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Fabric permittivity is critical for the manufacturing of wearable sensors and antennas as well as predicting how fabrics interact with electromagnetic fields. Engineers should also understand how permittivity changes under different temperatures, densities, and moisture content values, or when several fabrics are mixed in aggregates, when designing future applications such as microwave dryers. The permittivity of cotton, polyester, and polyamide fabric aggregates is investigated in this paper for a wide range of compositions, moisture content levels, density values, and temperature conditions around the 2.45 GHz ISM band using a bi-reentrant resonant cavity. The obtained results show extremely comparable responses for all characteristics investigated for single and binary fabric aggregates. Permittivity always increases as temperature, density, or moisture content levels rise. Moisture content is the most influential characteristic, causing enormous variations in the permittivity of aggregates. Fitting equations are supplied for all data, with exponential functions used to accurately model variation in temperature and polynomial functions employed to precisely model density and moisture content variations with low error levels. The temperature permittivity dependence of single fabrics without the influence of air gaps is also extracted from fabric and air aggregates by using complex refractive index equations for two-phase mixtures.

Facial emotion recognition (FER) has been extensively researched over the past two decades due to its direct impact in the computer vision and affective robotics fields. However, the available datasets to train these models include often miss-labelled data due to the labellers bias that drives the model to learn incorrect features. In this paper, a facial emotion recognition system is proposed, addressing automatic face detection and facial expression recognition separately, the latter is performed by a set of only four deep convolutional neural network respect to an ensembling approach, while a label smoothing technique is applied to deal with the miss-labelled training data. The proposed system takes only 13.48 ms using a dedicated graphics processing unit (GPU) and 141.97 ms using a CPU to recognize facial emotions and reaches the current state-of-the-art performances regarding the challenging databases, FER2013, SFEW 2.0, and ExpW, giving recognition accuracies of 72.72%, 51.97%, and 71.82% respectively.

We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented., SA and JM are supported by grants PID2019-108122GB-C32 and the Maria de Maeztu grant CEX-2019-000918-M of ICCUB. The work of UPCTand IFIC is supported by grant PID2019-108122GB-C33, funded by MCIN/AEI/10.13039/501100011033/ and by “ERDF A way of making Europe”. JMGB thanks the grant FPI BES-2017-079787, funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. The work of Universidad de Cantabria is supported by the Ministry of Science and Innovation under Grant PID2019-110610RB-C22. CAB and IMDEA-Nanoscience work is supported by grants PID2019-105552RB-C41 and PID2019-105552RB-C44 and by Comunidad de Madrid under Grant P2018/NMT-4291. IMDEA-Nanoscience acknowledges financial support from “Severo Ochoa” Programme for Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). D.G. and A.G also acknowledge Grant DEFROST N62909-19-1-2053 from ONR Global. RBB, FJC, BJK, EMG, JMS and PV thank the Spanish Agencia Estatal de Investigación (AEI, MICIU) for the support to the Unidad de Excelencia María de Maeztu Instituto de Física de Cantabria, ref. MDM-2017-0765. RBB, FJC, EMG and PV thank the Spanish Agencia Estatal de Investigación (AEI, MCI) for the funds received through the research project, ref. PID2019-110610RB-C21. RBB, FJC, BJK, EMG, JMS and PV also thank the ‘Dark Collaboration at IFCA’ working group for useful discussions. The work done by ANTERAL S.L. is supported by project QON-Space financed by the Navarra Government Project No. 0011-1365-2021-000220. UPNA acknowledges financial support from the Spanish State Research Agency, Project No. PID2019-109984RB-C43/AEI/10.13039/501100011033 and Project No. PID2020-112545RB-C53/MCIN/AEI/ 10.13039/501100011033.

et al., We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 μeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of gaγ ≳ 4 × 10−13 GeV−1 over a mass range of 34.6738 μeV < ma < 34.6771 μeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 μeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities., Article funded by SCOAP3., This work has been funded by the Spanish Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project FPA-2016-76978-C3-2-P (supported by the grant FPI BES-2017-079787) and PID2019-108122GB-C33, and was supported by the CERN Doctoral Studentship programme. The research leading to these results has received funding from the European Research Council and BD, JG and SAC acknowledge support through the European Research Council under grant ERC-2018-StG-802836 (AxScale project). BD also acknowledges fruitful discussions at MIAPP supported by DFG under EXC-2094 – 390783311. IGI acknowledges also support from the European Research Council (ERC) under grant ERC-2017-AdG-788781 (IAXO+ project). JR has been supported by the Ramon y Cajal Fellowship 2012-10597, the grant PGC2018-095328-BI00(FEDER/Agencia estatal de investigación) and FSE-DGA2017-2019-E12/7R (Gobierno de Aragón/FEDER) (MINECO/FEDER), the EU through the ITN “Elusives” H2020-MSCA-ITN-2015/674896 and the Deutsche Forschungsgemeinschaft under grant SFB-1258 as a Mercator Fellow. CPG was supported by PROMETEO II/2014/050 of Generalitat Valenciana, FPA2014-57816-P of MINECO and by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreements 690575 and 674896. AM is supported by the European Research Council under Grant No. 742104.

