V. Mariani Primiani

Measurement of the Properties of a Plasma Column Used as a Radiating Element

This paper presents two test benches for the characterization of a plasma column used as a radiating element. In particular, the main parameters to be quantified are the efficiency of the plasma antenna, the turn-on time of the column, and the conductivity of the plasma. The first two parameters are evaluated by measuring the field radiated by the plasma antenna compared with that of an equivalent copper antenna. For the conductivity, a reflectometric technique is used, wherein the plasma column is inserted inside a waveguide. The accuracy of the method is limited by the ill-conditioned relationship between the reflection coefficient and the plasma conductivity; nevertheless, it is sufficient to subdivide the range of the conductivity values into three regions (i.e., low, medium, and high conductivities) to determine the best operating conditions of the antenna.

Numerical Simulation of LOS and NLOS Conditions for an Antenna Inside a Reverberation Chamber

This paper presents a numerical analysis of the voltage received by an antenna operating in a complex environment such as a reverberation chamber (RC). Both scattered and direct components were considered for the excitation of the receiving antenna, ranging from line-of-sight (LOS) to non-line-of-sight (NLOS) conditions. A numerical solution based on a finite difference time domain code was achieved and compared with measurements inside a reverberation chamber. The method allows to balance the amount of random contributions, direct contribution and deterministic multipath contributions just like in actual propagation conditions.

Reverberation Chamber as a Multivariate Process: FDTD Evaluation of Correlation Matrix and Independent Positions

This paper evaluates the mode-stirring e-ciency in terms of uncorrelated positions of a mechanical stirrer operating inside a reverberation chamber (RC). The actual RC is simulated and viewed as a multivariate random process: the chamber fleld is sampled in a lattice of spatial points distributed uniformly over a volume of arbitrary dimensions. By adopting such a grid, the stirrer e-ciency is then computed through the correlation matrix, accounting for the residual correlation between stirrer positions. The second-order statistics are calculated averaging over the sampling volume. Results are presented for two stirrers that move in both synchronous and interleaved mode. A comparison with the traditional circular correlation (CC) method, for the determination of the uncorrelated positions, is done showing how CC overestimates stirrer e-ciency.

ABSORBING CROSS SECTION IN REVERBERATION CHAMBER: EXPERIMENTAL AND NUMERICAL RESULTS

Reverberation chamber (RC) test facility allows to determine the absorbing cross section (ACS) of lossy materials under a random fleld excitation. Measurements are based on the quality factor variation produced by the sample under test presence with respect to the empty chamber condition. Simulations are based on the representation of the RC electromagnetic fleld by means of a random plane wave superposition. A flnite-difierence time-domain code is used to compute the material absorbed power and to recover a numerical ACS. The method sensibility is stressed by application to small size samples. Comparison between numerical and experimental data reveals a satisfactory agreement. Results for difierent materials are presented in the paper: soft foam absorbers, carbon foam sheets, and carbon/carbon sheets.

Electromagnetic travel aids for visually impaired users

This paper describes the development of an electromagnetic travel aid aiming to the improvement of the mobility of blind and visually impaired subjects in unknown environments. The paper reports the preliminary results obtained with a portable prototype. They show the feasibility of the electromagnetic “cane”, the possibility to detect the presence of obstacles not detected with ordinary cane and address further improvements.

Shielding effectiveness of carbon nanotube reinforced concrete composites by reverberation chamber measurements

The shielding effectiveness of carbon nanotube reinforced concrete composite is analyzed by using a reverberation chamber. The frequency band is 0.8-8 GHz and the weight percentages of carbon nanotube are 0, 1, 3 wt%. Results highlight that about 30 mm thick of 3 wt% reinforced concrete composite is able to perform a shielding effectiveness greater than 15 dB around 2 GHz and up to 30 dB at 8 GHz. The here reported results suggest the employment of carbon nano-powder reinforced concrete in building structures, having issues related to the electromagnetic interference mitigation, such as the influence on the medical devices working in hospital environments as well as the increasing of protection against electromagnetic attacks to strategic targets and sensible places.

Domestic monitoring of respiration and movement by an electromagnetic sensor

The aim of this paper is to investigate the capabilities of a novel electromagnetic technique designed for contactless monitoring of breathing activity in Ambient Assisted Living applications. The method is based on the transmission of a frequency sweep and the measurement of the reflection coefficient to determine the respiration rate of a subject. To date, the method is under optimization, but it has already shown interesting capabilities of calculating not only the respiration rate, but also additional features, as the position of the subject inside a room and his/her movements. After a brief mathematical description of the algorithm, some preliminary tests will be described concerning the monitoring of a human target inside a room. These first results clearly show the capability of the method to detect the subject, his breathing rate, position and physical activity. Of course further signal processing is required in order to distinguish between different types of movements and to classify them.

Reverberation chamber field modeling for application to the source stirring technique

The paper describes an analytical model applied to study the behavior of an antenna moving inside a resonant cavity. It is the basic step to develop a source stirring mode reverberation chamber (RC). The model is able to account for the different coupling of the source with the many cavity modes. The results obtained for a simple dipole are used to design an array of 50 dipoles, whose generated electromagnetic field shows a good statistics when checked by the CDF and by means of a polar plot diagram. The antenna array allows to use a fixed source for the chamber. Finally, the paper presents how to practically fabricate a well working array using broadband antennas, more suitable for actual RC applications.

Stochastic differential equation for wave diffusion in random media

In this work, we present a statistical analysis of the wave motion through random media with perfect spatial disorder of inclusions. It is assumed that such a disorder can be tackled with the random potential function theory, whence the propagation of waves naturally turns to a diffusion process. The associated Itoô drift-diffusion process, and its Fokker-Planck equation are derived. It is found that the “ensemble” wave, i.e., the collective wave motion, fluctuates in space as a geometric Brownian motion. Finally, the effect of a double-well potential with random (vibrating) valleys is studied qualitatively by the Monte Carlo method. In practice, this situation occurs for high concentration and perfect dispersion of conductive/dielectric fillers, i.e., whose location and orientation are completely randomized.

Design and Testing of an Antenna System for the Source Stirring Technique in Reverberation Chambers

Abstract The paper describes the design and testing of a radiating structure developed to reverberate electromagnetic fields in shielded chambers. The radiating system consists of a set of conical broadband wire antennas, adapted to cover the operational frequency range of 1 to 3GHz. Twenty antennas are used to build up the structure, and field stirring is achieved by switching on 190 different combinations that generate field statistics and field uniformity quite similar to those of a mechanically stirred reverberation chamber (RC). All the measurements prescribed by standard and literature were carried out to test the stirring capabilities of the radiating structure, and to assess that the RC field fulfills the IEC 61000-4-21 requirements.