using the Generalized Scattering Matrix Method

The EMS inside slotted screens has been studied by using a hybrid technique. The screen is characterized, using the FEM, by a generalized admittance or impedance matrix, from which the scattering matrix can be straightforwardly obtained. The scattering matrix is then combined with a modal solution to compute the fields inside and outside the envelope. This circuital approach provides a systematic procedure for the analysis of very complex open structures.

Wood timber disinfestation by microwave power application

Different durations to treat bulk timbers have been assessed. The investigation is based on wood timber samples, woodworm larvae and a circular antenna prototype. The research establishes an initial treatment duration, measures the temperature at such duration and estimates durations and extermination rates at different depths. The current results demonstrate that he heating is more homogeneous in overlapped radiation and the treatment duration is strongly related to timber thickness or treatment depth. The treatment duration ranged from 20 to 50 seconds depending on application method and the applied power.

Shield&Reflex: A new technology for weaving shielding fabrics

A new yarn able to shield electromagnetic waves is presented. This yarn was used to manufacture different fabrics with identical texture and properties to woven fabric made with conventional yarns. The measures for check the electromagnetic waves shielding effectiveness (EMSE) have been made within a semi-anechoic chamber. The results show excellent shielding properties above 30 dB in the frequency range from 800 MHz to 4 GHz.

On the Feasibility of a Bistatic Radar for Detecting Bad Road Conditions

In this paper a study on the feasibility of a bi static radar system for bad road conditions, including water, snow and ice, is presented. First of all, the most suitable frequency is chosen among all the frequencies available for such a system from a regulatory point of view. Then, the best mathematical model for predicting the electromagnetic behaviour of different layers of water, snow or ice over an asphalt basis is presented. The numerical study is focused on the reflexion attenuation (the difference between the direct and the reflected signal levels). Results for linearly polarized waves are presented and some useful design guidelines are presented.