Alejandro Díaz-Morcillo

Multimode cavity efficiency optimization by optimum load location-experimental approach

In this paper, a novel load-matching procedure for microwave-heating applicators is presented and tested. In order to accomplish the optimization procedure, an optimization method based on the use of the Lebenverg-Marquardt technique has been specifically developed and tested on two different microwave ovens. The proposed procedure allows an efficient optimization of three-dimensional microwave applicators by means of the dielectric sample relocation as a function of its complex permittivity, size, and operating frequency. Experimental measurements of the reflection coefficient are presented and analyzed over several samples and multimode cavities. Results indicate that high power efficiencies can be obtained provided that operating frequency is not just below TM-mode cutoff frequencies for the transverse dimensions of the oven.

Heat flux and heat generation characterisation in a wet-laminar body in microwave-assisted drying: an application to microwave drying of leather

Heat fluxes through a laminar body have been modelled from a parabolic temperature distribution assumption when the material is irradiated with microwaves and immersed in a convective air flow. The heat equation has been analysed and a relationship between thermal conductivity, temperatures and net heat flux through the material surface has been established. This study has been successfully applied to leather hides when they are dried in a combined microwave-hot air oven. With regard to the development of this work, dielectric and temperature measurements have been demonstrated to be of the utmost importance.

Damping of resonances in a metallic enclosure through conductive polymers

In this paper, the use of plastic compound patches for removing radiated interferences inside electronic equipments is studied. Absorption and reflection properties of conductive polymers have been analysed in order to damp the resonances in a metallic enclosure. A 2D technique to obtain the shielding effectiveness of metallic enclosures with inner materials is evaluated. The influence of the conductivity of compounds and the location of the samples in the enclosure is studied. Results show that the 2D technique can be used to evaluate cavity contents or for design purposes.

Precise Evaluation of Coaxial to Waveguide Transitions by Means of Inverse Techniques

In this paper, a new two-tier inverse characterization technique for coaxial to waveguide transition evaluation is presented and properly validated. The transition is characterized by estimating its scattering parameters and a cascade procedure is employed in order to compare simulations and measurements during the unterminating procedure. In contrast to other unterminating methods there are no restrictions concerning the number and type of standards and two transitions are simultaneously characterized. Additionally, genetic algorithms and the gradient descent method are used for error minimization during the unterminating stage. The accuracy of this two-tier inverse technique is evaluated as a function of the employed standards and the obtained results are compared to those provided by different well-known calibration algorithms. Results show that it is possible to properly characterize the coaxial to waveguide transition in a very flexible and accurate way.

Electromagnetic Equivalent Models for Printed Circuit Boards Inside a Metallic Enclosure Using a Coaxial-to-Waveguide Transition Calibration

Equivalent models of printed circuit boards (PCBs) are useful to simplify electromagnetic problems by reducing the computational costs of numerical simulations. In this paper, a new procedure for obtaining a simple equivalent model of PCBs inside metallic enclosures is presented. The equivalent model is obtained in two steps: first we precisely characterize the coaxial to waveguide transitions used during measurements by means of an inverse procedure and then during a second inverse procedure, we carry out simulations by concatenating these transitions and the equivalent model and comparing to measurements. The optimized parameters for the equivalent model are: thickness, dielectric constant, and the electric conductivity. Results for a PCB in three scenarios have been obtained by using a sweep and two different optimization techniques. Benefits and drawbacks of the model are discussed. Results indicate that this procedure produces very precise characterization of the equivalent model of PCBs depending on the position and orientation of this device within the enclosure.

Coaxial to waveguide transitions and device under test characterization by means of inverse techniques

This work was supported in part by the Ministerio de Ciencia e Innovacion under the project with reference CIT-020000-2008-43.

Application of Genetic Algorithms in the Determination of Dielectric Properties of Materials at Microwave Frequencies

In this paper the application of an evolutionary procedure based on genetic algorithms for obtaining the dielectric properties of arbitrary shaped, homogeneous or inhomogeneous materials is presented. The optimization procedure matches the measured and simulated scattering parameters of a waveguide setup that contains the sample under study. Depending on the geometry of the sample, analytic or numerical (2D or 3D) electromagnetic simulations must be carried out in order to obtain the simulated scattering parameters for a set of electric permittivities. Results for different polymeric and biological materials are presented with similar uncertainties than conventional direct methods, with the advantage that this new technique can deal with non-canonical and heterogeneous samples.

Axion searches with microwave filters: the RADES project

We propose, design and construct a variant of the conventional axion haloscope concept that could be competitive in the search for dark matter axions of masses in the decade 10-100

An Ant Colony Optimization Algorithm for Microwave Corrugated Filters Design

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New broadband thermal noise primary standard in coaxial technology

eV. Theses masses are located somewhat above the mass range in which existing experiments have reached sensitivity to benchmark QCD axion models. Our haloscope consists of an array of small microwave cavities connected by rectangular irises, in an arrangement commonly used in radio-frequency filters. The size of the unit cavity determines the main resonant frequency, while the possibility to connect a {large} number of cavities allows to reach large detection volumes. We develop the theoretical framework of the detection concept, and present design prescriptions to optimize detection capabilities. We describe the design and realization of a first small-scale prototype of this concept, called Relic Axion Detector Exploratory Setup (RADES). It consists of a copper-coated stainless steel five-cavities microwave filter with the detecting mode operating at around 8.4 GHz. This structure has been electromagnetically characterized at 2 K and 298 K, and it is now placed in ultra-high vacuum in one of the twin-bores of the 9 T CAST dipole magnet at CERN. We describe the data acquisition system developed for relic axion detection, and present preliminary results of the electromagnetic properties of the microwave filter, which show the potential of filters to reach QCD axion window sensitivity at X-band frequencies.