An actual example is window glass designed to have a certain degree of electromagnetic shielding effect. Such material may be desirable if one for various reasons does not want electromagnetic emission from the inside to propagate out from a building, or if you want to reduce the radiation of heat from the building.

The cause of the former can be both to not allow that someone outside exploits the signal, or not want the emission to disturb wireless systems outside the building. Windows with electromagnetic shielding effect reduces the amount of received electromagnetic signals into the building.

This means that the signals from mobile telephone systems or other outdoor radio systems will be attenuated on the way into the building. This causes problems if one wishes to use such systems indoors. One such disadvantage can indeed be solved by creating slot antennas in the glass so that the mobile telephony signals or other signals within a certain frequency range will pass through.

At the same time it is important to check if there is undesired emission from the inside in the same frequency range that will leak out through such slots. Depending on the needs one has for the activities indoors and what need there is to attenuate signals out of the building, this can be a difficult dilemma.

EMC work is not always to attenuate signals. It also means ensuring that desired signals arrive to their intended destination.