Vignesh Rajamani

Validation of modal/MoM in shielding effectiveness studies of rectangular enclosures with apertures

This paper discusses the validation of Modal/method of moments (MoM) including cases when the apertures are made as big as the wall of the enclosure (equivalent to having one side of the cavity open). The validation is done using field computations involving bodies of arbitrary shape (FEKO), a commercially available code. The results show that Modal/MoM predicts the results close to the analytical results of Robinson et al. Electron. Lett., 32 (17), 1996; Robinson et al., IEEE Trans. Electromagn. Compat., 40 (3), 240-247, 1998 for single-aperture cases and for most double-aperture cases. Also, for the cases of considering oblique incident plane waves, through validation, it has been found that Modal/MoM can predict the shielding effectiveness close to measured results for smaller angles and not for larger angles of incidence due to the edge effects. In this work, the shielding effectiveness is calculated at only one point, the center of the cavity assuming it to be the worst case. This work discovers the limitation of Modal/MoM for certain applications.

Introduction to feature selective validation (FSV)

The feature selective validation (FSV) tool is a standalone application that implements the FSV method originally developed by Dr Anthony Martin. The feature selective validation (FSV) algorithm has been developed to compare any two sets of data and put them in an objective and comprehensible form. The FSV theory was conceived as a technique to quantify the comparison of data sets by mirroring the perceptions of engineers. The application of FSV to the validation of data is a key element in a current IEEE Standard under development as a means of describing quality of electromagnetic simulation results. FSV allows automated comparisons of large volumes of complex data whilst reliably categorising the results into a common set of quality bands. The motivation behind this research can be summed up as the need to control variations between visual assessment results, the reduction of cost (a skilled engineer is an expensive commodity), the desire to reduce ambiguities and the inability of humans to process and cache extremely large volumes of data

Accurate and Efficient Numerical Simulation of the Random Environment Within an Ideal Reverberation Chamber

An electromagnetic susceptibility test within an ideal reverberation chamber is numerically simulated using the moment method (MM). The random field environment within the chamber is synthesized using a superposition of plane waves that are propagating in fixed directions determined rigorously from spectral sampling theory. Randomness is introduced in the complex field amplitudes associated with each plane wave. This approach yields field statistics within a designated test region that approach ideal. Moreover, the fixed propagation directions allow very efficient calculation of the currents induced at specific test points on an equipment-under-test due to the random field realizations. MM calculations show that the proposed sampling method yields a better prediction of the statistics of the induced current while requiring far less computation time than the currently used technique of superimposing randomly propagating plane waves to yield field realizations.

Stirred-Mode Operation of Reverberation Chambers for EMC Testing

Continuous stirred-mode operation of a mechanically tuned reverberation chamber provides an alternative to stepped-mode operation that is both more cost effective and more robust in many electromagnetic compatibility testing applications. An experimental investigation shows that the spectral information available within the chamber is the same for both the stepped and the stirred operation and is independent of the tuner speed provided that the chamber transient time is small compared to the rate at which the fields change inside the chamber due to the tuner rotation. This is further confirmed for stirred operation at additional frequencies. However, the field must be properly sampled to ensure that all independent field configurations available at the test point within the chamber are included in the spectral analysis. Optimal sampling is obtained when sampling at the same tuner angular position increment over a single tuner rotation at any tuner speed. Equipment under test may be exposed to all available field configurations available within the chamber using stirred operation with a single rotation of the tuner, giving a more robust test than the minimum 12 steps that are used with the stepped operation. Testing time is also reduced. The exposure time to a particular field configuration can be controlled with knowledge of the number of independent samples available in the chamber and by changing the tuner rotational speed.

A New ANN-Based Modeling Approach for Rapid EMI/EMC Analysis of PCB and Shielding Enclosures

This paper introduces a new artificial neural networks (ANNs)-based reverse-modeling approach for efficient electromagnetic compatibility (EMC) analysis of printed circuit boards (PCBs) and shielding enclosures. The proposed approach improves the accuracy of conventional or standard neural models by reversing the input-output variables in a systematic manner, while keeping the model structures simple relative to complex knowledge-based ANNs (e.g., KBNNs). The approach facilitates accurate and fast neural network modeling of realistic EMC scenarios where training data are expensive and sparse. To establish accuracy, efficiency, and feasibility of the proposed reverse-modeling approach, PCB structures such as perforated surface-mount shields and partially shielded PCB traces are treated as proof-of-concept examples. Although the modeling examples presented in the paper are based on training data from EM simulations, the approach is generic and hence valid for EMC modeling based on the measurement data. The approach is particularly useful in the electronic manufacturing industry where PCB layouts are frequently reused with minor modifications to the existing time-tested designs.

