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Microwave Theory and Techniques, IEEE Transactions on

Issue 11  Part 2 • Date Nov 2000

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Displaying Results 1 - 25 of 29
  • Evaluation of electromagnetic interference from a cellular telephone with a hearing aid

    Page(s): 2148 - 2154
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    In a collaborative effort, electromagnetic interference (EMI) is evaluated from a global system for mobile communication telephone with one model of a hearing aid used in the ear canal. Since the electromagnetic fields cannot be measured in the ear canal, a reliable method of their modeling with the finite-difference time-domain method is established. Very good agreement has been achieved between the measured and computed electric and magnetic fields in free space in very close proximity to the telephone. Subsequently, electric and magnetic fields in the ear canal are computed for two models of the ear, and three positions of the telephone. The computed fields are compared with the acoustic measurements for a small number of humans subjected to the EMI test. View full abstract»

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  • Combined electromagnetic and heat-conduction analysis of rapid rewarming of cryopreserved tissues

    Page(s): 2185 - 2190
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    A combined solution of an electromagnetic (EM)-wave equation and head transfer equation is presented to analyze the microwave rewarming process of cryopreserved tissues. The solution process starts with an initial temperature of the tissue. The EM-field distribution inside the tissue is determined first by solving hybrid surface-volume integral equations. This solution provides a thermal source term for the heat-transfer equation. A finite-difference scheme is then applied to solve the heat-transfer equation, which determines the temperature distribution inside the tissue for the next time step. Since the tissue's electrical characteristics (ε and σ) are functions of temperature, their values are then updated based on the new temperature distribution. The iteration continues until a termination condition is satisfied. This combined iterative solution of wave equation and heat-transfer equation allows one to model the complex rewarming process. Numerical results are presented to demonstrate the application of the combined analysis approach. View full abstract»

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  • Experimental thermographic analysis of thermal effects induced on a human head exposed to 900-MHz fields of mobile phones

    Page(s): 2022 - 2032
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    This paper summarizes the results of an experimental research of thermal effects induced by electromagnetic exposure to wireless mobile communication equipment. A series of experiments has been performed in order to examine the time evolution of the temperature of some body-part surfaces exposed to electromagnetic radiation emitted by global system for mobile communication mobile phones (900 MHz). Special attention has been paid to the analysis of the human head, as this is the human part mainly exposed in normal conditions of mobile phone use. View full abstract»

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  • Electric fields induced in cells in the bodies of amateur radio operators by their transmitting antennas

    Page(s): 2155 - 2158
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    In this paper, an analytical study is made to determine the electric field induced in cells in the bodies of amateur radio operators by radiation from their respective transmitting antennas. Three types of antennas are considered and the electric field from each in the transmitting room of the operator is calculated. The electric field induced in the bodies of the operators is obtained with a cylindrical approximation of the body. The electric field induced in a cell in the central cross section of the body at f=60 MHz when the antenna radiates 1 kW is found to be as high as 50 V/m when the cell is near the surface. Due to skin effect, the field is much smaller in the interior of the body. View full abstract»

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  • Computer simulation and experimental studies of SAR distributions of interstitial arrays of sleeved-slot microwave antennas for hyperthermia treatment of brain tumors

    Page(s): 2191 - 2198
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    The specific-absorption-rate (SAR) distributions produced by three-, six-, and seven-element arrays of sleeved-slot interstitial antennas in brain-equivalent tissues are investigated in this paper. Computer simulations of SAR distributions are compared to experimental measurement made in a brain-equivalent gel phantom at 2450 MHz. Results showed that a 15-mm antenna spacing would produce SAR patterns with the least variation in its distribution compared to smaller or larger spacings. Moreover, the region of elevated SARs is inscribed by the array and extends 35 mm in length to include the distal antenna-tip region. In addition, results indicate that a hexagonal array configuration of either six or seven sleeved-slot interstitial antennas could provide elevated SARs in brain tissues. Since the six-element configuration uses one less interstitial antenna with comparable SARs, it offers a better scheme for hyperthermia treatment of brain tumors. View full abstract»

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  • Use of PML absorbing layers for the truncation of the head model in cellular telephone simulations

