articles by Marco Azpurua
The use of spherical wave expansion of the solution of the wave equation to predict Far-Field val... more The use of spherical wave expansion of the solution of the wave equation to predict Far-Field values from data measured in the Near-Field region is a well known technique, typically used to perform antenna measurements in compact anechoic chambers. However, when designing the computing algorithm it is fundamental to validate the results and to quantify the numerical error of the method. In this regard, a computer application that samples the electric Near-Field and calculates the values of the electric Far-Field region using spherical wave expansion was developed to measure antenna radiation patterns in the Fresnel zone inside a fully anechoic chamber. In order to validate the code, this paper describes three validation methods: firstly, using the theoretical electric Near-Field values of an infinitesimal dipole as the input to the algorithm to compare the output with the response analytically expected; secondly, using a Far-Field electric field data of a calibrated half wavelength dipole measured in an anechoic chamber and finally, using an electric Near-Field data of a calibrated half wavelength dipole measured in the same chamber. These methods provide simple procedures to calculate the error introduced by the code in different scenarios that should be considered to estimate the measurement uncertainty.
Electromagnetic interferences are potentially very complex signals formed by the superposition of... more Electromagnetic interferences are potentially very complex signals formed by the superposition of transient (broadband) and continuous wave (narrowband) components with significant randomness in both amplitude and phase. Decomposing the electromagnetic interference measured in the time domain into a set of intrinsic mode functions is useful to gain insights of the process that generates the interference. Evaluating the intrinsic mode functions contributes to improving the measurement capabilities of the time-domain electromagnetic emissions measurement systems based on the general-purpose oscilloscopes. In this paper, a combination of techniques that includes empirical mode decomposition and transient mode decomposition is used to separate the main components of complex electromagnetic disturbances. This approach requires no prior information on the spectral content of the measured EMI and it does not perform a domain transformation. Examples of electromagnetic interference decomposition verify the effectiveness and the accuracy of the proposed approach. Finally, a discussion on the advantages, practical applications, limitations, and drawbacks of the described techniques is addressed.
A common source of noise for digital communication systems is the radiated transient interference... more A common source of noise for digital communication systems is the radiated transient interference. As an example, it has been reported that the degradation is produced to the Global System for Mobile (GSM)-Railway signaling system when the impulsive noise is generated by sparks caused by the discontinuity between the catenary and the pantograph. Concerning the measurement and evaluation procedures defined in the electromagnetic compatibility standards, they are not suitable for these types of transient disturbances. Therefore, new techniques must be developed to determine, with a high confidence level, the degradation that impulsive noise will produce in communication systems. In this paper, novel time-domain measurement procedures are carried out to acquire transient interferences generated by sparks properly. Moreover, two different evaluation methodologies, employing base-band simulation and amplitude probability distribution detector, are used to analyze the impact of the disturbance applied into a GSM system interference scenario. Finally, the results obtained with the developed methodologies are successfully compared with a reference measure where the GSM downlink channel quality is monitored by a mobile station test unit.
This article is intended to provide a set of recommended practices for improving of the Time-Doma... more This article is intended to provide a set of recommended practices for improving of the Time-Domain EMI measurement systems by means of digital signal processing. We have focused on two major aspects: the optimal configuration settings of the direct measurement equipment and the deployment of algorithms to process the measurement result. In that sense, we believe that general purpose time-domain instruments, as oscilloscopes, can be successfully used as an alternative hardware to measure EMI, since they provide accurate and reliable results, surpassing the conventional frequency-domain approach when transient disturbances are present.
This paper presents a discussion on the inherent characteristics of the measurements performed wi... more This paper presents a discussion on the inherent characteristics of the measurements performed with time-domain electromagnetic interference measurement systems in regards of the detection of the maximum emissions levels. In that sense, some relevant statistical properties of the frequency components of the maximum emissions levels in the amplitude spectrum are investigated using the extreme value theory to provide a model based on the Gumbel probability distribution and estimates for its parameters, expected value, variance, and Cramer-Rao bounds. The results suggest that using the expected maximum value of the emissions levels instead of the just the observed maximum value improves the measurement repeatability and also reduces the uncertainty in the results. This paper presents an additional insight measure that enhances our understanding of the statistical behavior of the measured EMI and of the time-domain measurement process itself.