The success of a Ground-Tire Rubber (GTR) devulcanization process relies on the elimination of the sulphur atoms that are crosslinking the rubber polymer. From the chemical point of view, this requires providing enough energy to break the sulphur bonds while preserving the carbon bonds, to ensure a high quality devulcanized GTR for being of interest to the rubber manufacturing industry. GTR is very responsive to microwaves due to the presence of Carbon Blackin its composition, so the radiant energy is absorbed quickly in the form of thermal energy. When its temperature reaches 140°C, the breakage of sulphur bonds may happen under an exothermic reaction, but also some new links might be built under that condition. Therefore, from the physical point of view, the released sulphur in the gaseous form of SO2, H2S, and/or CS2 must be promoted to abandon the reactor to avoid its recombination. In this work, microwave devulcanization is monitored by detecting the concentration of sulphurous gases at the exhaust of the reactor. These sensors are very effective especially when pyrometer readings are degraded because of the gaseous layer on the GTR during the process.

In this contribution authors show the usage of several coaxial filters that avoid microwave leakage when using metallic mode stirrers within microwave multimode cavities. We describe the simulation schemes and characteristics for the different coaxial filters employed when introducing the metal axis of the mode-stirrer in the applicator. Additionally, the measurement setup that allows to validate the filtering capabilities is also described in detail. Figure 1 shows the cross-section scheme of a typical multimode microwave cavity. A waveguide feeding port is used to introduce the microwave energy in the cavity. The movement of the mode stirrer causes different electric field distribution patterns within the cavity and the material which may result in the reduction of cold and hot spots. Metallic materials are preferred versus dielectric ones to manufacture stirrers because metals are more effective than dielectrics to reflect and stir the microwave energy. However, when the metallic axis of the mode stirrer goes through the cavity walls a coaxial line is generated and the microwave electric field may leak through the coaxial port very easily. Several coaxial filtering structures are evaluated and validated to prevent electric field scaping from the applicator.

Metallic stirrers are commonly used in mode-stirred reverberation chambers but are less common in microwave ovens, because the use of a metallic axis creates a coaxial port in the cavity wall where the axis is introduced, which may result in significant microwave leakage levels. However, due to electromagnetic, mechanical, temperature, or chemical requirements, metallic axes must be used in some cases. In this paper, we present a high power coaxial filter that enables the use of metallic stirrers in microwave applications. The filter employs two-port coaxial cavities that are analyzed to determine their design parameters. These cavities are coupled via coaxial lines to achieve proper attenuation levels. The cavities were designed using commercial electromagnetic (EM) software, and a filter prototype was validated using vector network analyzer (VNA) measurements. The simulated and measured results show that a three-stage configuration can achieve attenuations greater than 70 dB at the 2.45 GHz ISM band, allowing the use and external handling of the metallic axis inserted into microwave ovens with negligible microwave radiation leakage.

RADES (Relic Axion Detector Exploratory Setup) is a project with the goal of directly searching for axion dark matter above the 30μeV scale employing custom-made microwave filters in magnetic dipole fields. Currently RADES is taking data at the LHC dipole of the CAST experiment. In the long term, the RADES cavities are envisioned to take data in the BabyIAXO magnet. In this article we report on the modelling, building and characterisation of an optimised microwave-filter design with alternating irises that exploits maximal coupling to axions while being scalable in length without suffering from mode-mixing. We develop the mathematical formalism and theoretical study which justifies the performance of the chosen design. We also point towards the applicability of this formalism to optimise the MADMAX dielectric haloscopes., Article funded by SCOAP3. This work has been funded by the Spanish Ministerio de Economia, Industria y Competitividad { Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project FPA-2016-76978, and was supported by the CERN Doctoral Studentship programme. The research leading to these results has received funding from the European Research Council and BD, JG and SAC acknowledge support through the European Research Council under grant ERC-2018-StG-802836 (AxScale project). IGI acknowledges also support from the European Research Council (ERC) under grant ERC-2017-AdG-788781 (IAXO+ project). JR has been supported by the Ramon y Cajal Fellowship 2012-10597, the grant PGC2018-095328-B-I00(FEDER/Agencia estatal de investigacion) and FSE-DGA2017-2019-E12/7R (Gobierno de Aragon/FEDER) (MINECO/FEDER), the EU through the ITN \Elusives" H2020-MSCA-ITN-2015/674896 and the Deutsche Forschungsgemeinschaft under grant SFB-1258 as a Mercator Fellow. CPG was supported by PROMETEO II/2014/050 of Generalitat Valenciana, FPA2014-57816-P of MINECO and by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreements 690575 and 674896. AM is supported by the European Research Council under Grant No. 742104.

