Intermediate Level Modelling for EMC : Examples

Here we give some example results, a description of the principles of intermediate level modelling are given in the "principles" frame.

Shielding of an Enclosure with an Aperture

Try our online shielding calculator which allows you to compute the shielding of an enclosure with an aperture.
This graph shows the computed shielding effectiveness from our intermediate level model compared with measured data (a stripline was used for the low frequency measurement and the enclosure was illuminated with an antenna for frequencies above 200MHz). The approximate solution given by Ott is also shown.
Note that the Intermediate level result shown here was calculated using a lossless waveguide model. A typical enclosure with contents has a Q-factor of 10 to 1000, and gives a less sharp resonance!
Shielding of enclosure with aperture
Electric field shielding effectiveness of a 300x300x120mm enclosure with a 100x5mm slot comparing measured data with our intermediate tool and Ott’s equation.


Coupling of Loops in an Enclosure

Here we  compare the computed coupling between two loops in an enclosure (as shown on the principles frame) and data measured with a network analyser. It can be seen that the model (which in this case only uses the TE10 waveguide mode) works well up to 600MHz, and give a significant error in amplitude above that frequency. The effects of including higher order waveguide modes is considered below.

Effect of Considering Higher Order Modes

Here TE10, TE11, TM11, TE30 modes are used to calculate the coupling between two monopoles in an enclosure. It can be seen that the intermediate level model follows the details of the response well.
Here only the TE10 mode is considered. The intermediate level model results are accurate up to nearly 600MHz where the higher order modes start to become significant.

Coupling via a Cable Penetration

The monopole model described in the principles frame can be used to determine the coupling into an an enclosure due to pickup on an external cable, due to the penetration of the cable into the enclosure.
Separate monopole models are used for the cable inside, and outside the enclosure.
The coupling of energy via a cable penetration is simulated here using only the TE10 mode and compares well with measured results. The result is shown as the S21 or transmission coefficient from the network analyser output to its input. 

Emissions from a PC Motherboard

Here the rf currents on the tracks on one side of a PC motherboard were measured. The measured currents were then used to drive an intermediate level model of the tracks in an enclosure, with the resultant energy received by a short monopole in the enclosure computed.
The energy received by the monopole was also measured and the results are compared here.
Due to the low level of emissions from this board measurement of radiated emissions show few measurements above the noise floor so we have been unable to succesfully test the method to predict radiated emissions.

Applied Electromagnetics and Electron Optics Research, Department of Electronics, University of YorkResearch in the Department of Electronics, University of YorkThe University of YorkThe University of York