Om P Gandhi

University of Utah | UOU · Department of Electrical and Computer Engineering

Introduction. The model prediction of human functional state during RF hyperthermia is the actual task as it helps to find necessary approach in use of radiofrequency hyperthermia without hazard to human health. The purpose of this study is to develop computer multicompartmental model for prediction of temperature dynamics during regional RF-expos...

The paper summarizes some of the highlights of the advances in the dosimetry of radio-frequency (RF) radiation that played an important role in the revision of the ANSI RF safety guidelines in 1982. Recent work has pointed to several potential problems with these guidelines. These pertain to large RF-induced currents and the commensurately high loc...

Our reports of published research in several of the peer-reviewed journal articles in 1996, 2002, and 2004 have generated a lot of controversy over the last two decades, including the most recent publication by Foster and Chou. In this paper, we present arguments based on physics that the main reason for higher exposure of children (also women and...

The modeling prediction of human thermal state during RF exposure is the actual task. Preliminary model prognosis allows preventing human health hazard. The aim of this work is to develop computer simulator for prediction of human thermophysiological responses during radiofrequency (RF) exposure. Human body is approximated by composition of multila...

The existing cell phone certification process uses a plastic model of the head called the Specific Anthropomorphic Mannequin (SAM), representing the top 10% of U.S. military recruits in 1989 and greatly underestimating the Specific Absorption Rate (SAR) for typical mobile phone users, especially children. A superior computer simulation certificatio...

Committee on Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communications Devices, National Research Council of the USA

Introduction Dipole and Monopole Antennas Loop Antennas References

Numerical methods have matured to a level that they are being increasingly used by many laboratories for dosimetric calculations for important and meaningful bioelectromagnetic problems. For certification of mobile telephones to be within the ANSI/IEEE C95.1-1992 RF Safety Guidelines, the approach discussed in this paper may be quite useful. We sho...

Dipole antennas and their associated arrays are among the most common antennas used for communication systems and measurement of electric and magnetic fields. This article describes the basic nature of these antennas and some of their applications. Variations such as biconical and bow-tie antennas, slot dipoles, folded dipoles, sleeve dipoles, and...

The bioheat equation is used to solve for the temperature rise of the various tissues including the brain for three anatomical models with 1-mm resolution for exposure to cellular telephones at 835 and 1900 MHz for radiated power levels allowed under the previous and the newly relaxed IEEE RF Safety Standards and the International Commission on Non...

The sections in this article are

This article describes the dipole antenna and common types of arrays built from dipole antennas.

Compliance testing of electronic article surveillance (EAS) devices requires that induced current densities in central nervous system (CNS) tissues, i.e. brain and the spinal cord, be less than the prescribed safety limits. Even though ferromagnetic cores are mostly used for activation/deactivation of embedded magnetic tags, assumed equivalent air-...

Compliance with safety guidelines prescribed in terms of maximum electromagnetic power absorption (specific absorption rate or SAR) for any 1- or 10-g of tissue is required for all newly introduced personal wireless devices such as wireless PCs. The prescribed SAR measuring system is a planar phantom with a relatively thin base of thickness 2.0 mm...

A 2-mm-thick plastic shell with 5-10-mm-thick tapered plastic spacer in the shape of a "pinna"-specific anthropomorphic mannequin (SAM) head model is being used for determination of the specific absorption rate (SAR) of cellular telephones for compliance testing against IEEE and the International Commission on Non-Ionizing Radiation Protection (ICN...

Compliance with 1- or 10-g specific absorption rate (SAR) safety guidelines is required in various countries for all newly-introduced personal wireless devices such as Wi-Fi PCs. Even though the dielectric properties of the human tissues are known to be nonuniform and highly variable, relatively rigid adherence to prescribed dielectric properties (...

A comparative, computational study of the modeling of transcranial magnetic stimulation (TMS) and electroconvulsive therapy (ECT) is presented using a human head model. The magnetic fields from a typical TMS coil of figure-eight type is modeled using the Biot-Savart law. The TMS coil is placed in a position used clinically for treatment of depressi...

Most of the recently revised safety limits worldwide are set in terms of the limits of rates of internal energy deposition [specific absorption rates (SARs)] for radio/microwave frequencies. Since procedures to ascertain compliance with the SAR limits are cumbersome, requiring complex computer modeling or bulky, mostly homogenous experimental phant...

Thin-wire antenna model of the human body exposed to the transient excitation is presented in the paper. The analysis is based on the solution of the corresponding integral equation and it is carried out directly in the time domain (TD) . The integral equation is handled via the TD Galerkin-Bubnov scheme of the boundary element method. Numerical re...

The paper uses the two methods suggested in both the ICNIRP and proposed IEEE safety guidelines for compliance testing of security systems based on time-varying magnetic fields being introduced for electronic article surveillance (EAS), radiofrequency identification, and other applications. For nonsinusoidal pulses that are often used, the two proc...

