Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 6 Articles
Amultifrequency radar system for detecting humans and classifying their activities at short and long ranges is described.The shortrange\nradar system operates within the S-Band frequency range for through-wall applications at distances of up to 3m. It utilizes\ntwo separate waveforms which are selected via switching: a wide-band noise waveform or a continuous single tone. The long-range\nradar system operating in the W-Band millimeter-wave frequency range performs at distances of up to about 100m in free space\nand up to about 30m through light foliage. It employs a composite multimodal signal consisting of two waveforms, a wide-band\nnoise waveformand an embedded single tone, which are summed and transmitted simultaneously.Matched filtering of the received\nand transmitted noise signals is performed to detect targets with high-range resolution, whereas the received single tone signal is\nused for the Doppler analysis. Doppler measurements are used to distinguish between different human movements and gestures\nusing the characteristic micro-Doppler signals. Our measurements establish the ability of this system to detect and range humans\nand distinguish between different human movements at different ranges....
This paper deals with the possibility of adopting microwave imaging to continuously monitor a patient after the onset of a brain\nstroke, with the aim to follow the evolution of the disease, promptly counteract its uncontrolled growth, and possibly support\ndecisions in the clinical treatment. In such a framework, the assessed techniques for brain stroke diagnosis are indeed not suitable to\npursue this goal. Conversely, microwave imaging can provide a diagnostic tool able to followup the disease�s evolution, while relying\non a relatively low cost and portable apparatus. The proposed imaging procedure is based on a differential approach which requires\nthe processing of scattered field data measured at different time instants. By means of a numerical analysis dealing with synthetic\ndata generated for realistic anthropomorphic phantoms, we address some crucial issues for the method�s effectiveness. In particular,\nwe discuss the role of patient-specific information and the effect of inaccuracies in themeasurement procedure, such as an incorrect\npositioning of the probes between two different examinations. The observed results show that the proposed technique is indeed\nfeasible, even when a simple, nonspecific model of the head is exploited and is robust against the above mentioned inaccuracies....
Polygonal metal waveguides are analyzed analytically and numerically. Classical equation for the wave impedance of arbitrary\nshaped waveguides is completed with approximate expression for the cutoff wavelength of the dominant mode. Proposed approach\nis tested with the help of 3D finite difference time domain models of microwave waveguides junctions. Obtained data are used for\ncomputer-aided design of microwave transition from coaxial line to cylindrical waveguide....
Satellite simulators are used to calculate the brightness temperature (Tb) that would be measured by a space borne sensor under a\nset of atmospheric conditions accounting for the radiometric characteristics of the sensor and the orbital parameters of the satellite.\nIn this study, a simple approach is proposed for the parameterization of emissivity over land, a key parameter for the calculation\nof microwave Tb.The rationale is to simulate a large ensemble of emissivity values for each frequency and surface characteristics\nand then relate the most likely observed value with soil characteristics. The derived emissivity values are used for the simulation\nof Tb and simulated radiance is then compared with satellite observations. It is shown that this method improves the simulation\nof radiance and that it is suitable to provide a first guess of the emissivity value (a prior) that can then be refined using iterative\nprocedures....
It is demonstrated that a theory of zero-order mode resonator (ZOR) metamaterial (MTM) structure can be used for the\ndevelopment of a novel class of applicators for microwave thermotherapy, for example, for hyperthermia in cancer treatment or\nfor physiotherapy.The main idea of creating such an applicator is to generate and radiate a plane electromagnetic (EM) wave into\nthe treated biological tissue, at least in a certain extent. The main aim of this paper is to investigate whether an EM wave generated\nby ZORMTM structure and emitted into the biological tissue can produce a homogeneous SAR distribution in the planes parallel\nto the applicator aperture and achieve a penetration depth approaching the theoretical limit represented by SAR distribution and\npenetration depth of an ideal EM plane wave. EM field distribution inside a virtual phantom of the treated region generated by the\napplicator that is based on the proposed ZOR MTMprinciple is investigated using a well-proven full-wave commercial simulation\ntool.The proposed applicator type shows both a low unwanted leaked electromagnetic field and a fairly homogeneous electric field\nin its aperture as well as in the virtual phantom of the treated region....
A wideband 90�° hybrid coupler has been presented and implemented in planar microstrip circuit. With similar structure of\nconversional 2-section branch-line coupler, the proposed coupler consists of a lumped high-pass network but not the quarter\nwavelength transmission at the center. The values of all lumped elements were optimized to replace a quarter-wavelength\ntransmission line with a phase inverter. To demonstrate the proposed concept, a 1-GHz prototype was fabricated and tested. It\nachieves 90% impedance bandwidth with magnitude of S11 less than -10 dB. Within this bandwidth, more than 13 dB port-toport\nisolation, less than 5.0 degree phase imbalance, and less than 4.5 dB magnitude imbalance are achieved, simultaneously. The\nproposed coupler not only achievesmuch wider bandwidth but also occupies less circuit area than that of the conversional 2-section\nbranch-line coupler....
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