Ferran Silva

Initial Analysis of SAR From a Cell Phone Inside a Vehicle by Numerical Computation

The purpose of this paper is to analyze the influence of the metallic structures of a realistic car body frame on the specific absorption rate (SAR) produced by a cell phone when a complete human body model is placed at different locations inside the vehicle, and to identify the relevant parameters responsible for these changes. The modeling and analysis of the whole system was conducted by means of computer simulations based on the full wave finite-difference time-domain (FDTD) numerical method. The excitation considered was an 835 MHz lambda/2 dipole located as a hands-free communication device or as a hand-held portable system. We compared the SAR at different planes on the human model, placed inside the vehicle with respect to the free space situation. The presence of the car body frame significantly changes the SAR distributions, especially when the dipole is far from the body. Although the results are not conclusive on this point, this change in SAR distribution is not likely to produce an increase above the limits in current guidelines for partial body exposure, but may be significant for whole-body exposure. The most relevant change found was the change in the impedance of the dipole, affecting the radiated power. A complementary result from the electromagnetic computations performed is the change in the electromagnetic field distribution inside a vehicle when human bodies are present. The whole vehicle model has been optimized to provide accurate results for sources placed inside the vehicle, while keeping low requirements for computer storage and simulation time

Transient FDTD simulation validation

In computational electromagnetic simulations, most validation methods have been developed until now to be used in the frequency domain. However, the EMC analysis of the systems in the frequency domain many times is not enough to evaluate the immunity of current communication devices. Based on several studies, in this paper we propose an alternative method of validation of the transients in time domain allowing a rapid and objective quantification of the simulations results.

Factors influencing the successful validation of transient phenomenon modelling

An increased requirement for validation of computational electromagnetic simulation and modelling through the publication of IEEE Standard 1597.1 brings to light some interesting issues surrounding the validation of transients. The structure of a transient event has three particular regions of interest that can have an influence on the results, of which only two are generally well defined. These are the initial quiescent phase from t = 0 to the transient event; the transient event itself up to the point where the energy has fallen to a predefined limit, and the post-transient phase where residual energy is still present in the system. This latter region is generally ill-defined and changes the way that a validation comparison should be made, from, for example a frequency domain coupling study where the region of interest is usually well defined. This study looks at the influence of the three regions on the validation results and suggests how the Feature Selective Validation (FSV) method can be applied in transient studies.

Full-Spectrum APD Measurement of Transient Interferences in Time Domain

Radiated transient interferences produce severe errors to digital communication systems. Conventional measurements defined in the electromagnetic compatibility (EMC) standards are not sufficient to predict the impact of this impulsive noise on the quality of a digital system, as measurements were originally defined to protect analogue communication systems. Measurement detectors and methods based on reaching the statistical of the interference have been studied as the best option to evaluate transient interferences. For a properly EMC emissions evaluation, an amplitude probability detector (APD) has been recommended as the best option, since APD results have been correlated with bit error probability. However, carrying out APD measurements using electromagnetic interference (EMI) receivers has strong inconvenience. One of the main limitations is that measurement can only be performed with the preset filters available at the EMI receiver, which sometimes are different from the communication bandwidths causing an incorrect estimation on the degradation produced. Another restriction is the elapsed time needed to acquire the statistical APD measurement at each frequency band. This document presents a methodology to obtain the APD measurement at any frequency band employing two single time-domain oscilloscope captures. The developed measurement method makes it possible to obtain the APD at any frequency band achieving as good results as the ones acquired from EMI receivers. To show the effectiveness of the time-domain method, an exhaustive validation study is presented, in which white Gaussian noise and several impulsive interferences are evaluated at frequencies from 50 MHz up to 1 GHz.

Decomposition of Electromagnetic Interferences in the Time-Domain

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.

On the Statistical Properties of the Peak Detection for Time-Domain EMI Measurements

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.

Improving time-domain EMI measurements through digital signal processing

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.

Analyzing Transient Phenomena in the Time Domain Using the Feature Selective Validation (FSV) Method

The increasing application of simulation tools to increasingly complex problems makes the use of validation tools essential to improve confidence in the veracity of those simulation results. IEEE Standard 1597.1 is the first true standard for the validation of computational electromagnetics method. This standard uses the feature selective validation (FSV) method as the key quantification tool. However, despite its many advantages, there have been some interesting issues surrounding the validation of transients. This paper presents a new approach to the validation of a set of generally representative transient types using the FSV method and shows how the previously experienced limitations can be overcome. In order to analyze the main parameters associated with transient comparison, a survey which included 20 experts was conducted. This information was used to identify the significant regions that need to be taken into account in the transient comparison. Finally, using the statistics obtained by the experts, a new solution was defined and its improvement over the existing approach was demonstrated.

Prediction of the impact of transient disturbances in real-time digital wireless communication systems

In this paper the simulation methodology has been useful to establish the effect of a transient interference coupled to a digital communication system. An RFID system according to ISO 14443 type B standard is interfered by transient interference according to EN 61000-4-4 standard producing decision errors. The usage of the software tools employed to analyze the distortion of digital communication systems in convergence of the EM simulation software is a powerful methodology to quantify the degradation of a real digital communication system.

The Role of Uncertainty in the Feature Selective Validation (FSV) Method

This paper presents a method of taking into account the uncertainty when the Feature Selective Validation (FSV) method is used. Nowadays, there is no doubt about the important role played by the FSV to do an objective process of validation. However, until now the uncertainty has not been considered in the validation process. This paper presents an alternative way to calculate the possible value of FSV, when the uncertainty is contemplated. We show the importance of this technique when defining the validation criteria for the computational electromagnetics method. Finally, in order to show the application and the importance of the method, a real case considering the test lab measurement uncertainty is analyzed.