Emanuele Piuzzi

Specific absorption rate and temperature increases in the head of a cellular-phone user

In this paper, a complete electromagnetic and thermal analysis has been performed considering the head of a subject exposed to various kinds of cellular phones available on the market, and focusing the attention on important organs like the eye lens and brain. Attention has first been posed on a particular phone model, and a comparison between the absorbed power distribution and steady-state temperature increases has been carried out. The influence of different antennas (dipole, monopole, whip, and planar inverted F antenna) on the power absorption and on the consequent tissue heating has then been analyzed. The obtained results show for a radiated power of 600 mW, maximum SAR values, averaged over 1 g, from 2.2 to 3.7 W/kg depending on the considered phone. The maximum temperature increases are obtained in the ear and vary from 0.22/spl deg/C to 0.43/spl deg/C, while the maximum temperature increases in the brain lie from 0.08/spl deg/C to 0.19/spl deg/C. These steady-state temperature increases are obtained after about 50 min of exposure, with a time constant of approximately 6 min. Finally, the results evidence a maximum temperature increase in the external part of the brain from 0.10/spl deg/C to 0.16/spl deg/C for every 1 W/kg of SAR, averaged over 1 g of brain tissue.

Specific absorption rate and temperature elevation in a subject exposed in the far-field of radio-frequency sources operating in the 10-900-MHz range

The exposure of a subject in the far field of radiofrequency sources operating in the 10-900-MHz range has been studied. The electromagnetic field inside an anatomical heterogeneous model of the human body has been computed by using the finite-difference time-domain method; the corresponding temperature increase has been evaluated through an explicit finite-difference formulation of the bio-heat equation. The thermal model used, which takes into account the thermoregulatory system of the human body, has been validated through a comparison with experimental data. The results show that the peak specific absorption rate (SAR) as averaged over 10 g has about a 25-fold increase in the trunk and a 50-fold increase in the limbs with respect to the whole body averaged SAR (SAR/sub WB/). The peak SAR as averaged over 1 g, instead, has a 30- to 60-fold increase in the trunk, and up to 135-fold increase in the ankles, with respect to SAR/sub WB/. With reference to temperature increases, at the body resonance frequency of 40 MHz, for the ICNIRP incident power density maximum permissible value, a temperature increase of about 0.7/spl deg/C is obtained in the ankles muscle. The presence of the thermoregulatory system strongly limits temperature elevations, particularly in the body core.

Human exposure to radio base-station antennas in urban environment

In this paper, the human exposure to the electromagnetic field radiated by a radio base-station antenna operating around 900 MHz in an urban environment has been analyzed. A hybrid ray-tracing/finite-difference time-domain (FDTD) method has been used to evaluate the incident field and the power absorbed in an exposed subject in the presence of reflecting walls. The base-station antenna has been characterized by means of its radiation pattern, evaluated with an FDTD analysis of a typical panel antenna. Three particular situations for a rooftop mounted antenna have been considered. In all the examined cases, the obtained results, in terms of incident field and absorbed power, are below the most recognized safety standard levels. The importance of an accurate modeling of the environment in which the exposure takes place has been evidenced.

Power absorption and temperature elevations induced in the human head by a dual-band monopole-helix antenna phone

A numerically efficient way to evaluate specific absorption rate (SAR) deposition and temperature elevation inside the head of a user of a cellular phone equipped with a dual-band monopole-helix antenna is proposed. The considered antenna operates at both frequencies (900 and 1800 MHz) employed in global system for mobile communication. The results obtained show that, for a given radiated power, although the maximum SAR value as averaged over 1 g in the brain is higher at 900 MHz than at 1800 MHz, the maximum temperature increase in the brain is higher at 1800 MHz. However, taking into account that the average power levels radiated at the two operating frequencies are different (250 mW at 900 MHz and 125 mW at 1800 MHz), higher temperature elevations are obtained at 900 MHz. In this last case, the temperature increases are of the order of 0.2/spl deg/C in the ear, and less than 0.1/spl deg/C in the external brain region close to the phone. When the heating effect due to the contact of the ear and cheek with the phone is also taken into account, it is found that the predominant heating effect in the ear, able to cause temperature increases as high as 1.5/spl deg/C, is the one due to the phone contact, while SAR deposition plays a significant role only in the heating of the external brain region.

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.