    Page(s): 2033 - 2039
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    An efficient implementation of the perfectly matched layer (PML) boundary has been used to truncate a 3-mm resolution head model used for cellular telephone simulations. An extensive analysis of the model truncation effects along all three axes has been performed. A basic observation is that a considerable fraction of the power radiated by a cellular telephone is absorbed in the proximal ear region, and there is no interest for safety certification and antenna design in retaining electromagnetic-field information in the weakly exposed regions. The authors have progressively reduced the finite difference time-domain space in the ear-to-ear, back-to-front, and bottom-to-top directions by embedding the weakly exposed sides of the head in the PML layers. Results show that, at the lower frequency of 835 MHz, only truncations in the ear-to-ear direction is appropriate for specific-absorption-rate (SAR) accuracy. However, at the personal communication system frequency of 1900 MHz, 1- and 10-g SARs within 1% of accuracy can be obtained by retaining just 4% of the original volume of the head model. This method indicates that high-resolution cellular telephone simulations can be performed with tremendous savings in execution times and memory requirements. All of the SAR results presented in this paper have been obtained with a laptop computer, and execution times as low as 1 min have been obtained for the fully optimized simulations at 1900 MHz. Furthermore, it is shown that by using a truncated half-model, it is possible to obtain accurate radiation patterns at both frequencies of 835 and 1900 MHz. Since both the SAR evaluation and radiation pattern calculation are needed for new antenna design, this should result in a highly efficient algorithm for electromagnetic design of new personal wireless devices. View full abstract»

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  • Integrated models for the analysis of biological effects of EM fields used for mobile communications

    Page(s): 2082 - 2093
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    The understanding of the modalities of interaction of electromagnetic (EM) fields with biological material is a key point in the identification of possible induced effects. Since the beginnings of bioelectromagnetic research studies, most of the attention has been focused on the effects on nervous systems and neuronal cells. The importance of this target has recently increased due to the wide diffusion of mobile terminals, used close to the head. In this paper, an integrated interaction model is proposed. The model, validated in each part of its components with experimental data, allows to obtain a quantitative link from the external applied field to the effects on neurons (isolated or linked to similar others). The models is firstly based on the evaluation of the EM field at cellular membrane level, then on the evaluation of the effects induced on each component of the model growing from the low biophysical level (membrane channels) to the biological one (neuron time behavior). The use of well-assessed models for the simulations of each part allows both the evaluation of the effect at different levels of complexity and the employment of this effect acting as an input on the upper level. This approach allows, for the first time, a complete quantitative evaluation of the effects on neurons due to the fields from the existing mobile systems, and can be a useful instrument for the evaluation of the possible health impact of new technologies. View full abstract»

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  • Accurate microwave resonant method for complex permittivity measurements of liquids [biological]

    Page(s): 2159 - 2164
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    A method available for accurate measurements of lossy liquids is presented, tested on standard materials, and compared with the perturbation technique commonly adopted in cavity measurements. The method is based on numerically solving a complex characteristic equation. Realization of the method was done using an E010 cylindrical cavity. Results show that measurement errors may be decreased with application of the method presented. The method excludes uncertainties in complex permittivity determination when material has losses and high permittivity. View full abstract»

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  • A model for predicting electromagnetic interference of implanted cardiac pacemakers by mobile telephones

    Page(s): 2121 - 2125
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    A prediction of the electromagnetic interference (EMI) of pacemakers due to mobile phones is significant in improving the immunity of pacemakers. The Pacemaker Committee of Japan recently conducted immunity tests of pacemakers for mobile phones, and consequently concluded that the connector between the pacemaker housing and the lead wire of the electrode plays a major role for the EMI due to mobile phones. Based on this finding, a computer model for predicting the EMI level has been presented, in which the internal impedance seen from the connector was considered as a load, and the metal portions consisting of the pacemaker housing and the lead wire of the electrode were considered as two elements of a receiving antenna. Interference voltages induced through the connector were analyzed by using the finite-difference time-domain method in conjunction with a torso and mobile phone model. The modeling was validated by comparison with previously reported experimental results. View full abstract»

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  • The dependence of electromagnetic energy absorption upon human head tissue composition in the frequency range of 300-3000 MHz