Increasingly, mobile telephones are becoming pocket-sized and are being left in the shirt pocket with a connection to the ear for hands-free operation. We have considered an anatomic model of the chest and a planar phantom recommended by US FCC to compare the peak 1 and 10 g SARs for four typical cellular telephones, two each at 835 and 1900 MHz. A...

A mode of frequency conversion in propagating non-linear media is presented which requires considerably less stringent phase-matching conditions than those in parametric mixing. This is due to the fact that the output frequencies are radiated at angles such that their phase constants along the direction of the `parent' waves exactly match the `gene...

This paper compares the maximum allowable powers of some typical cellular telephones at 835 and 1900 MHz for compliance with the limits of specific absorption rates (SAR) given in ANSI/IEEE, ICNIRP and the proposed modification of ANSI/IEEE safety guidelines. It is shown that the present ANSI/IEEE guideline is the most conservative with the ICNIRP...

Most of the recently revised safety standards worldwide are set in terms of internal rates of electromagnetic energy deposition (specific absorption rates or SAR) at radio frequencies (RF) and microwave frequencies, and of induced electric fields or current densities at lower frequencies up to 10 MHz. Numerical methods have been developed that use...

This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS)...

We have used the quasi-static impedance method to calculate the currents induced in the nominal 2 x 2 x 3 and 6 mm resolution anatomically based models of the human body for exposure to magnetic fields at 60 Hz. Uniform magnetic fields of various orientations and magnitudes 1 or 0.417 mT suggested in the ACGIH and ICNIRP safety guidelines are used...

We have used the quasi-static impedance method to calculate the currents induced in the nominal 2 x 2 x 3 and 6 mm resolution anatomically based models of the human body for exposure to magnetic fields at 60 Hz. Uniform magnetic fields of various orientations and magnitudes 1 or 0.417 mT suggested in the ACGIH and ICNIRP safety guidelines are used...

The bioheat equation is solved for an anatomically-based model of the human head with resolution of 3×3 mm to study the thermal implications of exposure to EM fields typical of cellular telephones both at 835 and 1900 MHz. Up to 4.5°C temperature elevation may be caused for some locations of the pinna by a cellular telephone warmed by electronic ci...

A mixed finite-difference time-domain (FDTD)-integral equation approach for the evaluation of the power deposition in the human body model immersed in a complex electromagnetic environment is proposed. The advantage of the proposed approach is that safety assessment for exposure to generic sources may be performed on-site, in a few minutes, with hi...

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 cellul...

In recent years, with the availability of high resolution models of the human body, numerical computations of induced electric fields and currents have been made in more than one laboratory for various exposure conditions. Despite the verification of computational methods, questions are often asked about the reliability of these data. In this paper...

Electronic article surveillance (EAS) systems based on the use of alternating magnetic fields at frequencies up to 10-20 MHz are being rapidly introduced into society to prevent unauthorized removal of items from stores, libraries, and hospitals. The EAS systems may take the form of one or two-sided panels of current-carrying loops or pillars at or...

With the increasing use of millimeter-wave radiation in communications and radar, it is necessary to know the dielectric properties of various tissues for the evaluation of potential hazards to humans. At millimeter-wave frequencies, the absorption of electromagnetic radiation is mostly restricted to the skin because of the submillimeter depths of...

We have used an efficient implementation of the PML boundary according to the formulation proposed by Sullivan (1977) to truncate the human head model for cellular telephone simulations. Different from the truncation method previously presented by the authors, the new method does not require any symmetry considerations. Because of the basic observa...

We have previously reported on a portable dosimetry system based on a mixed FDTD-integral equation approach for rapid on-site evaluation of the SAR distributions in an anatomically-based model of the human body immersed in a complex electromagnetic environment (Lazzi and Gandhi). In the present paper, we present a different approach where we use th...

Considerable progress has been made in the development of numerical methods for dosimetry of exposure to electromagnetic fields from extra low frequencies (ELF) to microwave frequencies. Even though the fmite-difference time-domain (FDTD) method has been used extensively, several other methods most notably the method of moments (MOM), the conjugate...

This session consisted of four papers with emphasis on numerical methods and models that can be used to obtain SAR distributions for electromagnetic safety assessment and for providing dosimetric information for biobehavioral animal experiments. In an overview of the developments in the field, it was noted that theoretical dosimetry has progressed...

An automated specific absorption rate (SAR) measurement system has been developed for compliance testing of personal wireless devices. Unlike other systems, this system uses a model with a lossy ear-shaped protrusion and the accuracy of this experimental setup has been checked by comparing the peak 1-g SARs for ten cellular telephones, five each at...

