Houmam Moussa

Directive wavefronts inside a time reversal electromagnetic chamber

In this paper, the feasibility of directive wave-fronts generation inside a time-reversal electromagnetic chamber (TREC) is investigated in order to propose the TREC system as an alternative EMC test facility. This may be accomplished by applying the time reversal technique on electromagnetic waves inside a reverberation chamber. We evaluate the performance of the TREC in creating directive radiation patterns towards an equipment-under-test (EUT). This evaluation is based on the directivity comparison of a wavefront generated by the TREC, and the one generated by a theoretical model of an antenna array in free space. Numerical simulations of the TREC are in a good agreement with the theoretical array model, showing a root-mean-square (rms) deviation from the mean value of the E-field, over a 3 dB main lobe angle, below 6%.

Wide band measurements in time domain with current and voltage probes for power losses evaluation and EMC measurements on power converters

Current and voltage signal must be correctly measured in order to evaluate accurately power losses and electromagnetic interferences in time domain. This paper proposes a way to compensate the measured signals using the gain of the probes and an evaluation of the Common Mode Rejection Ratio of the differential voltage probe. Deconvolution shows its efficiency: the shape of the signal and the phase shift between current and voltage after compensation allow an accurate measurement of the power losses. Common Mode Rejection Ratio estimation shows that it is constant for the studied amplitude levels and there is low impact on the differential voltage measurements.

Polarization selectivity for pulsed fields in a reverberation chamber

Time-reversal techniques have been demonstrated to be able to reverse the incoherence that usually characterizes the field distribution within reverberation chambers. Its ability of generating coherent pulsed fields has previously been applied to communications as well as the generation of controlled wavefronts for immunity testing. Nevertheless, the issue of polarization has not yet received due attention. We prove in this paper that time-reversal techniques, when applied to reverberating media, also allow controlling the polarization of the focused pulsed fields. This result, although apparently paradoxical, relies on the very incoherence properties of reverberation chambers. Remarkably, this allows to generate fields with any polarization by using one single static excitation antenna, enabling a changing polarization just by modifying the signal driving it. A theoretical model is proposed for proving this feature, together with experimental results validating it. Cross-polarization rejections much higher than 20 dB are observed, making the quality of the generated pulses comparable to those obtained in anechoic chambers. Interestingly, the cross-polarization rejection is not expected to depend on that of the transmission antenna as measured in a free-space environment, but just on the properties of reverberation chambers and the frequency bandwidth of the pulse.

Experimental analysis of the performance of a time-reversal electromagnetic chamber

In this paper, the first experimental demonstration of coherent directive and polarized wavefront generation within a reverberation chamber (RC) is presented. This feature is possible with the use of a time-reversal electromagnetic chamber (TREC), a concept that we previously introduced in [1] which principally relies on the use of time-reversal techniques in a highly reverberating medium.

Impact of the temperature of a power module on conducted EMI emitted by a buck converter

Predictive modelling of EMI is complex due to the large number of existing parameters and components. One of the relevant parameters is the temperature of semiconductors. This paper shows the influence of the temperature of the power module of a buck converter on the parasitic conducted emissions. An analysis of some parameters is done by simulation to show the impact of the temperature on the diode reverse recovery and on the IGBT switching times; it shows the consequences on the interference emitted in the 2-MHz-50MHz bandwidth. Up to 20MHz, simulations and measurements behave similarly with respect to the temperature variations in the range [-40°-100°C].