    Page(s): 1988 - 1995
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    The requirements for testing compliance of cellular phones with electromagnetic safety limits demand evaluation of the maximum exposure that may occur in the user group under normal operational conditions. Under these conditions, the tissues of the ear region are most exposed, the tissue composition of which is complex and varies considerably from user to user. The objective of this paper is to derive head tissue equivalent dielectric parameters that enable the utilization of one generic homogeneous head for testing compliance for the entire user group, i.e., granting no underestimation, but also not greatly overestimating the actual maximum user exposure. As a primary study, a simple analytical model of an infinite half-space layered tissue model exposed to a plane wave was utilized to investigate the impact of impedance matching standing waves, etc. On the spatial-peak specific absorption rate. The tissue layers were varied in composition and thickness, representing the anatomical variation of the exposed head region covering the user group including adults and children (<10% to >90% percentile). Based on the worst-case tissue layer compositions with respect to absorption at each frequency, head tissue equivalent dielectric parameters for homogeneous modeling were derived, which result in the same spatial-peak absorption. The validity of this approach for near-field exposures was demonstrated by replacing the plane wave by different near-field sources (dipoles and generic phones) and the layered structure with magnetic-resonance-image-based nonhomogeneous human head models. View full abstract»

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  • Comparison of averaging procedures for SAR distributions at 900 and 1800 MHz

    Page(s): 2180 - 2184
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    The authors studied the effect of the position of the averaging volume on the averaged specific-absorption-rate values at the typical European cellular telephone frequencies around 900 and 1800 MHz. The Council of the European Union recommends a 10-g contiguous volume, as the averaging volume. A simple cubic tissue can be used provided that the calculated dosimetric quantities have conservative values relative to the exposure guidelines of the Council of the European Union. Large differences can occur depending on the averaging procedure. The situation is definitely most critical at 1800 MHz. View full abstract»

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  • FDTD analysis of microwave hearing effect

    Page(s): 2126 - 2132
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    This paper presents a numerical analysis of the thermoelastic waves excited by the absorbed energy of pulsed microwaves in a human head. First, the authors calculate the distribution of the specific absorption rate using a conventional finite-difference time-domain (FDTD) algorithm for the Maxwell's equation. They then calculate the elastic waves excited by the absorbed microwave energy. The FDTD method is again applied to solve the elastic-wave equations. The validity of the analysis for elastic waves is confirmed through comparison of the FDTD results with the analytical solutions in a sphere model. Two anatomically based human head models are employed for numerical calculations. The waveforms of the calculated pressure waves are different from the previously reported ones. It is especially shown that the surface heating is important in exciting the fundamental mode of the pressure waves in the head. The pulsewidth dependency of the loudness of microwave hearing is clearly explained by the simulation with realistic head models. The peak pressure of elastic waves in the realistic head models is of the same order as the previously reported values obtained with a homogeneous sphere model. The strength of elastic wave is discussed in consideration of the safety of this phenomenon. View full abstract»

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  • Nonthermal effects of extremely high-frequency microwaves on chromatin conformation in cells in vivo-dependence on physical, physiological, and genetic factors

    Page(s): 2172 - 2179
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    There is a substantial number of studies showing biological effects of microwaves of extremely high-frequency range [i.e., millimeter waves (MMWs)] at nonthermal intensities, but poor reproducibility was reported in few replication studies. One possible explanation could be the dependence of the MMW effects on some parameters, which were not controlled in replications. The authors studied MMW effects on chromatin conformation in Escherichia coli (E. coli) cells and rat thymocytes. Strong dependence of MMW effects on frequency and polarization was observed at nonthermal power densities. Several other factors were important, such as the genotype of a strain under study, growth stage of the bacterial cultures, and time between exposure to microwaves and recording of the effect. MMW effects were dependent on cell density during exposure. This finding suggested an interaction of microwaves with cell-to-cell communication. Such dependence on several genetic, physiological, and physical variables might be a reason why, in some studies, the authors failed to reproduce the original data of others. View full abstract»

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  • Analysis of the interaction between a layered spherical human head model and a finite-length dipole