The finite-difference time-domain method (FDTD) is currently the most used numerical technique for dosimetry of wireless devices. A concern is that the structurally complex antennas might not be modeled accurately. Specifically, helical antennas are often used and these are incompatible with rectangular grid FDTD without resorting to staircase appr...

This paper discusses techniques for the use of accurate models of wireless communication devices for the determination of SAR compliance. We discuss how computer-aided design and manufacturing files can be used to provide accurate models of both the internal and external components of these types of devices. Results are compared from simulations in...

The objective of this paper is to investigate, numerically and experimentally, the radiation patterns of various commercial cellular telephones held in a realistically slanted position relative to the head, to understand the performance of such devices for normal use conditions. The investigation has been performed with and without the human head m...

A 6-mm resolution, 30-tissue anatomy-based model of the human body is used to calculate specific absorption rate (SAR) and the induced current density distributions for radiofrequency and switched gradient magnetic fields used for MRI, respectively. For SAR distributions, the finite-difference time-domain (FDTD) method is used including modeling of...

The use of primates for examining the effects of electromagnetic radiation on behavioural patterns is well established. Rats have also been used for this purpose. However, the monkey is of greater interest as its physiological make-up is somewhat closer to that of the human. Since the behavioural effects are likely to occur at lower field strengths...

Some recent developments in both the numerical and experimental methods for determination of SARs and radiation patterns of handheld wireless telephones are described, with emphasis on comparison of results using the two methods. For numerical calculations, it was possible to use the Pro-Engineer CAD Files of cellular telephones for a realistic des...

We describe two computational techniques that have been extensively used to calculate the coupling of electromagnetic fields to an anatomically-based models of the human body from ELF to microwave frequencies. The focus of the talk is on applications both for the quasi-static impedance method used at low frequencies, and on the finite-difference ti...

Microwave dosimetry has frequently relied on the used of phantoms to measure microwave dose for biological exposures. Here we report the use a homogeneous rhesus monkey phantom, the “green monkey”, to verify the results of a FD-TD computer model. The same techniques previously used to develop heterogeneous models of rat, goat and rhesus monkey from...

Time-domain potentials measured at 64 points on the surface of a large canine heart, considered comparable with those of a human heart, were used to calculate the electric fields and current densities within various organs of the human body. A heterogeneous volume conductor model of an adult male with a resolution of approximately 6 mm3 and 30 segm...

At certain frequencies, when the human head becomes a resonant structure, the power absorbed by the head and neck, when the body is exposed to a vertically polarized plane wave propagating from front to back, becomes significantly larger than would ordinarily be expected from its shadow cross section. This has possible implications in the study of...

The presence of the human head and hand significantly alter the performance of cellular telephones. A considerable fraction of the power (30-70 percent) is generally absorbed by the human body, causing SAR concerns and drastic reduction in antenna efficiency. The use of high-gain, broad-band, microstrip patch antenna would alleviate the problem, le...

We have previously discussed our use of computer aided design and manufacturing (CAD/CAM) files for use in FDTD simulations of mobile communication devices. We address the problems involved with the description of the internal components of the mobile telephone. These are of particular importance as the other plastic shell of the device is no longe...

Determination of peak 1-g SAR is required for all new personal wireless devices to ensure that it complies with the RF safety guidelines approved by US Federal Communications Commission (FCC). We have developed an automated SAR measurement setup which uses a 3D stepper motor system to move the Narda Model 8021 implantable E-field probe to determine...

A method for importing data from computer-aided design (CAD) files for a mobile telephone into finite-difference time-domain (FDTD) simulation software is described. Although the FDTD method is well suited for the bio-electromagnetic simulations and has become the method of choice for most researchers in this area, there may be some limitations to...

The finite-difference time domain (FDTD) computed radiation patterns of mobile telephones are carefully compared with those measured in our laboratory. The question of the capability of the FDTD method to correctly predict the radiated electromagnetic fields of today's structurally complex mobile telephones is addressed. Two commercially available...

A novel method to model helical antennas working in the normal mode, as well as helix-monopole antennas with finite-difference time-domain (FDTD) code is presented. This method is particularly useful to model antennas used for personal wireless communication handsets, where the fairly small dimensions of the helical antennas with respect to wavelen...

The increasing use of cellular telephones has spawned considerable research effort on the design of compact, high-efficiency antennas for mobile telephones, exhibiting low EM coupling to the human head. Microstrip antennas seem now to render possible the achievement of all these characteristics. We present some results on a stacked microstrip anten...

The finite-difference time-domain (FDTD) method has previously been used to calculate induced currents in anatomically based models of the human body at frequencies ranging from 20 to 915 MHz and resolutions down to about 1.25 cm. Calculations at lower frequencies and higher resolutions have been precluded by the huge number of time steps that woul...

