Mireya Fernandez

A comprehensive model for power-line interference in biopotential measurements

Power line interference is a major problem in high-resolution biopotential measurements. Because interference coupling is mostly capacitive, shielding electrode leads and a high common-mode rejection ratio (CMRR) are quite effective in reducing power-line interference but do not completely eliminate it. We propose a model that includes both interference external to the measuring system and interference coming from its internal power supply. Moreover, the model considers interference directly coupled to the measuring electrodes, because, as opposed to connecting leads, electrodes are not usually shielded. Experimental results confirm that reducing interference coupled through electrodes yields a negligible interference. The proposed model can be applied to other differential measurement systems, particularly those involving electrodes or sensors placed far apart.

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 perturbation analysis in digital radio

This paper presents a new simulation methodology to study the effect of radiated transient disturbances on digital communication systems. The procedure is divided in two stages. In the first one, FDTD numerical simulation is used to determine the transient levels coupled to the antennas. In the second stage, these levels are analyzed by means of a signal processing simulation software to determine the degradation caused in the system. The procedure is applied to a DAB system in car when a radiated interference is generated by a transient in a vehicle cable. The results show that the amplitude of the radiated transient coupled signal is a key parameter, but it is also essential to take into account other parameters such as burst duration and frequency.

Validation of low-level, high-frequency transient FDTD simulation with radiated field measurements

Validation of numerical simulation results for low-level, high-frequency transient radiated EMC signals is difficult because of the limitations of time domain measurement instruments. A measurement method combining the sensitivity of a RF spectrum analyzer and the time domain abilities of a digitizing oscilloscope is used to validate FDTD simulations of a fast transient coupled between two antennas inside a car.

Transient Electromagnetic Field Computation in Automotive Environments using FDTD

Numerical electromagnetic computation at high frequencies in automotive environments is a challenging problem because of the dimensions of the problem compared to the wavelength. Results obtained so far have been presented in the frequency domain. We are presenting comparisons between calculated and measured transient waveforms, so in the time domain, by using a model of a realistic car body frame. Results are presented for different settings in the simulation grid parameters. The agreement of the signals in time and also in the frequency domain allows us to conclude that such computations are feasible up to the GHz frequency band and using modest computation resources.

SIVA UAV: A Case Study for the EMC Analysis of Composite Air Vehicles

The increased use of carbon-fiber composites in unmanned aerial vehicles is a challenge for their EMC assessment by numerical solvers. For accurate and reliable simulations, numerical procedures should be tested not only for individual components, but also within the framework of complete systems. With this aim, this paper presents a benchmark test case based on experimental measurements coming from direct-current injection tests in the SIVA unmanned air vehicle, reproduced by a numerical finite-difference-time-domain solver that employs a new subgridding scheme to treat lossy composite thin panels. Validation was undertaken by applying the feature selective validation method, which quantifies the agreement between experimental and numerical data.

Car windshield behavior transient analysis by FDTD

The present article studies the influence of a car heatable windshield by means of an equivalent material that allows an appropriate meshing of the vehicle. This study has been performed analyzing the propagation of an electromagnetic radiated transient pulse generated by a wire inside a car with and without the windshield. The Finite Differences Time Domain (FDTD) is the method used to obtain the field coupled to antennas located inside and outside the car. We concluded that it is important to take into account the heatable windshield to make a suitable electromagnetic model of the vehicle.

Bulk current injection test uncertainty assessment

Modern automobiles incorporate increasing amount of electronic systems, many with vehicle safety concerns, working in a harsh electromagnetic environment. The vehicle components immunity to electromagnetic interference is fundamental and is covered by international standards like ISO 11452-x and SAE J1113-x series for automotive EMC immunity testing. Also, each automobile manufacturer has its own EMC immunity requirements covering the different types of disturbances: radiated, conducted and ESD. Usually, the uncertainty related to the determination of the applied immunity level is not considered in the automotive EMC standards, but it is an important issue in test reliability and repeatability. We describe a methodology for uncertainty assessment in EMC immunity tests particularizing it on the bulk current injection test.

Noise properties in the isoelectric intervals of the ECG: a comparison

The authors have compared the variance and the histogram for the three isoelectric intervals of the ECG of 8 subjects. They have used a spectral filter in order to eliminate the power line frequency. They have found that when the noise variance is low, the histogram is bell shaped and similar for the three intervals. But when the noise variance is high, the histogram does not have any definite shape. When the relative difference between variances for the isoelectric intervals is low, these intervals can be considered as similar. But in some instances, noise histograms for different intervals have rather different variances. The authors have tested their analysis method by adding noise with different amplitude distributions to a clean ECG. They conclude that although the time record gives a clue about when to reject a noisy ECG, the measurement of the noise variance in the three isoelectric intervals would be better. Also, when searching for micropotentials in the PR or ST intervals, the noise behavior in the TP interval is not necessarily representative of the noise in the other intervals.<<ETX>>