    Page(s): 2003 - 2013
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    The coupling between a finite-length dipole antenna and a three-layer lossy dielectric sphere, representing a simplified model of the human head, is analyzed theoretically in this paper. The proposed technique is based on the theory of Green's functions in conjunction with the method of auxiliary sources (MAS). The Green's function of the three-layer sphere can be calculated as the response of this object to the excitation generated by an elementary dipole of unit dipole moment. The MAS is then applied to model the dipole antenna by distributing a set of auxiliary current sources on a virtual surface lying inside the antenna physical surface. By imposing appropriate boundary conditions at a finite number of points on the real surface of the antenna, the unknown auxiliary sources coefficients can be calculated and, hence, the electric field at any point in space can be easily obtained. Numerical results concerning the specific absorption rate inside the head, the total power absorbed by the head, the input impedance, and the radiation pattern of the antenna are presented for homogeneous and layered head models exposed to the near-field radiation of half-wavelength dipoles at 900 and 1710 MHz. The developed method can serve as a reliable platform for the assessment of purely numerical electromagnetic methods. The method can also provide an efficient tool for accurate testing and comparison of different antenna designs since generalizations required to treat more complex antenna configurations are straightforward. View full abstract»

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  • Microwave radiation induces a heat-shock response and enhances growth in the nematode Caenorhabditis elegans

    Page(s): 2076 - 2081
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    This paper shows that prolonged (overnight) exposure to continuous microwave fields (750 MHz, 0.5 W) can induce both a heat-shock response and enhanced growth in the nematode worm Caenorhabditis elegans. Exposures were conducted in a TEM cell with matched load, producing an E-field of approximately 45 V m-1 at the center (where test worms are placed). Biomonitoring of heat-shock responses has been simplified by using two transgenic strains (PC72 and PC161), which both carry stress-inducible reporter constructs, respectively, placing lacZ (β-galactosidase) and lacZ plus green fluorescent protein expression under the control of C. elegans hsp16-1 promoters. In situ localization of reporter expression reveals a minority of test worms, which respond strongly to microwave exposure. Enzyme activity measurements average these reporter responses across many thousands of individual worms, giving a reliable indication of the overall stress imposed on a population. The temperature profile of reporter responses induced by microwave exposure parallels that induced in controls by heat alone, but is displaced down the temperature scale by some 3°C. Length measurements were conducted at intervals in synchronized C. elegans cultures seeded with L1 larvae. Using pooled data from nine separate runs, growth was stimulated by 8.5% after overnight microwave exposure (relative to controls), and this disparity increased to 11% after 24 h of further growth without irradiation. Both heat-shock responses and increased growth would be consistent with a modest increase in temperature, raising the possibility that microwave exposure might cause limited heating in this system. However, there is no detectable rise in the temperature of either medium or worms during overnight exposure under these conditions, discounting both generalized and localized (worm-specific) heating effects. It is concluded that both growth and heat-shock responses are induced by microwave exposure through one or more nonthermal routes. View full abstract»

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  • Simulation of human interaction with mobile telephones using hybrid techniques over coupled domains

    Page(s): 2014 - 2021
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    An approach to hybridization of the method of moments and the finite-difference time-domain method is investigated in this paper. This hybrid method is capable of analyzing a system of multiple discrete regions by employing the principle of equivalent sources to excite their coupling surfaces. The case of multiple sources in the presence of scattering objects is discussed. To develop the approach and test its validity, some examples are given using the same numerical method in multiple regions: the results compare well with other available data. The theory of the heterogeneous hybrid method is then developed and validated. It is shown that this technique has the great advantage of accurately modeling complex and arbitrarily oriented mobile telephone handset antennas in the proximity of a detailed voxel representation of the human head, as required for safety and radiation pattern assessments. View full abstract»

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  • An efficient RF exposure system with precise whole-body average SAR determination for in vivo animal studies at 900 MHz