Validations of the accuracy of the FDTD method for near-field simulations are critical at this time to assess the accuracy of the FDTD method for the simulation of personal communication devices. Excellent comparisons between the FDTD method and analytical or measured results are shown for a dipole antenna next to a layered half-space, a layered bo...

An optimization technique for the perfect matched layer (PML) absorbing boundary conditions has been presented using the FDTD code. The analytical approach to predict the theoretical reflection introduced by a PML backed by a metal plane has been used to determine optimized profiles for the conductivity of the PML material. The optimized PML has be...

Previous articles on the perfectly matched layer (PML) boundary condition have focused on the reflections from the boundary itself. This article examines an application of the PML boundary condition to determine if it is preferable to use the PML or the more traditional boundary conditions for finite-difference-time-domain (FDTD) simulations of per...

An analytical method to predict and optimize the performance of Berenger's (see J. Computat. Phys., vol.114, p.185-200, 1994) perfectly matched layer (PML) absorbing boundary condition (ABC) for finite-difference time-domain (FDTD) simulations is described. The shape of the conductivity in the PML layers has to be chosen carefully to obtain the bes...

The frequency-dependent finite-difference time-domain [(FD)²TD] method is used to calculate internal electric fields and induced current densities in a 1.31-cm resolution anatomically-based model of the human body for exposure to ultrawideband vertically polarized electromagnetic pulses (EMPs). From a single (FD)²TD simulatio...

A theoretical approach to obtain optimised profiles of the conductivity for the perfect matched layer (PML) absorbing boundary conditions is presented. The analytical expression recently introduced by the authors to estimate the error caused by the use of the PML backed by a metal plane as the absorbing boundary condition, has been minimised with r...

We have used the finite-difference time-domain method to calculate the distributions of absorbed energy for a 1.34 x 1.34 x 1.4 cm resolution anatomically based model of the human body for exposure to leakage electromagnetic fields of a radiofrequency dielectric heater operating at 40.68 MHz. To simulate workplace conditions, the dielectric heater...

Realistically tilted models of the human head have been developed to improve the accuracy of the numerical simulation of coupling between the human head and cellular telephones for the likely tilted positions of the antennas vis a vis the head. A “best fitting” technique is used to rotate an approximately 2×2×3 mm resolution model of the human head...

The antenna of a cellular telephone in close proximity to the human head for a variety of time periods raises questions. This research uses the finite-difference time-domain (FDTD) method to calculate the power deposition from a cellular telephone on a high-resolution model of a human head as measured by the specific absorption rates (SAR) in W/kg....

The authors have used the finite-difference time-domain method and a new millimeter-resolution anatomically based model of the human to study electromagnetic energy coupled to the head due to mobile telephones at 835 and 1900 MHz. Assuming reduced dimensions characteristic of today's mobile telephones, the authors have obtained SAR distributions fo...

The finite-difference time-domain method is used to calculate radiation pattern and specific absorption rate (SAR) in the human head due to cellular telephones. For realistic simulation of the ordinary positions of holding the phone, the ear of the model is pressed against the head, the head is tilted at an appropriate angle, and the hand is approx...

The finite-difference time-domain (FDTD) method has previously been used to calculate induced currents in anatomically based models of the human body at frequencies ranging from 20 to 915 MHz and resolutions down to 1.31 cm. Calculations at lower frequencies and higher resolutions have been precluded by the huge number of time steps which would be...

Specific absorption rate (SAR) distributions in man models are often calculated using the finite-difference time-domain (FDTD) method. The traditional method of calculating SAR requires calculation and storage of the three electric field components in each cell and is therefore very time- and memory-intensive. A new algorithm, based on the mass-nor...

We have used a new millimeter-resolution MRI-based model of the human body to calculate the electromagnetic absorption in the head and neck for three experimental Yagi antennas suggested for handheld transceivers of a proposed 6-GHz personal communication network (PCN) system. The SAR distributions are obtained with a resolution of 1.974×1.974×1.5...

Although it is a time-domain method, the finite-difference time-domain (FDTD) method has been used extensively for calculating frequency domain parameters such as specific absorption rate, radar cross-section, and S-parameters. When a broad frequency band is of interest, using a broad-band pulsed excitation can provide this frequency response with...

In order to limit the specific absorption rate (SAR) in the ankles of a person exposed to an electric field at frequencies below 100 MHz, induced current limits are prescribed in the 1992 ANSI/IEEE safety standard. The authors have measured the induced currents passing through the feet of nine subjects exposed to vertically polarized electric field...

We have used the impedance method to calculate the induced electric (E) fields and current densities (J) for the spatially varying vector magnetic fields due to a hair dryer. In this method, applicable for low-frequency exposures where the quasi-static approximation may be made, the biological body or the exposed parts thereof are represented by a...