Andrea Cozza

Echo Response of Faults in Transmission Lines: Models and Limitations to Fault Detection

This paper introduces models of the time-domain echoes generated by faults in transmission lines excited by test signals, e.g., as in applications of time-domain reflectometry (TDR). Faults considered here include local modifications of the propagation characteristics of a transmission line. It is shown that the responses of faults are strongly dispersive in nature, which implies that the peak of their echo is far from providing an accurate measure of the severity of the fault, as it heavily depends on the frequency content of the test signal as well as on the length of the fault. It is argued that fault detection in transmission lines is an ill-posed problem that requires a priori knowledge on the fault itself. These results are important for applications of TDR methods, particularly for early warning monitoring of potentially critical faults from their onset, since it is shown that echoes from faults tested at relatively low frequencies can lead to underestimate their actual severity.

An efficient technique based on DORT method to locate multiple soft faults in wiring networks

Decomposition of the time reversal operator (DORT) recently adopted to wiring fault detection and localization presented effectual results when dealing with a single soft fault along with complex network configurations. On the other hand, it failed in handling the task of locating multiple faults within even simple ones. In this paper, we propose an enhanced version of the standard DORT technique (EDORT) which is based on a complementary procedure enabling the accurate and selective localization of multiple soft faults in various wiring systems.

Time-Reversed Excitation of Reverberation Chambers: Improving Efficiency and Reliability in the Generation of Radiated Stress

The ability of reverberation chambers to generate high-intensity field levels from relatively low-power input signals is reexamined for the case of time-reversed signals, proving that they lead to a higher efficiency. Moreover, the strong statistical spread typical of time-harmonic excitations can be dramatically reduced, thus, improving the reliability of radiative tests, while limiting the need for a large number of independent realizations. The two excitation schemes are compared when forcing their respective input signals to display the same peak instantaneous power. Experimental results are provided, supporting the conclusions of our theoretical analysis.

Steering Focusing Waves in a Reverberation Chamber With Generalized Time Reversal

Generalized time reversal was introduced in a previous paper from a theoretical point of view. In this paper, experiments are conducted to demonstrate its application to a reverberation chamber, as a method for generating coherent wavefronts in a medium displaying random propagation. Wavefronts thus generated were sampled over a planar surface, confirming that they propagate as if in a free-space environment. The accuracy with which they match their free-space counterpart is not affected by changing their features, e.g., direction of arrival and focus. These results prove that a single excitation antenna can generate complex wavefronts when coupled to diffusive wave propagation.

Preliminary study on the use of complex media for antenna characterization

Propagation in complex media can be thought of as an advantageous way to speed up antenna characterization. If the geometry of the medium is well controlled, the different reflections that take place can be fruitfully used for antenna radiation pattern (ARP) measurement. The feasibility of this concept is presented here for the case of a simple geometry. Preliminary results are presented and it is shown how frequency diversity can be fruitfully used to retrieve the free space radiation pattern (RP). A special care is given to the conditioning of the mathematical model as retrieving the free space radiation pattern consists in solving an inverse problem.

Near-field and vector signal analysis techniques applied to specific absorption rate measurement

The complexity of radiofrequency technologies used in smartphones and tablets has considerably increased the need for more efficient Specific Absorption Rate assessment approaches. SAR measurement systems covered by IEC 62209-3 which implement vector near-field techniques appear as the most promising alternatives to legacy robot equipment. While showing the benefits of Maxwellian field reconstruction compared to more simplistic fast SAR extrapolations, this paper presents the new angle of view that amplitude and phase measurements combined with near-field transforms introduce in RF dosimetry.