    Page(s): 2040 - 2049
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    A radial electromagnetic cavity has been designed and optimized for the in vivo whole-body exposure of mice to 900-MHz RF fields. Parallel circular plates shorted around the perimeter form the cavity, which is fed at the center in order to excite a cylindrical TEM wave. Plastic housings allow the insertion and equidistant positioning from the exciter of 40 mice, with the electric field parallel to the body axis. The resulting exposure system is highly efficient, featuring more than 80% of the incident power dissipated in the mice. The whole-body average SAR can be determined with remarkable precision by means of straightforward power balance since the RF power leakage from the cavity is extremely low. Fairly uniform exposure of the mice, individually and collectively, has been achieved by means of the symmetric arrangement. This exposure system has been adopted in a replication study on transgenic mice currently being carried out in South Australia, and is being considered for upcoming animal studies in Europe. View full abstract»

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  • Feasibility of noninvasive measurement of deep brain temperature in newborn infants by multifrequency microwave radiometry

    Page(s): 2141 - 2147
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    Clinical studies of hypothermal neural rescue therapy for newborn infants who have suffered hypoxia-ischaemia are currently hindered by the difficulty in measuring deep brain temperature. This paper addresses: the specific requirements for this measurement problem, the design of a proposed radiometer system, a method for retrieving the temperature profile within the cooled head, and an estimation of the precision of the measurement of deep brain temperature using the technique. A five-frequency-band radiometer with a contact-type antenna operating within the range 1-4 GHz is proposed to obtain brightness temperatures corresponding to temperature profiles predicted by a realistic thermal model of the cooled baby head. The problems of retrieving the temperature profile from this set of brightness temperatures, and the estimation of its precision, are solved using a combination of model fitting and Monte Carlo techniques. The results of this paper show that the proposed technique is feasible, that it is expected to provide a good estimate of the temperature profile within the cooled baby-head, and that the estimated precision (2σ) of the temperature measured in the deep brain structures is better than 0.8 K, depending upon the estimation procedure used. View full abstract»

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  • On the feasibility of detecting flaws in artificial heart valves

    Page(s): 2165 - 2171
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    Investigates the feasibility of detecting defects in certain artificial heart valves by determining the electromagnetic behavior of some simple models with the aid of thin-wire integral equations. The idea is to use the stationary current that occurs at late times after the excitation of a closed loop as a discriminator. This current exhibits an exponential decay when a resistive load is included that is representative of fatigue or a partial fracture. The decay rate is indicative of the severity of the defect. For a wire with an opening, which is representative of a complete fracture, the late-time current is completely absent. As a simplified model of remote detection by a small loop antenna that could be introduced via a catheter, the authors consider the coupling between two parallel circular wires. In all cases, the dispersive environment of the valve is taken to be homogeneous and filled with blood since this medium exhibits a representative dispersion. View full abstract»

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  • SAR generated by commercial cellular phones-phone modeling, head modeling, and measurements

    Page(s): 2064 - 2071
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    This paper presents the computation of the specific absorption rate (SAR) generated by cellular phones inside an anatomical model of a head. Four models of commercially available phones have been considered working at 900- and 1800-MHz bands (global system for mobile communication system). The phones have been modeled by using a computer-aided design representation obtained through the reverse engineering technique. Both SAR distributions and SAR averaged values have been computed inside the anatomical model of a head, by using the finite-difference time-domain method. Computations have been experimentally validated through measurements performed inside anthropomorphic phantoms irradiated by a dipole and cellular phones. View full abstract»

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  • Human exposure to radio base-station antennas in urban environment

    Page(s): 1996 - 2002
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    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. View full abstract»

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  • Cell membrane permeabilization of human erythrocytes by athermal 2450-MHz microwave radiation

    Page(s): 2072 - 2075
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    The effects of low-level microwaves (2.45 GHz) on the membrane of human erythrocytes were studied measuring the hemoglobin loss and osmotic resistance of erythrocytes exposed to different power densities (0.025-10.0 mW/cm2) at different irradiation times. A significant increase of the hemoglobin loss by exposed erythrocytes as well as a strong dependence of the rate of the increase of hemoglobin loss on the initial level of spontaneous hemolysis were observed. It was found that at low power densities (0.84 and 1.36 mW/cm2), the hemolysis degree increases quasi-linearily with the exposure time, while at higher density (5 mW/cm2), this tendency is reversed after first 10 h of irradiation. It appears like long-term irradiation exerts a protective effect against spontaneous hemolysis caused by blood ageing. The osmotic fragility test performed on samples exposed to 5 mW/cm2 at different irradiation times showed that the osmotic resistance of exposed erythrocytes increases in time, reaching a maximum at the end of irradiation (60 h), while the osmotic resistance of the controls is constant. View full abstract»

