Marco A. Azpurua

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.

Uncertainty estimation in complex permittivity measurements by shielded dielectric resonator technique using the Monte Carlo method

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 TE011. 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.

A measurement system for radiated transient electromagnetic interference based on general purpose instruments

This paper presents a measurement system intended to be used to assets the radiated electromagnetic interference (EMI) in both time and frequency domains. In order to keep the measurement setup as accessible and practical as possible, the direct measurements are recorded with a general purpose digital oscilloscope and processed with a commonly available personal computer. The measurement system was validated for radiated emissions testing using well-known, controlled transient and continuous signals emulating typical interferences. The results are in satisfactory agreement with those provided by a conventional EMI receiver for different types of detectors. The proposed approach shows that, currently, it is possible to implement a timesaving, accurate and generally inexpensive time domain measurement system for radiated emissions that is capable to overcome the limitations of the superheterodyne EMI receivers regarding the measurement of discontinuous electromagnetic disturbances and also able to provide additional enhanced features to evaluate and troubleshoot EMI problems.

A Review on the Drawbacks and Enhancement Opportunities of the Feature Selective Validation

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.

Vector Feedback Homogeneity and Inner Layout Influence on Fluxgate Sensor Parameters

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 nonlinearity-cross-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.

Time-domain measurement technique to analyze cyclic short-time interference in power supply networks

Conducted interference caused by equipment connected to power supply networks, and the interference in these networks, is conventionally measured using (slow) scanning tuned electromagnetic interference (EMI) receivers. A voltage sensor which separates common mode and differential mode in a three-phase setup combined with a 8-channel digital oscilloscope allows measuring voltage and current via many samples in the three phases plus neutral. Using fast fourier transform for the data processing the conventional amplitude-as-function-of-frequency plots, similar to what would be obtained using conventional EMI receivers, can be generated. But with the presented measurement technique it is also possible to present time-frequency plots in a waterfall diagram. The time - domain measurement technique shows that the conducted noise is cyclic short-time interference.

Measurement and Evaluation Techniques to Estimate the Degradation Produced by the Radiated Transients Interference to the GSM System

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.

Feature Selective Normalized Mutual Information Index for the validation of computational electromagnetics

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.