Valter Mariani Primiani

Broadband Electromagnetic Absorbers Using Carbon Nanostructure-Based Composites

In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures.

Optimization of Multilayer Shields Made of Composite Nanostructured Materials

In this paper, we propose a multilayer nanostructured composite for broadband shielding applications. Layers disposal, electrical parameters, and thicknesses are optimized through a winning particle optimization algorithm to achieve the minimization of the transmitted waves. The structures are simulated by including the forward/backward scattering matrix formalism in the optimization code. The adopted algorithm is the recently introduced winning particle optimization. Manufacturing of the composites is grounded on the optimization procedure. Thanks to the macroscopic absorption features of such nanostructured layers, very thin and lightweight composites can be produced. Several weight percentages of multiwall carbon nanotubes are considered in composite base material manufacturing, also including 6wt% and 15wt% in order to enhance the electromagnetic shielding performance. Prototypes are tested in the microwave region, showing the reliability of the optimization procedure.

Analysis of the Independent Positions of Reverberation Chamber Stirrers as a Function of Their Operating Conditions

The independent positions of the stirrers are computed when one or two stirrers rotate inside the chamber. In the case of the two operating stirrers, they are moved in both tuned and stirring modes. In the tuned mode, they are rotated in a synchronized or interleaved way, showing that this second modality yields a larger independent position number. In the stirring mode, both modalities are replicated varying the rotation speed. In the case of one stirrer and two synchronized stirrers, the independent positions are computed using the classical autocorrelation function, whereas in the case of two completely independent stirrers a 2-D autocorrelation is proposed. The result obtained in this second way does not depend on the order chosen to move the stirrers. The performance of the stirrers is also verified checking the ratio between the maximum and the average received power inside the chamber, the statistics of the received power by applying a goodness-of-fit test, and the uniformity of the field in some points of the working volume. Tuned and stirring operating modalities are also compared in terms of measurement time, calibration and software complexity, motor stress, and so on.

Numerical Analysis of a New Location for the Working Volume Inside a Reverberation Chamber

This paper analyzes the performance of a reverberation chamber when the working volume (WV) is positioned inside the stirrer rotating volume. More precisely, considering a very large stirrer, its inner surface and axis are removed to gain a large space to be used as WV. The design of this new WV position and stirrer shape is done using our finite-difference time domain code, previously optimized for reverberation chamber simulations and tested with experimental results. The proposed setup increases the WV and improves the reverberation chamber behavior with respect to a traditional setup. Moreover, it needs just one motor to control the stirrer, and it does not require more complex mechanical part.

Performance and Immunity Evaluation of Complete WLAN Systems in a Large Reverberation Chamber

This paper concerns the use of a large reverberation chamber (RC) to test a wireless local area network system based on both 802.11b/g and 802.11n standards including multiple input and multiple output (MIMO). A whole link established between commercial devices operates inside the RC under different loading conditions, varying the stirrer rotating speed and the paddle dimensions. The effects of this multipath environment on system performance are checked measuring the number of cyclic redundancy check error and the number of data retries. The comparison between the two systems is done adopting the same chamber loading condition and also stressing the system reducing the load, up to the link connection limit. Results show the higher performance of the MIMO system, able to maintain a 6-Mb/s data rate connection also with a chamber quality factor of 21 000. The same RC is used to carry out a radiated immunity test. The undesired signal is both a modulated and continuous wave injected into the active channel and into adjacent channels. Results reveal the high robustness of the 802.11n standard with respect to b and g standards when it operates in a hostile environment reproduced by an RC.

Accurate Analysis of Reverberation Field Penetration Into an Equipment-Level Enclosure

The paper focuses on the reverberation chamber method for the shielding properties evaluation of equipment-level enclosures. The enclosure under test is numerically modeled by an in-house finite-difference time-domain code that is able to predict the field inside the enclosure and the voltage captured by the probe placed inside it. The chamber fields have been modeled by applying the plane-wave superposition. The code is validated by measurements in our reverberation chamber. Subsequently, the effect of probe positioning and length on the induced voltage is analyzed. Finally, the enclosure shielding effectiveness is evaluated by applying two different definitions, and a statistical analysis is carried out, thus allowing an estimation of the measurement uncertainty.

Numerical Simulation of Reverberation Chamber Parameters Affecting the Received Power Statistics

This paper presents a reverberation chamber (RC) numerical modeling based on a discrete plane wave representation. In particular, the attention is focused on those parameters that may influence the field statistics. It is shown that a random choice of the angle of incidence, the initial phase, and the polarization in a particular range and a proper choice of the number of the plane waves allow us to reproduce the same behavior of experimental data. Both experimental and numerical field data are checked applying the Anderson-Darling (AD) test. More precisely, we count the frequencies where the received power statistics is rejected by the adopted goodness-of-fit test. This paper shows a correspondence between numerical and experimental parameters affecting the occurrence of the rejected frequencies, also giving a probability density function for the observed occurrence. The analysis is completed showing that the AD test rejection does not compromise the chamber use for typical radiated emission or radiated susceptibility tests.

Source stirring mode for reverberation chambers

The paper investigates the possibility of reverberating a shielded room by means of source mode stirring. The transmitting antenna position and orientation are randomly changed inside a sub-volume of the chamber. In general, antenna displacement can be achieved by a proper design of an array of antennas, where one or more antennas are activated at different time instants. This technique eliminates mechanical rotating paddles inside the chamber, and offers the advantage of a continuous wave (CW) operation with respect to the frequency stirring method. The preliminary experimental and simulated results encourage further investigation of the proposed technique.

Experimental Investigation of Electromagnetic Obstacle Detection for Visually Impaired Users: A Comparison With Ultrasonic Sensing

The use of electromagnetic (EM) fields for obstacle detection to aid mobility of visually impaired people is presented in this paper. The method proposed is based on the launch of EM pulses and on the measurement of the reflected signal which explores a region in front of the user of about 3 m. A laboratory system is set up, its performances (detecting the presence and the distance of obstacles) are investigated, and the measurements are compared with the data measured by an ultrasonic obstacle detection system. Results show that, with the EM system, all the obstacles tested (up to a minimum size of 3 cm × 3 cm, at a distance of 3 m) are correctly detected, as well as some specific targets (a chain, a pole, etc.) that are not visible by the ultrasonic system. The EM system has been tested in indoor and outdoor cluttered scenarios at the presence of real obstacles (single and multiple), and in all cases, it detects their presence with a signal-to-noise ratio ranging from 10 to 23 dB. Despite the use of a laboratory system, still not specifically designed for daily use, this paper demonstrates the possibility of adopting EM held pulses for obstacle detection, highlighting advantages with respect to ultrasonic systems and addressing future research activity to design an improved ad hoc EM system.

Field Penetration Through a Wire Mesh Screen Excited by a Reverberation Chamber Field: FDTD Analysis and Experiments

Field penetration into a metallic enclosure with a large aperture protected by a wire mesh screen is analyzed in this paper, using an in-house finite-difference time-domain code with a thin-wire approximation that accurately accounts for the cross between wires of the mesh. All results are experimentally validated using a reverberation chamber. Different enclosure dimensions and mesh sizes are considered, highlighting their implication on shielding performances.