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## Establishing probability of failure of a system due to electromagnetic interference

Rajamani, Vignesh

Rajamani, Vignesh

##### Abstract

Scope and Method of Study:

A wire placed inside the metallic box will serve as the equipment under test and the distributions of current and fields will be calculated via measurements. From the distribution, the probability of the observable exceeding a certain threshold can be determined. From the nature of the EME generated, the probability of threat due to EMI can be derived under some assumptions. Combining both the probabilities, the net probability of failure of the system could be determined. Reverberation chambers will be useful in measurements in this study as they simulate operating conditions of the EUT inside a cavity and as the EUT is exposed in all directions to the electromagnetic field, the uncertainty is also reduced. The probability models can provide insight into what type of testing is required to assure worst case testing with reasonable accuracy.

Findings and Conclusions:

The final outcome of this work is to establish the probability of failure due to current coupled onto a cable or a cable bundle located close to the wall of a cavity due to external or internal coupling of EM. The electromagnetic environment of the cavity was determined to estimate the probability of threat depending on the location of the cable inside the cavity. Given that the probability of threat exists, then the probability that the value of the current exceeding a certain threshold was determined. The environment in which the EUT operates and the influence of the environment on the observable that is being targeted was also determined which aids in the calculation of threshold probability. Finally, the net probability of failure of a system was determined from the individual probabilities. The major focus of this work was on the development of the methodology that is sufficiently general to obtain the distribution of any observable. The procedure developed could be used in different scenarios and from a class of distributions developed for each scenario, the probability of threat and probability of failure of a system due to EMI can be calculated.

A wire placed inside the metallic box will serve as the equipment under test and the distributions of current and fields will be calculated via measurements. From the distribution, the probability of the observable exceeding a certain threshold can be determined. From the nature of the EME generated, the probability of threat due to EMI can be derived under some assumptions. Combining both the probabilities, the net probability of failure of the system could be determined. Reverberation chambers will be useful in measurements in this study as they simulate operating conditions of the EUT inside a cavity and as the EUT is exposed in all directions to the electromagnetic field, the uncertainty is also reduced. The probability models can provide insight into what type of testing is required to assure worst case testing with reasonable accuracy.

Findings and Conclusions:

The final outcome of this work is to establish the probability of failure due to current coupled onto a cable or a cable bundle located close to the wall of a cavity due to external or internal coupling of EM. The electromagnetic environment of the cavity was determined to estimate the probability of threat depending on the location of the cable inside the cavity. Given that the probability of threat exists, then the probability that the value of the current exceeding a certain threshold was determined. The environment in which the EUT operates and the influence of the environment on the observable that is being targeted was also determined which aids in the calculation of threshold probability. Finally, the net probability of failure of a system was determined from the individual probabilities. The major focus of this work was on the development of the methodology that is sufficiently general to obtain the distribution of any observable. The procedure developed could be used in different scenarios and from a class of distributions developed for each scenario, the probability of threat and probability of failure of a system due to EMI can be calculated.

##### Date

2010-07