Electromagnetic (EM) shielding in the presence of transient waveforms has recently obtained a renewed interest because of the ever-increasing consciousness that almost all the sources of interference (EMI) are characterized by a time-domain trend. Typical EMI are due to lightning electromagnetic pulses, electrostatic discharges, switching operations and, recently, intentional disturbances aimed at provoking malfunctioning conditions or failures.
The associated waveforms are very different as to peak values, energy content and induced effects (proportional to time derivative of the relevant EM field components). Also the victims may differ as to their susceptibility to peak values, induced effects (voltages) or to the energy delivered to them. For this reason, in the recent past a careful attention has been paid to the introduction of appropriate figures of merit capable of quantifying the performance of shielding structures against transient EM fields.
The configurations of actual shielding structures are typically three-dimensional and in closed shape: most of the available literature oversimplifies the geometry and the electromagnetic properties of the materials yielding to rough approximations; most of the analysis methods focuses on the CW behavior and on local (as suggested by all the available standards) and not on the global performance (i.e., in the whole shielded domain).
In the past, this research team has developed analysis procedures for the extraction of global figures of merit for the time ¿ domain shielding, obtaining also the analytical exact time domain solutions in several canonical configurations, useful as benchmark or limit solutions.
The goal research project is twofold:
1. it is of interest to extend the suitability of the analytical solutions to 3-D configurations ,
2. the main goal is developing a design procedure or at least design guidelines for the realization of shielding structures with prescribed levels of performance.
Recently, there has been an increasing interest in solving electromagnetic shielding problems in the time domain since some classical sources of electromagnetic interferences are typically of transient type, like lightning and electrostatic discharge, while others, like intentional electromagnetic interference, are more and more emerging as possible electromagnetic compatibility transient threats. More in general, such a time-domain analysis becomes necessary whenever the frequency spectrum of the source waveform has a large fractional bandwidth or, equivalently, the transient waveform has pulse-like features. In addition to electromagnetic-shielding problems (where new figures of merit have also been recently introduced to deal with transient problems), a transient analysis is becoming mandatory in a number of applications of increasing diffusion and importance, such as ultra-wideband antenna systems, integrated circuits and associated interconnects for ultra-high bitrate signal processing.
The common method to solve the transient electromagnetic problem consists in solving a related frequency-domain problem (in the Fourier or Laplace domain) and then recovering the transient solution by a brute-force numerical inverse Fourier- (or Laplace-) transform operation. Other classical approaches are the purely numerical Finite-Difference Time-Domain (FDTD) method and, more recently, the Time-Domain Method of Moments (MoM), which, however, are typically computationally intensive and cumbersome. Therefore, the emerging and increasing need of time-domain evaluations calls for developing new methods of transient analysis in addition to those mentioned above: such new methods have to offer both computational advantages and valuable physical insight into the involved transient wave phenomena, with respect to blind numerical approaches and/or indirect analyses based on inverse transformation of the relevant Fourier/Laplace-domain solutions.
With particular reference to planar structures, we will make use of powerful analytical methods (like the integral method known as the Cagniard-de Hoop technique and the time-domain Exact Image Theory) to solve simple transient shielding problems in classical configurations (infinite planar metallic screens). The goal is to find the field solution in a closed form or represented through simple one-dimensional integrals, in order to be able to efficiently perform parametric analyses of the considered structures. It should be pointed out that such kind of structures have not been analyzed yet through these analytical techniques and the results will be therefore original and completely new.
More practical configurations will then be analyzed by introducing suitable approximate methods, still based on the Cagniard-de-Hoop and time-domain Exact-Image-Theory techniques and all the results will be compared with those obtained through brute-force numerical codes. It is expected that the semi-analytical (and possibly approximate) formulations will give a tremendous insight into the time-domain behavior of a class of commonly employed shielding structures if compared to brute-force numerical methods.
On the other hand, with reference to shielding problems involving cavities, our goal is to develop new accelerated and converging representations of time-domain Green's functions which could dramatically improve the performance of the Time-Domain Method of Moments in addressing the problem of the transient analysis of metallic enclosures, thus contributing to the diffusion of the use of the powerful Method of Moments also in the time domain.
All the obtained results will be used to outline design procedures or, at least, design guidelines for the realization of shielding structures with prescribed levels of performance taking into account all the involved transient phenomena directly in the time domain.