M. Okoniewski

A study of the handset antenna and human body interaction

The antenna radiation pattern and other characteristics are significantly altered by the presence of the human body. This interaction as well as the resultant deposition of microwave power in the body (specific absorption rate-SAR) are of particular interest for cellular telephones and similar communication devices. This paper builds on and extends the previous analyses of parameters that influence the antenna-user interaction. Computer tomography (CT) and magnetic resonance imaging (MRI)-derived, high-resolution models of the human head are used. The numerical analysis is performed with the finite-difference time-domain (FDTD) method. The specific findings are: 1) a box model of a human head provides grossly distorted and unreliable results for the antenna radiation pattern; 2) a spherical model of the human head provides results that are relatively close to those obtained with a relatively simple, but more realistic, head model; 3) the SAR values obtained with spherical or simplified head models, that do not include the ear, are greater than those for a realistic head model that includes the ear; and 4) a hand holding the handset absorbs significant amount of antenna output power, which can be considerably decreased by modifying the geometry of the handset metal box.

Three-dimensional subgridding algorithm for FDTD

In many computational problems solved using the finite-difference time-domain (FDTD) technique, there is a need to model selected volumes with higher resolution than the whole computational space. An efficient algorithm has been developed for this purpose that provides the mesh refinement by the factor of two in each direction. The algorithm can be used in two-dimensional (2-D) and three-dimensional (3-D) problems and provides for subgridding in both space and time. Performance of the 3-D algorithm was tested in waveguides and resonators. A high accuracy and efficiency were observed in all test cases with insignificant (of an order of -60 dB) reflections from mesh interfaces. Practical applications of the algorithm in the analyses of a resonator with a dielectric rod and of a cellular phone behavior in the vicinity of the operator head are also reported.

Simple treatment of multi-term dispersion in FDTD

Three new simple and efficient algorithms are proposed for the numerical treatment of the multi-term Debye or Lorentz dispersion in the FDTD method. The formulation is based on the auxiliary differential equation, but requires much fewer operations than the published schemes. The approach is equivalent to the best higher order recursive schemes in terms of memory and computational expense, but without the linearity assumptions.

Dual-frequency strip-sleeve monopole for laptop computers

A novel dual-frequency strip-sleeve monopole antenna for use on a laptop computer is described. The antenna operates simultaneously in the 0.824-0.894 GHz and 1.85-1.99 GHz bands of the AMPS and the PCS systems with return-loss less than -9.5 dB. Effects of several antenna and computer parameters on the input impedance, radiation pattern, and directivity are given. The parameters considered include an angle between the keyboard and the screen, dielectric materials of the keyboard and the screen, number of parasitic antenna sleeves, and the dielectric covering the antenna.

FDTD analysis of magnetized ferrites: a more efficient algorithm

A more efficient FDTD algorithm is introduced for the analysis of structures involving magnetized ferrites. A critical issue of time and space synchronism ensuring second order accuracy is discussed, and a method to provide it based on extrapolation rather than interpolation used by previous authors is presented. Numerical examples validating the method are given.<<ETX>>

Practical 3-D contour/staircase treatment of metals in FDTD

The standard finite-difference time-domain (FDTD) method incorporates an inaccurate staircase representation of perfect electric conductors. More accurate, contour-type update formulas have been proposed. These approaches suffer from bookkeeping complexity, difficulties in mesh generation, and stability problems. Only simplified special cases have been implemented in three dimensions. A new contour-like FDTD algorithm is presented. Subcell formulas and staircase logic are combined to produce a three-dimensional (3-D) algorithm that is simple, robust, and fully automatic.

Further analysis of open-ended dielectric sensors

The effect on the input reflection coefficient of the dimensions of open-ended coaxial lines is investigated. Using a standard FDTD technique, the effects of variations in the flange and conductor dimensions on the reflection coefficient of a 3.6 mm coaxial line immersed in water or methanol are simulated. Simulation results are compared with measurements and previous moment method calculations. It is found that the presence or absence of a flange affects the input reflection coefficient substantially in some cases. The results also show that inversion formulas developed for lines with infinite flanges are not valid for flanges with finite radii. >

Interactions of electrostatic discharge with the human body

Electrostatic discharge (ESD) pulses comprise frequencies up to approximately 1 GHz. These pulses have been reported to be associated with health effects. Human exposure standards also set limits on the specific absorption (SA) in tissue. Electric fields and SA are computed using the finite-difference time-domain method and heterogeneous model of the human body. The average SA values in all organs and tissues are below the limits in the IEEE Standard for typical and realistically high ESD pulses.

Vector wave equation 2-D-FDTD method for guided wave problems

A compact FDTD algorithm for the full wave analysis of inhomogeneous wave guiding structures, using a two dimensional mesh is proposed. The formulation is based on the vector wave equation, and in contrast with previous approaches, allows for the formulation of the algorithm in a real domain only. Moreover, since only transverse electric fields are used, two real, instead of six complex components have to be updated and stored, and since they are both defined at the same mesh nodes, the treatment of dielectric inhomogeneities is simplified. Numerical examples validating the method are presented.<<ETX>>

Distributed Effects in a Pair of Parallel Guides Coupled Via a Chiral Medium and Their Possible Applications

Propagation of the electromagnetic wave in a symmetrical structure of two identical parallel guides coupled via a chiral medium is investigated using the coupled mode method. It is found that the chirality causes periodic transfer of energy between guides. Possible applications of the effects observed in the structure to the construction of depolarizers, polarimeters, diplexers, frequency meters, frequency/amplitude converters, sensors, switches, and modulators is discussed.