Vector feedback is a concept which can significantly improve linearity and stability of a magneti... more Vector feedback is a concept which can significantly improve linearity and stability of a magnetic field sensor. The feedback coils effectively cancel the measured magnetic field in the inner volume of the triaxial sensor. Thus, in case of fluxgates, it suppresses one possible source of nonlinearitycross-field sensitivity error. The triaxial sensor axes orthogonality should be primarily defined by the orientation of the feedback coils, while the sensitivities are defined by feedback coil constants. The influence of the homogeneity of the feedback field and the influence of the sensor inner layout on calibration parameters of a vectorially compensated triaxial fluxgate magnetometer are presented.
The growing application of simulation tools to increasingly complex problems makes the use of val... more The growing application of simulation tools to increasingly complex problems makes the use of validation techniques essential to improve confidence in the veracity of those simulation results. The feature selective validation (FSV) method is widely used today, because of its versatility and simplicity. However, despite its many advantages, some problems have been identified in the standardized FSV method. Those drawbacks can produce misleading results for the validation process and constitutes enhancement opportunities for further research on FSV improvement. This paper presents a review that summarizes the major problems of the FSV and their possible solutions as a justification to reform the FSV method and also looking towards the forthcoming update of the standards IEEE 1957.1/2.
Recently, super compact test chambers are being used for electromagnetic compatibility precomplia... more Recently, super compact test chambers are being used for electromagnetic compatibility precompliance testing and for antenna calibration because they offer a cost effective method to investigate the electromagnetic behavior of new developed products. Those compact range environments are usually associated to measurements in the Near-Field (NF) zone which are commonly extrapolated to the Far-Field (FF) region in order to calculate the radiated fields. In this paper, the Monte Carlo method is used to propagate errors in the NF measures through the Spherical Wave Expansion transformation method used to calculate the radiated fields in order to estimate the uncertainty in the FF radiation pattern. As an example, this methodology is applied for the particular case of a half-wavelength dipole antenna at 2.45 GHz. The results show that the width of the confidence interval for the measured points in the radiation pattern is different, showing that the test uncertainty might depend on the orientation between the EUT or antenna with respect to the measurement probe.
In the past 30 years, the Electromagnetic Compatibility has established itself as one of the most... more In the past 30 years, the Electromagnetic Compatibility has established itself as one of the most important quality disciplines, supported by both national and international standards and regulations. The increasing technological development of emerging economies of Latin America and their greater participation in the global market has created the need for continued regulation of their production of electrical and electronic devices. Latin America has a significant potential for economic growth not only as a producer of raw material but also as an exporter and importer of technology and in consequence the Electromagnetic Compatibility has an important role to play. This study shows the current status of the region in terms of regulations, standards and testing facilities relating to electromagnetic compatibility, through a comparison between the four Latin American countries with the largest gross domestic product: Argentina, Brazil, Mexico and Venezuela. Finally, a projection was made on the potential future development of this technological area.
†IVIC, Caracas, Venezuela y Universidad del Turabo, Gurabo, Puerto Rico † †PDVSA INTEVEP, Los Teq... more †IVIC, Caracas, Venezuela y Universidad del Turabo, Gurabo, Puerto Rico † †PDVSA INTEVEP, Los Teques, Miranda, Venezuela RESUMEN -En este trabajo se utilizó un doble resonador dieléctrico blindado para la determinación de la permitividad dieléctrica de líquidos de bajas pérdidas. La probeta cilíndrica que contiene a la muestra de petróleo líquido de permitividad desconocida, es de cuarzo con 99% de pureza. La probeta se sitúa en el centro de la cavidad a los fines de determinar la permitividad efectiva de la mezcla petróleo -cuarzo mediante la solución de las ecuaciones de Maxwell. Posteriormente empleando la teoría de Bruggeman referente a la medida de las permitividades efectivas de mezclas se determinó la permitividad de petróleo. Se construyó un resonador dieléctrico blindado de aluminio resonante en el modo TE 011 en 4,881 GHz. Keywords: dieléctricos de bajas pérdidas, propiedades electromagnéticas del petróleo, cavidades resonantes, puntos críticos.
