Antonio Lozano-Guerrero

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.

Microwave heating modelling of a green smoothie: Effects on glucoraphanin, sulforaphane and S-methyl cysteine sulfoxide changes during storage

BACKGROUND The heating of a green smoothie during an innovative semi-continuous microwave treatment (MW; 9 kW for 15 s) was modelled. Thermal and dielectric properties of the samples were previously determined. Furthermore, the heating effect on the main chemopreventive compounds of the smoothie and during its subsequent storage up to 30 days at 5 or 15 °C were studied. Such results were compared to conventional pasteurisation (CP; 90 °C for 45 s) while unheated fresh blended samples were used as the control. RESULTS A procedure was developed to predict the temperature distribution in samples inside the MW oven with the help of numerical tools. MW-treated samples showed the highest sulforaphane formation after 20 days, regardless of the storage temperature, while its content was two-fold reduced in CP samples. Storage of the smoothie at 5 °C is crucial for maximising the levels of the bioactive compound S-methyl cysteine sulfoxide. CONCLUSION The proposed MW treatment can be used by the food industry to obtain an excellent homogeneous heating of a green smoothie product retaining high levels of bioactive compounds during subsequent retail/domestic storage up to 1 month at 5 °C.

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.

Design and Validation of a Ten-Port Waveguide Reflectometer Sensor: Application to Efficiency Measurement and Optimization of Microwave-Heating Ovens

This work presents the design, manufacturing process, calibration and validation of a new microwave ten-port waveguide reflectometer based on the use of neural networks. This low-cost novel device solves some of the shortcomings of previous reflectometers such as non-linear behavior of power sensors, noise presence and the complexity of the calibration procedure, which is often based on complex mathematical equations. These problems, which imply the reduction of the reflection coefficient measurement accuracy, have been overcome by using a higher number of probes than usual six-port configurations and by means of the use of Radial Basis Function (RBF) neural networks in order to reduce the influence of noise and non-linear processes over the measurements. Additionally, this sensor can be reconfigured whenever some of the eight coaxial power detectors fail, still providing accurate values in real time. The ten-port performance has been compared against a high-cost measurement instrument such as a vector network analyzer and applied to the measurement and optimization of energy efficiency of microwave ovens, with good results.

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

New broadband thermal noise primary standard in coaxial technology

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A Novel Technique for Sterilization Using a Power Self-Regulated Single-Mode Microwave Cavity

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.

Time-Domain Shielding Effectiveness of Enclosures Against a Plane Wave Excitation

A broadband primary standard for thermal noise measurements is presented and its thermal and electromagnetic behavior is analyzed by means of analytical and numerical simulation techniques. It consists of a broadband termination connected to a 3.5mm coaxial airline partially immersed in liquid Nitrogen. The main innovative part of the device is the thermal bead between inner and outer conductors, designed for obtaining a proper thermal contact and to keep low both its contribution to the total thermal noise and its reflectivity. A sensitivity analysis is realized in order to fix the manufacturing tolerances for a proper performance in the range 10MHz–26.5GHz.