R. De Leo

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.

Wide-band characterization of current probes

The use of current probes for the injection of wide-band disturbance in electromagnetic compatibility applications requires their accurate characterization up to few gigahertz. While the representation of the current probe with a simple transformer is acceptable at low frequencies, the spectral content of fast signals requires models which are accurate even at gigahertz frequencies. This can be accomplished directly by measurements in the frequency domain (FD), making use of a S-matrix representation of the probe, or in the time domain (TD), recovering the transfer functions from the impulse responses measurement. Both techniques suffer limitations due to numerical and experimental problems; in particular, the FD approach leads to the solution of an inverse problem, with numerical instabilities in the high-frequency range, whereas the TD approach is not so accurate in the low-frequency range of the sought transfer function. The paper combines the two techniques to overcome these difficulties and achieve a better accuracy across the overall bandwidth. The characterization of a commercially available current probe allows comparison of numerical results with experimental measurements.

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.

Electrical fast-transient test: conducted and radiated disturbance determination by a complete source modeling

Tests against electrical fast transient/burst (EFT) represent a serious threat for modern high-speed electronics: besides the conducted injection of high amplitude pulse, a strong radiated field is produced during this test. The prediction of the effects of this test during the equipment early design stage requires the equivalent circuit of the generator: the output waveform into a resistive 50-/spl Omega/ load is not sufficient to recover the complete circuit, including inductive component and parasitic elements. These are essential to predict the disturbance produced in arbitrary loads, as the equipment under test can be viewed. This paper describes how to characterize the EFT generator by means of the measurement of the output voltage and current produced in presence of known loads; moreover, a procedure to calculate the current on the equipment power cord is shown, based on the use of a circuit simulator (PSPICE). Finally, the disturbance produced on different loads and the radiated field during the test are calculated and experimentally validated.

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

Theoretical and experimental evaluation of electromagnetic fields radiated by ESD

The paper describes applications of a field reconstruction technique, and in particular comparisons between theoretical results and measured data are reported. The developed method requires the knowledge of the transfer function of a commercial sensor, in amplitude and phase, in a range of frequencies wider than the significant bandwidth of the expected field radiated from the transient current. A simple numerical code reconstructs the incident field waveform from the probe output signal. Moreover, a comparison between transient fields measured by a commercial active field probe and by magnetic field sensor are also shown. Satisfactory results are achieved in both tests, and highlight that a simple and cheap technique is reliable and effective to measure fast varying fields.

'Thermic end-fire' interstitial applicator for microwave hyperthermia

The analysis of a thermic end-fire interstitial applicator for microwave hyperthermai, i.e. an applicator that performs a tip-localized heating of the surrounding lossy medium, is presented. The antenna consists of a shorted coaxial cable with an annular radiating aperture at the end. the analytical approach is based on the equivalence principle, which leads to an integral equation for the equivalent magnetic current distribution on the aperture; solution is achieved by the method of moments. All theoretical results are compared to experimental ones, showing a good agreement in a wide frequency range. >

Radiated immunity tests: reverberation chamber versus anechoic chamber results

The paper concerns the comparison between reverberation chamber measurements (RC) and anechoic chamber (AC) measurements: in particular, the case of an immunity test is considered. A two-wire transmission line is adopted as a device under test (DUT), and the current induced on the line by the external field is monitored to construct a possible susceptibility profile. Both the averaged current, over the stirrer rotation, and the maximum current are considered to show how robust is the RC measurement against the positioning and the orientation of the DUT inside the chamber. As expected from theory, the maximum value is related to the average one by means of the number of the independent position of the stirrer. Finally, it is highlighted how in RC it is possible to lost some worst case situations, related to a particular incident field polarization and incoming direction, and the underestimation of the induced current depends upon the chosen number of the stirrer positions

Theoretical and experimental characterization of transient electromagnetic fields radiated by electrostatic discharge (ESD) currents

The problem of the evaluation of the electromagnetic (EM) field radiated by an electrostatic discharge (ESD) current is examined, and an efficient numerical code for the evaluation of the radiated field is developed. The considered radiating structures, a monopole and a loop, are analyzed in the time domain using a modified electric field integral equation (EFIE). A modification of the integral equation was introduced in order to take into account the reflection of the incident pulse at the input terminals of the antenna, when fed by a transmission line. The reflected wave is very significant and its evaluation is fundamental for the comparison of theoretical and experimental data. The ESD current flowing along the wire is determined using the method of moments in time domain (MoMTD). From the knowledge of the transient current, the radiated EM field is evaluated by a standard technique. The developed model is the first stage of a project for the characterization of the measurement environment during an ESD test. All numerical results are validated by measurements and good agreement is shown.

Shielding effectiveness evaluation of densified-small-particles (DSP) cement composite

This paper presents a shielding effectiveness evaluation of densified with small particle (DSP) cement composite at microwave frequencies by means of an improved nested reverberation chamber (NRC) technique, more faster than the classical one. In fact, the mechanical stirring inside the inner chamber was replaced by the frequency stirring method (FS) and only one scattering parameter was acquired to estimate both empty and loaded aperture. By this method, the stirrer movement becomes unnecessary. A software was used to manage the measurement and the post-processing operations.