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  • Skin heating effects of millimeter-wave irradiation-thermal modeling results

    Page(s): 2111 - 2120
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    Millimeter microwaves (MMWs) are a subset of RF in the 30-300-GHz range, The proliferation of devices that operate in the MMW range has been accompanied by increased concern about their safety. As MMW irradiation has a very shallow penetration in tissue, the specific absorption rate is not a relevant parameter for dosimetry purposes. A thermal modeling program was used to investigate the tissue heating effects of MMW irradiation (100 GHz nominal) on the primate head. The objectives were to determine the extent to which the surface and subsurface tissue temperatures depend on applied energy density and the effects of blood flow and surface cooling on tissue temperatures. Two power ranges were considered: short-duration exposure to high power microwaves (HPMs), with power densities of 1.0, 1.5, 2.0, 2.5, or 3.0 W cm-2 for 3 s, and longer duration exposure to low-power microwaves (LPMs), with power densities of 0.1, 0.15, 0.2, 0.25, 0.3 W cm-2 for 30 s. The applied energies were comparable for both HPM and LPM exposures. The authors found both surface and subsurface temperatures increase as the energy level increases, with HPMs having a higher peak temperature than the LPMs for similar exposure energy densities. The surface temperature increase is linear with energy density for the HPMs, except under combined conditions of high blood flow (blood-flow rate of 8×10-3 g s-1 cm-3) and high-energy density (greater than 7.5 J cm-2), The LPM surface temperatures are not linear with incident energy. The peak surface temperature is affected by environmental conditions (convection coefficient, sweat rate). The magnitude of the temperature increase due to MMW exposure did not change with environmental conditions. The subsurface temperature increases are considerably damped, compared to the surface temperatures. View full abstract»

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  • Analysis, design, and experimental verification of microwave filters for safety issues in open-ended waveguide systems

    Page(s): 2133 - 2140
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    Safety issues must be seriously considered in the practical implementation of microwave industrial systems with open ports. To preserve the radiation of these open-ended waveguide systems into permissible levels, bandstop microwave filters are widely used. In this paper, the accurate analysis, design, and experimental verification procedure of such filters are extensively studied. A singly and a doubly corrugated filter for continuous flow microwave industrial systems are designed. Two prototypes of such devices have been manufactured and experimentally verified. View full abstract»

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  • Polarization and human body effects on the microwave absorption in a human head exposed to radiation from handheld devices

    Page(s): 1979 - 1987
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    A multigrid finite-difference time-domain code was used to calculate specific absorption rate (SAR) distribution in a human head exposed to microwave radiation from handheld antennas. The effect of the human body was taken into account and different antennas and polarization conditions were considered, The distance between the antenna and human head were varied to examine the effect of the human body on the SAR distribution, From the numerical results, it is shown that the human body plays a significant role on the SAR value and its distribution in the head [as high as 53% monopole, 41% planar inverted F antenna (PIFA)]. It is also shown that the effect of the body is more dominant at lower frequencies (monopole 900 MHz versus 1.9 GHz). For the monopole case, effect of body is particularly important at larger separation distances from the head, e.g., at d=4 cm versus d=0.5 cm. Effect of body is particularly important for the vertical orientation cases for both the monopole and PIFA. View full abstract»

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The IEEE Transactions on Microwave Theory and Techniques focuses on that part of engineering and theory associated with microwave/millimeter-wave components, devices, circuits, and systems involving the generation, modulation, demodulation, control, transmission, and detection of microwave signals. This includes scientific, technical, and industrial, activities. Microwave theory and techniques relates to electromagnetic waves usually in the frequency region between a few MHz and a THz; other spectral regions and wave types are included within the scope of the Society whenever basic microwave theory and techniques can yield useful results. Generally, this occurs in the theory of wave propagation in structures with dimensions comparable to a wavelength, and in the related techniques for analysis and design..

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