EXPERIMENTAL VERIFICATION OF TLM WIRE MODEL FOR DETERMINING SHIELDING EFFECTIVENESS OF METAL ENCLOSURE WITH RECTANGULAR APERTURE
Keywords:
measurements, metal enclosure, rectangular aperture, TLM method, TLM wire model, shielding effectivenessAbstract
In this paper, both experimental and numerical analysis of metal enclosure with rectangular aperture on
frontal enclosure wall is obtained. The numerical technique for computational analysis is performed by creating an
enclosure model with one slot-type aperture on frontal enclosure wall and for the same enclosure with a slightly
wider rectangular aperture. The presence of an aperture or air-flow aperture arrays on the enclosure walls is very
important and it has a dominant effect on the shielding function of the enclosure. Also, the influence of the other
parameters such as magnetic permeability and electrical conductivity of material from which enclosure is made of,
different wall thicknesses, shape and size of enclosure should be taken into consideration, in order to fully estimate
the extent to which the shielding allows the system to function, in accordance with electromagnetic compatibility
standards. Applying a computer method that uses transmission line matrices for spatial discretization of the
electromagnetic field, so-called Transmission-Line Matrix method, TLM method. It is used for modelling
conductive enclosure with slot aperture on front enclosure wall and with receiving monopole antenna inside.
Furthermore, during practical engineering measurements, there is a receiving measuring antenna inside an
equipment under test. Usually, a monopole or dipole antenna is employed for electrical field measurements while a
loop antenna is used for magnetic fields. In order to faithfully simulate the enclosure on which tests are performed in
terms of electromagnetic compatibility, the TLM wire model is used in order to reliably model the receiving antenna
inside the enclosure. As an excitation source, the vertically polarized plane wave is used. In order to confirm the
numerical results of the electromagnetic TLM solver, measurements are conducted in the Laboratory for high
frequency measurements. Since the Laboratory does not have an anechoic room, the first step was to create a
measuring place in order to carry out quality measurements, without significant influence of the environment.
Therefore, electromagnetic absorbers for the frequency range of interest were installed. In places where
electromagnetic interferences were observed, the necessary shielding with conductive plates was performed.
Measuring configuration consists of spectrum analyzer, tracking generator, computer, coaxial cables, ultra-wideband
dipole antenna, and enclosure under test. In order to perform measurements of shielding effectiveness, firstly, the
signal level of the metal enclosure with the receiving antenna should be measured. Secondly, the signal level from
the receiving antenna without the enclosure should be measured, under the same conditions. Therefore, the shielding
effectiveness of enclosure can be found by determining the ratio between measurements. The measurements are
carried out from the view point of the electromagnetic compatibility, in order to determine the shielding
effectiveness of the enclosure at ultra-high and super high frequencies. Finally, the experimental results showed
excellent agreement with the results obtained by the TLM method. According to that the measurements confirmed
the results obtained by the TLM simulations; it can be noticed that computer modelling of metal structures is a very
important. Above all, it is an effective tool in solving EMC problems even in the initial phase of designing an
enclosure or some microwave structure.
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