Distribution of SAR and temperature elevation induced in a phantom by a microwave cardiac ablation catheter

A two-dimensional cylindrical-coordinate (2-D-cyl) finite-difference (FD) time-domain code together with an explicit 2-D-cyl FD solution of the bioheat equation were used for studying a 2450-MHz cap-choke antenna designed for microwave cardiac ablation. Following validation based on results available in literature, the numerical tools were used to evaluate the performance of the catheter antenna embedded in a homogeneous dielectric phantom. The results highlight the ability of the cap-choke catheter antenna to produce high specific absorption rate (SAR) values near the tip and, in contrast, very low SAR values along the antenna length. The comparison of computed data with measurements shows a good agreement between numerical and experimental results. The numerical tools were subsequently applied to analyze the catheter antenna embedded in a two-layer heart model in order to evaluate the depth of induced lesions in a more realistic model of the operating condition. In particular, both the effect of the antenna position relative to the blood-muscle interface (simply touching or pressed inside the muscle) and the effect of blood velocity (taking into account over-leaflets and underneath-leaflets positions) were investigated. It is shown that a lesion depth of 5 mm in a heart region with low blood perfusion could be obtained with approximately 16 W of radiated power, applied for 60 s.

Design, Realization, and Test of a UWB Radar Sensor for Breath Activity Monitoring

An analytical model of an ultrawideband range gating radar is developed. The model is used for the system design of a radar for breath activity monitoring having sub-millimeter movement resolution and fulfilling the requirements of the Federal Communications Commission in terms of effective isotropic radiated power. The system study has allowed to define the requirements of the various radar subsystems that have been designed and realized by means of a low cost hybrid technology. The radar has been assembled and some performance factors, such as range and movement resolution, and the receiver conversion factor have been experimentally evaluated and compared with the model predictions. Finally, the radar has been tested for remote breath activity monitoring, showing recorded respiratory signals in very good agreement with those obtained by means of a conventional technique employing a piezoelectric belt.

Dielectric Spectroscopy of Liquids Through a Combined Approach: Evaluation of the Metrological Performance and Feasibility Study on Vegetable Oils

In this work, a time domain-based approach for the estimation of the dielectric parameters of liquids is presented. The proposed approach combines traditional time-domain reflectometry measurements with a specific data processing and modeling that leads to the evaluation of the Cole-Cole parameters. The pivotal step of the procedure is the implementation of an accurate transmission line model of the used measurement cell. In this way, the error contributions due to undesired parasitic effects are minimized; hence, the overall accuracy is significantly enhanced. The proposed approach is tested through repeated measurements on well-referenced materials; this also allowed performing the related metrological analysis. Successively, the proposed procedure is applied for the evaluation of the Cole-Cole parameters of vegetable oils. In fact, at the state-of-the-art, only limited data are available for the dielectric characteristics of vegetable oils. In particular, ten different types of vegetable oils are considered. Results show that the proposed approach has strong potential also for possible practical applications in the area of anti-adulteration and quality control.

Power density and temperature distributions produced by interstitial arrays of sleeved-slot antennas for hyperthermic cancer therapy

A graded-mesh finite-difference time-domain (FDTD) code, together with an alternate-direction-implicit finite-difference (ADI-FD) solution of the bioheat equation, are used for studying arrays of sleeved-slot antennas imbedded in a brain-equivalent phantom. The FDTD code allows efficient and accurate modeling of the fine structure of each antenna and of a sufficiently wide surrounding region. The ADI-FD solution of the bioheat equation allows evaluation of transient and steady-state temperature distributions in the brain-equivalent phantom with acceptable computational costs. The solution of the dosimetric-thermal problem in the volume irradiated by the antenna array permits the assessment of dimensions of the region where the temperature increase is above 43/spl deg/C (the threshold for an effective hyperthermia treatment) as a function of the array input power. Arrays made of three identical antennas placed at the vertices of equilateral triangles of 10-, 15-, and 20-mm sides have been studied. The temperature of 43/spl deg/C is reached in approximately 3 min in a deep-seated tumor region, from 10 to 40 mm in diameter, by applying input power levels between 2-32 W.

A Combined TD–FD Method for Enhanced Reflectometry Measurements in Liquid Quality Monitoring

Measurement and control of the dielectric parameters of liquids play a major role in industrial quality-control applications. Although several techniques are currently available to this aim, none of them is simultaneously accurate, cost-effective, and reasonably quick. On the other hand, reflectometry has become a very attractive method for monitoring applications, mostly thanks to its accuracy and flexibility. In this paper, a combined method based on time-domain reflectometry (TDR) and frequency-domain (FD) analysis is presented: the aim is to substantially improve the measurement accuracy of the dielectric parameters of liquids. Starting with typical TDR measurements, the associated FD evaluation of the dielectric parameters is considerably enhanced through the combined effect of the following: 1) specific data-processing techniques; 2) the implementation of a calibration procedure; and 3) the final modeling and minimization routine. Furthermore, to definitively assess the proposed combined procedure, results are compared with measurements directly performed in the FD through a vector network analyzer (VNA). The ultimate goal of the work is to pave the way for the adoption of inexpensive and portable TDR devices in practical industrial monitoring applications.