An important concern in the validation of computational electromagnetics (CEM) is to incorporate ... more An important concern in the validation of computational electromagnetics (CEM) is to incorporate quantitative indicators in order to perform conclusive comparisons between model predictions with respect to a reference expected response, such as data obtained from measurements, closed-form equations references or standard reference problems values. Besides, the aforementioned index must be qualitatively interpreted using established and objective criteria, mimicking the perception of individuals or teams of expert engineers and aiding them in the interpretation process. So far, this problem has been addressed by the standardized Feature Selective Validation (FSV) method which has become the most widespread technique in the validation of CEM. Nonetheless, the FSV has some drawbacks which have driven subsequent and non consolidated enhancements proposed to improve its performance under specific situations. This paper proposes a global and normalized mutual information based index that includes feature selective considerations as an alternative to evaluate and compare datasets involved in the validation of CEM. Finally, three numerical examples are developed using the presented methodology and the results are compared with the overall indicator for the amplitude and the feature measures obtained using the FSV. The results suggest that the proposed index is able to provide intuitive, consistent and compressive interpretation about the global results of the validation process. Nevertheless, research must be continued in order to refine the proposed method and testing its complete range of applicability and suitability.
En esta publicación se presenta el trabajo realizado en la creación del primer laboratorio en Ven... more En esta publicación se presenta el trabajo realizado en la creación del primer laboratorio en Venezuela de compatibilidad electromagnética (EMC), determinación de parámetros de antenas (APM) y ensayos en dispositivos móviles según el protocolo de certificación de la CTIA (Cellular Telecommunications & Internet Association) de la Fundación Instituto de Ingeniería. Para evaluar la compatibilidad electromagnética de sistemas eléctricos y electrónicos se dispone de una cámara semianecoica que está acreditada en el rango de frecuencia desde 30 MHz hasta 18 GHz. En lo que respecta a la caracterización de sistemas radiantes y certificación de dispositivos móviles de acuerdo al estándar CTIA, se ha diseñado una cámara completamente anecoica que está acreditada en el rango de frecuencias desde 700 MHz hasta 6 GHz. Todos los ensayos a realizar están basados en normas internacionales de organismos acreditados como la IEC, CISPR, IEEE, ANSI y normas militares. Este laboratorio amplia el campo de trabajo de la Fundación Instituto de Ingeniería (FII) en las áreas de metrología y ensayos bajo normas hacia el sector telecomunicaciones y servirá de plataforma de apoyo a la actividad reguladora del ente nacional, CONATEL (Consejo Nacional de las Telecomunicaciones) para evaluación y desarrollo de dispositivos y equipos fabricados en el país, para la investigación básica y aplicada en el área de antenas, propagación y compatibilidad electromagnética.
The use of spherical wave expansion of the solution of the wave equation to predict Far-Field val... more The use of spherical wave expansion of the solution of the wave equation to predict Far-Field values from data measured in the Near-Field region is a well known technique, typically used to perform antenna measurements in compact anechoic chambers. However, when designing the computing algorithm it is fundamental to validate the results and to quantify the numerical error of the method. In this regard, a computer application that samples the electric Near-Field and calculates the values of the electric Far-Field region using spherical wave expansion was developed to measure antenna radiation patterns in the Fresnel zone inside a fully anechoic chamber. In order to validate the code, this paper describes three validation methods: firstly, using the theoretical electric Near-Field values of an infinitesimal dipole as the input to the algorithm to compare the output with the response analytically expected; secondly, using a Far-Field electric field data of a calibrated half wavelength dipole measured in an anechoic chamber and finally, using an electric Near-Field data of a calibrated half wavelength dipole measured in the same chamber. These methods provide simple procedures to calculate the error introduced by the code in different scenarios that should be considered to estimate the measurement uncertainty.
In this paper, we present a novel general methodology which ensure a minimum uncertainty in the m... more In this paper, we present a novel general methodology which ensure a minimum uncertainty in the measurement of the real part of the permittivity of a material measured using cylindrical shielded dielectric resonators. The method is based on the fact that for any given value of the dielectric permittivity there is an optimal radius of the cylindrical dielectric rod sample. When the dielectric rod sample has the optimum radius, the width of the coverage interval associated to the real part of the dielectric permittivity measurement result -for a given confidence level -is reduced due to a lower sensitivity of the dielectric permittivity to be measured versus the variations in the resonant frequency. The appropriated radius of a given sample under test is calculated using Monte Carlo simulations for a specific mode and a specific resonant frequency. The results show that the confidence interval could be reduced by one order of magnitude with respect to its maximum width predicted by the uncertainty estimation performed using the Monte Carlo method (MCM) as established by the supplement 1 of the Guide to the Expression of Uncertainty in Measurement (GUM). The optimum radius of the sample under examination is fundamentally determined by the electromagnetic equations that describe the measurement and does not depend specifically of the sources of uncertainty considered.
