G. Cerri

A study of uncertainties in modeling antenna performance and power absorption in the head of a cellular phone user

A set of finite-difference time-domain (FDTD) numerical experiments modeling canonical representations of the human head/cellular phone interaction has been performed in order to investigate the effect of specific simulation details (e.g., antenna numerical representation and absorbing boundary conditions) on computed results. Furthermore, hybrid techniques based on the dyadic Greens function and the method of auxiliary sources, and on a hybrid method-of-moments-FDTD technique have been used to compute parameters of interest for comparison with the FDTD evaluated parameters. It was found that small, but potentially significant, differences in computed results could occur, even between groups that were nominally using a very similar method. However, these differences could be made to become very small when precise details of the simulation were harmonized, particularly in the regions close to the source point.

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.

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.

FDTD Solution of the Maxwell–Boltzmann System for Electromagnetic Wave Propagation in a Plasma

In this paper, a self-consistent model is developed of the propagation of an electromagnetic wave into a plasma region, based on the solution of the Maxwell-Boltzmann system of equations. The system is resolved using a finite-difference time-domain approach that gives as results the behavior of both the particle velocity distribution function and the electromagnetic fields. The method is applied to a simple situation in which a wave impinges on a plasma region, but can easily be extended to more complicated configurations.

A Theoretical Feasibility Study of a Source Stirring Reverberation Chamber

A novel theoretical feasibility study to reverberate a large metallic chamber is proposed. The method is based on the displacement of a radiating antenna inside the chamber, and the reverberating effect is obtained by coupling the antenna current in different ways with the cavity modes. This technique eliminates mechanical rotating paddles inside the chamber and offers the advantage of a continuous-wave operation compared with the frequency stirring method. The reverberating characteristics of the proposed technique are evaluated by calculating the field statistics. The analyzed situation concerns a real antenna, and its radiation into the reverberation chamber is modeled using Greens function of cavity. The numerical problem is solved by the method of moment. The model has been tested and is able to rigorously characterize the reverberating environment for the design and optimization of antenna configurations to be addressed in future studies.

A rigorous model for radiated emission prediction in PCB circuits

The problem of the radiated emission from printed circuit boards, (PCBs) is theoretically and experimentally investigated. Differential mode and common mode currents are separately studied by means of a rigorous method based on proper Greens functions. The solution of the integral equations for the current distribution, derived from the problem formulation, is numerically achieved by the method of moments. Simulated results are in good agreement with measurements. The final products of this study are masks that establish the maximum allowable currents or voltage values as a function of frequency to comply with CISPR regulation. >

Design and Prototyping of a Switching Beam Disc Antenna for Wideband Communications

The design procedure for a switching beam antenna for wireless communication systems is given. The antenna can rotate the beam over the whole azimuthal angle exploiting its geometrical and electrical cylindrical symmetry. The required directivity and the beam rotation are provided by a sequential insertion of metallic posts into the radial waveguide that forms the main body of the antenna. The first stage of the design involves setting up the dimensions of an omnidirectional antenna, to which the desired directivity is subsequently provided. After optimization to maximize the impedance bandwidth, the final antenna was prototyped. A comparison between simulated results and experimental data is presented

Experimental Characterization of a Surfaguide Fed Plasma Antenna

The possibility of using a surfaguide device as plasma source for plasma antenna application has been experimentally investigated. The surfaguide was optimized, realized and used for the ignition of a plasma column to be used as a radiating structure: the coupling with the radiated signal network and plasma antenna efficiency were measured showing that a surfaguide can be effectively used to create and sustain the plasma conductive medium. A plasma diagnostic technique was also developed to evaluate the plasma column length and plasma conductivity with respect to the power supplied. These measurements highlighted that plasma antenna properties are strongly affected by the pump signal and therefore this signal has to be optimized in order to have the highest conductivity.

Measurement of magnetic fields radiated from ESD using field sensors

The goal of this paper is to show that commercial sensors, whose frequency response is not specifically designed, can be effectively used to measure very fast transient fields applying a proper reconstructing procedure based on the knowledge of the sensor transfer function. To do this, it is necessary to characterize a structure supporting a transverse electromagnetic (TEM) field, that will be used to set up a calibration procedure for elementary magnetic field sensors. The approach is completely analytical and allows us to know rigorously the field inside the structure. From the knowledge of this field, the transfer function of the sensor, in amplitude and phase, is evaluated up to 2 GHz. The complete characterization of the sensor allows us to reconstruct the sensed field from its output voltage waveform. The calibration procedure is carried out in time domain and therefore the fast Fourier transform (FFT) algorithm is used to achieve the sensor transfer function, as well as an inverse FFT (IFFT) is necessary to retrieve the transient impinging field. An experimental validation of the procedure shows the consistency of the approach.