Electromagnetic shielding of metallic enclosures with an aperture are simulated and measured in the frequency and time domain in this paper. Recently, several new figures of shielding effectiveness (SE) in the time domain have been proposed. Much work has been done regarding numerical simulations; however, little work related to measurements has been carried out. In this paper, we obtain the simulated and measured results for these SE definitions when an incident plane wave, with a determined bandwidth, excites the enclosure. The plane wave can be treated as a reference interference to compare with other cases. Measurements and simulations are in good agreement. This study evaluates the new definitions and compares them with the classical definition in the frequency domain. The effect of the probes, a dipole or a loop, has also been analyzed. Finally, the SE values are obtained for a sweep of the size of the aperture providing a unique value of equivalent SE for the most critical parameter and for a determined bandwidth, and allowing direct comparison with other enclosures.

Microwave processing can be a valid alternative to conventional heating for different types of products. It enables a more efficient heat transfer in the food matrix, resulting in higher quality products. However, for many food products a uniform temperature distribution is not possible because of heterogeneities in their physical properties and non-uniformtiy in the electric field pattern. Hence, the effectiveness of microwave inactivation treatments is influenced by both intrinsic (differences between cells) and extrinsic variability (non-uniform temperature). Interpreting the results of the process and considering its impact on microbial inactivation is essential to ensure effective and efficient processing. In this work, we quantified the variability in microbial inactivation attained in a microwave pasteurization treatment with a tunnel configuration at pilot-plant scale. The configuration of the equipment makes it impossible to measure the product temperature during treatment. For that reason, variability in microbial counts was measured using Biological Inactivation Indicators (BIIs) based on spherical particles of alginate inoculated with spores of Bacillus spp. The stability of the BIIs and the uncertainty associated to them was assessed using preliminary experiments in a thermoresistometer. Then, they were introduced in the food product to analyse the microbial inactivation in different points of the products during the microwave treatment. Experiments were made in a vegetable soup and a fish-based animal by-product (F-BP). The results show that the variation in the microbial counts was higher than expected based on the biological variability estimated in the thermoresistometer and the uncertainty of the BIIs. This is due to heterogeneities in the temperature field (measured using a thermographic camera), which were higher in the F-BP than in the vegetable soup. Therefore, for the process studied, extrinsic variability was more relevant than intrinsic variability. The methodology presented in this work can be a valid method to evaluate pasteurization treatments of foods processed by heating, providing valuable information of the microbial inactivation achieved. It can contribute to design microwave processes for different types of products and for product optimization.

The Relic Axion Detector Experimental Setup (RADES) is an axion search project that uses a microwave filter as resonator for Dark Matter conversion. The main focus of this publication is the description of the 3 different cavity prototypes of RADES. The result of the first tests of one of the prototypes is also presented. The filters consist of 5 or 6 stainless steel sub-cavities joined by rectangular irises. The size of the sub-cavities determines the working frequency, the amount of sub-cavities determine the working volume. The first cavity prototype was built in 2017 to work at a frequency of $\sim$ 8.4 GHz and it was placed at the 9 T CAST dipole magnet at CERN. Two more prototypes were designed and built in 2018. The aim of the new designs is to find and test the best cavity geometry in order to scale up in volume and to introduce an effective tuning mechanism. Our results demonstrate the promising potential of this type of filter to reach QCD axion sensitivity at X-Band frequencies., Comment: Proceedings for the 3rd Axion Cavity and Detector Workshop, Livermore Valley Open Campus August 21-25th, 2018

The permittivity of a material can be obtained from resonant measurements in an accurate way [1] at a single frequency (where the resonance occurs). In figure (1) results for the Debye Model at 298K temperature can be seen in the 10MHz-50GHz frequency band for distilled water. In this work we explore the possibilities of obtaining the permittivity of materials from resonant measurements in a certain frequency bandwidth around the resonance frequency. With this purpose a Debye model jointly with a certain conductivity useful for polar liquids [1], are studied to evaluate this possibility jointly with inverse techniques.