In this paper, we estimate the uncertainty in complex permittivity measurements performed in a sh... more In this paper, we estimate the uncertainty in complex permittivity measurements performed in a shielded dielectric resonator, by using the Monte Carlo Method. We selected this approach since the theoretical expressions required to interpret the experimental results are highly non-linear. Furthermore the resonant frequency of the system and its quality factor are highly correlated. Thus we propose a model for the measurement process which considers the major sources of uncertainty previously reported in published experimental results. The proposed model combined with the Monte Carlo method was used to propagate the probability distributions of each uncertainty contribution, obtaining a) the approximate probability density function for the measured complex permittivity, and b) the estimated expanded uncertainty for the mode TE 011 . The results show that this procedure leads to small uncertainty intervals for the real part of the dielectric permittivity, while it is not very reliable in the loss tangent measurement. Additionally, for each input quantity, we calculated the standard deviation in the experimental results produced independently by each uncertainty contribution.
This paper proposes a simple semi-analytical method for designing coil-systems for homogeneous ma... more This paper proposes a simple semi-analytical method for designing coil-systems for homogeneous magnetostatic field generation. The homogeneity of the magnetic field and the average magnitude of the magnetic flux density inside of the volume of interest are the objective functions chosen for the selection of the coil-system geometry (size and location), number of coils and the number of turns of each winding. The spatial distribution of the magnetostatic field is estimated superposing the magnetic induction numerically computed from the analytical expression of the magnetic field generated by each coil, obtained using the Biot-Savart's law and the current filament method. The homogeneous magnetic field is synthesized using an iterative algorithm based on TABU search with geometric constraints, which varies the design parameters of the windings to meet the requirements. The number of turns of each coil and gauge of wire used for the windings is adjusted automatically in order to achieve the target average magnitude of the magnetic induction under the constraints imposed by power consumption. This method was used to design a coil arrangement that can generate up to 10 mT within a volume 0.5 m×0.5 m×1 m with 99% of spatial homogeneity, with square loops of length less than or equal to 1.5 m, and with a power dissipated by Joule effect less than or equal to 1 W per coil. The synthesized magnetic field distribution was validated using Finite Element Method simulation, showing a good correspondence between the objective values and the simulated fields. This method is an alternative to design magnetic field exposure systems over large volumes such as those used in bioelectromagnetics applications.
The aim of this study was to establish the necessary setups for the measurement of the basic para... more The aim of this study was to establish the necessary setups for the measurement of the basic parameters of a commercial DTH receiver based on the standardized measurement techniques in order to provide the Venezuelan state a system of quality management to ensure well-functioning of equipment being procured to provide the end user, the digital satellite television service. The tests were done by measuring the variables of interest from the three major subsystems that comprise DTH system: internal unit, low noise block and the antenna system.
Desde hace varios años la compatibilidad electromagnética (CEM) es un tema de creciente interés e... more Desde hace varios años la compatibilidad electromagnética (CEM) es un tema de creciente interés en el diseño de los productos eléctricos, electrónicos y de telecomunicaciones. Entre estos productos se encuentran los equipos electromédicos. Tal y como es declarado por distintos organismos (FDA/CDRH, COMAR, IEEE-EMBS, IEC) los centros de salud deben tener normativas que permitan controlar, monitorear y evaluar sus equipos médicos y su entorno electromagnético a fin de prevenir posible errores en diagnósticos y minimizar riesgos de operatividad. Este estudio realiza una evaluación en distintos tipos de centro de salud con respecto a las normativas en compatibilidad electromagnética (IEC 60601-1-2) y otras recomendaciones, para identificar las condiciones técnicas de estas instalaciones. Los resultados arrojaron que actualmente no se aplican tales normativas, y que dicha situación puede ser resuelta a través de simples acciones que mejorarían la seguridad y la calidad del servicio de salud con respecto a la compatibilidad electromagnética.
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articles by Marco Azpurua