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.

This work tests the ability of a frequency-modulated continuous wave (FMCW) radar to measure the respiratory rate and the heartbeat of a subject in challenging indoor scenarios. To simulate a realistic configuration for ambient assisted living (AAL) applications, in which the thorax orientation towards the antenna is typically unknown, four different scenarios were considered. Measurements were performed on five volunteers positioned with the chest, left, back, and right side facing the antenna, respectively. The $5.8$ GHz radar and the antennas used for the measurements were suitably designed for the considered application. To obtain a low cost and compact system, series-fed arrays were preferred over other antenna topologies. The geometry of the patches was opportunely shaped to reduce the side lobe level (SLL) and increase the bandwidth, thus ensuring good system performances. In all scenarios, the vital signs extracted from the radar signal were compared with the ones collected by a photoplethysmograph and a respiratory belt, used as references. A statistical analysis of the measured data on the different subjects and orientations was performed, showing that the radar was able to measure with high accuracy both the respiratory rate and the heartbeat in all considered configurations.

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.

An experimental setup for complex mono-static radar cross section (RCS) measurements in the 1-10-GHz-frequency band, employing a suitably modified semianechoic chamber, is presented and characterized. The foreseen application is the measurement of the complex RCS of the human body during respiratory activity, to ease the design and optimization of ultrawideband (UWB) radar systems for breath-activity monitoring. The proposed RCS test range is calibrated by means of a readily available aluminum flat panel and its performance is tested against canonical targets, evaluating uncertainty in magnitude, and phase measurements. The setup is then employed to carry out investigations on the complex RCS of a volunteer, focusing on its changes resulting from breath activity. Applying the measured RCS patterns to a specifically developed model, the feasibility of the UWB radar approach for achieving a continuous contact-less monitoring of breath activity in a subject at rest is clearly demonstrated. Finally, experimental tests of the application of the proposed radar technique to real-world scenarios are shown, and the safety of RCS measurements and UWB radar monitoring, with reference to exposure of the monitored subject to the radiated electromagnetic fields, is evaluated.

In this paper, a time domain reflectometry (TDR)-based system for measuring water content of raw construction materials is presented. The proposed system relies on the fact that the presence of water leads to an increase of the dielectric permittivity of materials; therefore, from TDR-based permittivity measurements, it is possible to infer the water content value. In practical applications, the proposed system could be used for assessing the intrinsic water content of construction materials before they are poured into the concrete mixture. Knowing the intrinsic water content of the raw materials, in fact, would allow to evaluate the optimal amount of water that should be added to the mixture in order to achieve the desired water-to-cement ratio. This, in turn, would permit to fine-tune and control the mechanical properties of the final concrete structures. For assessing the feasibility of using the proposed system for the intended purpose, water content measurements were carried out on three construction materials, namely, sand, gray cement, and white portland cement. For each of these materials, a calibration curve relating water content to the apparent dielectric permittivity was derived; additionally, through repeated measurements, also a confidence interval was associated with the calibration curves.