Emotion estimation systems based on brain and physiological signals such as electro encephalography (EEG), blood-volume pressure (BVP), and galvanic skin response (GSR) are gaining special attention in recent years due to the possibilities they offer. The field of human–robot interactions (HRIs) could benefit from a broadened understanding of the brain and physiological emotion encoding, together with the use of lightweight software and cheap wearable devices, and thus improve the capabilities of robots to fully engage with the users emotional reactions. In this paper, a previously developed methodology for real-time emotion estimation aimed for its use in the field of HRI is tested under realistic circumstances using a self-generated database created using dynamically evoked emotions. Other state-of-the-art, real-time approaches address emotion estimation using constant stimuli to facilitate the analysis of the evoked responses, remaining far from real scenarios since emotions are dynamically evoked. The proposed approach studies the feasibility of the emotion estimation methodology previously developed, under an experimentation paradigm that imitates a more realistic scenario involving dynamically evoked emotions by using a dramatic film as the experimental paradigm. The emotion estimation methodology has proved to perform on real-time constraints while maintaining high accuracy on emotion estimation when using the self-produced dynamically evoked emotions multi-signal database.

Conducting polymer composite is an alternative to conventional shielding materials. The present study aims to investigate the electromagnetic shielding characteristics and shielding effectiveness of the sheet of 3,4 ethylenedioxythiophene associated with maghnite and sodium. Waveguide measurements are used to obtain the shielding effectiveness of the studied material. Measurements have been carried out over a 9 GHz to 11 GHz frequency band. Also, dielectric probe measurements are performed to recover the dielectric permittivity of the composite. In addition, the reflection loss, the absorption loss and the shielding effectiveness measured from tests were compared with the values calculated from the transmission line theory.

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 μeV. 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., This work has been funded by the Spanish Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project FPA-2016-76978, and Fundacion Seneca Ref. 20147/EE/17, and was supported by the CERN Doctoral Studentship programme. IGI acknowledges also support from the European Research Council (ERC) under grant ERC-2009-StG-240054 (T-REX project). JR is supported by the Ramon y Cajal Fellowship 2012-10597, the grant FPA2015-65745-P (MINECO/FEDER), the EU through the ITN “Elusives” H2020-MSCA-ITN-2015/674896 and the Deutsche Forschungsgemeinschaft under grant SFB-1258 as a Mercator Fellow. CPG was supported by PROMETEO II/2014/050 of Generalitat Valenciana, FPA2014-57816-P of MINECO and by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreements 690575 and 674896.

In this paper, a novel technique to achieve precise temperatures in food sterilization has been proposed. An accurate temperature profile is needed in order to reach a commitment between the total removal of pathogens inside the product and the preservation of nutritional and organoleptic characteristics. The minimal variation of the target temperature in the sample by means of a monitoring and control software platform, allowing temperature stabilization over 100 °C, is the main goal of this work. A cylindrical microwave oven, under pressure conditions and continuous control of the microwave supply power as function of the final temperature inside the sample, has been designed and developed with conditions of single-mode resonance. The uniform heating in the product is achieved by means of sample movement and the self-regulated power control using the measured temperature. Finally, for testing the sterilization of food with this technology, specific biological validation based on Bacillus cereus as a biosensor of heat inactivation has been incorporated as a distribution along the sample in the experimental process to measure the colony-forming units (CFUs) for different food samples (laboratory medium, soup, or fish-based animal by-products). The obtained results allow the validation of this new technology for food sterilization with precise control of the microwave system to ensure the uniform elimination of pathogens using high temperatures. This work was supported by the Ministerio de Economía y Competitividad under the project with reference DPI2014-61857-EXP.

In this work, a waveguide impedance generator based on the use of three motor-controlled metallic stubs, a monomode cavity loaded with water and PTFE cylinders is used to calibrate a waveguide ten-port reflectometer. Radial basis function neural networks are used to learn the relationship between the actual reflection coefficient and the power detectors’ output. Results indicate that this impedance generator can be successfully used to calibrate the ten-port reflectometer. This work was supported in part by the Ministerio de Ciencia e Innovación under the project with reference CIT-020000-2008-43.

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.

In this study, radiated immunity and emission of a metallic box with apertures have been evaluated through a fast approach. The influence of printed circuit boards inside the enclosure has been studied and also the effect of placing conductive polymer sheets in the housing in order to characterize the behaviour of these materials used nowadays for shielding cabinets. Measurements have been carried out in anechoic chamber in order to evaluate the approximated technique showing its limitations and advantages. Since good agreement has been found between simulations and measurements, this approach can be used for design or optimization purposes with the main advantage of reduced time calculations. This work has been funded by Fundación Séneca, Agencia Regional de Ciencia y Tecnología through the project 00700/PPC/04.

