ABSTRACT
CONTENTS 10.1 Introduction ..................................................................................................................... 294
10.1.1 Induced Field Intensity and Dosimetric Quantities.................................... 295 10.1.2 Characterizing EMFs........................................................................................ 296
10.2 Planar Tissue Models ..................................................................................................... 297 10.2.1 Thick or Semi-Infinite Layers ......................................................................... 297 10.2.2 Multiple Layers ................................................................................................. 301
10.3 Bodies of Revolution ...................................................................................................... 304 10.3.1 Spherical Models............................................................................................... 304 10.3.2 Prolate Spheroidal Models .............................................................................. 308
10.4 Anatomically Based Models ......................................................................................... 311 10.4.1 Brief Survey of Numerical Methods.............................................................. 311
10.4.1.1 Quasi-Static Impedance Method ................................................... 311 10.4.1.2 Volume Integral Equation MoM ................................................... 312 10.4.1.3 SMoM................................................................................................. 313 10.4.1.4 FEM .................................................................................................... 314 10.4.1.5 FDTD Method................................................................................... 314
10.4.2 Human Bodies Exposed to EMFs .................................................................. 318 10.4.2.1 Realistic Models of the Human Body........................................... 318 10.4.2.2 Currents Induced in the Human Body
by Low-Frequency EMFs................................................................ 319 10.4.2.3 Absorption in Human Bodies Exposed
to Far Field of RF Sources .............................................................. 327 10.4.2.4 Human Exposure to the Field Radiated
by Transceiver Base-Station Antennas ......................................... 335 10.4.2.5 Coupling of Transient EM Pulses into the Human Body ......... 340 10.4.2.6 Absorption in the Head of Cellular Phone Users ...................... 343
10.5 Temperature Elevations Induced in Biological Tissues by EM Power Absorption.............................................................................................. 348 10.5.1 Introduction ....................................................................................................... 348 10.5.2 Bio-Heat Equation............................................................................................. 348
10.5.2.1 Initial Conditions ............................................................................. 350 10.5.2.2 Boundary Conditions ...................................................................... 350
10.5.3 Thermoregulatory Responses ......................................................................... 351 10.5.4 Numerical Methods for Solving the Thermal Problem.............................. 353
10.5.4.1 Explicit Finite Difference Formulation......................................... 353 10.5.4.2 ADI Formulation.............................................................................. 355
10.5.5 Temperature Elevations in Subjects Exposed to EM Fields ...................... 357 10.5.5.1 Temperature Increments in the Human Body Exposed
to the Far Field of Radiating RF Sources ..................................... 357 10.5.5.2 Temperature Increments in the Head of a
Cellular Telephone User ................................................................. 359 10.6 Thermal Therapeutic Applications of Microwave Energy ...................................... 361
10.6.1 Ablation for Cardiac Arrhythmias................................................................. 362 10.6.2 Ablation for Endometrial Disorders .............................................................. 363 10.6.3 Microwave Interstitial Hyperthermia for Cancer Treatment .................... 364
10.7 Concluding Remarks...................................................................................................... 366 Acknowledgment....................................................................................................................... 368 References ................................................................................................................................... 368
Electromagnetic energy at both high and low-frequencies can be transmitted into biological materials through the use of antennas or applicators. Antennas launch the electromagnetic energy into the medium. They serve to couple the generating source of electromagnetic energy into the medium, which surrounds it. The spatial distribution of electromagnetic energy from an antenna is directional and varies with distance from the antenna. At distances sufficiently far from an antenna, so that local field distribution changes predictably and varies mostly with distance, the region is called a far field or radiation zone. In the near field or near zone close to the antenna, the electromagnetic energy distribution varies as a function of both angle and distance. Moreover, the behavior of electromagnetic fields (EMFs) and their coupling and interaction with biological systems are very different, depending on whether they are in the near or far zone. In fact, these differences constitute the major variances between radio frequency (RF) and low-frequency energy deposition into biological systems. As shown in subsequent sections, the induction of electric and magnetic fields, deposition of electromagnetic power, absorption of electromagnetic energy, and their penetration into tissue, all are functions of the source and its frequency or wavelength. In general, when considering the interaction of EMFs with biological systems, it is necessary to account for the frequency or wavelength and its relationship to the physical dimensions of the body.
