Electromagnetic analysis and shielding of slots on resonant and non-resonant realistic structures with MLFMM

Coupling and interference in electronic devices is of increasing concern due to the presence of either intentional or unintentional internal or external electromagnetic sources. Such sources can cause sufficient disruption to the circuit or chip logic to the point where the functionality and logic state of the electronic device can be altered due to such extraneous sources. Coupling into these devices can occur either from ventilation slots or though power/signal lines which penetrate into the enclosure of the cavity structure. The latter can introduce conduction noise and ground fluctuations into the signal ports. Plane wave illumination, of unity field strength, onto a microwave filter is calculated to give an induced voltage of 4 mV at the 50 Ω output port. The actual excitation was a pulse train with a period of 300 ns with the same center frequency as the filter (2.150 GHz). These calculations were carried out using a well-validated method of moments simulator. Thus, a large amplitude pulse signal of 300 V/m may induce a noise signal of 0.12 V. This could potentially cause failures in logic states for digital circuits and spurious waveforms for analog amplifier circuits. Furthermore, cavity enclosures can amplify the external signals by as much as 10 dB to 20 dB, especially in the overmoded region. This can be seen where the EFS fluctuations due to cavity and slot resonances pose a problem for a circuit configuration. Moreover, the presence of wires through the slot enhance coupling into the cavity. This is demonstrated where we show the electric field shielding factor measured in the middle of the cavity due to a plane wave incidence, for wires penetrating through aperture and into the cavity. The penetration is through a circular slot of area 60 cm². Both the straight and bent (longer) wires deteriorate the EFS quite significantly at lower frequencies and even at higher frequencies for the bent wire. We particularly note that the bent wire causes low EFS even away from the cavity resonances due to greater re-radiation of energy from external illumination into the cavity enclosure. This is computed with the well-validated multilevel fast multipole method (MLFMM).