One-port time domain measurement technique for quality factor estimation of loaded and unloaded cavities

In this paper a one-port time domain measurement technique for quality factor estimation of a loaded and unloaded metallic cavity is presented. By observing the power decay profile of S11 the quality factor can be computed. Validation of the one-port time domain technique is done by comparing quality factor estimation with the Q estimations from both two-port frequency and time domain data. The usefulness of the one-port time domain technique is also demonstrated using a physically small but electrically large cavity with different types of RF absorber material.

Measurement and Simulation of the Induced Current on a Wire Using S-Parameter Method

This study investigates the measurement of current on a wire located inside a cavity with an aperture as a function of excitation frequency with the use of a simple S parameter model. Validation is provided by comparing simulations and measurements. Using this approach, it will be possible to make an accurate prediction of the current distribution on the wire, and thereby to describe potential interference effects to equipment placed along the wire bundle at frequencies of interest.

Numerical study of currents induced on a partially shielded wire within an ideal reverberation test chamber

An electromagnetic susceptibility test in a reverberation chamber has been simulated numerically. The electromagnetic environment of the chamber was simulated using a previously introduced method that samples the plane wave spectrum of the random fields at fixed incidence angles determined from spherical sampling theory. The sampling scheme gives excitation fields that have ideal statistics over the volume occupied by the equipment under test (EUT) while reducing the computation time over traditional approaches. A refinement of the technique has been introduced that exploits the reciprocity principle to further reduce the computational load when simulating electromagnetically large EUTs with a limited number of test points of interest. Up to 1000 000 samples of the random chamber fields were considered. The simulations show that the current coupled onto a wire that is partially shielded by a conducting box with a large aperture exhibits strong resonances. The resonant frequencies appear to be determined mainly by the box dimensions, with aperture resonances also contributing. Statistical testing shows that the induced wire currents follow an ideal Rayleigh distribution independent of the frequency of the excitation.

Optimal plane-wave representation of random fields in a reverberation chamber

The random electromagnetic field within a reverberation chamber is modeled using a superposition of plane waves. Based on rigorous sampling theory, the ideal continuous plane-wave spectrum within the chamber is sampled over the sphere to yield nearly ideal field statistics (including spatial autocorrelation) over a specified test volume such as that occupied by an equipment under test (EUT). The same spectral sampling (as defined by the individual plane-wave directions) is used for each trial, with randomness added to the specific fields associated with the individual plane-wave samples in the different trials. Since the sampling is fixed, the response of the EUT to only a single plane wave at each sample point must be found numerically. The response of the EUT to specific realizations of random fields within the chamber is found through a linear superposition of the individual plane-wave responses weighted by appropriate random coefficients. This minimizes the number of times the field on the EUT must be solved using a numerical electromagnetics technique, giving an efficient method to numerically simulate susceptibility tests within reverberation chambers.

Sensitivity Analysis of a Reverberation Chamber with Respect to Tuner Speeds

The energy distribution among the modes in an over-moded reverberation chamber operating at a particular frequency is studied for varying tuner speeds. The understanding of this spread is important in quantifying upsets of equipment in the chamber. The spectral characterization of a time varying electromagnetic field is done using the averaged periodogram approach. The complex insertion loss S21 is the measured quantity and an estimation of the power insertion loss that will be used in the determination of Q factor, is obtained from the sampling data for varying angular positions of the tuner. The same procedure is followed for varying tuner speeds and the Q is reported. The autocovariance for this random process can be found by taking a Fourier transform of the spectral density function. The autocovariance function helps in determining the number of independent samples of the field. The field experienced by a EUT in the usable volume due to continuous rotation of the tuner is analyzed.