The lack of dielectric properties data has often been named as one of the reasons that has hampered the simulation of microwave processing of biomass feedstock and process design. In this work, the dielectric behavior of an organic fraction from municipal solid wastes during pyrolysis has been monitored as a function of temperature. Furthermore, the effect of the addition of a microwave absorbent material (carbonaceous char) to the raw biowaste upon the dielectric properties has been investigated for the first time. The efficiency of the conversion of microwave energy to heat, measured by means of the tan δ parameter, is shown in this study to be nearly 20 times higher when the absorbent char is added to the reaction bulk at room temperature and this gap is even greater in the 600–800 °C range. Nevertheless, the results suggest that the addition of increasing amounts of microwave absorbent (up to ca. 40%) impairs microwave penetration, which gives rise to a less homogeneous heating of the bulk. There is therefore an optimum proportion that balances heat conversion and penetration depth. The results of this study lend support to the use of char as a means to induce thermochemical treatments by microwaves and reduce energy consumption in the process., The research leading to these results has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement n° 311815 (SYNPOL project). D.B. also acknowledges the financial support received from PCTI and FICYT of the Government of the Principado de Asturias

In this paper, the design of a dielectric multilayer around a clay sample is presented to achieve a uniform electric field distribution over that sample. This structure is located within a multimode microwave-heating oven and is designed by means of genetic algorithms. The permittivity and geometric values for the sample surrounding layers are the selected parameters to be optimized in order to minimize the ratio between the typical deviation and the absolute value of the electric field. The results demonstrate the improvement of the electric field uniformity over the sample using dielectric layers. This work was supported in part by the Fundación Séneca under Project 00700/PPC/04

In this paper, the design of a dielectric multilayer around a dielectric sample in order to avoid the appearance of undesired reflections and achieve higher matching-efficiency values within multimode microwave-heating ovens is presented. The permittivity and geometric values for the sample surrounding layers are optimized by means of genetic algorithms (GAs) in order to maximize the system matching. Several dielectric-mould configurations are studied and the results show that the use of dielectric layers surrounding the product substantially improves the load matching. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 426–430, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21191

Commercial dielectric materials placed around a sample are studied as load-matching elements for multimode microwave-heating applicators. The dimensions of these dielectric materials are optimized with an iterative procedure in order to achieve high-power efficiency, thus enhancing electric-field deposition within the sample. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 414–417, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20156

Usage of a dielectric multilayer around a dielectric sample is studied as a means for improving the efficiency in multimode microwave-heating cavities. The results show that by using additional dielectric constant layers the appearance of undesired reflections at the sample-air interface is avoided and higher power-absorption rates within the sample and high-efficiency designs are obtained. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 318–322, 2004

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.

In this work, a very simple and accurate model for the microwave-assisted drying of laminar bodies, based on their dielectric properties, is developed and tested over a laminar material such as leather. Several assumptions are made to simplify the obtained expressions. The results show that the correct determination of the dielectric properties as well as the internal characteristics of the solid are very relevant in order to achieve a correct modeling of the drying process. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 465–469, 2002.

In this work, the efficiency of a static microwave-assisted dryer for laminar materials is studied. Drying tests, carried out in this drier with leather samples, show that the application of the microwave energy significantly accelerates the drying rates without damaging the product. Energetic calculations allow inferring the microwave-absorbed power without measuring the transmitted and reflected power, leading to results that agree with the literature and that demonstrate the efficiency of this drying technique and its feasibility when combined with forced airflow. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 470–474, 2001.

The microwave-assisted drying of laminar materials has been studied, and a model is proposed to explain the behavior of these materials under microwave radiation. Different selective heating and drying tests of leather samples have been carried out, and drying curves showed a fast convergence as a proof of this effect. The obtained results look promising for applying this technique on an industrial scale. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 165–168, 2001.

In this communication the design, manufacturing and reflectivity measurements of a broadband primary standard for thermal noise measurements, which will be the Spanish national standard, are presented. In the novel approach presented here, the noise temperature is calculated by means of a hybrid analytical-numerical simulation methodology, which is able to obtain the thermal and electromagnetic behavior of the standard, pointing out the critical characteristics that mostly affect the uncertainty in the noise temperature.

Equivalent models of printed circuit boards 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 printed circuit boards 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 printed circuit board 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. This work was supported in part by the Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia, under the Séneca predoctoral fellowship with reference 16381/FPI/10 and under the project 00700/PPC/04